Pneumatic cylinder velocity.?

Question

How can I figure out the velocity of a pneumatic cylinder? Given an 11" stroke single acting cylinder with a 1.25" bore and an input pressure of 40psi. Also, will the cylinder be under constant acceleration thru the entire 11" stoke or does it reach a "terminal velocity" at a certain distance. If it is under constant acceleration, is there a formula that can predict it's velocity at a particular moment in time?

Answer 1

Velocity of pneumatic cylinders notoriously inconsistent. If the load at higher speeds does not equal thrust from the cylinder, it will continue to accelerate. Under dynamic situation, you can't count on having 40psi on piston, due to pressure drops in tubing and valves.

You could approximate performance using F = ma,

where F = Pressure * area minus load. Mass is mass of load and piston+rod.

Assuming constant acceleration, v = a * t.

Note that area in extending is bore area,  in retracting is bore area - rod area.

Answer 2

In theory, it would be under constant acceleration, but several things would limit this.  There will always be some friction, but not enough for it to reach terminal velocity in 11 inches.  The other limiting factor is the flow of the liquid or gas.  If the source of pressure or the inlet of the cylinder can't provide enough flow, the pressure will drop.  

To determine the (theoretical) acceleration use F = ma. Multiply the area of the bore by the pressure to get force.  You also need to know the mass of the piston and the load.  

Once you have determined acceleration, use v = at to determine velocity