A possible alternative is to leave the sizes metric and just use the metric units for Force etc. It's a bit of a struggle at the start (especially for us old guys), but in the long run it's clearer and (ultimately) easier. Mainly because there are no arbitary conversion constants needed just different powers of 10. Jeff

I have felt that the United States have been holding back maybe not progress, but the efficiency by staying with imperial measurement instead of going metric.

I was taught to design using imperial units. Until I started working doing heat transfer, I realized that's all it was was units, whether it be imperial or metric.

And for the States to change it is going to be pretty difficult, due to stubbornness, if not atleast a little ingorance. When I was working in a naval shipyard, an attempt was made to go to metric. When drawing were released to the yard, a measurement would come up on a print for a 10 MM hole, the response was, that's about 3/8".

Not only is it challanging, its expensive. One has to have two sets of tools, to work on anything. (may be good for the manufacturers who makes the tool)

Making the switch was talked about, when I was in grade school, but it looks like its going to take another generation for metric the take hold if not atleast dominate units of measurment.

Gentlemen, #1 and #2,

Thank you for your thoughts and comments. My point is not to promote English Engineering units or defend us old timers and other lazy people. I attempted to make it easier for those of us struggling in an imperfect world. My original comments are copied and pasted for you here.

The majority of compressed air information in North America that relates to flow rates and usage is given in SCF (Standard Cubic Feet) or SCFM (Standard Cubic Feet per Minute). The compressed air pressure is most frequently listed in PSIG (Pounds per Square Inch, Gage)

This presents a challenge when designing, sizing or evaluating the amount of compressed air required or used. It is laborious to convert each metric dimension to the English inch, psig and scfm system.

I am on the advisory board of one of the best Fluid Power Tech. Schools in the US who teach Hydraulic, Pneumatic, Automation Technology including Electronic Controls, AutoCad etc. Makes me blush to admit that SCFM, PSI, Inch size pipe, hose and tubing etc. are the primary designations for examples and test problems.

An application may use 4 sizes of NFPA cylinders (Inches), 3 sizes of ISO cylinders (mm) and 2 sizes of Air Bags. It would be really silly and tedious to convert every thing to mm and Cubic Liters. At least we agree on the time.

The data I posted may assist conversions to save time and reduce errors.

Would anyone know if there is an industry standard TEST METHOD for cfm for an air tool. I understand how to calculate the scfm but I am trying to compare the scfm between two tools and I would like to know if the industry uses a standardized test setup.

Any help is appreciated.

Hi Rick,Try this.

Requirements

1 air tank. Possible source Grainger, 5 or 6 gallon rated 125 psig. Under $50

2 ball valves. 1/2"

1 pipe cross 1/2"

2 pipe nipples, 1/2"

2 reducer, male 1/2" to female 1/4"

1 gauge, 0-160 psig with 2" dial or larger and 1/4 connection

1 stop watch or timer

One ball valve controls inlet to tank. One ball valve controls outlet from tank to tool inlet. Mount gauge in between inlet and outlet valves to show tank pressure.

1. Close outlet valve and open inlet valve. Connect source of compressed air to inlet to fill tank to approximately 90 or 100 psig (see gauge).
2. Connect tool A to the outlet valve then close inlet valve.
3. Open outlet valve. Start Tool A and the timer simultaneously.
4. Stop the tool and timer simultaneously when the gauge shows a 10 psig loss.

Repeat steps 1-4 with tool B. The tool that used 10 psig in the shortest time is the greatest consumer.

If start pressure, P1, was 95 psig calculate the compression factor = (P1+ 14.7)/14.7 Then the compression factor Cf1,would be 7.46

If the tank, V1, is 5 gallons divide by 7.48 to get cubic feet. Then 5/7.48 = .67 ft³

The initial volume would be 4.98 SCF

After test the compression factor Cf2, is P1-10 psi = 85 Then (85 + 14.7)/14.7 = 6.78

Cf1 - Cf2 = 7.46 - 6.78 = .68 The air consumed would be .68 x .67 =.456 scf

Tool A used (.456 scf x 60 sec/min)/T_{timeA Sec}= Stand Cubic Feet per Minute for A

Repeat for tool B. Then (.456 x 60)/T_{timeB Sec} = SCFM for B

Obviously you would use the actual pressure, volume and time from each test with the same recipe.

Tom,

You have really helped me out here. Thank you for your clear and consice answer.

My pleasure.