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Author Topic: compressor calculation needed....please  (Read 1702 times)

hopeitfloats

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compressor calculation needed....please
« on: January 31, 2010, 07:13:26 am »

i have a twin cylinder air compressor that has  2'' bore x 2'' stroke running at 750 RPM can anyone tell me how many cuft/min  it will produce.  thanks.  craig
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FullLeatherJacket

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Re: compressor calculation needed....please
« Reply #1 on: January 31, 2010, 08:02:00 am »

Cylinder Volume in Cu Ins is πR2h, where R=Radius of Bore and h=Stroke
= 3.142 x 12 x 2
= 6.284 Cu Ins
Swept volume in 1 minute = 6.284 x 750
= 4713 Cu Ins
= 4713/1728 Cu Ft
= 2.73 Cu Ft
Two cylinders is twice this i.e. 5.46 Cu Ft

But opinions may vary  %)
FLJ
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Patrick Henry

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Re: compressor calculation needed....please
« Reply #2 on: January 31, 2010, 09:04:53 am »

Don't you just love clever people.... O0


Rich
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hopeitfloats

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Re: compressor calculation needed....please
« Reply #3 on: January 31, 2010, 09:46:08 am »

thanks FLJ.
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FullLeatherJacket

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Re: compressor calculation needed....please
« Reply #4 on: January 31, 2010, 11:32:31 am »

Don't you just love clever people.... O0
Rich
You're on your own, 'uggett. No-one I know likes a smart-a***...................("alec", of course! What else??)

Hopeitfloats
You're most welcome, old thing!

FLJ  (GCE Maths O-level 1967)
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Patrick Henry

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Re: compressor calculation needed....please
« Reply #5 on: January 31, 2010, 11:37:29 am »

Rich
You're on your own, 'uggett. No-one I know likes a smart-a***...................("alec", of course! What else??)

Hopeitfloats
You're most welcome, old thing!

FLJ  (GCE Maths O-level 1967)

Huh...RSA English Language and English Literature(stages 1 and 2) RSA Mathematics (stage 1) NVQ, HGV1, STGO cat2, TIR, AA, RAC. Etc...



Rich
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FullLeatherJacket

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Re: compressor calculation needed....please
« Reply #6 on: January 31, 2010, 11:42:18 am »

Huh...RSA English Language and English Literature(stages 1 and 2) RSA Mathematics (stage 1) NVQ, HGV1, STGO cat2, TIR, AA, RAC. Etc...
Rich

.......and Bar?  :P
FLJ
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Patrick Henry

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Re: compressor calculation needed....please
« Reply #7 on: January 31, 2010, 12:12:24 pm »

Pint of the Black liquid, please...oh, not that sort of bar? oops... %)




Rich
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CGAux26

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Re: compressor calculation needed....please
« Reply #8 on: February 01, 2010, 01:47:46 am »

If it is a 2 cylinder compressor, is it one or two stages?  That is, are the cylinders piped in parallel or in series?  If in series it's to improve the efficiency in reaching higher pressure.  And you would get just half the capacity calculated by FLJ, above.  Plus any compressor has an efficiency, guessing around 60 to 80% on a small one like this.  So starting at FLJ's 2.73 CFM, multiply by say .6 to get an actual capacity of 1.64 CFM.  AND this is INLET capacity.  The discharge capacity is much less, by the ratio of discharge to inlet pressure, and the ratio of inlet temperature to discharge temperature, in degrees absolute (Fahrenheit + 459.6 = degrees Rankine).
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FullLeatherJacket

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Re: compressor calculation needed....please
« Reply #9 on: February 01, 2010, 07:33:18 am »

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hopeitfloats

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Re: compressor calculation needed....please
« Reply #10 on: February 01, 2010, 09:41:43 am »

i like daves figures best :-)) strange but i thought from the size of the unit it would be around 9 or 10 cu/ft. our work compressor is a single cylinder about the same size and it does 7cu/ft.  much higher revving though.
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pneumatician

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Re: compressor calculation needed....please
« Reply #11 on: February 03, 2010, 12:10:09 am »

Assuming your machine is a single stage and both cylinders have identical bores then the previous calcs of 5.46 CFM Piston Displacement should equate to approx 3 CFM Free Air  ( 60% of 5.46).
Free Air Delivery and working Pressure are the only figures you are really interested in.  All tools, spray equipment etc consumption figures are given in Free Air.
I imagine your machine has approx 1 < 1.5 kw Motor to give you about 125 PSI.

To give you some idea of what you can and can't do.  A Motor Bodyshop Spraygun uses 12 > 14 CFM FAD @ 40> 60 psi, an Airbrush from almost nothing upto about 1.0CFM.
Small Air tools 1/4 < 3/8 drill approx 12cfm.

I do appologise as although I have worked in the squashed wind industry for most of my life I am trying to recall these figures as most of my tekky books appear to have been binned some time ago.
To think I used to be able to quote Compressor and Tool Specs straight from memory.

 Tempus Fujit                       Steve
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hopeitfloats

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Re: compressor calculation needed....please
« Reply #12 on: February 21, 2010, 08:03:56 am »

looks like it wont be much use other than to run an airbrush or dusting gun. thanks for the info.
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