How to detairmain the free air delivery of a air compressor 1

[derickv]

What equipment and flow formulas do a person need to compare the efficiency of compressor (free air delivery) to it's designed output. I need something basic but reasonably accurate. The easiest way properly is to calculate the flow rate of air through an orifice plate, this is basically what I know but how and with what?

 

[quark]

derickv!

You can have flow meters installed for accurate results. (with vortex flow meters or density compensated orifice meters by fischer rosemount) But they will cost you a fortune for once checking. I will tell you how I roughly check it as a standard practice every week. Empty out your receiver. Close all drain valves and receiver outlet valve. Start the compressor, load it and note down the time. Let the pressure built up to the level you require and say it P1 and note down the time. Now the formula is

[(P1+1.0336)*V]/(1.0336*t) P1 should be in kg/sq.cm g, V is in cu.m and t the time in minutes (duration for which you pressurised the receiver) then the free air discharge you get is in cu.m/min. Devide it by 35.67 and you will get CFM.

Generally when manufacturers test the capacity they take temperature also into consideration.

Regards,
Repetition is the foundation of technology

 

[derickv]

Quark thanks a million ... for your answer, I will definitely put this to the test. I never even thought of such a solution unfortunately will this not help me in my case. The compressors CFM I needs to determine is a 1900 CFM screw-compressor on a drill with no receiver about 40km from the nearest receiver. To transport a large enough pressure vessel to the drill to enable which would give me enough volume to get fairly accurate in my calculations with your method would not be possible.

 

[quark]

Derick!

One change in my post is you have to put atmospheric pressure at your elivation instead of 1.0336. I think a flowmeter will be a better option. Make sure that flow should be compensated for pressure as well as temperature in your case because after pressurising the air we cool it again.

Regards,
Repetition is the foundation of technology

 

[derickv]

Quark

Thanks again I did presume that your 1.0336 constant did stand for atmospheric pressure... one small correction for the purpose of the forum to convert cu.m/min to CFM you need to multiply cu.m/min by 35.67 constant to get CFM.

It looks like I have to invest in a flow meters (very expensive solution if your compressors range from 200 to 2000 cfm, I know there is ways and means to determine flow with a orifice but all the info I can get is very general it seems as if nobody really wants to stick his neck out when it comes to this type of calculations.
Regards,

Derick

 

[quark]

Derick!

Thanks for correcting. That is why one should not post in hurry. If you can contact fischer rosemount they will tell you how not easy it is to check compressed air flow using orifice. There are lot of corrections to be made to get the accuracy around 1%.

One year back I had a paper(given to me by F&R) which was submitted to science congress by one of the employees of F&R. You have every sort of corrected calculations in it.

Regards,

Repetition is the foundation of technology