Hydraulic lock valve issue

[BukitCase]

If that picture is the way the unit came, it looks like the cylinder itself is plumbed as a single action ("raise, or NOT raise) - only way that could work with a double action circuit is if that crappy valve hanging in the wind is some kind of pilot operated check valve??? IOW, is that second port on the cylinder itself actually BLOCKED, or am I missing something?

Both of my tractors' hydraulic toplinks have a check valve, but it's HARD plumbed BETWEEN the two ports of the cylinder, and wouldn't even be necessary except for valve leakage control. Works as is, if that changes I'd probably just bypass it.

More confused than usual... Steve

Nevermind, took a third look, guessing the UPPER bolt head in the pic USED TO BE the second connection...

 

[oldnslo]

Dadnatron
Are there any part numbers on the valve assembly? If yes post them and then maybe someone can identify what that valve assembly is.

 

[Dave M7040]

I think it's either a pilot check valve or a crossover relief or maybe both combined in one. The hex sided things on each end look like adjustable relief valves. Those would (hopefully) prevent damage to the mower head from overpowering it with the hydraulics.

Pilot check valves would keep the cylinder from "bleeding down" due to leakage past the valve on the tractor. They are common on hydraulic 3pt top links. They don't allow float so if it floats then the valve doesn't have checks.

The fix would be to get new longer hoses made to run from the mystery valve to the cylinder. That would allow you to mount the valve solidly to the cylinder using hose clamps or a fabricated bracket. They spent the $$ to put it on so I would lean towards making it work rather than removing it.

Cross Over relief valves only work with two equal sized cylinders. Two angle cylinders on a plow or two swing cylinders on a backhoe. The valve needs to be able to move fluid from one part of the hydraulic system to another of equal volume. With a double acting cylinder, the volumes on either side of the piston are not equal and the valve cannot work.

Dave M7040

 

[ericm979]

Thanks Dave. I used the wrong word, I'd been thinking of a valve like this:
1/2 NPT 3 GPM 15-3 PSI Hydraulic Cushion Valve | Relief & Cushion Valves | Hydraulic Valves | Hydraulics | www.surpluscenter.com
because of the adjusting nuts on either end.
But maybe they're for adjustable check valves.

 

[Dave M7040]

Thanks Dave. I used the wrong word, I'd been thinking of a valve like this:
1/2 NPT 3 GPM 15-3 PSI Hydraulic Cushion Valve | Relief & Cushion Valves | Hydraulic Valves | Hydraulics | www.surpluscenter.com
because of the adjusting nuts on either end.
But maybe they're for adjustable check valves.

Eric
I looked at the Prince valve and believe the same issue applies:.

Brand new PRINCE DRV-4HH. Cushion valve or double relief valve. Use to stop or minimize surge, shock and overload in hydraulic circuits. Install between control valve and motor or cylinder. Bypasses to opposite side to prevent cavitation.

For this type of valve to work it has to have somewhere to send the over pressured fluid that that can accept it. With the control valve for a double acting cylinder in its neutral position, the fluid is locked in the cylinder. Because each half of the double acting cylinder contains different volumes of fluid, no exchange between opposite side of the cylinder piston can occur.

I still wonder if someone added this valve to the implement not understanding its specific application

Dave M7040

 

[ericm979]

Is the cushion valve intended to work when the control valve is not in neutral? I.e. when you're extending or retracting a cylinder. If the cylinder pressure is too high because the stuff attached to the cylinder is running into something, then the cushion valve would send fluid to the other side which would be open to tank through the control valve. I've seen people use cushioning valves like this on backhoe thumbs. But yes you're right it would not do anything when the control valve was in neutral closing off the work ports.

(well maybe it might but only in one direction due to the rod side volume being smaller than the piston side volume. If the control valve is closed and something is extending the cylinder hard enough to trip the relief in the cushion valve, fluid could flow through the cushion valve relief from the rod side to the piston side. But as you pointed out it wouldn't work the other way.)

I'm probably wrong about it being a cushion valve and it's a two way adjustable check valve. If it is and you want float (and your control valve has float) it could be removed.

 

[Dave M7040]

When the control valve is anywhere but its neutral position then the control valve's relief valve is in the circuit protecting things in one direction and in the other direction, fluid can easily return to the tank.

Remember that fluid is in-compressible so for any fluid to change sides in a cylinder, that cylinder's piston has to move.

With a power angling blade, when you hit something on one side, the cross over relief allows the blade to move away from the object being hit. It is not just a matter of fluid moving but cylinders moving.

Dave M7040