before changing any parts, back up please and rethink all the basics of a simple hydraulic circuit..
Under what conditions do you read 150 or 200 psi on the pressure gauge? When the cylinder is at full extend, lever held to extend as though you were trying to split? That forces oil across relief valve and will be testing the setting of the relief valve. That should be 2500 psi or whatever. If you see 200 under that condition, there are problems.
If the 150 is read when valve handle is in neutral and nothing is moving, that is the open center pressure drops back to tank. No resistance, no pressure buildup. 150-200 would be quite normal.
If pressure is low while deadheaded, there is a path to tank with no resistance for whatever amount of oil the pump is trying to move.
-Is there good oil supply to the pump? Hoses, strainer, etc. you have looked at
-Is the pump turning at proper rpm, good coupling not spinning on the shaft, strong engine?
-If the pump is badly worn, it can leak around the gear set. But it takes really bad gears to bypass 11 gpm at only 200 psi.
-If the unloading section is not operating properly, it can bypass the large section oil back to the inlet port. That is how an unloader should work, but it could be doing it at a very low pressure setting.
-If the check valve in the pump is not sealing, the small high pressure section pushes its oil backwards, to the large low pressure section, and out the unloader of the large low pressure section. Typically this is obvious because it works and moves great at pressures below the unloader setting, say 800 psi, then it just stops motion but holds 800 psi on the gauge. Doesn’t sound like what you are seeing.
To properly check the pump it has to have a load and measure flow. ‘Holding pressure’ at deadhead does not mean the pump is good. A good ’11 gpm’ pump would be putting about 3 gpm (once it unloads the large section) across the relief valve at 2500 psi. However, a bad pump could be putting 2.999 gpm across leaks everywhere and still hold just enough to crack the relief valve at 2500 psi.
So, the presence of 2500 psi at stall does not indicate a good pump. The presence of 200 psi at stall does not indicate a bad pump either.
If pump is perfect, but there is an easy path to tank with no resistance, it won’t build up pressure. That path can be cylinder seals gone (but it would have to be bypassing 11 gpm at 200 psi and that is a very big gap).
The spool valve could have some broken spool that always paths to tank. Unlikely.
Most likely the relief valve in the manual valve is dirty, held open, broken spring, etc.
To check cylinder seals, you have to disconnect the rod side hose and check for leakage out of that hose at end of stroke. Better, disconnect both hoses and plug the valve off. Now the cylinder is completely out of the circuit. See if the problem changes.
Side note: This will stir some arguments: pushing back against the cylinder pushing the rod into retract will not test cylinder piston seals UNLESS the rod side hose is open to tank. The rod could move due to leaking spool in the manual valve. However, if the rod side hose is still connected and sealed up by a good tight valve spool, or a plug on the cylinder port, the pistons seals (or even the entire piston) could be totally removed and the rod won’t retract. It turns into a single acting ram like a porta power,. The force is resisted only by the area of the steel rod, and the pressures in the cylinder can get very high. This is called intensification. The rod could be pulled out against bad piston seals, but not pushed in.
So before changing pump, I would verify the suction is good, the coupling is good, take stall pressure with rod fully extended. Then I would open/clean/inspect/reassemble the pump check valve, the pump unloader spool, the manual valve relief spring or ball or spool.
If you didn’t see shiny steel in the return filter, I am betting against the pump as problem. I suspect old 10 year trash or gummy or disintegrated filter element is holding something in the pump or in the manual valve open.
kcj
I love messing with spliters. They amaze the ever loving #### outta me for some reason!!!
