Control Double Acting Hydraulic Cylinder

[LaurenceSachs]

Hi there,

I hope you can help me understand the following:

I would like to supply pressure to a double acting cylinder so that it forces in one direction and retracts in the other direction under minimal load.

what is the simplest way to alternate the routing of the hydraulic fluid so that it forces in one direction and retracts in the other, automatically?

Think jack hammer, or rock drill.

Laurence

 

[hydtools]

Breakers and rock drills have an internal valve designed to be moved when the piston passes over either a pressure port or a tank port. The auto valve is biased by pressure to cause the valve to shuttle when the opposing pressure is dumped to tank when the piston uncovers the tank port in the cylinder body.

You would need to come up with circuitry to drive the valve depending on the position of the piston. A pilot operated direction control valve could be plumbed to respond to pilot signals from the piston position.

Ted

 

[LaurenceSachs]

Thanks for the message hydtools!

I have designed a valve that is cnstantly pressurized to be in the closed position, except when the piston forces it open, which then switches the flow for the retract movement.

Laurence

 

[MikeHalloran]

Yeah, I have messed with that sort of thing for testing rigs, using pneumatic cylinders.

The ideal control that you need, to do the job without a whole lot of external circuitry, is a true toggle valve, where the main piston stores energy in a spring in the pilot valve, and at the true end of stroke, the pilot valve is triggered to change position using only that stored energy to do so, and reverses the directional stage controlling the main cylinder.

Unfortunately, no one makes such a thing commercially, AFAIK.

Just hooking a pilot valve to the main cylinder and using the main cylinder directly to change the pilot valve position will stall at the end of stroke.

Clippard's modular valve catalog used to show a circuit that did what you want, using three of their modular valves. The circuit worked well enough for my purposes, and was cheaper than coming up with a custom valve.



Mike Halloran
Pembroke Pines, FL, USA

 

[LaurenceSachs]

Thanks Mike,

One issue I am concerned about is; ensuring that the valve stays open long enough in the retract cycle to supply enough hydraulic power.

Any suggestions here?

L

 

[hydtools]

Trap the pressure that opens the valve until the piston fully retracts, then dump that pressure and then the piston extends since you say you bias your valve to remain in the state to extend the piston. Check valve.
In hydraulic breakers the time required to hold a signal state is so short that check valves are not necessary. The state-holding pressure decay time through leakage was very long compared to piston cycle time that the power valve remained in one state or the other until the next pressure signal.

Ted