NORMAL OPERATION OR PROBLEMS W/ REAR REMOTE

[GIJOE]

I used a pressure gage with a QD and briefly dead headed one side of the rear remote hydraulics to get a pressure reading of approx. 2200 psi. When the lever was returned to the neutral position the pressure fell off till it reached zero (about 10 sec). To me, that didn't seem right, so I tried the other side and had the same results. I understand that when a double acting cylinder is installed it will move until the pressure equalizes on both sides, but when one side is dead headed shouldn't it be able to hold the pressure? Is this normal, or do I have a problem?

Joe

 

[kennyd]

Not 100% sure if it's "normal" or not, but mine does the same thing.

 

[rdbrumfield]

yes the pressure should stay up if the line is deadheaded. With a cylinder you only have pressure on one side of the ram when you are using it, the other side is going back to the tank. when you center the spool valve, it should lock up the hydraulics going to both sides of the ram.
Your problem sounds like the spool is worn a bit and the oil is bypassing there. If it is over time, I wouldn't worry about it as the pressure is strictly hyd, any seepage past the spool will cause a pressure drop very quickly as it doesn't take much at all to relieve a short line. As spools don't have O rings on the spools, at least I have never seen them, any hyd leakage is usually in the cylinder as the oil bypasses the piston from one side of the cylinder to the other.

 

[dynasim]

Because oil is incompressible, a very small amount of leakage will cause the pressure to drop a bunch in a dead headed system. Compared to the volume in the cylinder, the leakage would be miniscule.

If the cylinder is not under near max loads, the leakage would be small, indeed.

Chris

Edit: No valve is "leak free". The leakeage is just a matter of magnitude, and some have truly small amount of leakage.

 

[GIJOE]

Hey Guys,

Thanks for the replies. I went by my dealer today to pick up some supplies and asked him about it. His reply was the same as what y'all said. He said, since there is no o-rings in the valve, and the volume was so small using a pressure gage with a QD (about 2") any leakage in the valve would be a big pressure drop reading on the gage. With two hydraulic hoses, a cylinder and the weight of an implement, he said it should hold at between 1200-1500 psi with very minimal leakage.

I guess, in all actuality, that's what a DP check valve is made for.

Thanks,
Joe