sticking in hydraulic cylinders

[concorde3333]

I am running two hydraulic cylinders in series to pressurize a water tank. where one cylinder recieves air and drive a smaller water cylinder. The pressure in the tank needs to be precisely 225psi. I currently use a pressure regulator to control air pressure going to the air cylinder. The problem is that as I increase the air pressure closer to 225psi the cylinders tend to jolt and ramp the water pressure higher than 225. How could I control the system better, and more smoothly?

 

[budt]

Air powered intensifiers are lousy at controlling output pressure accurately since seal friction and fluid resistance requires an elevated pressure drop to start movement. Once movement commences the higher starting pressure cause the piston to lunge until the air expands and lowers to running pressure.

You could try an accumulator in the out let to soften the pressure spikes but I don't believe it would help the overshoot very much.

I would use higher air pressure to give higher water pressure and use a Pressure reducing valve on the water outlet to set the 225 PSI constant. You will probably still need an accumulator to allow time for air pressure to drop enough to start the pump before water pressure goes below the 225 PSI required.

Some companies supply intensifiers that use a diaphragm instead of a piston. This eliminates one friction maker in the pump. If the diaphragm is driving a rod into a chamber the seal on the rod needs to be low friction as well. This would still not maintain a constant pressure however.

Also you could use higher air pressure and use a Relief Valve set at 225 PSI on the outlet line so the intensifier would have to pump continuously.


Bud Trinkel CFPE
HYDRA-PNEU CONSULTING, INC.
fluidpower1 @ hotmail.com

http://www.fluidpower1.us

 

[MikeHalloran]

Link the cylinders with a piece of timing pulley stock. Drive that with a timing belt and a real slow gearmotor, so that both pistons rotate continuously, slowly.

Expect seal problems.




Mike Halloran
Pembroke Pines, FL, USA