# Air flowrate required for testing a pneumatic cylinder?

First time designing with pneumatics here. I want to build a continuous use device (with ~30 back and forth actuation per minute) but do not currently have access to a large compressor.

Is there a way to manually test my device as I build it, and then use a real compressor later? I calculated that my device (a simple cylinder that lifts a 500g mass) will use 5 cubic feet of air per minute (cfm). I will need a compressor capable of 15 cfm and cannot afford this cost at the moment (need to invest it on other things).

I am guessing the pressures I will be working with are around 90 psi, but maybe up to 120 or 180 depending on the cylinder I use.

Is there a way I can rig something up with say a bicycle pump? Surely someone has been in this situation of wanting to engineer/prototype without a big compressor available. There's math and calculations of course, but I am more of a hands-on engineer.

Thanks for suggestions.

• Welcome to Robotics, user391339. As it stands, this is an engineering question and not really related to robotics. I'm going to migrate your question to the Engineering site, as I think you would get better answers over there. Apr 27 '17 at 19:31
• I'll comment that you can of course use a bicycle pump, you'd just need a pressure tank to store the air until you're ready to use it, but you're going to give up using that method probably before you're even ready to try it once. Apr 27 '17 at 19:37
• Source an air tank from a truck braking system - then use an airline at a garage to charge it : necessary : a pressure regulator. Apr 27 '17 at 19:52

It depends on what you are trying to test; if you are trying to test leakage a bike pump will work fine, but if you are trying to test ring wear or operation at full power there is no way around supplying the required amount of air.

Double check your volume calculations and force calculations. That seems like way to much power to do the task required.

0.5kg *9.81m/s^2 = 620kpa * Area
Area= 7.9E-6m^2 = PI()*R^2
R=0.0016m
Diameter= 3.3mm at the 90psi you are proposing

I don't know your stroke length but lets say 1 meter (~39inches)
Volume = 7.9E-6m^2 * 1m = 7.9E-6m^3 = 0.00028ft^3

30cycles/min * 2(double acting, assuming same volume both directions) * 0.00028ft^3 = 0.0168CFM required @ 90psi

You will need to run though these calculations again with a more reasonable cylinder diameter and pressure combination, but as you can see the cfm requirement is going to be much less than you estimated.

With 1/3 air compressor flowrate, just test your actuator at ~10 strokes per minute.

• I think you misread the question. He believed he required 5 CFM per minute going through the actuator; and wanted a 15 CFM compressor.
– JMac
May 15 '17 at 11:18
• When you don't have actual compressor, lower flowrate compressor I considered acceptable for functional testing. Multiply speed for speed approximation. Jun 18 '17 at 12:20