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pneumatic cyclinder speed
2

pneumatic cyclinder speed

pneumatic cyclinder speed

(OP)
Is there some one that can help me with the relafant formulas for calculating the speed of the piston on a pneumatic system . The gas pressure will be known the port opening will be known. Friction I need to take into account (get value). The piston weight will be known. What else is necassary and what formulas can be used.
Nico

RE: pneumatic cyclinder speed

All you really need is the volume of the cylinder per unit length and the required gas pressure to move your resistance.

Fill your unit length of cylinder in 1 minute and that will be the velocity of the piston in lengths/minute.  Fill it in one second and that will be the velocity in lengths/sec.

For lower pressure cylinders,
V2 = P1/P2 x V1 x T2/T1

For high pressure cylinders you may need to include the compessibility factor of the gas.

V = volume, P = pressure, T = temperature
1 is initial,
2 is inside the cylinder

The fill rate through the valve will be proportional to the fill pressure and the pressure inside the cylinder at any given time.  Get the Cv for the fill valve, and fill rate is = (P_fill^2 - P_inside^2) * Cv

If you maintain the same differential pressure across the valve when filling, the fill rate will be more or less constant.  With a constant fill pressure, fill time will increase as pressure inside the cylinder increases.

http://virtualpipeline.spaces.msn.com

"We can't solve problems by using the same kind of thinking we used when we created them." -Albert Einstein

RE: pneumatic cyclinder speed

One problem with getting a Pneumatic Cylinder to start and travel quickly is the speed of getting rid of the air (Back-Pressure) in the exhaust end of the cylinder.

Reduced pressure in the exhaust end and/or a Quick Exhaust Valve can speed up the cycle speed and time GREATLY.

Most Air Valve manufacturers offer a Quick Exhaust in their valve line.

Bud Trinkel, Fluid Power Consultant
HYDRA-PNEU CONSULTING

RE: pneumatic cyclinder speed

Rapid opening and closing speeds are rarely needed.  Using ball valves, my normal estimate is one inch valve size per second for the average time.  I accept the offshore criteria from the Department of Interior Minerals Management Service on 45-seconds maximum to close a shutdown valve.  Quick exhaust valves are normally required for valves NPS 20 and larger.  Consider additional accelleration techniques at NPS 30 and larger.

If the one-line size per second estimate is too slow for your application, assure that all tubing fittings are at least as large as the quick exhaust valve.  A 1/4" fitting somewhere could eliminate all of the advantages provided by a 3/4" quick exhaust.

RE: pneumatic cyclinder speed

One BIG thing I forgot in the basics of Air Cylinder Sizing is:

If you want the load to move at a reasonable rate size the cylinder to have DOUBLE the FORCE required to overcome the loads resistance to moving, such as sliding a block across a surface or lifting a known weight, at the Air Pressure available.

For fastest movement size the cylinder for TWICE the FORCE required at the available pressure.

The FORCE Pneumatic Cylinder charts show at the Noted Pressure is what the cylinder thrust will be when it is Clamping a part. The extra force to move a load of a given resistance is required to make the cylinder move while overcoming Flow Losses and Internal Friction.

Bud Trinkel, Fluid Power Consultant
HYDRA-PNEU CONSULTING

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