# Pneumatics question

1. Apr 22, 2005

### Serj

How do you determine how fast a pneumatic cylinder will move when you force air into it with a tank of compressed air. I also need to know how fast it will accelerate. I only need an equation but resistance from the airtight rings must also be included. Thank you.
-Serj

2. Apr 22, 2005

### FredGarvin

The only way to really know is to know the velocity or the volumetric flow rate into the cylinder. From there it's simply flow divided by the area. The actual measurement of the flow rate is a bit tricky due to compressibility.

3. Apr 22, 2005

### clive

I think you can solve the problem if you know the pressure of the compressed air (p) , the atmospheric pressure (p_0) and the resistance force(F_f). From the second principle,

$$m\cdot a=pS-p_0S-F_f$$

(S is the cross-section area of the cylinder)

If you have the acceleration, with the length and the Galilei's law the final velocity is piece of cake.

Last edited: Apr 22, 2005
4. Apr 22, 2005

### Integral

Staff Emeritus
The best way to control the speed of a air cylinder is to use a needle valve on the exhaust port. This will control how fast the air exits the cylinder. They make a combination needle valve/check valve just for this purpose. The check valve allows free flow of air into the cylinder the needle valve controls the rate that air exits, thus controling the speed of activation.

For example

These parts are not very expensive on the scale of things.

Last edited: Apr 22, 2005