Help with Neumatics

How do u get a neumatic piston to stay in one place half way up the shaft. We though of putting pressure on both sides but we dont want to waste the pressure.



SEARCH GRRRRR!! There has been a thread about this on the highlights section of the main page for about oh… the last week. If you searched “How to stop a pneumatic half way” It would probably be the first result!


thanks and i wasnt sure if pnuematics was spelled with a p or what! lol


First off, your team doesnt seem to have a concept of the physics of air pressure.

Putting pressure on both sides of a piston at the same time will just make for a slow extension of the cyclinder with a lot of stress.

The change in position is the relation of:
pi * r * PSI = output

r is your “bore”, so for the 2" bore, 3.14 * 1" * 60psi = 188.4 lbs of output power.

Then inward pressure is slightly smaller because of where the rod attaches to the “bore cylinder” of the cylinder. So instead of an actual 2" surface diameter, it’s (2" - rod diam). Thus more pressure is applied to extend the cylinder instead of retract it.

To stop the cylinder at 1/2 mast you need to control the exaust flow and the intake flow with another cylinnoid. I can’t think of the wiring diagram right now sorry.



You’re absolutely right – our team doesn’t have much a concept of air physics other than we are familiar with “Path of least resistance”.

After reading some suggestions on the board, we’ve managed to control the air intake to the double solenoid by inserting a single solenoid between the pump and the double.

The only problem that we’re running into now is that cutting off the single will result in a slow reversal in direction of the cylinder until we release the button that controls the single solenoid’s relay. Once we release it, there is a rush of air into the cylinder, causing a much faster movement than we normally have.

Do we have it set up incorrectly, or is that just the nature of the beast? Again, I know very little about air physics (I teach math :rolleyes: )

Any suggestions would be greatly appreciated.

might i suggest using those flow control connectors? the ones with the thumbscrews in the top? they control the exhaust air from the respective side… the tighter you make the thumbscrew, the slower the piston pushes the air out of that side… thus if you want to make the piston go out slower, you tighten the side closest to the rod. if you want it to retract slower, you tighten the side farthest from the rod. that’ll slow down that rush of air… it helps to regulate the speed(if you get a big burst of air or a small one, it’s still going to go the same speed pretty much… good luck

p.s. those flow control valves are white with orange(im pretty sure) and BE CAREFUL screwing them into the piston… the threads grind off really easy(they’re kinda junky)… this morning i had to re-tap a piston because one of those killed the threads on the piston… :frowning:

good luck

With the valves we have, sufficient pressure must be applied to the pressure port P to allow the electrically-operated pilot valve to push the main, air-operated valve hard enough to switch.

If you put cyclinder exhaust through a pressure port, with these dinky valves, the low volume-rate pressure will go out through the open port, and never build up high enough to operate the valve.

You could try to put the cylinder exhaust through one of the X (exhaust) ports on the valve via the related output port A, or B, and you would have to supply air to port P.

If you use A and Xa to switch the cylinder exhaust, then when the valve is operated, P is passed through to B, and Xb is blocked. To close the path through P to atmosphere, use a plug in B. All the while the cylinder exhaust is attached to Xa which is connected to A, and is at 0 psig = atmosphere.

But when you relax the valve, Xb, is connected to the plugged port B, so no change, and while Xa is disconnected from A, so it is plugged (not guaranteed), P is connected to A, and is passing your precious pressurized air to atmosphere. You need pressure on P to operate the valve, and you need A not blocked to open Xa to atmosphere hwen operated, so you need these connections unchanged.

There isn’t any way I have thought of to accomplish blocking a cylinder with these valves.

And putting equal pressure on both sides, without blocking the air flow from one side of the piston via the valves to the other side, is almost the same as letting both sides go to 0 psig. Physics assumes that balanced forces give Fnet of zero (neglecting the difference in piston area between the sides, which doesn’t help).

So go ahead and prove it wrong - stop it mid-stroke, if you can !