Hello everyone, I have a 2000 924g that I had the valve bank rebuilt, I have a third function and I had it rebuilt because the aluminum gaskets between the valve started leaking. It's all back together and I can't get over 500 psi out of it. I had no pressure problems prior to taking it apart. I bled off the signal line to the pump as cat describes in the manual. I'm lost at this point. Any advise is appreciated!
Partial guess here because I don't know the exact prefix of your machine. Pretty sure that is a variable displacement piston pump, and has PPPC, pilot operated hydraulics. Sounds to me like no LS (load sense) signal is getting back to the pump to signal the pump to stroke up. Sounds like 500 psi is an indication that the pump is sitting at low pressure standby. On the hydraulic control valve ( should be above front axle between lift arm) can you pressure test signal pressure (may be marked "LS") through a quick coupler/disconnect? Once tee'd into the port, feather the tilt control (rack back) and see if you get a pressure reading from the port. As you get close to crowd (rack back) the signal should spike to a pressure set by the high pressure cut off spool/spring, 3000-4000 psi. If you get no reading from this signal line my guess is that there is a leak inside the control valve where the LS signal is being lost. O-ring missing, incorrect assembly, etc. That machine also uses a thing called a resolver network, meaning if you are using more than 1 circuit at a time the highest load signal is sent to the pump so everything will work. Try to move multiple functions at the same time while using the aux. If something starts to happen you may have a leak in the network (usually a resolver ball missing or leaking) Another thing to check is pilot pressure. No pilot pressure = no spool movement = no operating functions. Cheers, Z
Hi Z, The machine prefix is a 9sw. Trying to rack back and lift will help the lift to about 750 psi. It won't lift its own arm up all the way. The steering works fine in the machine. I checked between the loader arm and axle and found no control valve there. All lines seem to head right back to the valve body on the side. All functions have the same limited amount of pressure. The steering system will pressure right up to an easy 1500 if you slightly grab the wheel so I assume the pump is fine. I heard about the resolvers, although I don't fully understand how they work at this point, is there one in particular that is responsible for the making the pump kick up?
Hi Ford, The steering system uses the pilot pump for operation, so that seems to tell me the pilot pump circuit should be ok because the steering is fine. Would be worth checking pilot pressure though. Pilot/steering pump is variable displacement piston pump. Implements have their own variable displacement piston pump. I believe on that machine (9SW) the hyd control valve should be on the RH side, mid machine, in behind RH stairs. H-K-M series are between the loader arms above the front axle. Dumb question: Before you removed the valve what issues were you having? Just leakage or function trouble as well? Were any screws/adjustments changed on the pump control valve? If functions were all ok I still suspect a damaged o-ring or something within the repair that now allows signal pressure to leak away rather than being sent to the flow compensator (margin spool spring) on the pump controller (signal is necessary to upstroke pump). It is also possible that it could just be an o-ring that is damaged on a resolver valve. Quite easy to do on assembly. A resolver is a double check valve that will send the highest pressure towards the pump controller from the highest load on the cylinder. Pump needs to see this to overcome the load (pressure). Flow is determined by how far you move the control spool for that circuit. Each circuit will have it's own resolver. If you are moving two circuits then the highest pressure from the two circuits will eventually reach the pump margin spool. Here is another one. There is a signal relief in the inlet manifold of the control valve. It is possible that this signal relief is stuck in "Relief" meaning that the signal could be lost there before reaching the pump. Another thing to check. My suggestion is to find the port for signal pressure, tee in and check to see if the pressure increases when you function a circuit. If not you have an issue in the signal network = leaking resolver from o-ring or check ball - stuck signal relief or an o-ring between the sections of the control valve. I still think when you find this one it will be a simple fix I could be wrong, it wouldn't be the first time. Hope this helps, I will stay with you to try and help if you wish. Cheers, Z
Fordtrk05, Ever find a resolution to your issue? Just curious.