Any hydraulic engineers here?

catfishblues

catfishblues

Well-Known Member
Joined
Jul 26, 2005
Location
Pfafftown, NC
I have a friend working on a product. He's trying to run a ram and a hydraulic motor off a single pump using a double spool valve. My understanding of the problem is that when he goes to run the ram up, once it reaches a certain pressure, the motor suddenly becomes the path of least resistance and it bypasses the pressure through it. Is there a valve on the market that can accomplish this? He's tried several things, including one pricey valve that was supposed to but to no avail.
 
I'm guessing he has a valve stack with two manual spool valves? A picture or idea what he's doing would help quite a bit. He has something plumbed wrong it sounds like.
 
I used to run hydraulics for a living. Sounds to me like what @braxton357 said....either something is plumbed incorrectly, or he doesn't have the bypass on the pump set correctly. Would need specifics of what he's running. If the pressure at the cylinder reaches what the pump relief is set to (if he's using a piston pump instead of a gear driven pump) or has a relief on his valve set too low, the pressure will bypass.

A few ways of accomplishing what he needs...first needs to understand what the load on the cylinder is, then set the valve relief higher than that load. Run the cylinder all the way out (or in) full stroke, set the pump relief to a given pressure (something higher than his load pressure needed). Then back the valve relief down a little lower than that, so that the reliefs are staggered. You don't want both reliefs blowing by at the same pressure, otherwise you'll never know where a problem is trying to troubleshoot.

Example: you need a cylinder to have a maximum 1500 psi to move the load. I would set the pump relief (if it is a piston pump) to 1850 psi, then the valve relief to 1650 psi. If it is a gear pump (no relief on those typically in my experience), it might not be a bad idea to have a redundant relief, or at least a pressure regulator set above the work load pressure.

A manual spool (closed center) valve should hold the load when the valve is in neutral. A motor spool valve will drop the load in neutral, unless you use a dual-lock check valve inline.
 
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He needs a relief, the relief is stuck, the relief is plumbed wrong or the relief needs to be asjusted. Good working pressures are 2300 to 2700 with 3k max. Spike to 3500 if useing 2 wire hose.
 
Jeff B said:
He needs a relief, the relief is stuck, the relief is plumbed wrong or the relief needs to be asjusted. Good working pressures are 2300 to 2700 with 3k max. Spike to 3500 if useing 2 wire hose.
Click to expand...

Sounds like he has a relief but instead of going to tank it ends up running his motor.
 
Actually sounds like you may need a flow divider to separate motor from cylinder. The back pressure may be running the motor when the cylinder runs over the relief.
 
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