anybody know how to figure the cfm for a homemade compressor? 30
gallon tank, emglo GU compressor head, 3 HP marathon motor running at
1725 ROM. motor has a 6 1/4 inch pully and compressor has a 10 1/2
inch pully. it goes from 0 to 145 PSI in 2 minuits and 27 seconds. im
trying to figure out if it will run more than one sprayer. thanks
all...
skeez
A lot more than my 60g 4hp unit. If you can fill that tank that fast you
pushing a lot of air. I'm sure you can calculate it but first one needs to
know the displacement of the compressor.
"skeezics" <[email protected]> wrote in message
news:[email protected]...
> anybody know how to figure the cfm for a homemade compressor? 30
> gallon tank, emglo GU compressor head, 3 HP marathon motor running at
> 1725 ROM. motor has a 6 1/4 inch pully and compressor has a 10 1/2
> inch pully. it goes from 0 to 145 PSI in 2 minuits and 27 seconds. im
> trying to figure out if it will run more than one sprayer. thanks
> all...
>
>
> skeez
The 30 gallon tank is about 4 cu ft but compressor air flow is measured as
"Standard Temperature and Pressure" or STP. Not botering with adjustments
for temperature and doing a rough calculation each cubic foot at 145# is
about 10 cu-ft at STP so it looks like around 40cu-ft compressed in 2-1/2
min or about 16 cfm. All of this assumes I remember my college chem classes
from 30 years ago. Us computer types don't run into compressed gas problems
too often.
Ken
"skeezics" <[email protected]> wrote in message
news:[email protected]...
> anybody know how to figure the cfm for a homemade compressor? 30
> gallon tank, emglo GU compressor head, 3 HP marathon motor running at
> 1725 ROM. motor has a 6 1/4 inch pully and compressor has a 10 1/2
> inch pully. it goes from 0 to 145 PSI in 2 minuits and 27 seconds. im
> trying to figure out if it will run more than one sprayer. thanks
> all...
>
>
> skeez
In article <[email protected]>,
[email protected] <[email protected]> wrote:
>The 30 gallon tank is about 4 cu ft but compressor air flow is measured as
>"Standard Temperature and Pressure" or STP. Not botering with adjustments
>for temperature and doing a rough calculation each cubic foot at 145# is
>about 10 cu-ft at STP so it looks like around 40cu-ft compressed in 2-1/2
>min or about 16 cfm. All of this assumes I remember my college chem classes
>from 30 years ago. Us computer types don't run into compressed gas problems
>too often.
I came at it from the other direction, and got similar results.
145psi (net) is 9.8666 atmospheres ( @14.6959psi/atm). The 30 gal. tank is
4.0104 cu. ft. Now the pump put out 9.88 atm * 4.0104 cu. ft., or 39.5690
cu. ft. of air in 2 min 27 sec; dividing gives 16.1506 cu. ft./min.
One has to de-rate that number somewhat, because the compressor was working
into a variable pressure load. And, obviously, moves more air when the
'back pressure' is low, relative to when the tank pressure is high. In
addition, there were probably secondary effects (heating) contributing to
the pressure rise. With all that considered, a conservative rating would
be 14 cu. ft/min @ 60PSI -- it will probably do somewhat more than that. :)
For a =real= engineering analysis, one has to know the volume in the cylinder
with the piston at the top of the stoke, and at the bottom of the stroke.
Just knowing the 'displacement' (the difference in those two figures) is
_not_ sufficient. With both cylinder volumes, and shaft RPM, one can come
up with firm numbers for any 'realistic' pressure level. *And* tell when
the pressure level is -not- realistic -- i.e., the compressor cannot produce
that pressure level, even at -zero- air flow.
>"skeezics" <[email protected]> wrote in message
>news:[email protected]...
>> anybody know how to figure the cfm for a homemade compressor? 30
>> gallon tank, emglo GU compressor head, 3 HP marathon motor running at
>> 1725 ROM. motor has a 6 1/4 inch pully and compressor has a 10 1/2
>> inch pully. it goes from 0 to 145 PSI in 2 minuits and 27 seconds. im
>> trying to figure out if it will run more than one sprayer. thanks
>> all...
>>
>>
>> skeez
>
>
On Thu, 14 Oct 2004 22:27:19 GMT, skeezics <[email protected]> wrote:
ok. now im mor confused! lol.... but looks like between 14 and 16 cfm.
that should be more than sufficient for anything i throw at it. BTW i
did a little test today that surprised the h!!l outta me. i held a
blower nozzel wide open and the compressor cycled as normal. meaning
it kicked on and off even with an open blower going as fast as the air
would flow. i was ammazed that it caught up with itself like that.
looks like a keeper to me. thanks for all the help guys.
skeez
I would think that figuring the area of the cylinders times the stroke times the speed ration times the ratio of the final
pressure to atmosphere would get you in the neighborhood.
Example
2 dia cylinders times 1 stroke times 4 = (1x1x3.14159x1) = 12.566 cu inches
12.566 times 1725 time 6 1/4 divided by 10 1/2 =12,902 cu inches
12,902 x 14.7 (atmosphere pressure) divided by 145 (final pressure) = 1,308 cu inches
1,308 cu inches divided 1728 (cu inches per cu ft) =.75 cu ft per minute
Substitute your piston diameter and stroke and you should be able to figure out what you have.
R. Wink
On Thu, 14 Oct 2004 22:27:19 GMT, skeezics <[email protected]> wrote:
>anybody know how to figure the cfm for a homemade compressor? 30
>gallon tank, emglo GU compressor head, 3 HP marathon motor running at
>1725 ROM. motor has a 6 1/4 inch pully and compressor has a 10 1/2
>inch pully. it goes from 0 to 145 PSI in 2 minuits and 27 seconds. im
>trying to figure out if it will run more than one sprayer. thanks
>all...
>
>
>skeez