How compressor power rating is related to air pressure?

"Gary Coffman" <[email protected]> wrote in message
> If you don't consider an air brush a precision tool, you can run one
> from a crappy pulsating air source. But you won't get the results that
> can be obtained using a smooth well regulated air source.

Yes, but you don't need the $1000 compressors that were suggested either.
Most any air can will dampen the pulsations.
Ed

> I am trying to home-build an air pump for hobby modeling airbrushing
> application using a 220V domestic fridge air compressor.

Not a great idea IMHO. A domestic fridge air compressor relies on oil in the
'freon' for lubrication. I realize it's no longer *freon*, but cannot recall
the new trade name. Without lubrication your compressor run time will be
short.

I suggest a used compressor from the medical field such as from a CPAP. I
have one I converted for use as a de-soldering station and it works great.
It would likely be able to power an airbrush too.



Larry Wager
www.BackwoodsMetalArt.com
Truly unique creations
for Home and Yard



"CFF" <[email protected]> wrote in message
news:[email protected]...
> I am trying to home-build an air pump for hobby modeling airbrushing
> application using a 220V domestic fridge air compressor. To make
> things simpler, the basic arrangement is to connect the compressor
> output to an air regulator (with gauge attached) which, in turn,
> connects to a water trap before going to the airbrush. The idea is to
> keep the size of the whole thing as small as possible. I still haven't
> bought the compressor but need something to be clarified beforehand.
> My question is:
>
> What is the minimum power rating required for the compressor to
> deliver (at least) 40 psi (or 0.276 MPa) pressure?
>
> Thanks for any suggestion.
>
> CFF

"CFF" <[email protected]> wrote in message
news:[email protected]...
> I am trying to home-build an air pump for hobby modelling airbrushing
> application using a 220V domestic fridge air compressor. To make
> things simpler, the basic arrangement is to connect the compressor
> output to an air regulator (with guage attached) which, in turn,
> connects to a water trap before going to the airbrush. The idea is to
> keep the size of the whole thing as small as possible. I still haven't
> bought the compressor but need something to be clarified beforehand.
> My question is:
>
> What is the minimum power rating required for the compressor to
> deliver (at least) 40 psi (or 0.276 MPa) pressure?
>
> Thanks for any suggestion.
>
> CFF


You need to buy a compressor to do this?? You will also need an air tank,
and pressure switch. As for power rating you need to give more information,
how many cubic feet per minute at a given PSI.
Your money will be better spent on a factory made unit. A refrigeration
compressor is not the best way to compress air. It will work for a while,
but you will probably have some oil in the discharge due to the construction
of the compressor. By the time you buy water fiters, oil filters, and all
the hardware to do this you could buy a factory unit.
Also you may not even need a water trap. A friend does commercial art and he
has never used a water trap when air brushing.
Greg

"Larry" <[email protected]> wrote in message
news:[email protected]...
> > I am trying to home-build an air pump for hobby modeling airbrushing
> > application using a 220V domestic fridge air compressor.
>
> Not a great idea IMHO. A domestic fridge air compressor relies on oil in
the
> 'freon' for lubrication. I realize it's no longer *freon*, but cannot
recall
> the new trade name. Without lubrication your compressor run time will be
> short.
>
> I suggest a used compressor from the medical field such as from a CPAP. I
> have one I converted for use as a de-soldering station and it works great.
> It would likely be able to power an airbrush too.
>
>
>
> Larry Wager
.
I agree, plus I doubt you get enough volume.

Why not use a small 12 volt air compressor, like for a car tire. You could
get a couple fittings to "t" into an air valve on a tire (valve stem
removed) for the storage tank. Those little compressors are cheap, and will
easily run a half hour, but then let it cool for a few minutes, as you draw
off the tire. Cheap and easy.

How's that for Rube Goldburg'en, gang? <g>
--
Jim in NC

"Edwin Ross Quantrall" <[email protected]> wrote

> Wouldn't a 9" or 12" section of 3" or 4" dia. PVC, capped at each end
> and sealed with silicon sealant; then drilled, tapped on opposite
> sides/ends and the fittings sealed with silicon, Teflon® tape or wax be
> just as good, simpler to make and take up less space?
>
> Just another thought.
>
> --
> Edwin

BAD IDEA ! ! ! ! ! ! ! ! ! ! ! DO NOT DO THIS!!!!!

Look on the side of pvc drain pipe. I am sure this is what you meant to
use. It says, not for pressure. It can shatter with explosive results,
when struck while pressurized.
--
Jim in NC

"Edwin Ross Quantrall" <[email protected]> wrote in message
news:[email protected]...
> Morgans wrote:
>
> > "Edwin Ross Quantrall" <[email protected]> wrote
> >
> >
> >>Wouldn't a 9" or 12" section of 3" or 4" dia. PVC, capped at each end
> >>and sealed with silicon sealant; then drilled, tapped on opposite
> >>sides/ends and the fittings sealed with silicon, Teflon® tape or wax be
> >>just as good, simpler to make and take up less space?
> >>
> >>Just another thought.
> >>
> >>--
> >>Edwin
> >>
> >
> > BAD IDEA ! ! ! ! ! ! ! ! ! ! ! DO NOT DO THIS!!!!!
> >
> > Look on the side of pvc drain pipe. I am sure this is what you meant to
> > use. It says, not for pressure. It can shatter with explosive results,
> > when struck while pressurized.
> >
>
> Let me clarify. I'm suggesting this *STRICTLY(!!!)* as a pulsation
> damper. If one is worried about an overpressure "explosion"; one could
> either drill and install a relief-valve, or insert a small rubber plug
> (chained or otherwise attached to the damper, of course -- wouldn't want
> it flying into the next room...) that has been firmly pushed into place
> but will pop out if the air inside reaches, say, 40-60 psi. (I spray at
> about 20-25 psi, so I don't think I'd have too many problems if I needed
> such a set-up.)
>
> --
> Edwin
>
> (Remove "DIESPAMDIE!")
>
> "Me? I'm dishonest, and a dishonest man you can trust to be dishonest...
> Honestly. It's the honest ones you want to watch out for, because you
> can never predict when they're going to do something incredibly stupid."
> - Captain Jack Sparrow (Disney's Pirates of the Caribbean: The Curse of
> the Black Pearl)
>

Let ME clarify. It is a bad ides, and it does not matter what function it
is doing, it is A BAD idea to put even 40 lbs pressure into it.

Tell you what. Go get some 4" PVC, cap it and put your 60 lbs into it, and
then hit it with a hammer. Report back after your wounds have healed.
--
Jim in NC

"Rich S." <[email protected]> wrote in message
news:[email protected]...
> "Morgans" <[email protected]> wrote in message
> news:[email protected]...
> >
> > Let ME clarify. It is a bad ides, and it does not matter what function
it
> > is doing, it is A BAD idea to put even 40 lbs pressure into it.
> >
> > Tell you what. Go get some 4" PVC, cap it and put your 60 lbs into it,
> and
> > then hit it with a hammer. Report back after your wounds have healed.
> > --
> > Jim in NC
>
> Damn! And I was just on the verge of being able to drop a nice, fresh,
crisp
> Idaho #2 on my neighbor's deck - 220 yards away. Now you have to go and
> spoil my fun.
>
> http://www.spudtech.com/
>
> Rich "Outgoing" S.
>
>
Chuckle>

You are still OK, for this use. Just Don't hit the pipe with a hammer, or
drop it, just as the combustion process makes max. pressure!
--
Jim in NC

"Rich S." <[email protected]> wrote

the 2" PVC I'm using as the air chamber is rated way
> higher than that. I got a popoff valve on it set at 125

> Rich "Food Flinger" S.

So you are using schedule 40 PVC, not foam core PVC drain pipe?

Good. Still be careful, especially when cold.

Jim (Boom) in NC

On Wed, 21 Jan 2004 01:00:42 -0500, Edwin Ross Quantrall
<[email protected]> wrote:

>Morgans wrote:
>
>> "Edwin Ross Quantrall" <[email protected]> wrote
>>
>>
>>>Wouldn't a 9" or 12" section of 3" or 4" dia. PVC, capped at each end
>>>and sealed with silicon sealant; then drilled, tapped on opposite
>>>sides/ends and the fittings sealed with silicon, Teflon® tape or wax be
>>>just as good, simpler to make and take up less space?
>>>
>>>Just another thought.
>>>
>>>--
>>>Edwin
>>>
>>
>> BAD IDEA ! ! ! ! ! ! ! ! ! ! ! DO NOT DO THIS!!!!!
>>
>> Look on the side of pvc drain pipe. I am sure this is what you meant to
>> use. It says, not for pressure. It can shatter with explosive results,
>> when struck while pressurized.
>>
>
>Let me clarify. I'm suggesting this *STRICTLY(!!!)* as a pulsation
>damper. If one is worried about an overpressure "explosion"; one could
>either drill and install a relief-valve, or insert a small rubber plug
>(chained or otherwise attached to the damper, of course -- wouldn't want
>it flying into the next room...) that has been firmly pushed into place
>but will pop out if the air inside reaches, say, 40-60 psi. (I spray at
>about 20-25 psi, so I don't think I'd have too many problems if I needed
>such a set-up.)


Hey Edwin,

I still think that you are dancing with the Devil. In your original
post, I took it that you were attempting to come up with a very
simple, very economical, readily available DIY accumulator. Simply
put, what you suggested isn't a good idea, because it lacks the safety
factor for pressure handling that should have been in your
"requirement".
Now, to add the safety requirement that was missing, you're suggesting
adding parts that do away with at least two of your original thoughts;
readily available and economical. To me, it's easier to do what you
suggest, but use steel pipe instead. I can go right now and pick up
all I would need to do this at the local hardware store, for less than
the cost of just the unloader, and not ever have to worry about
regulator being set above the 25PSI safety factor you used. And if
a "rubber plug" were used, would it not be similar to a rubber bullet?
And what would be "simple" about designing its use and release
pressure?

Hope they never play a fast tune for you and your Partner here!

Take care.

Brian Lawson,
Bothwell, Ontario.

Take care.

Brian Lawson,
Bothwell, Ontario.

A fridge compressor won't give you much volume. They are designed to liquefy
freon (puron or whatever). They can generate a lot of pressure but not at much
volume. You will also have to squirt oil in it fairly often to keep it from
siezing up and this will end up in your paint.
I am using a big window shaker compressor for a vacuum pump but it sucks as an
air source.

[email protected] (CFF) wrote in message news:<[email protected]>...
> I am trying to home-build an air pump for hobby modelling airbrushing
> application using a 220V domestic fridge air compressor. To make
> things simpler, the basic arrangement is to connect the compressor
> output to an air regulator (with guage attached) which, in turn,
> connects to a water trap before going to the airbrush. The idea is to
> keep the size of the whole thing as small as possible. I still haven't
> bought the compressor but need something to be clarified beforehand.
> My question is:
>
> What is the minimum power rating required for the compressor to
> deliver (at least) 40 psi (or 0.276 MPa) pressure?
>
> Thanks for any suggestion.
>
> CFF

Thank you for the information and useful suggestions. In fact, I have
been doing some online research on this issue and I am sure this can
be done, at least, for the purpose of operating a hobby airbrush. I
came accross numerious reports on similar setup using compressors
whose power ratings vary from 1/8 hp to 2 hp. I don't want excessive
power because it would then be bulky and costly. Neither do I want
under-power because I have to be sure it is yet powerful enough to
deliver the required air pressure. I have no intention to use the
setup for any other purpose other than operating my Badger airbrush.
The point I would like to emphasise is I will not be including an air
reserviour in the setup as many designs would. That makes me a bit
suspecious about if 1/8 hp is sufficient to deliver 40 psi air
pressure. Only if this can be assured, I will then be able to buy what
I need in order to proceed with the assembly.

CFF

I fully understand the significane of employing an air tank. As an
hobbist, the major difficulty in putting an air tank in the design is
it is difficult to find a cheap, commerically small air tank. While
ruling out all the options of making the whole thing look big, some
suggest using an empty fire extinguisher to convert. But, as far as I
understand, there is quite an amount of drilling and welding work need
to be done in order to mount the host connectors plus guage at the
inlet and outlet. That is something that I just don't have the
engineering facility to accomplish. Considering the relatively low
pressure required for airbrushing application, I am quite happy to
sacrify consistence of air flow as long as it does provide a
reasonably constant presure at short bursts. However, if there are
feasible suggestions that I can manage to modify a fire extinguisher
without the need of welding, I will be glad to consider. I am sure
that will make it an ideal setup.

CFF

In the search of an alternative to professional, commerically
available air tank, I came up with the idea of using a stainless steel
traveller's flask for the conversion but not sure if it can sustain
the pressure, say, at 1 MPa. I am talking about the type that is
commonly available from departmental stores or camping equipment
suppliers. It looks like an air tank, it is cheap and it looks rather
durable to me. Has there been anybody who have made such attempt or
can somebody point me out the potential problems?

CFF

In article <[email protected]>,
[email protected] says...
>
>I am trying to home-build an air pump for hobby modelling airbrushing
>application using a 220V domestic fridge air compressor. To make
>things simpler, the basic arrangement is to connect the compressor
>output to an air regulator (with guage attached) which, in turn,
>connects to a water trap before going to the airbrush. The idea is to
>keep the size of the whole thing as small as possible. I still haven't
>bought the compressor but need something to be clarified beforehand.
>My question is:
>
>What is the minimum power rating required for the compressor to
>deliver (at least) 40 psi (or 0.276 MPa) pressure?
>
>Thanks for any suggestion.
>
>CFF

The other guys mentioned lubrication problems with refrigeration
compressors and they are correct. If you only want to use an airbrush,
the smallest compressors at Northern, Harbor Freight or Lowes will do
the job. It doesn't take much for an airbrush and they are the oil
less type which is better for painting. If you plan on adding air
tools or a large paint gun later buy a bigger unit. Oil less types are
noisy so if you want a larger unit installed inside you might want to
avoid them.

CFF wrote:
>
> I am trying to home-build an air pump for hobby modelling airbrushing
> application using a 220V domestic fridge air compressor. To make
> things simpler, the basic arrangement is to connect the compressor
> output to an air regulator (with guage attached) which, in turn,
> connects to a water trap before going to the airbrush. The idea is to
> keep the size of the whole thing as small as possible. I still haven't
> bought the compressor but need something to be clarified beforehand.
> My question is:
>
> What is the minimum power rating required for the compressor to
> deliver (at least) 40 psi (or 0.276 MPa) pressure?
>
> Thanks for any suggestion.
>
> CFF

Compressor power is related to how much air it moves at a given
pressure.
The higher the CFM at a given pressure the higher the power requirement.
If you only plan to use the airbrush I think just about anything will do
but if you want to power air tools or a big sprayer you need a higher
power unit. Check the pressure and volume requirements of what tools you
want to use and then decide what to buy.
Good Luck
Jim Stockton

Orval Fairbairn wrote:
>
> In article <[email protected]>,
> [email protected] (CFF) wrote:
>
> > I am trying to home-build an air pump for hobby modelling airbrushing
> > application using a 220V domestic fridge air compressor. To make
> > things simpler, the basic arrangement is to connect the compressor
> > output to an air regulator (with guage attached) which, in turn,
> > connects to a water trap before going to the airbrush. The idea is to
> > keep the size of the whole thing as small as possible. I still haven't
> > bought the compressor but need something to be clarified beforehand.
> > My question is:
> >
> > What is the minimum power rating required for the compressor to
> > deliver (at least) 40 psi (or 0.276 MPa) pressure?
> >
> > Thanks for any suggestion.
> >
> > CFF
>
> It isn't so much the PSI, but the CFM * PSI that governs power.

Is that kinda like electricty?
PSI for volts E
CFM for current I
Power = I^2 E

???

Where's Jim Weir when ya need him?

Please for more even spraying use a reserviour.

CFF wrote:
>
> [email protected] (CFF) wrote in message news:<[email protected]>...
> > I am trying to home-build an air pump for hobby modelling airbrushing
> > application using a 220V domestic fridge air compressor. To make
> > things simpler, the basic arrangement is to connect the compressor
> > output to an air regulator (with guage attached) which, in turn,
> > connects to a water trap before going to the airbrush. The idea is to
> > keep the size of the whole thing as small as possible. I still haven't
> > bought the compressor but need something to be clarified beforehand.
> > My question is:
> >
> > What is the minimum power rating required for the compressor to
> > deliver (at least) 40 psi (or 0.276 MPa) pressure?
> >
> > Thanks for any suggestion.
> >
> > CFF
>
> Thank you for the information and useful suggestions. In fact, I have
> been doing some online research on this issue and I am sure this can
> be done, at least, for the purpose of operating a hobby airbrush. I
> came accross numerious reports on similar setup using compressors
> whose power ratings vary from 1/8 hp to 2 hp. I don't want excessive
> power because it would then be bulky and costly. Neither do I want
> under-power because I have to be sure it is yet powerful enough to
> deliver the required air pressure. I have no intention to use the
> setup for any other purpose other than operating my Badger airbrush.
> The point I would like to emphasise is I will not be including an air
> reserviour in the setup as many designs would. That makes me a bit
> suspecious about if 1/8 hp is sufficient to deliver 40 psi air
> pressure. Only if this can be assured, I will then be able to buy what
> I need in order to proceed with the assembly.
>
> CFF

Leo Lichtman wrote:
>
> Richard Lamb wrote:
> > Is that kinda like electricty?
> > PSI for volts E
> > CFM for current I
> > Power = I^2 E
> ^^^^^^^^^^^^^^^
> You have the idea, but accidentally slipped on the formula. P = I E.
>
> I believe you were thinking of another equation, P = I^2R.
>
> I don't know how they get away with it--a number of people I know use old
> refrigeration compressors as vacuum pumps. I don't know of any lubrication
> problems. Maybe they are all in for a surprise.

P = I E and P = I^2 R are both valid for purely resitive circuits
since E = I R, where:
E is electromotive force (in volts)
I is current (in amps)
R is resistance (in ohms)
P is power (in watts)

The letter V is not properly used in elctrical and electronic formulae.

The issue related to current, and therefore to power, are far more complex
in reactive circuits, whether inductive (such as most electric motors)
or capacitive.

Therefore, the compressor rating could be expressed as:
Horsepower (is proportional to) Volume * Pressure
or as
Horsepower = Volume * Pressure (* some constant)

A couple things to keep in mind. Refrigeration compressors are intended
to pump refrigerant. This often contains a lubricant (oil). If running
free and pumping air, they will get no lubrication.
Be sure and use a compressor than can handle this application. I suspect
few can, for long.

Power is not related to pressure alone. Power would affect the RATE
(volume) of air delivery at some specified pressure.

A very small motor can produce great pressure at very low volumes.

A very large motor cannot produce much pressure if the volume is too great.

That said, for casual airbrushing applications, perhaps 1/6 horsepower
(735/6 = 125 watts) should be sufficient. A lot of the small commercial
compressors are only about 1/8 hp. these are rather feeble in my
opinion. A quarter horsepower (735/4 = 185 watts) should be ample for
ANY airbrushing need. Note that actual power consumption will be MORE,
since motors are NOT perfectly efficient. And, ALL motors will take
considerably MORE power when starting.

200 watts with a little momentary overload capacity SHOULD be sufficient
for your application. That's only a couple amps at 220 VAC.

Dan Mitchell
==========

CFF wrote:
>
> I am trying to home-build an air pump for hobby modelling airbrushing
> application using a 220V domestic fridge air compressor. To make
> things simpler, the basic arrangement is to connect the compressor
> output to an air regulator (with guage attached) which, in turn,
> connects to a water trap before going to the airbrush. The idea is to
> keep the size of the whole thing as small as possible. I still haven't
> bought the compressor but need something to be clarified beforehand.
> My question is:
>
> What is the minimum power rating required for the compressor to
> deliver (at least) 40 psi (or 0.276 MPa) pressure?
>
> Thanks for any suggestion.
>
> CFF

That analogy is pretty much correct. Such a way of thinking can be
helpful for the casual user, but it's NOT the same, exactly.

In both cases, POWER is the RATE of doing WORK.

Without a time factor (a rate, such as flow or current), there is NO
power involved (regardless of pressure or voltage).

Dan Mitchell
==========

Richard Lamb wrote:
>
> Orval Fairbairn wrote:
> >
> > In article <[email protected]>,
> > [email protected] (CFF) wrote:
> >
> > > I am trying to home-build an air pump for hobby modelling airbrushing
> > > application using a 220V domestic fridge air compressor. To make
> > > things simpler, the basic arrangement is to connect the compressor
> > > output to an air regulator (with guage attached) which, in turn,
> > > connects to a water trap before going to the airbrush. The idea is to
> > > keep the size of the whole thing as small as possible. I still haven't
> > > bought the compressor but need something to be clarified beforehand.
> > > My question is:
> > >
> > > What is the minimum power rating required for the compressor to
> > > deliver (at least) 40 psi (or 0.276 MPa) pressure?
> > >
> > > Thanks for any suggestion.
> > >
> > > CFF
> >
> > It isn't so much the PSI, but the CFM * PSI that governs power.
>
> Is that kinda like electricty?
> PSI for volts E
> CFM for current I
> Power = I^2 E
>
> ???
>
> Where's Jim Weir when ya need him?

Correct. In my post I should have caught the error in "Power = I^2 E"
... it SHOULD be just Power = I E.

I meant to address the analogy between voltage and pressure, and between
current and flow rate. I missed the poster's error in 'power'.

Dan Mitchell
==========

Andy Dingley wrote:
>
> On Fri, 16 Jan 2004 04:04:37 GMT, Richard Lamb <[email protected]>
> wrote:
>
> >Is that kinda like electricty?
>
> Yes
>
> >PSI for volts E
> >CFM for current I
> >Power = I^2 E
>
> No
>
> Power = V * I
>
> (which is also equal to I^2 * R)
>
> A fridge compressor wouldn't be my choice for an airbrush. They're
> filled with an oil bath internally and they put a lot of oil in their
> output. OK for robotics, bad for spraying.
>
> If you can find one cheaply, look out for a small diaphram compressor.
> Quieter too. Alternatively, any air-nailer compressor with a
> reservoir will work. A modelling airbrush uses minimal air, so the
> compresor will probably only run a couple of times a day.
>
> Then buy yourself a really good water/oil separator to go on the
> outlet.

I most STRONGLY recommend that you use SOME kind of small storage
(surge) tank with ANY compressor. Otherwise the airbrush will 'sputter'
with the rapidly changing pressure in the air line. The tank need not be
large, perhaps a quart in volume would do fine for this purpose. a small
tire (like a wheelbarrow tire) will do fine, as one suggestion.

Most small commercial compressors have a SMALL air reservoir built into
their cylinder heads that serves this purpose (often poorly).

Dan Mitchell
==========

CFF wrote:
>
> [email protected] (CFF) wrote in message news:<[email protected]>...
> > I am trying to home-build an air pump for hobby modelling airbrushing
> > application using a 220V domestic fridge air compressor. To make
> > things simpler, the basic arrangement is to connect the compressor
> > output to an air regulator (with guage attached) which, in turn,
> > connects to a water trap before going to the airbrush. The idea is to
> > keep the size of the whole thing as small as possible. I still haven't
> > bought the compressor but need something to be clarified beforehand.
> > My question is:
> >
> > What is the minimum power rating required for the compressor to
> > deliver (at least) 40 psi (or 0.276 MPa) pressure?
> >
> > Thanks for any suggestion.
> >
> > CFF
>
> Thank you for the information and useful suggestions. In fact, I have
> been doing some online research on this issue and I am sure this can
> be done, at least, for the purpose of operating a hobby airbrush. I
> came accross numerious reports on similar setup using compressors
> whose power ratings vary from 1/8 hp to 2 hp. I don't want excessive
> power because it would then be bulky and costly. Neither do I want
> under-power because I have to be sure it is yet powerful enough to
> deliver the required air pressure. I have no intention to use the
> setup for any other purpose other than operating my Badger airbrush.
> The point I would like to emphasise is I will not be including an air
> reserviour in the setup as many designs would. That makes me a bit
> suspecious about if 1/8 hp is sufficient to deliver 40 psi air
> pressure. Only if this can be assured, I will then be able to buy what
> I need in order to proceed with the assembly.
>
> CFF

|A couple things to keep in mind. Refrigeration compressors are intended
|to pump refrigerant. This often contains a lubricant (oil). If running
|free and pumping air, they will get no lubrication.
|Be sure and use a compressor than can handle this application. I suspect
|few can, for long.

Don't tell that to my dad. He's been using the same old refrigerator compressor
since the late 60's, doing professional A/C repair on home ands cars. Stil has
it, still works fine. In fact he gave it tome last year, then came and took it
back 2 months later (Indian giver!). I think he gives it a shot of
refrigeration oil occasionally.
Rex in Fort Worth

I'd be concerned about the duty cycle of that small compressor.
I bet it would work it's little butt to death trying to keep that 80-gallon tank
full.

On 16 Jan 2004 08:53:41 -0800, [email protected] (Daniel) wrote:

|Jim Stockton wrote ...
|
|> Compressor power is related to how much air it moves at a given
|> pressure.
|> The higher the CFM at a given pressure the higher the power requirement.
|> If you only plan to use the airbrush I think just about anything will do
|> but if you want to power air tools or a big sprayer you need a higher
|> power unit. Check the pressure and volume requirements of what tools you
|> want to use and then decide what to buy.
|
|
|I've been playing with the notion of a compressor on a budget. I
|simply can't justify the cost of a "mother-of-all-compressors" model,
|yet I'd like the benefits of same. I have an old propane tank that
|measures to be around 80 gallons capacity. I wondered if it was
|feasible to marry it to a $200 compressor (nail gun pancake type). It
|might take forever to fill, but I'd have a big reservoir to draw on.
|Rather than blow $200+ to find out, I looked at the basic
|relationships of PSI, CFM in & CFM out. What follows is my own back
|of the envelope analysis.
|
|Compressor ratings:
|3.7 CFM @ 40 PSI
|2.6 CFM @ 90 PSI
|Stop switch at 150 PSI so that's 0 CFM @ 150 PSI
|
|I ran a regression on those relationships & got:
|CFM = -6.048*PSI² - 7.3521*PSI + 150
|CFM as a function of PSI is obviously eponential (it delevers less and
|less as PSI goes up) and it turns out that this 2nd order polynomial
|fits the manufacturer's data extremely well (R²=1).
|
|The first question is how long will this little compressor take to
|fill this bigass tank? Rather than throw calculus into it, I took an
|incremental approach & used the above to compute CFM at each level of
|PSI from 0 to 145, dividing the result into 1 minute at each PSI level
|to get the time needed to raise the pressure by 1 PSI. Summing the
|results, it takes right at 90 minutes to fill an empty tank to 145
|PSI.
|
|The next question is how long does it take to draw down the tank from
|145 PSI to some minimum useful pressure, depending on the tool? In
|other words, can I get any work done?
|
|Given:
|145 PSI in the tank
|90, 80 or 40 PSI at the regulator according to the tool
|15 pressure/atmospheric pressure
|80 gallons capacity
|7.5 gallons/ft³
|
|Then:
|(145 / 15) * (80 / 7.5) = 103 ft³ of air in the tank at 145 PSI
|and:
|(90 / 145) * 103 = 64 ft³ of air in the tank at 90 PSI
|(80 / 145) * 103 = 57 ft³ of air in the tank at 80 PSI
|(40 / 145) * 103 = 28 ft³ of air in the tank at 40 PSI
|
|Therefore the usable amount of air is:
|103 - 64 = 39 ft³ stopping at 90 PSI, or
|103 - 57 = 46 ft³ stopping at 80 PSI, or
|103 - 28 = 75 ft³ stopping at 40 PSI.
|At that point I have to stop and let the tank refill.
|
|How much time that equates to depends on the tool being used and its
|CFM requirements. Using that wonderful resource for truth and
|accurate figures called the internet, I find:
|Little suction type sandblasters use as little as 7 CFM @ 80 PSI.
|Sanders, maybe 8 CFM @ 90 PSI.
|A rivet gun at 25% usage is perhaps 4 CFM.
|Spray guns require around 10 CFM but can run down to 40 PSI or so.
|
|Therefore I'm looking at 5 to 10 minutes work depending on the tool
|before I get a beer and wait for the compressor. All of this assumes
|that the compressor doesn't even kick on until I stop working. In
|truth, it would start making an effort to refill the tank at say 110
|PSI, so work times would be _very_ slightly longer.
|
|The final question is how long do I have to suck suds before I can go
|back to work? Using the incremental data from above, to recover from
|90 PSI back up to 145 PSI will take just over an hour, and to recover
|from 40 PSI (in the midst of a paint job) would take an hour and
|twenty minutes!
|
|My conclusion is that of conventional wisdom. You can't substitute
|for power. Besides, even if I could live with the recovery times, the
|bill for beer would negate the savings on the compressor!
|
|Cautions: Anyone contemplating a similar scheme needs to make sure
|the old propane tank is empty (duh), pressure test it (fill it almost
|full of water & run it to 200 PSI, preferrably from a distance or
|behind a berm) and of course find a way to remove the stinko residue
|from the tank.
|
|Daniel

Rex in Fort Worth

If you're willing to spend $ 200 and need it only for airbrushing and want a
small reservoir, try the Paasche D 3000. You can get it from online suppliers
for $ 220 complete with moisture trap and regulator. Retail if you want to
help your local hobby shop be there it's about $ 300. You won't need to build
it its own room either. ;-)

Cheers!!!

BobbyG



Daniel wrote:

> I've been playing with the notion of a compressor on a budget. I
> simply can't justify the cost of a "mother-of-all-compressors" model,
> yet I'd like the benefits of same. I have an old propane tank that
> measures to be around 80 gallons capacity. I wondered if it was
> feasible to marry it to a $200 compressor (nail gun pancake type). It
> might take forever to fill, but I'd have a big reservoir to draw on.
> Rather than blow $200+ to find out, I looked at the basic
> relationships of PSI, CFM in & CFM out. What follows is my own back
> of the envelope analysis.
>
> Compressor ratings:
> 3.7 CFM @ 40 PSI
> 2.6 CFM @ 90 PSI
> Stop switch at 150 PSI so that's 0 CFM @ 150 PSI
>
> I ran a regression on those relationships & got:
> CFM = -6.048*PSI² - 7.3521*PSI + 150
> CFM as a function of PSI is obviously eponential (it delevers less and
> less as PSI goes up) and it turns out that this 2nd order polynomial
> fits the manufacturer's data extremely well (R²=1).
>
> The first question is how long will this little compressor take to
> fill this bigass tank? Rather than throw calculus into it, I took an
> incremental approach & used the above to compute CFM at each level of
> PSI from 0 to 145, dividing the result into 1 minute at each PSI level
> to get the time needed to raise the pressure by 1 PSI. Summing the
> results, it takes right at 90 minutes to fill an empty tank to 145
> PSI.
>
> The next question is how long does it take to draw down the tank from
> 145 PSI to some minimum useful pressure, depending on the tool? In
> other words, can I get any work done?
>
> Given:
> 145 PSI in the tank
> 90, 80 or 40 PSI at the regulator according to the tool
> 15 pressure/atmospheric pressure
> 80 gallons capacity
> 7.5 gallons/ft³
>
> Then:
> (145 / 15) * (80 / 7.5) = 103 ft³ of air in the tank at 145 PSI
> and:
> (90 / 145) * 103 = 64 ft³ of air in the tank at 90 PSI
> (80 / 145) * 103 = 57 ft³ of air in the tank at 80 PSI
> (40 / 145) * 103 = 28 ft³ of air in the tank at 40 PSI
>
> Therefore the usable amount of air is:
> 103 - 64 = 39 ft³ stopping at 90 PSI, or
> 103 - 57 = 46 ft³ stopping at 80 PSI, or
> 103 - 28 = 75 ft³ stopping at 40 PSI.
> At that point I have to stop and let the tank refill.
>
> How much time that equates to depends on the tool being used and its
> CFM requirements. Using that wonderful resource for truth and
> accurate figures called the internet, I find:
> Little suction type sandblasters use as little as 7 CFM @ 80 PSI.
> Sanders, maybe 8 CFM @ 90 PSI.
> A rivet gun at 25% usage is perhaps 4 CFM.
> Spray guns require around 10 CFM but can run down to 40 PSI or so.
>
> Therefore I'm looking at 5 to 10 minutes work depending on the tool
> before I get a beer and wait for the compressor. All of this assumes
> that the compressor doesn't even kick on until I stop working. In
> truth, it would start making an effort to refill the tank at say 110
> PSI, so work times would be _very_ slightly longer.
>
> The final question is how long do I have to suck suds before I can go
> back to work? Using the incremental data from above, to recover from
> 90 PSI back up to 145 PSI will take just over an hour, and to recover
> from 40 PSI (in the midst of a paint job) would take an hour and
> twenty minutes!
>
> My conclusion is that of conventional wisdom. You can't substitute
> for power. Besides, even if I could live with the recovery times, the
> bill for beer would negate the savings on the compressor!
>
> Cautions: Anyone contemplating a similar scheme needs to make sure
> the old propane tank is empty (duh), pressure test it (fill it almost
> full of water & run it to 200 PSI, preferrably from a distance or
> behind a berm) and of course find a way to remove the stinko residue
> from the tank.
>
> Daniel

"Daniel" <[email protected]> wrote in message
news:[email protected]...
>
> I've been playing with the notion of a compressor on a budget. I
> simply can't justify the cost of a "mother-of-all-compressors" model,
> yet I'd like the benefits of same. I have an old propane tank that
> measures to be around 80 gallons capacity. I wondered if it was
> feasible to marry it to a $200 compressor (nail gun pancake type).

For a *modeling* airbrush, you'd have to be insane to be seriously
considering an 80 gallon air tank. My *first* airbrush propellant setup
was: My 5-gallon autocross air tank with a regulator on it. Pumped it up to
about 100 psi at the nearest gas station and painted for awhile until the
pressure dropped down to about 25 psi, then refilled it. It would do a
couple of coats on a typical car body, IIRC. My first 'upgrade' was adding
a $50 B&D tire pump compressor so I didn't have to drive 4-5 miles to a gas
station. It was earsplitting, but at least I could fill it at home.

I later stumbled across a bargain ($5!) airbrush compressor from a modeler
who'd upgraded to another one. The quiet is heavenly.

For those who already have a compressor of any kind, a 5-10-gallon air tank
is a very modest investment that should serve all of your modeling needs.
--
C.R. Krieger
(Been there; done that)

On Fri, 16 Jan 2004 18:00:59 GMT, Mark <[email protected]> wrote:

|
|
|Rex B wrote:
|
|>
|> Don't tell that to my dad. He's been using the same old refrigerator
compressor
|> since the late 60's, doing professional A/C repair on home ands cars.
|
|
|Are you sure it isn't an oil bath compressor?

No, but it's the round, sealed type about the size of a slightly flattened
bowling ball. Same color too.
Rex in Fort Worth

> Correct. In my post I should have caught the error in "Power = I^2 E"
> ... it SHOULD be just Power = I E.
>
> I meant to address the analogy between voltage and pressure, and between
> current and flow rate. I missed the poster's error in 'power'.
>
> Dan Mitchell
> ==========
>

Yepp, you nailed it - Power = I^2 * R, or V * I

It's that old 'magic triangle' again!

/\
/ \
/ W \
/ ...... \
/ : \
/ V : I \
/........:........\

Cover up one letter, and what's left is the sum to calculate it!

David.

> > > Is that kinda like electricty?
> > > PSI for volts E
> > > CFM for current I
> > > Power = I^2 E
> > ^^^^^^^^^^^^^^^
> > You have the idea, but accidentally slipped on the formula. P = I E.
> >
> > I believe you were thinking of another equation, P = I^2R.
> >
> > I don't know how they get away with it--a number of people I know use old
> > refrigeration compressors as vacuum pumps. I don't know of any lubrication
> > problems. Maybe they are all in for a surprise.
>
> P = I E and P = I^2 R are both valid for purely resitive circuits
> since E = I R, where:
> E is electromotive force (in volts)
> I is current (in amps)
> R is resistance (in ohms)
> P is power (in watts)
>
> The letter V is not properly used in elctrical and electronic formulae.
>
> The issue related to current, and therefore to power, are far more complex
> in reactive circuits, whether inductive (such as most electric motors)
> or capacitive.
>
> Therefore, the compressor rating could be expressed as:
> Horsepower (is proportional to) Volume * Pressure
> or as
> Horsepower = Volume * Pressure (* some constant)


That just about covers it all! For ALL types of circuits, we
used 'VA' in place of Watts. Watts are dependant on the
phase relationship of the Current and Voltage in Inductive
or Capacitive loads fed by an AC supply.

For those reading this who really 'want to know' -

VA = V * I.
Watts = (V * I) * (cosine of Phase Difference).
Power Factor = (Watts / VA).

Normally, as the workload of a motor increases, the power
factor increases proportionately, but can never exceed 1.0.

Not sure about the analogy of Horsepower though, but close
enough! It's been a long time since I dabbled in Horsepower.
Something to do with raising xxx pounds at a rate of yy feet
per second - in physical terms?

I used to design and test Mains Power Transformers.

David.

Gary Coffman wrote:
>

> >Hey, its a friggen airbrush. They work with cheapo diaphragm compressors.
> >The hose is a big enough reservoir to run it for a while.
> >Ed
>
Wrong!! Very Wrong!


> If you don't consider an air brush a precision tool, you can run one
> from a crappy pulsating air source. But you won't get the results that
> can be obtained using a smooth well regulated air source. If you're
> the type to use a micrometer as a C clamp, pulsating air will do just
> fine for you. But if you want to be able to lay down a smooth even
> fine line, you'd better provide your air brush with a smooth even air
> source.
>
> Gary

Well Said!

Bill Shuey

not.fishplate wrote:
>
> On 17 Jan 2004 20:47:37 -0800, [email protected] (CFF) wrote:
>
> >I fully understand the significane of employing an air tank. As an
> >hobbist, the major difficulty in putting an air tank in the design is
> >it is difficult to find a cheap, commerically small air tank.
>
> Why not use one of those portable air tanks used for inflating tires?
> Not too expensive, and trivial to plumb as required. In a pinch, you
> can even use it to blow up a slack tire.
>
> A 5 gallon tank is $16 at Sears right now
>

Correct! You can also get the necessary valves and pressure gauge and I
would advise quick connect fittings at Sears too. Only drawback is it
becomes a nuisance hauling it to the gas station to re-charge it. If you
do a lot of painting, as I do now that I'm retired, it is worth looking
at one of Sears 2 or 4 gallon tank/compressor combinations. I paid about
$200 when on sale but it is a really convenient set up to use and should
last me till I'm gone.

Bill Shuey

Depends on the size of hose ... a 1" diameter hose 10' long should do
it. :-(

The usual, perhaps 3/16" X 6' long, airbrush hose doesn't have nearly
enough internal volume to even out the compressor pulsations. They seem
to travel along it with almost NO 'smoothing' effect at all.

Most commercial compressors have an air reservoir built into their
cylinder heads. This is rarely adequate as a good surge tank, but helps.

For best results an external surge tank is almost a necessity. Even a
pint or so capacity makes a big improvement, a quart is totally
adequate. Note that this serves ONLY as a surge tank to smooth airflow
... NOT as a storage reservoir.

A moisture trap is probably also reqired, depending on your ambient
humidity conditions.

A regulator and storage reservoir are also desirable, but these are less
important than the surge tank and moisture trap IMHO.

Dan Mitchell
==========

Edwin Pawlowski wrote:
>
> "Gary Coffman" <[email protected]> wrote in message
>
> > On 16 Jan 2004 02:29:28 -0800, [email protected] (CFF) wrote:
> > >I have no intention to use the
> > >setup for any other purpose other than operating my Badger airbrush.
> > >The point I would like to emphasise is I will not be including an air
> > >reserviour in the setup as many designs would.
> >
> > You need at least a small reservoir to smooth out the
> > pulsations in the air caused by a piston compressor.
> > So if your plan is to not include a reservoir, you can't
> > use a piston compressor. You need a vane or turbine
> > type compressor which supplies constant flow.
>
> Hey, its a friggen airbrush. They work with cheapo diaphragm compressors.
> The hose is a big enough reservoir to run it for a while.
> Ed

Look for a used commercial compressed-air system 'moisture trap' at a
junkyard. These often consist of a small pressure tank about the size of
a grapefruit. They have a drain valve in the bottom to release the
moisture. These little 'tanks' are *NOT* the kind of moisture trap
being recommended for airbrushing (they're for power tools). However,
they're ideal for your pressure tank purpose, and can be 'had' for a
couple bucks.

Spray painting moisture traps have filter elements to remove the
moisture.

Dan Mitchell
==========

CFF wrote:
>
> I fully understand the significane of employing an air tank. As an
> hobbist, the major difficulty in putting an air tank in the design is
> it is difficult to find a cheap, commerically small air tank. While
> ruling out all the options of making the whole thing look big, some
> suggest using an empty fire extinguisher to convert. But, as far as I
> understand, there is quite an amount of drilling and welding work need
> to be done in order to mount the host connectors plus guage at the
> inlet and outlet. That is something that I just don't have the
> engineering facility to accomplish. Considering the relatively low
> pressure required for airbrushing application, I am quite happy to
> sacrify consistence of air flow as long as it does provide a
> reasonably constant presure at short bursts. However, if there are
> feasible suggestions that I can manage to modify a fire extinguisher
> without the need of welding, I will be glad to consider. I am sure
> that will make it an ideal setup.
>
> CFF

Dennis Loep wrote:

> <not.fishplate> wrote in message
news:[email protected]...
>

>
>> On 17 Jan 2004 20:47:37 -0800, [email protected] (CFF) wrote:
>>
>>
>>> I fully understand the significane of employing an air tank. As
>>> an hobbist, the major difficulty in putting an air tank in the
>>> design is it is difficult to find a cheap, commerically small
>>> air tank.
>>>
>> Why not use one of those portable air tanks used for inflating
>> tires? Not too expensive, and trivial to plumb as required. In a
>> pinch, you can even use it to blow up a slack tire.
>>
>> A 5 gallon tank is $16 at Sears right now
>>
>>
>
http://www.sears.com/sr/javasr/product.do?BV_UseBVCookie=Yes&vertical=TOOL&p
>

> id=00915200000
>
>> Jeff Sc. Low Pressure, Ga.
>>
>
> Go to this page and you wil find a complete compressor with all the
> bits and pieces for $113 and some.
>
> If you are going to use an air tank just for pulsation dampening
> reasons. Why not take a yard/meter long metal tube get it welded
> shut at both ends by someone who knows how to weld. (I think every
> body knows someone) Let someone drill two holes in the ends (or do
> it yourself) and cut thread in them which will accept the fittings
> for your specific brand of airbrush/hose. Most repair shops have a
> good tap and die set handy and a lot of mechanics will not have a
> lot of trouble doing that for you. (at least not here in Holland). This
> wil give you a cheap pulsation damper that won't take too much
> space and which you can simply connect in line of your air hose.
>
> PS. The welds don't need to be the best in the world because you are
> not really presurising the tube/tank.
>
> Just a thought

Wouldn't a 9" or 12" section of 3" or 4" dia. PVC, capped at each end
and sealed with silicon sealant; then drilled, tapped on opposite
sides/ends and the fittings sealed with silicon, Teflon® tape or wax be
just as good, simpler to make and take up less space?

Just another thought.

--
Edwin

(Remove "DIESPAMDIE!")

"Me? I'm dishonest, and a dishonest man you can trust to be dishonest...
Honestly. It's the honest ones you want to watch out for, because you
can never predict when they're going to do something incredibly stupid."
- Captain Jack Sparrow (Disney's Pirates of the Caribbean: The Curse of
the Black Pearl)

Regarding the welds, AND the tank. While your suggestion would work fine
with the typical inexpensive airbrush compressor, which is limited to
about 30 psi anyway, it may be dangerous in the context being discussed.

As someone pointed out, refrigeration compressors regularly attain about
300 psi. While this can be limited with a safety (bleeder) valve, it is
a potentially dangerous pressure. Many common tanks and compressed air
appliances are *NOT* designed to work at such inlet pressures. I've
seen regulators limited to about 180 psi on the HIGH side.

Yes, high pressure appliances ARE available, but they're NOT the ones
likely to be found in the usual hardware, hobby, or paint store.

Use extreme caution here!

Dan Mitchell
==========

Dennis Loep wrote:
>
<snip>
>
> If you are going to use an air tank just for pulsation dampening reasons.
> Why not take a yard/meter long metal tube get it welded shut at both ends by
> someone who knows how to weld. (I think every body knows someone)
> Let someone drill two holes in the ends (or do it yourself) and cut thread
> in them which will accept the fittings for your specific brand of
> airbrush/hose. Most repair shops have a good tap and die set handy and a lot
> of mechanics will not have a lot of trouble doing that for you. (at least
> not here in Holland).
> This wil give you a cheap pulsation damper that won't take too much space
> and which you can simply connect in line of your air hose.
>
> PS. The welds don't need to be the best in the world because you are not
> really presurising the tube/tank.
>
> Just a thought
>
> --
> Dennis Loep
> The Glueing Dutchman
>
> "The most exciting phrase to hear in science, the one that heralds new
> discoveries, is not 'Eureka!' but 'That's funny ...'"
> Isaac Asimov

CAREFUL!

While you might well get away with this at the usual 30 psi or so used
in airbrushing, common PVC pipe is **NOT** rated for compressed air use,
and can rupture easily. People see the 600 psi, or whatever, printed on
the tubing and think that means it's safe ... **NOT**! That rating is
for COLD water only. Compressed air is a 'whole different animal'. Yes,
sometimes it works 'OK', for a while, at pressures below 100 psi. but
it's NEVER a good idea.

And some compressors, probably including the refrigeration compressor
being discussed, peak out at about 300 psi ... That can be DANGEROUS!

A failed PVC structure typically throws hard sharp 'shrapnel' all over
the place, and can be very dangerous.

Compressed air plumbing should be ONLY made from iron (steel) or copper.
Even if it fails, it does not usually fragment like PVC.

There IS a type of PVC that's made and rated for compressed air use.
It's NOT commonly available at home centers and such. A good industrial
compressed air supplier should be able to get it, but why bother. Common
copper water pipe is readily available, no more expensive, and perfectly
suitable for the use in question.

Dan Mitchell
==========

Edwin Ross Quantrall wrote:
>
><snip>
>
> Wouldn't a 9" or 12" section of 3" or 4" dia. PVC, capped at each end
> and sealed with silicon sealant; then drilled, tapped on opposite
> sides/ends and the fittings sealed with silicon, Teflon® tape or wax be
> just as good, simpler to make and take up less space?
>
> Just another thought.

Very true. It's a BAD suggestion!

Dan Mitchell
==========

Morgans wrote:
>
> "Edwin Ross Quantrall" <[email protected]> wrote
>
> > Wouldn't a 9" or 12" section of 3" or 4" dia. PVC, capped at each end
> > and sealed with silicon sealant; then drilled, tapped on opposite
> > sides/ends and the fittings sealed with silicon, Teflon® tape or wax be
> > just as good, simpler to make and take up less space?
> >
> > Just another thought.
> >
> > --
> > Edwin
>
> BAD IDEA ! ! ! ! ! ! ! ! ! ! ! DO NOT DO THIS!!!!!
>
> Look on the side of pvc drain pipe. I am sure this is what you meant to
> use. It says, not for pressure. It can shatter with explosive results,
> when struck while pressurized.
> --
> Jim in NC

A " pulsation damper" **IS** an air tank! ... even if a small one. It's
still a safety hazard if made of common PVC, especially in an
application where the pressure MIGHT (even if by accident) reach 300 psi!

Dan Mitchell
==========

Dennis Loep wrote:
>
<snip>

> Just don't use it as an air tank!!! Only as a pulsation damper!!
>
> Great thinking Edwin!!
> --
> Dennis Loep
> The Glueing Dutchman
>
> "The most exciting phrase to hear in science, the one that heralds new
> discoveries, is not 'Eureka!' but 'That's funny ...'"
> Isaac Asimov

Morgans wrote:

> "Edwin Ross Quantrall" <[email protected]> wrote
>
>
>>Wouldn't a 9" or 12" section of 3" or 4" dia. PVC, capped at each end
>>and sealed with silicon sealant; then drilled, tapped on opposite
>>sides/ends and the fittings sealed with silicon, Teflon® tape or wax be
>>just as good, simpler to make and take up less space?
>>
>>Just another thought.
>>
>>--
>>Edwin
>>
>
> BAD IDEA ! ! ! ! ! ! ! ! ! ! ! DO NOT DO THIS!!!!!
>
> Look on the side of pvc drain pipe. I am sure this is what you meant to
> use. It says, not for pressure. It can shatter with explosive results,
> when struck while pressurized.
>

Let me clarify. I'm suggesting this *STRICTLY(!!!)* as a pulsation
damper. If one is worried about an overpressure "explosion"; one could
either drill and install a relief-valve, or insert a small rubber plug
(chained or otherwise attached to the damper, of course -- wouldn't want
it flying into the next room...) that has been firmly pushed into place
but will pop out if the air inside reaches, say, 40-60 psi. (I spray at
about 20-25 psi, so I don't think I'd have too many problems if I needed
such a set-up.)

--
Edwin

(Remove "DIESPAMDIE!")

"Me? I'm dishonest, and a dishonest man you can trust to be dishonest...
Honestly. It's the honest ones you want to watch out for, because you
can never predict when they're going to do something incredibly stupid."
- Captain Jack Sparrow (Disney's Pirates of the Caribbean: The Curse of
the Black Pearl)

Daniel A. Mitchell wrote:

> A " pulsation damper" **IS** an air tank! ... even if a small one. It's
> still a safety hazard if made of common PVC, especially in an
> application where the pressure MIGHT (even if by accident) reach 300 psi!
>

Let me clarify. I'm suggesting this *STRICTLY(!!!)* as a pulsation
damper. If one is worried about an overpressure "explosion"; one could
either drill and install a relief-valve, or insert a small rubber plug
(chained or otherwise attached to the damper, of course -- wouldn't want
it flying into the next room...) that has been firmly pushed into place
but will pop out if the air inside reaches, say, 40-60 psi. (I spray at
about 20-25 psi, so I don't think I'd have too many problems if I needed
such a set-up.)

--
Edwin

(Remove "DIESPAMDIE!")

"Me? I'm dishonest, and a dishonest man you can trust to be dishonest...
Honestly. It's the honest ones you want to watch out for, because you
can never predict when they're going to do something incredibly stupid."
- Captain Jack Sparrow (Disney's Pirates of the Caribbean: The Curse of
the Black Pearl)

Dennis Loep wrote:

> 8<---------------
>
>> > If you are going to use an air tank just for pulsation dampening
>> > reasons. Why not take a yard/meter long metal tube get it welded
>> > shut at both ends by someone who knows how to weld. (I think every
>> > body knows someone) Let someone drill two holes in the ends (or do
>> > it yourself) and cut thread in them which will accept the fittings
>> > for your specific brand of airbrush/hose. Most repair shops have a
>> > good tap and die set handy and a lot of mechanics will not have a
>> > lot of trouble doing that for you. (at least not here in Holland). This
>> > wil give you a cheap pulsation damper that won't take too much
>> > space and which you can simply connect in line of your air hose.
>> >
>> > PS. The welds don't need to be the best in the world because you are
>> > not really presurising the tube/tank.
>> >
>> > Just a thought
>>
>>Wouldn't a 9" or 12" section of 3" or 4" dia. PVC, capped at each end
>>and sealed with silicon sealant; then drilled, tapped on opposite
>>sides/ends and the fittings sealed with silicon, Teflon® tape or wax be
>>just as good, simpler to make and take up less space?
>>
>>Just another thought.
>>
>>--
>>Edwin
>
> I think that that is a nice and indeed simpler solution to the problem.
> I just used to have an old piece of pipe and made mine of metal. but I think
> PVC will do too.
> Just don't use it as an air tank!!! Only as a pulsation damper!!
>
> Great thinking Edwin!!

Thanks.


--
Edwin

(Remove "DIESPAMDIE!")

"Me? I'm dishonest, and a dishonest man you can trust to be dishonest...
Honestly. It's the honest ones you want to watch out for, because you
can never predict when they're going to do something incredibly stupid."
- Captain Jack Sparrow (Disney's Pirates of the Caribbean: The Curse of
the Black Pearl)

Perfectly acceptable for all normal airbrushing uses.

The only reservation is the original poster's suggestion to use a
refrigeration compressor ... these can sometimes produce about 300 psi
or so. Few tires would withstand that kind of pressure!

Dan Mitchell
==========

Des Bromilow wrote:
>
> Sorry coming in late here, but i know a few people who use car tyres for the
> "tank" when airbrusing.
> For some pocket change you can add any number of valve stems to an old rim
> (with a tubeless tyre) and connect as little or as much to it as you want.
> A car tyre is larger than a fire extinguisher, but it may be able to be
> hidden in the bottom of a workbench, or somewhere else out of the way.
>
> HTH,
> Des
> "Daniel A. Mitchell" <[email protected]> wrote in message
> news:[email protected]...
> > Look for a used commercial compressed-air system 'moisture trap' at a
> > junkyard. These often consist of a small pressure tank about the size of
> > a grapefruit. They have a drain valve in the bottom to release the
> > moisture. These little 'tanks' are *NOT* the kind of moisture trap
> > being recommended for airbrushing (they're for power tools). However,
> > they're ideal for your pressure tank purpose, and can be 'had' for a
> > couple bucks.
> >
> > Spray painting moisture traps have filter elements to remove the
> > moisture.
> >
> > Dan Mitchell
> > ==========
> >
> > CFF wrote:
> > >
> > > I fully understand the significane of employing an air tank. As an
> > > hobbist, the major difficulty in putting an air tank in the design is
> > > it is difficult to find a cheap, commerically small air tank. While
> > > ruling out all the options of making the whole thing look big, some
> > > suggest using an empty fire extinguisher to convert. But, as far as I
> > > understand, there is quite an amount of drilling and welding work need
> > > to be done in order to mount the host connectors plus guage at the
> > > inlet and outlet. That is something that I just don't have the
> > > engineering facility to accomplish. Considering the relatively low
> > > pressure required for airbrushing application, I am quite happy to
> > > sacrify consistence of air flow as long as it does provide a
> > > reasonably constant presure at short bursts. However, if there are
> > > feasible suggestions that I can manage to modify a fire extinguisher
> > > without the need of welding, I will be glad to consider. I am sure
> > > that will make it an ideal setup.
> > >
> > > CFF

Steve Caple wrote:
>
> Rich S. wrote:
> > Damn! And I was just on the verge of being able to drop a nice, fresh, crisp
> > Idaho #2 on my neighbor's deck - 220 yards away. Now you have to go and
> > spoil my fun.
>
> Way overkill for my needs: I just want a small mortar, very
> high trajectory so as not to indicate origin when round hits,
> range no more than 50 yards; and find some sort of sabot to
> keep a quart-size water baloon full of fermented cat sh-t
> slurry intact on launch; target: rolling boom-boxes.

Ooohhh, Man! Frustrated music critic! Most dangerous creature there
is! :-)

Bill Shuey

We get a few fools late at night that like to park and BS with their
friends while thumpa-ing.....I simply go out axe in hand and inform them
that if they wake up my wife and the crazy redhead bitches at me, I'll
come back out and use the axe to take out the pain of being bitched at
on their soon to be ex-car. I've yet to have to go back out.......

"Rich S." wrote:

> The problem with the high trajectory is the lengthy "time to target". You
> did say a *rolling* boombox, which adds the problem of lead and wind
> deflection. A moving windshield vent at 50 yards is a mighty small target.
> Might I suggest a dispersal device such as the CPU (Catshit Bomb Unit)
> which, in this case, would disperse "Terdlets" in a pattern designed to
> eliminate the variables in aim. Sort of a "Weapon of Bass Destruction" or
> "No More Thumper".
>
> Rich "Make My Day" S.

e wrote:

> best stay away from spk, einsturzende niebaten or skinny puppy.

Einsturzende NEUBAUTEN

(Collapsing New Buildings)

Mark Newton wrote:

> e wrote:
>
> > best stay away from spk, einsturzende niebaten or skinny puppy.
>
> Einsturzende NEUBAUTEN
>
> (Collapsing New Buildings)

True, however if you're too close it doesn't
matter how you spell it. HTH.
--
SATOR AREPO TENET OPERA ROTAS
Have 5 nice days! John
******************************
--- ILN 000.000.001 ---

e wrote:

>>> best stay away from spk, einsturzende niebaten or skinny puppy.
>>
>> Einsturzende NEUBAUTEN
>>
>> (Collapsing New Buildings)
>>
> hey, someone's awake out there. blixa would be pleased.

The kids have recently discovered all my old vinyl LPs, and resurrected
a turntable to play them on. Which is all fine and well, but they have
gotten into things I would have never guessed they would - apart from
Einsturzende Neubauten, we're hearing a lot of Cabaret Voltaire and
Throwing Muses lately!!! :-)

Mark.

e wrote:

>>The kids have recently discovered all my old vinyl LPs, and resurrected
>>a turntable to play them on. Which is all fine and well, but they have
>>gotten into things I would have never guessed they would - apart from
>>Einsturzende Neubauten, we're hearing a lot of Cabaret Voltaire and
>>Throwing Muses lately!!! :-)

> i just posted a vinyl-mp3 encode od cab volts ymca from 79.
> you must have smart kids.
> tell then to keep an eye out for posts by (e)
> in alt.binaries.sounds.mp3.nospam and the decade groups.
> maybe some scraping foetus off the wheel
> or throbbing gristle....

Throbbing Gristle - now there's a force to be reckoned with!

Years ago, I used to rent a flat above a cafe in one of the trendier
suburbs here. The stereotypical Newtown queen who ran the cafe used to
do his cleaning and prep early on a Sunday morning, all the while
listening to Madonna, played VERY loudly.

After my polite requests to turn it down were ignored, I decided that
two could play that game. To counter his Madonna, I had Genesis P.
Orridge, and a 200 watt Peavey bass amp face down on the floor above his
kitchen. I won.

And thanks for the heads up, we'll look for your posts.

All the best,

Mark.

Good advice!

There IS a type of PVC pipe that's compressed air rated ... I believe
it's color coded GREEN. It's an industrial product, and NOT available in
consumer outlets.

But all the common white, tan, and gray PVC is NOT compressed air rated,
and is unsafe, even at low pressures. It may hold, for a while, but is
subject to catastrophic failure, sooner or later. The rupture itself
isn't particularly the problem, but that the PVC, when it fails, fails
MASSIVELY (unlike a similar failure in iron or copper pipe) resulting in
a bigger (faster) release of energy, AND much sharp shrapnel being
thrown all over the place, with accompanying collateral damage. NOT GOOD!

Dan Mitchell
==========

"Xbase (Please note spammers email address used)" wrote:
>
> I know of a glass toughening plant which used compressed air as a quench -
> it had plastic pipes - they burst causing a lot of damage - including cars
> at a next door BMW dealership.
>
> Do not put compressed air anywhere near plastic pipes

Sounds a bit like Corelle plates, they're tough right up until they
explode into millions of shards.

"Daniel A. Mitchell" wrote:

> But all the common white, tan, and gray PVC is NOT compressed air rated,
> and is unsafe, even at low pressures. It may hold, for a while, but is
> subject to catastrophic failure, sooner or later. The rupture itself
> isn't particularly the problem, but that the PVC, when it fails, fails
> MASSIVELY (unlike a similar failure in iron or copper pipe) resulting in
> a bigger (faster) release of energy, AND much sharp shrapnel being
> thrown all over the place, with accompanying collateral damage. NOT GOOD!
>
> Dan Mitchell
> ==========
>
> "Xbase (Please note spammers email address used)" wrote:
> >
> > I know of a glass toughening plant which used compressed air as a quench -
> > it had plastic pipes - they burst causing a lot of damage - including cars
> > at a next door BMW dealership.
> >
> > Do not put compressed air anywhere near plastic pipes

Might well be so.

Dan Mitchell
==========

Gary Coffman wrote:
>
> On Mon, 26 Jan 2004 10:09:41 -0500, "Daniel A. Mitchell" <[email protected]> wrote:
> >There IS a type of PVC pipe that's compressed air rated ... I believe
> >it's color coded GREEN. It's an industrial product, and NOT available in
> >consumer outlets.
>
> I don't believe that's PVC. It is a different plastic. PEX?
>
> Gary

'OK', I did some more checking. The compressed-air rated plastic pipe is
"ductile ABS" ("Acrylonitrate-Butadiene-Styrene"), it is *NOT* PVC or
PEX. Th eposter, below, confirms this and adds more information. It is
rated to 185 psi. At least some make(s) of this ABS pipe is color coded green.

This is a plastic pipe which is rated for compressed air use. It is
intended only for "shielded" use, not "exposed", for the safety reasons
previously mentioned. It's not compatible with some synthetic compressor
oils. It is EXPENSIVE. Chem-Aire is one brand name. IPEX "Duraplus" (see
below) is another.

These are industrial products, are not commonly available, and are expensive.

As far as I can find, this is the ONLY type plastic pipe that's safe to
use with compressed-air systems.

In many areas it is a citable code violation to use PVC for compressed
air purposes. Anyone contemplating such use should read, among other
things, the information provided by the poster below.

Note that the maximum pressure for the ABS pipe is only 185 psi ... FAR
below the 300 psi potential int he refrigeration compressor sytem
discussion that started this thread.

Dan Mitchell
==========


Edwin Pawlowski wrote:
>
> > Gary Coffman wrote:
> >>
> >> On Mon, 26 Jan 2004 10:09:41 -0500, "Daniel A. Mitchell"
> >> <[email protected]> wrote:
> >>> There IS a type of PVC pipe that's compressed air rated ... I
> >>> believe it's color coded GREEN. It's an industrial product, and NOT
> >>> available in consumer outlets.
> >>
> >> I don't believe that's PVC. It is a different plastic. PEX?
> >>
> >> Gary
>
> PEX is not rated for air. It is cross linked polyethelyne and is safe for
> potable water and at temperatures to 180. It can be use for radient heat
> also.
> http://www.ppfahome.org/pex/
>
> According to this, ABS may be possible.
> http://www.lni.wa.gov/wisha/regs/PDFs/WRD5.40-PVCPipe.pdf
>
> Ipex is one company that makes it.
> http://www.ipexinc.com/Content/EN_CA/2_0_Products/2_1_Industrial/2_1_4_Compressed_air.asp
>
> --
> Ed
> [email protected]
> http://pages.cthome.net/edhome

"Gary Coffman" <[email protected]> wrote in message

> On 16 Jan 2004 02:29:28 -0800, [email protected] (CFF) wrote:
> >I have no intention to use the
> >setup for any other purpose other than operating my Badger airbrush.
> >The point I would like to emphasise is I will not be including an air
> >reserviour in the setup as many designs would.
>
> You need at least a small reservoir to smooth out the
> pulsations in the air caused by a piston compressor.
> So if your plan is to not include a reservoir, you can't
> use a piston compressor. You need a vane or turbine
> type compressor which supplies constant flow.

Hey, its a friggen airbrush. They work with cheapo diaphragm compressors.
The hose is a big enough reservoir to run it for a while.
Ed

"Daniel A. Mitchell" <[email protected]> wrote:

>CAREFUL!
>
>While you might well get away with this at the usual 30 psi or so used
>in airbrushing, common PVC pipe is **NOT** rated for compressed air use,
>and can rupture easily.

I've got a pond (wife raises fish) and she had a specialized
low pressure, high volume "compressor" installed to put
extra air into the bottom of the pond. It's not a blower
style (the other type sold for this job), as she needed to
push air to 12' down max. She says it's a rotary vane style
compressor, and the mnfr says it has a 15 psi limiter on it.
They say it's OK to use PVC schedule 40 2" pipe to run from
the garage to the pond. Anyone want to comment on how low a
pressure would be considered safe? I called a guy who
installs tank bubblers in plating systems, and he says they
use PVC, but the tanks are seldom over 6 feet deep.

Todd Pattist
(Remove DONTSPAMME from address to email reply.)
___
Make a commitment to learn something from every flight.
Share what you learn.

Edwin Ross Quantrall wrote:
> Wouldn't a 9" or 12" section of 3" or 4" dia. PVC . . .

Why on earth would you do that, when a perfectly qualified and
portable air source is only $16 - take down to the [hah!
just find one! - with an air hose] "corner gas station" and
fill it up until you get your own low cost general purpose
compressor.


--
Steve Caple

Dennis Loep wrote:
> Steve some people already have a compressor.
I have a compressor and it has a 2 gallon tank; but the 5 gal
tank without the compressor on it is much easier to carry
around and has enough capacity to run an airbruch quite a
while.

--
Steve Caple

Rich S. wrote:
> Damn! And I was just on the verge of being able to drop a nice, fresh, crisp
> Idaho #2 on my neighbor's deck - 220 yards away. Now you have to go and
> spoil my fun.

Way overkill for my needs: I just want a small mortar, very
high trajectory so as not to indicate origin when round hits,
range no more than 50 yards; and find some sort of sabot to
keep a quart-size water baloon full of fermented cat sh-t
slurry intact on launch; target: rolling boom-boxes. A few
aiming stakes to mark target position for firing with expected
coincident arrival at impact point. Ideal: schploot! on hood,
with large part of payload going into below windshield vent.


thumpa thumpa thumpa phwwtt thumpa schploot! eeewwwww!

--
Steve Caple

Rich S. wrote:
> A moving windshield vent at 50 yards is a mighty small target.

Anywhere on the hood would do. And a rooftop hit would not be
without merit. Even a near miss should have some splash hits.

--
Steve Caple

William H. Shuey wrote:
> Ooohhh, Man! Frustrated music critic!

I was about to say that it was the impolite noise, not the
music, but then realized that I don't mind ranchero or banda
music nearly as much as the crap like repetitive sameness of
rap or hip-hop or whatever, or the pouty industrial "country"
product like that grimacing a--hole with the merkin on his
chin that does Ford truck ads. But anything at those absurd
volume levels past 10pm is rude, even Zappa or Zevon.

--
Steve Caple

Mark Schynert wrote:
> C'mon, Zappa's supposed to be rude.

Not all of it, actually; most of Burnt Weenie Sandwich is
often lovely liquid instrumentals (although some stodgy
persons might find the time signatures quite rude!). But then
it _does_ start out with "WPLJ"

"White port and lemon juice, oooh what it do to you!"

--
Steve Caple

"Morgans" <[email protected]> wrote in message
news:[email protected]...
>
> Let ME clarify. It is a bad ides, and it does not matter what function it
> is doing, it is A BAD idea to put even 40 lbs pressure into it.
>
> Tell you what. Go get some 4" PVC, cap it and put your 60 lbs into it,
and
> then hit it with a hammer. Report back after your wounds have healed.
> --
> Jim in NC

Damn! And I was just on the verge of being able to drop a nice, fresh, crisp
Idaho #2 on my neighbor's deck - 220 yards away. Now you have to go and
spoil my fun.

http://www.spudtech.com/

Rich "Outgoing" S.

>
>e wrote:
>
>>>The kids have recently discovered all my old vinyl LPs, and resurrected
>>>a turntable to play them on. Which is all fine and well, but they have
>>>gotten into things I would have never guessed they would - apart from
>>>Einsturzende Neubauten, we're hearing a lot of Cabaret Voltaire and
>>>Throwing Muses lately!!! :-)
>
>> i just posted a vinyl-mp3 encode od cab volts ymca from 79.
>> you must have smart kids.
>> tell then to keep an eye out for posts by (e)
>> in alt.binaries.sounds.mp3.nospam and the decade groups.
>> maybe some scraping foetus off the wheel
>> or throbbing gristle....
>
>Throbbing Gristle - now there's a force to be reckoned with!
>
>Years ago, I used to rent a flat above a cafe in one of the trendier
>suburbs here. The stereotypical Newtown queen who ran the cafe used to
>do his cleaning and prep early on a Sunday morning, all the while
>listening to Madonna, played VERY loudly.
>
>After my polite requests to turn it down were ignored, I decided that
>two could play that game. To counter his Madonna, I had Genesis P.
>Orridge, and a 200 watt Peavey bass amp face down on the floor above his
>kitchen. I won.
>
>And thanks for the heads up, we'll look for your posts.
>
>All the best,
>
>Mark.
>
>
>
i do reqs and can find any music. that goes to anyone here.
and yes, i do have the sique sique sputnik flexi shaped like
a luscious hooter.
and the ravers christmas tree single of punk rock christmas.
we kill for colored vinyl.

You can buy a 2.5 gallon, 8 amp complete compressor from Harbor Freight right
now for $79.95 + $5 handling that is probably lighter and will work
better than your home-made refrigeration unit based improvisation, or
for the same price, a specialized "air-brush compressor" that weighs
about 10 lbs & includes regulators & filters.




--

Larry Wasserman Baltimore, Maryland
[email protected]

>
>William H. Shuey wrote:
>> Ooohhh, Man! Frustrated music critic!
>
>I was about to say that it was the impolite noise, not the
>music, but then realized that I don't mind ranchero or banda
>music nearly as much as the crap like repetitive sameness of
>rap or hip-hop or whatever, or the pouty industrial "country"
>product like that grimacing a--hole with the merkin on his
>chin that does Ford truck ads. But anything at those absurd
>volume levels past 10pm is rude, even Zappa or Zevon.
>
best stay away from spk, einsturzende niebaten or skinny
puppy.

Jim Stockton wrote ...

> Compressor power is related to how much air it moves at a given
> pressure.
> The higher the CFM at a given pressure the higher the power requirement.
> If you only plan to use the airbrush I think just about anything will do
> but if you want to power air tools or a big sprayer you need a higher
> power unit. Check the pressure and volume requirements of what tools you
> want to use and then decide what to buy.


I've been playing with the notion of a compressor on a budget. I
simply can't justify the cost of a "mother-of-all-compressors" model,
yet I'd like the benefits of same. I have an old propane tank that
measures to be around 80 gallons capacity. I wondered if it was
feasible to marry it to a $200 compressor (nail gun pancake type). It
might take forever to fill, but I'd have a big reservoir to draw on.
Rather than blow $200+ to find out, I looked at the basic
relationships of PSI, CFM in & CFM out. What follows is my own back
of the envelope analysis.

Compressor ratings:
3.7 CFM @ 40 PSI
2.6 CFM @ 90 PSI
Stop switch at 150 PSI so that's 0 CFM @ 150 PSI

I ran a regression on those relationships & got:
CFM = -6.048*PSI² - 7.3521*PSI + 150
CFM as a function of PSI is obviously eponential (it delevers less and
less as PSI goes up) and it turns out that this 2nd order polynomial
fits the manufacturer's data extremely well (R²=1).

The first question is how long will this little compressor take to
fill this bigass tank? Rather than throw calculus into it, I took an
incremental approach & used the above to compute CFM at each level of
PSI from 0 to 145, dividing the result into 1 minute at each PSI level
to get the time needed to raise the pressure by 1 PSI. Summing the
results, it takes right at 90 minutes to fill an empty tank to 145
PSI.

The next question is how long does it take to draw down the tank from
145 PSI to some minimum useful pressure, depending on the tool? In
other words, can I get any work done?

Given:
145 PSI in the tank
90, 80 or 40 PSI at the regulator according to the tool
15 pressure/atmospheric pressure
80 gallons capacity
7.5 gallons/ft³

Then:
(145 / 15) * (80 / 7.5) = 103 ft³ of air in the tank at 145 PSI
and:
(90 / 145) * 103 = 64 ft³ of air in the tank at 90 PSI
(80 / 145) * 103 = 57 ft³ of air in the tank at 80 PSI
(40 / 145) * 103 = 28 ft³ of air in the tank at 40 PSI

Therefore the usable amount of air is:
103 - 64 = 39 ft³ stopping at 90 PSI, or
103 - 57 = 46 ft³ stopping at 80 PSI, or
103 - 28 = 75 ft³ stopping at 40 PSI.
At that point I have to stop and let the tank refill.

How much time that equates to depends on the tool being used and its
CFM requirements. Using that wonderful resource for truth and
accurate figures called the internet, I find:
Little suction type sandblasters use as little as 7 CFM @ 80 PSI.
Sanders, maybe 8 CFM @ 90 PSI.
A rivet gun at 25% usage is perhaps 4 CFM.
Spray guns require around 10 CFM but can run down to 40 PSI or so.

Therefore I'm looking at 5 to 10 minutes work depending on the tool
before I get a beer and wait for the compressor. All of this assumes
that the compressor doesn't even kick on until I stop working. In
truth, it would start making an effort to refill the tank at say 110
PSI, so work times would be _very_ slightly longer.

The final question is how long do I have to suck suds before I can go
back to work? Using the incremental data from above, to recover from
90 PSI back up to 145 PSI will take just over an hour, and to recover
from 40 PSI (in the midst of a paint job) would take an hour and
twenty minutes!

My conclusion is that of conventional wisdom. You can't substitute
for power. Besides, even if I could live with the recovery times, the
bill for beer would negate the savings on the compressor!

Cautions: Anyone contemplating a similar scheme needs to make sure
the old propane tank is empty (duh), pressure test it (fill it almost
full of water & run it to 200 PSI, preferrably from a distance or
behind a berm) and of course find a way to remove the stinko residue
from the tank.

Daniel

Juergen Hannappel wrote ...
> [email protected] (Daniel) writes:
>
>
> [...]
>
> > Compressor ratings:
> > 3.7 CFM @ 40 PSI
> > 2.6 CFM @ 90 PSI
> > Stop switch at 150 PSI so that's 0 CFM @ 150 PSI
> >
> > I ran a regression on those relationships & got:
> > CFM = -6.048*PSI² - 7.3521*PSI + 150
> > CFM as a function of PSI is obviously eponential (it delevers less and
> > less as PSI goes up) and it turns out that this 2nd order polynomial
> > fits the manufacturer's data extremely well (R²=1).
>
> ... which is not to be wondered at, because you can always fit n data
> points exactly with a (n-1)th order polynomial.

Right you are! Thank you, I should have been suspicious when I saw a
"perfect" fit.

> But your result is
> false because the zero throughput at 150PSI is not due to lack of
> power but due to the stop switch...

I had thought about that. Since this is all back of the envelope, we
can omit the 0 @ 150 data point & even (falsely) assume a best
posssible relationship between the remaining data points that is
linear. Though that would extend the 0 CFM output to somewhere
upwards of 200 PSI, we know the compressor will still shut off at 150
PSI, so I had figured the recovery times using the same maximum tank
pressure of 145 PSI. In that scenario, the times still run nearly an
hour to fill an empty tank, 30 minutes to recover from 90 PSI, and 45
minutes from 40 PSI. The practical result remains unchanged, it's
just not feasible to work some 20% of the time and wait on the
compressor 80%.

Re comments from several others, it was the original poster who was
needing a model airbrush setup, I was wanting a budget biggie
(something for nothing). But had the capacities even been feasible on
paper, Rex is right - I'd burn it up.

Daniel

"Rex B" <[email protected]> wrote in message
news:[email protected]...
> On Fri, 16 Jan 2004 18:00:59 GMT, Mark <[email protected]>
wrote:
>
> |
> |
> |Rex B wrote:
> |
> |>
> |> Don't tell that to my dad. He's been using the same old refrigerator
> compressor
> |> since the late 60's, doing professional A/C repair on home ands cars.
> |
> |
> |Are you sure it isn't an oil bath compressor?
>
> No, but it's the round, sealed type about the size of a slightly flattened
> bowling ball. Same color too.
> Rex in Fort Worth

That is the same shape as my Sil-air Compressor and that is an oil bath type
compressor.
It indeed looks like a fridge compressor.

--
Dennis Loep
The Glueing Dutchman

"The most exciting phrase to hear in science, the one that heralds new
discoveries, is not 'Eureka!' but 'That's funny ...'"
Isaac Asimov

8<-------
>If you're the type to use a micrometer as a C clamp,
> Gary
8<---------

AAAAARGH, that hurts!!!!!!!!!!!!!!!!
--
Dennis Loep
The Glueing Dutchman

"The most exciting phrase to hear in science, the one that heralds new
discoveries, is not 'Eureka!' but 'That's funny ...'"
Isaac Asimov

<not.fishplate> wrote in message
news:[email protected]...
> On 17 Jan 2004 20:47:37 -0800, [email protected] (CFF) wrote:
>
> >I fully understand the significane of employing an air tank. As an
> >hobbist, the major difficulty in putting an air tank in the design is
> >it is difficult to find a cheap, commerically small air tank.
>
> Why not use one of those portable air tanks used for inflating tires?
> Not too expensive, and trivial to plumb as required. In a pinch, you
> can even use it to blow up a slack tire.
>
> A 5 gallon tank is $16 at Sears right now
>
http://www.sears.com/sr/javasr/product.do?BV_UseBVCookie=Yes&vertical=TOOL&p
id=00915200000
>
> Jeff Sc.
> Low Pressure, Ga.

Go to this page and you wil find a complete compressor with all the bits and
pieces for $113 and some.

If you are going to use an air tank just for pulsation dampening reasons.
Why not take a yard/meter long metal tube get it welded shut at both ends by
someone who knows how to weld. (I think every body knows someone)
Let someone drill two holes in the ends (or do it yourself) and cut thread
in them which will accept the fittings for your specific brand of
airbrush/hose. Most repair shops have a good tap and die set handy and a lot
of mechanics will not have a lot of trouble doing that for you. (at least
not here in Holland).
This wil give you a cheap pulsation damper that won't take too much space
and which you can simply connect in line of your air hose.

PS. The welds don't need to be the best in the world because you are not
really presurising the tube/tank.

Just a thought

--
Dennis Loep
The Glueing Dutchman

"The most exciting phrase to hear in science, the one that heralds new
discoveries, is not 'Eureka!' but 'That's funny ...'"
Isaac Asimov

8<---------------
> > If you are going to use an air tank just for pulsation dampening
> > reasons. Why not take a yard/meter long metal tube get it welded
> > shut at both ends by someone who knows how to weld. (I think every
> > body knows someone) Let someone drill two holes in the ends (or do
> > it yourself) and cut thread in them which will accept the fittings
> > for your specific brand of airbrush/hose. Most repair shops have a
> > good tap and die set handy and a lot of mechanics will not have a
> > lot of trouble doing that for you. (at least not here in Holland). This
> > wil give you a cheap pulsation damper that won't take too much
> > space and which you can simply connect in line of your air hose.
> >
> > PS. The welds don't need to be the best in the world because you are
> > not really presurising the tube/tank.
> >
> > Just a thought
>
> Wouldn't a 9" or 12" section of 3" or 4" dia. PVC, capped at each end
> and sealed with silicon sealant; then drilled, tapped on opposite
> sides/ends and the fittings sealed with silicon, Teflon® tape or wax be
> just as good, simpler to make and take up less space?
>
> Just another thought.
>
> --
> Edwin
>
> (Remove "DIESPAMDIE!")
>
> "Me? I'm dishonest, and a dishonest man you can trust to be dishonest...
> Honestly. It's the honest ones you want to watch out for, because you
> can never predict when they're going to do something incredibly stupid."
> - Captain Jack Sparrow (Disney's Pirates of the Caribbean: The Curse of
> the Black Pearl)

I think that that is a nice and indeed simpler solution to the problem.
I just used to have an old piece of pipe and made mine of metal. but I think
PVC will do too.
Just don't use it as an air tank!!! Only as a pulsation damper!!

Great thinking Edwin!!
--
Dennis Loep
The Glueing Dutchman

"The most exciting phrase to hear in science, the one that heralds new
discoveries, is not 'Eureka!' but 'That's funny ...'"
Isaac Asimov

"Steve Caple" <[email protected]> wrote in message
news:[email protected]...
> Edwin Ross Quantrall wrote:
> > Wouldn't a 9" or 12" section of 3" or 4" dia. PVC . . .
>
> Why on earth would you do that, when a perfectly qualified and
> portable air source is only $16 - take down to the [hah!
> just find one! - with an air hose] "corner gas station" and
> fill it up until you get your own low cost general purpose
> compressor.
>
>
> --
> Steve Caple

Steve some people already have a compressor.
And just need a pulsation damper.
(ME)

--
Dennis Loep
The Glueing Dutchman

"The most exciting phrase to hear in science, the one that heralds new
discoveries, is not 'Eureka!' but 'That's funny ...'"
Isaac Asimov

"Morgans" <[email protected]> wrote in message
news:[email protected]...
>
> "Edwin Ross Quantrall" <[email protected]> wrote
>
> > Wouldn't a 9" or 12" section of 3" or 4" dia. PVC, capped at each end
> > and sealed with silicon sealant; then drilled, tapped on opposite
> > sides/ends and the fittings sealed with silicon, Teflon® tape or wax be
> > just as good, simpler to make and take up less space?
> >
> > Just another thought.
> >
> > --
> > Edwin
>
> BAD IDEA ! ! ! ! ! ! ! ! ! ! ! DO NOT DO THIS!!!!!
>
> Look on the side of pvc drain pipe. I am sure this is what you meant to
> use. It says, not for pressure. It can shatter with explosive results,
> when struck while pressurized.
> --
> Jim in NC
>

That's what I said!!
DO NOT USE THIS AS AN AIR TANK!!

Only as a pulsation damper

Dennis Loep
The Glueing Dutchman

"The most exciting phrase to hear in science, the one that heralds new
discoveries, is not 'Eureka!' but 'That's funny ...'"
Isaac Asimov

I know of a glass toughening plant which used compressed air as a quench -
it had plastic pipes - they burst causing a lot of damage - including cars
at a next door BMW dealership.

Do not put compressed air anywhere near plastic pipes

"Xbase (Please note spammers email address used)" <[email protected]>
wrote in message news:[email protected]...
> I know of a glass toughening plant which used compressed air as a quench -
> it had plastic pipes - they burst causing a lot of damage - including
cars
> at a next door BMW dealership.
>
> Do not put compressed air anywhere near plastic pipes
>
Was it a meat eating glass toughening plant??

--
Dennis Loep
The Glueing Dutchman

"The most exciting phrase to hear in science, the one that heralds new
discoveries, is not 'Eureka!' but 'That's funny ...'"
Isaac Asimov

Hello:

Although I have a large compressor in a garage, running
air lines to a relocated spray booth was impractical.
Often blasting brass rollingstock at up to 70 PSI and
painting as low as 8 PSI, an in expensive air supply
was developed using an inexpensive 125 PSI tire pump
and a portable 5 gallon tank.. The basic cost was less
than $90 US. With refinements including a manifold to
connect 5 devices and a fine pressure gauge, the total
jumped to about $150.

One of the big secrets is removing water. The very hot air
leaving a compressor may have a low humidity, making a
moisture trap ineffective here. When the air cools to
room temperature, the humidity may increase to
saturation, where the water condenses. Water can
collect in lines and tank, which requires frequent
removal. The solution is a cooling coil and moisture
trap between compressor and tank. If you are up to a
little bit of simple plumbing, this can be made from
readily available parts.

The pump is noisy, but once the tank is charged many
hours of quiet spraying are yielded.

Some of the elements may not suit your requirements,
but they may spur your thoughts.

For a discussion and image see: Methods Index/Spraying
Accessories on Modelrailroad Technical Information
below.


Hope this helps.,

Budb

Author of:

Modelrailroad Technical Information

http://www.geocities.com/budb3/

PROTOTYPE TECHNICAL INFO FOR MODELRAILROADERS

http://www.freeyellow.com/members4/budb/

Moderator of:

MR TECHNICAL HELP GROUP

href="http://groups.yahoo.com/group/mrtechhelp

COUPLER HELP GROUP

http://groups.yahoo.com/group/mrcouplers








[email protected] (CFF) wrote in message news:<[email protected]>...
> I am trying to home-build an air pump for hobby modelling airbrushing
> application using a 220V domestic fridge air compressor. To make
> things simpler, the basic arrangement is to connect the compressor
> output to an air regulator (with guage attached) which, in turn,
> connects to a water trap before going to the airbrush. The idea is to
> keep the size of the whole thing as small as possible. I still haven't
> bought the compressor but need something to be clarified beforehand.
> My question is:
>
> What is the minimum power rating required for the compressor to
> deliver (at least) 40 psi (or 0.276 MPa) pressure?
>
> Thanks for any suggestion.
>
> CFF

>
>The kids have recently discovered all my old vinyl LPs, and resurrected
>a turntable to play them on. Which is all fine and well, but they have
>gotten into things I would have never guessed they would - apart from
>Einsturzende Neubauten, we're hearing a lot of Cabaret Voltaire and
>Throwing Muses lately!!! :-)
>
>Mark.
>
i just posted a vinyl-mp3 encode od cab volts ymca from 79.
you must have smart kids.
tell then to keep an eye out for posts by (e)
in alt.binaries.sounds.mp3.nospam and the decade groups.
maybe some scraping foetus off the wheel
or throbbing gristle....

Richard Lamb wrote:
> Is that kinda like electricty?
> PSI for volts E
> CFM for current I
> Power = I^2 E
^^^^^^^^^^^^^^^
You have the idea, but accidentally slipped on the formula. P = I E.

I believe you were thinking of another equation, P = I^2R.

I don't know how they get away with it--a number of people I know use old
refrigeration compressors as vacuum pumps. I don't know of any lubrication
problems. Maybe they are all in for a surprise.

On 16 Jan 2004 02:29:28 -0800, [email protected] (CFF) wrote:
>I have no intention to use the
>setup for any other purpose other than operating my Badger airbrush.
>The point I would like to emphasise is I will not be including an air
>reserviour in the setup as many designs would.

You need at least a small reservoir to smooth out the
pulsations in the air caused by a piston compressor.
So if your plan is to not include a reservoir, you can't
use a piston compressor. You need a vane or turbine
type compressor which supplies constant flow.

GAST carbon vane type compressors work well for this
application. They're oil-less, so all you need is a particulate
trap on the output to catch any carbon dust as the vanes
wear, and a shunt type (bleed) air regulator to maintain
an even load on the compressor.

I use one I salvaged out of an IBM reel to reel computer
tape drive (the tape was air buffered over the guides).
Unlike a piston pump, it is pretty quiet in operation too.

An alternative would be a turbine unit. Ampex used 2
turbines powered by a 5 hp motor in their ACR-25.
That's serious overkill for an air brush, but there were
smaller units made too. Again you need a shunt (bleed)
regulator so the turbine sees a constant load.

I suspect that the turbine unit of an HVLP spray outfit
could be used too. You might need to modify the bleed
regulator to give you the desired pressure at the desired
flow, ie an air brush needs much less flow and somewhat
more pressure than a HVLP gun.

Gary

> Gary Coffman wrote:
>>
>> On Mon, 26 Jan 2004 10:09:41 -0500, "Daniel A. Mitchell"
>> <[email protected]> wrote:
>>> There IS a type of PVC pipe that's compressed air rated ... I
>>> believe it's color coded GREEN. It's an industrial product, and NOT
>>> available in consumer outlets.
>>
>> I don't believe that's PVC. It is a different plastic. PEX?
>>
>> Gary

PEX is not rated for air. It is cross linked polyethelyne and is safe for
potable water and at temperatures to 180. It can be use for radient heat
also.
http://www.ppfahome.org/pex/

According to this, ABS may be possible.
http://www.lni.wa.gov/wisha/regs/PDFs/WRD5.40-PVCPipe.pdf

Ipex is one company that makes it.
http://www.ipexinc.com/Content/EN_CA/2_0_Products/2_1_Industrial/2_1_4_Compressed_air.asp

--
Ed
[email protected]
http://pages.cthome.net/edhome

On Sun, 18 Jan 2004 16:41:39 -0500, "William H. Shuey" <[email protected]> wrote:
>not.fishplate wrote:
>>
>> On 17 Jan 2004 20:47:37 -0800, [email protected] (CFF) wrote:
>>
>> >I fully understand the significane of employing an air tank. As an
>> >hobbist, the major difficulty in putting an air tank in the design is
>> >it is difficult to find a cheap, commerically small air tank.
>>
>> Why not use one of those portable air tanks used for inflating tires?
>> Not too expensive, and trivial to plumb as required. In a pinch, you
>> can even use it to blow up a slack tire.
>>
>> A 5 gallon tank is $16 at Sears right now
>>
>
>Correct! You can also get the necessary valves and pressure gauge and I
>would advise quick connect fittings at Sears too. Only drawback is it
>becomes a nuisance hauling it to the gas station to re-charge it. If you
>do a lot of painting, as I do now that I'm retired, it is worth looking
>at one of Sears 2 or 4 gallon tank/compressor combinations. I paid about
>$200 when on sale but it is a really convenient set up to use and should
>last me till I'm gone.

Well, if you want to buy Chinese junk, you might as well buy it
where it is cheapest. Harbor Freight has a 2 gallon oil-less
compressor for $79.95, item number 47407-0JKH. Noisy devil,
but it'll do the job.

Better would be their HVLP turbine, $79.99, stock number
44677-2JKA. It is quiet, and it comes with a HVLP gun too,
so you can use it for both purposes. You will have to rig a
bleed regulator.

Gary

In article <[email protected]>,
Steve Caple <[email protected]> wrote:

> William H. Shuey wrote:
> > Ooohhh, Man! Frustrated music critic!
>
> I was about to say that it was the impolite noise, not the
> music, but then realized that I don't mind ranchero or banda
> music nearly as much as the crap like repetitive sameness of
> rap or hip-hop or whatever, or the pouty industrial "country"
> product like that grimacing a--hole with the merkin on his
> chin that does Ford truck ads. But anything at those absurd
> volume levels past 10pm is rude, even Zappa or Zevon.

C'mon, Zappa's supposed to be rude.

Mark Schynert
presently listening to Moe and Herb's Vacation 3rd Movement, with Yellow
Shark selections up soon.

In article <[email protected]>,
[email protected] (CFF) wrote:

> I am trying to home-build an air pump for hobby modelling airbrushing
> application using a 220V domestic fridge air compressor. To make
> things simpler, the basic arrangement is to connect the compressor
> output to an air regulator (with guage attached) which, in turn,
> connects to a water trap before going to the airbrush. The idea is to
> keep the size of the whole thing as small as possible. I still haven't
> bought the compressor but need something to be clarified beforehand.
> My question is:
>
> What is the minimum power rating required for the compressor to
> deliver (at least) 40 psi (or 0.276 MPa) pressure?
>
> Thanks for any suggestion.
>
> CFF

It isn't so much the PSI, but the CFM * PSI that governs power.

On 17 Jan 2004 20:47:37 -0800, [email protected] (CFF) wrote:

>I fully understand the significane of employing an air tank. As an
>hobbist, the major difficulty in putting an air tank in the design is
>it is difficult to find a cheap, commerically small air tank.

Why not use one of those portable air tanks used for inflating tires?
Not too expensive, and trivial to plumb as required. In a pinch, you
can even use it to blow up a slack tire.

A 5 gallon tank is $16 at Sears right now
http://www.sears.com/sr/javasr/product.do?BV_UseBVCookie=Yes&vertical=TOOL&pid=00915200000

Jeff Sc.
Low Pressure, Ga.

"Steve Caple" <[email protected]> wrote in message
news:[email protected]...
>
> Way overkill for my needs: I just want a small mortar, very
> high trajectory so as not to indicate origin when round hits,
> range no more than 50 yards; and find some sort of sabot to
> keep a quart-size water baloon full of fermented cat sh-t
> slurry intact on launch; target: rolling boom-boxes. A few
> aiming stakes to mark target position for firing with expected
> coincident arrival at impact point. Ideal: schploot! on hood,
> with large part of payload going into below windshield vent.
>
>
> thumpa thumpa thumpa phwwtt thumpa schploot! eeewwwww!

The problem with the high trajectory is the lengthy "time to target". You
did say a *rolling* boombox, which adds the problem of lead and wind
deflection. A moving windshield vent at 50 yards is a mighty small target.
Might I suggest a dispersal device such as the CPU (Catshit Bomb Unit)
which, in this case, would disperse "Terdlets" in a pattern designed to
eliminate the variables in aim. Sort of a "Weapon of Bass Destruction" or
"No More Thumper".

Rich "Make My Day" S.

On Sat, 17 Jan 2004 23:51:29 GMT, "Edwin Pawlowski" <[email protected]> wrote:
>"Gary Coffman" <[email protected]> wrote in message
>
>> On 16 Jan 2004 02:29:28 -0800, [email protected] (CFF) wrote:
>> >I have no intention to use the
>> >setup for any other purpose other than operating my Badger airbrush.
>> >The point I would like to emphasise is I will not be including an air
>> >reserviour in the setup as many designs would.
>>
>> You need at least a small reservoir to smooth out the
>> pulsations in the air caused by a piston compressor.
>> So if your plan is to not include a reservoir, you can't
>> use a piston compressor. You need a vane or turbine
>> type compressor which supplies constant flow.
>
>Hey, its a friggen airbrush. They work with cheapo diaphragm compressors.
>The hose is a big enough reservoir to run it for a while.
>Ed

If you don't consider an air brush a precision tool, you can run one
from a crappy pulsating air source. But you won't get the results that
can be obtained using a smooth well regulated air source. If you're
the type to use a micrometer as a C clamp, pulsating air will do just
fine for you. But if you want to be able to lay down a smooth even
fine line, you'd better provide your air brush with a smooth even air
source.

Gary

On Sun, 18 Jan 2004 22:30:20 GMT, "Edwin Pawlowski" <[email protected]> wrote:
>"Gary Coffman" <[email protected]> wrote in message
>> If you don't consider an air brush a precision tool, you can run one
>> from a crappy pulsating air source. But you won't get the results that
>> can be obtained using a smooth well regulated air source.
>
>Yes, but you don't need the $1000 compressors that were suggested either.
>Most any air can will dampen the pulsations.

He doesn't want to use a tank. Neither of the options I suggested costs
anywhere near $1,000 either. Surplus vane pumps regularly show up for
around $50 at hamfests, and HF sells a turbine pump that would work
for $79. You would need a bleed regulator, but you can make one of
those simply enough.

Gary

On Mon, 26 Jan 2004 10:09:41 -0500, "Daniel A. Mitchell" <[email protected]> wrote:
>There IS a type of PVC pipe that's compressed air rated ... I believe
>it's color coded GREEN. It's an industrial product, and NOT available in
>consumer outlets.

I don't believe that's PVC. It is a different plastic. PEX?

Gary

On Fri, 16 Jan 2004 04:04:37 GMT, Richard Lamb <[email protected]>
wrote:

>Is that kinda like electricty?

Yes

>PSI for volts E
>CFM for current I
>Power = I^2 E

No

Power = V * I

(which is also equal to I^2 * R)


A fridge compressor wouldn't be my choice for an airbrush. They're
filled with an oil bath internally and they put a lot of oil in their
output. OK for robotics, bad for spraying.

If you can find one cheaply, look out for a small diaphram compressor.
Quieter too. Alternatively, any air-nailer compressor with a
reservoir will work. A modelling airbrush uses minimal air, so the
compresor will probably only run a couple of times a day.

Then buy yourself a really good water/oil separator to go on the
outlet.

Orval Fairbairn wrote:
> In article <[email protected]>,
> [email protected] (CFF) wrote:
>
>> I am trying to home-build an air pump for hobby modelling airbrushing
>> application using a 220V domestic fridge air compressor. To make
>> things simpler, the basic arrangement is to connect the compressor
>> output to an air regulator (with guage attached) which, in turn,
>> connects to a water trap before going to the airbrush. The idea is to
>> keep the size of the whole thing as small as possible. I still
>> haven't bought the compressor but need something to be clarified
>> beforehand. My question is:
>>
>> What is the minimum power rating required for the compressor to
>> deliver (at least) 40 psi (or 0.276 MPa) pressure?
>>
>> Thanks for any suggestion.
>>
>> CFF
>
> It isn't so much the PSI, but the CFM * PSI that governs power.

No, but maybe we shouldn't get started again on that issue.

"Rich S." <[email protected]> wrote in message
news:[email protected]...

> Whoa! I gave up that hair spray / Coleman lantern spark process. I'm with
> the Greeers now.

Oops. That should be "Greeners".

Rich

>Ooohhh, Man! Frustrated music critic! Most dangerous creature there
>is! :-)
>
> Bill Shuey
second only to frustrated rap artist.
learned that at wzbc.

A reservoir does MORE than just smooth out the pulsating flow from the pump.
Since an airbrush is almost always used in short bursts, it allows the pump
to "catch up" between bursts. Therefore, you can get by with a smaller
pump. In other words, with a reservoir, the pump only needs to provide the
*average* flow. Without a reservoir, the pump needs to provide the
*maximum* flow.

Rex B wrote:

>
> Don't tell that to my dad. He's been using the same old refrigerator compressor
> since the late 60's, doing professional A/C repair on home ands cars.


Are you sure it isn't an oil bath compressor?




--

Mark

N.E. Ohio


Never argue with a fool, a bystander can't tell you apart.
(S. Clemens, A.K.A. Mark Twain)

When in doubt hit the throttle. It may not help but it sure
ends the suspense. (Gaz, r.moto)

On 15 Jan 2004 19:11:52 -0800, [email protected] (CFF) vaguely
proposed a theory
......and in reply I say!:

Have you thought of a car tyre inflater compressor? Cheap, probably
adequate (if not use two. They are dirt cheap). Then use a small tyre
as a reservoir. You will need a reservoir. Just remember that you will
need some sort of pressure switch-off, whatever compressor you use.
Hobby airbrushes are pretty critical for pressure, and a tyre inflator
will (eventually) explode a tyre.

>I am trying to home-build an air pump for hobby modelling airbrushing
>application using a 220V domestic fridge air compressor. To make
>things simpler, the basic arrangement is to connect the compressor
>output to an air regulator (with guage attached) which, in turn,
>connects to a water trap before going to the airbrush. The idea is to
>keep the size of the whole thing as small as possible. I still haven't
>bought the compressor but need something to be clarified beforehand.
>My question is:
>
>What is the minimum power rating required for the compressor to
>deliver (at least) 40 psi (or 0.276 MPa) pressure?
>
>Thanks for any suggestion.
>
>CFF

**************************************************** sorry
remove ns from my header address to reply via email

I was frightened by the idea of a conspiracy that was
causing it all.
But then I was terrified that maybe there was no plan,
really. Is this unpleasant mess all a mistake?

"Morgans" <[email protected]> wrote in message
news:[email protected]...
>
> Chuckle>
>
> You are still OK, for this use. Just Don't hit the pipe with a hammer, or
> drop it, just as the combustion process makes max. pressure!

Whoa! I gave up that hair spray / Coleman lantern spark process. I'm with
the Greeers now. Plain ol' simple compressed air. My wheezer of a compressor
tops out at 125 lbs and the 2" PVC I'm using as the air chamber is rated way
higher than that. I got a popoff valve on it set at 125 in case something
fails.I guess it's carrying the tube from the shop to the launch point where
I gotta be a bit delicate.

I copied Bill Phillip's design. Ousterhout has a picture at
http://www.jouster.0catch.com/jean-02/p2190041.jpg (We're #1) that'll give
you an idea of the plumbing. BWB uses a regulated SCUBA tank for recharge in
the boonies.

Rich "Food Flinger" S.

[email protected] (Daniel) writes:


[...]

> Compressor ratings:
> 3.7 CFM @ 40 PSI
> 2.6 CFM @ 90 PSI
> Stop switch at 150 PSI so that's 0 CFM @ 150 PSI
>
> I ran a regression on those relationships & got:
> CFM = -6.048*PSI² - 7.3521*PSI + 150
> CFM as a function of PSI is obviously eponential (it delevers less and
> less as PSI goes up) and it turns out that this 2nd order polynomial
> fits the manufacturer's data extremely well (R²=1).

... which is not to be wondered at, because you can always fit n data
points exactly with a (n-1)th order polynomial. But your result is
false because the zero throughput at 150PSI is not due to lack of
power but due to the stop switch, which would not be needed if the
compressor itself would deliver no throughput at that pressure; it
will still have some throughput just below the switchoff point.

--
Dr. Juergen Hannappel http://lisa2.physik.uni-bonn.de/~hannappe
mailto:[email protected] Phone: +49 228 73 2447 FAX ... 7869
Physikalisches Institut der Uni Bonn Nussallee 12, D-53115 Bonn, Germany
CERN: Phone: +412276 76461 Fax: ..77930 Bat. 892-R-A13 CH-1211 Geneve 23

Sorry coming in late here, but i know a few people who use car tyres for the
"tank" when airbrusing.
For some pocket change you can add any number of valve stems to an old rim
(with a tubeless tyre) and connect as little or as much to it as you want.
A car tyre is larger than a fire extinguisher, but it may be able to be
hidden in the bottom of a workbench, or somewhere else out of the way.

HTH,
Des
"Daniel A. Mitchell" <[email protected]> wrote in message
news:[email protected]...
> Look for a used commercial compressed-air system 'moisture trap' at a
> junkyard. These often consist of a small pressure tank about the size of
> a grapefruit. They have a drain valve in the bottom to release the
> moisture. These little 'tanks' are *NOT* the kind of moisture trap
> being recommended for airbrushing (they're for power tools). However,
> they're ideal for your pressure tank purpose, and can be 'had' for a
> couple bucks.
>
> Spray painting moisture traps have filter elements to remove the
> moisture.
>
> Dan Mitchell
> ==========
>
> CFF wrote:
> >
> > I fully understand the significane of employing an air tank. As an
> > hobbist, the major difficulty in putting an air tank in the design is
> > it is difficult to find a cheap, commerically small air tank. While
> > ruling out all the options of making the whole thing look big, some
> > suggest using an empty fire extinguisher to convert. But, as far as I
> > understand, there is quite an amount of drilling and welding work need
> > to be done in order to mount the host connectors plus guage at the
> > inlet and outlet. That is something that I just don't have the
> > engineering facility to accomplish. Considering the relatively low
> > pressure required for airbrushing application, I am quite happy to
> > sacrify consistence of air flow as long as it does provide a
> > reasonably constant presure at short bursts. However, if there are
> > feasible suggestions that I can manage to modify a fire extinguisher
> > without the need of welding, I will be glad to consider. I am sure
> > that will make it an ideal setup.
> >
> > CFF

>
>e wrote:
>
> > best stay away from spk, einsturzende niebaten or skinny puppy.
>
>Einsturzende NEUBAUTEN
>
>(Collapsing New Buildings)
>
hey, someone's awake out there.
blixa would be pleased.