My 30 year old Sears air compressor has given up the ghost. Actually it was
made by Devilbiss and went by sears only in name .
The primary use has been for spraying furniture finishes.
I went to the local Lowes and HD to find a new one . In the meantime I
figured I would get one a little more powerful. My old one was rated at 2
HP.
I found a 7HP unit at Lowes and the similar one at HD. Then checking the
specs I noticed that the 7HP was "peak" and that the continuous rating was 1
1/2 HP. On the side of the unit was a sticker showing which tools it could
be used to operate . A Spraygun was not one of them .
So what the heck should I be looking for in this day and age a 20 HP unit ?
--
http://members.tripod.com/mikehide2
Don't worry about the HP as much as the CFM. HP ratings can be all over the
place as you have found out but CFM is CFM. Just determine what CFM your
spray gun uses and its working pressure and look for a compressor that
matches that or comes close.
--
If at first you don't succeed, you're not cut out for skydiving
"Mike Hide" <[email protected]> wrote in message
news:WJCkd.393656$D%.220002@attbi_s51...
>
> My 30 year old Sears air compressor has given up the ghost. Actually it
was
> made by Devilbiss and went by sears only in name .
> The primary use has been for spraying furniture finishes.
>
> I went to the local Lowes and HD to find a new one . In the meantime I
> figured I would get one a little more powerful. My old one was rated at 2
> HP.
>
> I found a 7HP unit at Lowes and the similar one at HD. Then checking the
> specs I noticed that the 7HP was "peak" and that the continuous rating was
1
> 1/2 HP. On the side of the unit was a sticker showing which tools it could
> be used to operate . A Spraygun was not one of them .
>
> So what the heck should I be looking for in this day and age a 20 HP unit
?
>
>
> --
> http://members.tripod.com/mikehide2
>
"Mike Hide" <[email protected]> wrote in message
news:WJCkd.393656$D%.220002@attbi_s51...
>
> My 30 year old Sears air compressor has given up the ghost. Actually it
was
> made by Devilbiss and went by sears only in name .
> The primary use has been for spraying furniture finishes.
>
>
Did you loose your post from yesterday on this??
I have this model, Runs my paint gun and air sander.
http://www.porter-cable.com/index.asp?e=547&p=4701
Greg
"Mike Marlow" <[email protected]> wrote in message
news:[email protected]...
>
> "Old Nick" <[email protected]> wrote in message
> news:[email protected]...
> >
> > And I've seen a few porkies around about _this_ aspect as well. I have
> > a "12CFM" compressor that cannot drive a "4CFM" ROS. The compressor's
> > _real_ output is about 7CFM @ 90 PSI. The ROS's _real_ requirements at
> > _working pressure_ (90CFM) is more like 20CFM+.
>
> Holy shit! That's some ROS. A good DA isn't that demanding. I think I'd
> be rid of that ROS.
> --
>
>
I wondered about that too. My 10 CFM Porter Cable compressor keeps up with
my DA sander. Runs constantly, but keeps up! At least when the compressor
needs a break, so do I!
Greg
On Thu, 11 Nov 2004 19:43:55 GMT, "TBone" <[email protected]>
vaguely proposed a theory
......and in reply I say!:
remove ns from my header address to reply via email
Read my post. CFM is _not_ CFM. :-<
>Don't worry about the HP as much as the CFM. HP ratings can be all over the
>place as you have found out but CFM is CFM.
>Just determine what CFM your
>spray gun uses and its working pressure and look for a compressor that
>matches that or comes close.
And I've seen a few porkies around about _this_ aspect as well. I have
a "12CFM" compressor that cannot drive a "4CFM" ROS. The compressor's
_real_ output is about 7CFM @ 90 PSI. The ROS's _real_ requirements at
_working pressure_ (90CFM) is more like 20CFM+.
*****************************************************
Dogs are better than people.
People are better than dogs for only one purpose. And
then it's only half of ofthe people. And _then_ most
of them are only ordinary anyway. And then they have a
headache.........
True HP is about 11 amps on 115 volts. Some heavy duty one HP motors
pull 14 amps. So if it runs on 115v and plugs into a wall socket, 1.75
real HP is all you can get on a 20 amp circuit! All the 7 HP vacuums,
3.5 HP routers, 2.5 HP circular saws, 6 HP compressors, are LIES,
LIES, LIES.
Bill Turpin in WNC mountains
RE: Subject
As many of you have noted, rating a compressor in CFM is strictly a
marketing game.
The only true way to rate a compressor output is SCFM (Standard Cubic Feet
per Minute), and nobody does it that way.
For those of you whole are interested in the math, check out the
compressible gases section of a high school physics text.
Frankly it's been too long since I've used it to have it in the memory back.
HTH
Lew
"Old Nick" <[email protected]> wrote in message
news:[email protected]...
>
> And I've seen a few porkies around about _this_ aspect as well. I have
> a "12CFM" compressor that cannot drive a "4CFM" ROS. The compressor's
> _real_ output is about 7CFM @ 90 PSI. The ROS's _real_ requirements at
> _working pressure_ (90CFM) is more like 20CFM+.
Holy shit! That's some ROS. A good DA isn't that demanding. I think I'd
be rid of that ROS.
--
-Mike-
[email protected]
"Mike Hide" <[email protected]> wrote in message
news:WJCkd.393656$D%.220002@attbi_s51...
>
> So what the heck should I be looking for in this day and age a 20 HP unit
?
If your old compressor was 30 years old, then it probably was not one of the
oil free, high speed designs. I have one of these that's about 10 years old
and I hate it. Its way too noisy. Its finally trying to give up the ghost
and I can hardly wait.
I'm going to a real cast iron compressor this time that uses oil. I'm
looking at $400-$600 for my needs/wants. Lowe's has several examples that
are claimed to be 83 db sound level. Ahhh!
Bob
"Lew Hodgett" <[email protected]> wrote in message
news:[email protected]...
> RE: Subject
>
> As many of you have noted, rating a compressor in CFM is strictly a
> marketing game.
>
> The only true way to rate a compressor output is SCFM (Standard Cubic Feet
> per Minute), and nobody does it that way.
>
Actually Lew, most are now rated by SCFM.
--
-Mike-
[email protected]
You are correct. I forgot about that BS. The better ones list compressor
CFM at a few pressures which is always 100% duty cycle. I guess the cheeper
ones include the tank but I do believe that they need to include the duty
cycle when they do it that way although it may be hard to find.
--
If at first you don't succeed, you're not cut out for skydiving
"Tim Douglass" <[email protected]> wrote in message
news:[email protected]...
> On Fri, 12 Nov 2004 07:58:12 +0800, Old Nick <[email protected]>
> wrote:
>
> >And I've seen a few porkies around about _this_ aspect as well. I have
> >a "12CFM" compressor that cannot drive a "4CFM" ROS. The compressor's
> >_real_ output is about 7CFM @ 90 PSI. The ROS's _real_ requirements at
> >_working pressure_ (90CFM) is more like 20CFM+.
>
> I think the confusion on CFM comes about because there is no
> duty-cycle rating given. Most compressors are rated at some
> ridiculously low duty cycle (which is not published). My compressor
> will supposedly put out 6.4 CFM @ 90 PSI, but the duty cycle is only
> about 25%. It works fine pulling a 6 CFM impact wrench for 6 of 8 lug
> nuts, but then I have to wait while it re-fills. On the other hand, if
> I am moving around and there is a break between each bolt I can run
> the tool with no problem. What they *should* be required to list is
> the continuous output, which is way low for just about any small
> compressor.
>
> Tim Douglass
>
> http://www.DouglassClan.com
On Thu, 11 Nov 2004 05:26:14 GMT, "Mike Hide" <[email protected]>
vaguely proposed a theory
......and in reply I say!:
remove ns from my header address to reply via email
What you need to do is find out the air delivery capacity of the
compressor you had. This will be in CFM at some pressure, usually 90
PSI. It may be called Free Air Delivery (FAD). But it _must_ show a
delivery pressure to mean anything.
Largely ignore the horsepower, it is indeed horse shit.
Also ignore the ratings that do _not_ show a pressure. They are also
rubbish. To give you some idea, I have a compressor rated at "12CFM"
but it can only deliver about 7 CFM @ 90 PSI. Its horsepower, BTW is
2.5HP, but that is an honest constant and is about right for the rated
air capability.
How they can be allowed to get away with claims of 7HP I have no idea.
It's crazy. Like 1000W shelf-sized "HiFi"s, measured for a fraction of
a second at 100% distortion just as the output blows up! <G>
If your old machine was 2HP, 30 years ago it would have been genuine
HP. So I would estimate that its FAD capability would be around 5-6
CFM @ 90 PSI. So you need to look for that or larger.
If it was a belt-drive unit, you will also find that many of the
cheaper direct drive ones are noisier, or at least more unpleasant to
listen to, because they run the cylinder at twice the rate. Bear that
in mind.
>
>My 30 year old Sears air compressor has given up the ghost. Actually it was
>made by Devilbiss and went by sears only in name .
>The primary use has been for spraying furniture finishes.
>
>I went to the local Lowes and HD to find a new one . In the meantime I
>figured I would get one a little more powerful. My old one was rated at 2
>HP.
>
>I found a 7HP unit at Lowes and the similar one at HD. Then checking the
>specs I noticed that the 7HP was "peak" and that the continuous rating was 1
>1/2 HP. On the side of the unit was a sticker showing which tools it could
>be used to operate . A Spraygun was not one of them .
>
>So what the heck should I be looking for in this day and age a 20 HP unit ?
*****************************************************
Dogs are better than people.
People are better than dogs for only one purpose. And
then it's only half of ofthe people. And _then_ most
of them are only ordinary anyway. And then they have a
headache.........
In article <[email protected]>,
Bill Turpin <[email protected]> wrote:
>True HP is about 11 amps on 115 volts. Some heavy duty one HP motors
>pull 14 amps. So if it runs on 115v and plugs into a wall socket, 1.75
>real HP is all you can get on a 20 amp circuit! All the 7 HP vacuums,
>3.5 HP routers, 2.5 HP circular saws, 6 HP compressors, are LIES,
>LIES, LIES.
One horsepower is 745.7 watts. which translates to 6.214 amps at 120V.
At 80% mechanical efficiency, it the draw is 7.767 A. de-rate another 20%
for phase angle, and the apparent draw is 9.70A. multi-horsepower, poly-
phase motors will achieve overall efficiency in the 90% range; on the other
hand, 75% is *extremely good for a 1-to-2 HP single-phase unit -- 57-65 is
much more typical int that power range. And at small fractional HP (say
1/6-1/4 HP), getting 50% efficiency is a major accomplishment.
A circuit breakered at 20A is limited to plug-in devices drawing no more than
18A 'Full load', per NEC. At 120V, that gets a 'theoretical' 2.89HP, under
perfect conditions. A 2-1/4 to 2-1/2 HP load on that circuit requires
overall efficiency in the 80-85% range.
*NOT* 'impossible'; but *is* 'bloody unlikely'. <grin>
On Fri, 12 Nov 2004 02:23:29 GMT, "Mike Marlow"
<[email protected]> vaguely proposed a theory
......and in reply I say!:
remove ns from my header address to reply via email
>
>"Old Nick" <[email protected]> wrote in message
>news:[email protected]...
>>
>> And I've seen a few porkies around about _this_ aspect as well. I have
>> a "12CFM" compressor that cannot drive a "4CFM" ROS. The compressor's
>> _real_ output is about 7CFM @ 90 PSI. The ROS's _real_ requirements at
>> _working pressure_ (90CFM) is more like 20CFM+.
>
>Holy shit! That's some ROS. A good DA isn't that demanding. I think I'd
>be rid of that ROS.
I am. It was a cheap thing. Nonetheless it was rated at 4 CFM/90PSI.
There are plenty out there like it.
Quite frankly I would go with electrical, anyway. I get a 400 watt /
0.5 HP sander to do what it takes a 2.5 HP compressor to do.
*****************************************************
Dogs are better than people.
People are better than dogs for only one purpose. And
then it's only half of ofthe people. And _then_ most
of them are only ordinary anyway. And then they have a
headache.........
On Thu, 11 Nov 2004 16:58:04 -0800, Tim Douglass
<[email protected]> vaguely proposed a theory
......and in reply I say!:
remove ns from my header address to reply via email
I thought duty cycle referred to the capability of the machine to keep
running without overheating. I have never heard it applied to the
ability of a compressor to keep supplying air while running.
If the compressor has to keep pumping to get up to speed, that's
simply the tool using more than the comp can provide.
AFAIK, the confusion about compressors comes about because they supply
an _intake_ (Swept volume) figure at atmospheric pressure.
OTOH, the _tools_ are calculated using some sort of "weighted" average
(which could be called a "duty cycle"), that assumes that in a shop,
with 10 tools, they will all only be used a bit of the time. IUt's BS,
but has nothing to do with the compressor. The idea is you add them
all up "as run" and buy a comp to suit. But if you are using a single
toold flat out on a comp that is based on that rating, it will fail to
keep up.
The lie here is in the tool, not the compresor.
>
>I think the confusion on CFM comes about because there is no
>duty-cycle rating given. Most compressors are rated at some
>ridiculously low duty cycle (which is not published). My compressor
>will supposedly put out 6.4 CFM @ 90 PSI, but the duty cycle is only
>about 25%. It works fine pulling a 6 CFM impact wrench for 6 of 8 lug
>nuts, but then I have to wait while it re-fills. On the other hand, if
>I am moving around and there is a break between each bolt I can run
>the tool with no problem. What they *should* be required to list is
>the continuous output, which is way low for just about any small
>compressor.
*****************************************************
Dogs are better than people.
People are better than dogs for only one purpose. And
then it's only half of ofthe people. And _then_ most
of them are only ordinary anyway. And then they have a
headache.........
"Mike Hide" <[email protected]> wrote in message
news:WJCkd.393656$D%.220002@attbi_s51...
> So what the heck should I be looking for in this day and age a 20 HP unit
?
I don't know if you want to get into a stationary compressor size, but
thought I would pass on a good deal to you. The Husky VT6314 (60 gal, 10.3
cfm @ 90 psi) is available at Home Depot for regular price of $429.
Campbell Hausfeld has the same compressor on their website listed as a hot
buy at $329 plus $46 shipping and no sales tax. I'm looking seriously at
it.
www.chpower.com click on hot buys.
Bob
On Fri, 12 Nov 2004 07:58:12 +0800, Old Nick <[email protected]>
wrote:
>And I've seen a few porkies around about _this_ aspect as well. I have
>a "12CFM" compressor that cannot drive a "4CFM" ROS. The compressor's
>_real_ output is about 7CFM @ 90 PSI. The ROS's _real_ requirements at
>_working pressure_ (90CFM) is more like 20CFM+.
I think the confusion on CFM comes about because there is no
duty-cycle rating given. Most compressors are rated at some
ridiculously low duty cycle (which is not published). My compressor
will supposedly put out 6.4 CFM @ 90 PSI, but the duty cycle is only
about 25%. It works fine pulling a 6 CFM impact wrench for 6 of 8 lug
nuts, but then I have to wait while it re-fills. On the other hand, if
I am moving around and there is a break between each bolt I can run
the tool with no problem. What they *should* be required to list is
the continuous output, which is way low for just about any small
compressor.
Tim Douglass
http://www.DouglassClan.com
On Thu, 11 Nov 2004 06:02:16 GMT, "Lew Hodgett"
<[email protected]> calmly ranted:
>"Mike Hide" writes:
>
><snip>
>
>> So what the heck should I be looking for in this day and age a 20 HP unit
>?
>
>I bought a 5HP/240V1PH dual stage compressor on an 80Gal vertical tank and
>never looked back.
>
>I can spray all day or use air tools that are air hogs without any problem.
Yabbut you've got enough money to buy 55 gallon drums of epoxy
and build 50 cubit long boats. A 4hp (HAR!) HF oily pump fit
my budget at $159. I don't think I'll be using DAs all day long
so it should handle anything I'm likely to throw at it. Then
when I'm rich and famous some day, I'll get a real Ingy.
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