My 1986 JCB loses hydraulic pressure as the fluid reaches warmer temperatures. I am running new ISO 46. The machine has a gear pump and a relief valve that controls the loader and hoe pressure independently. When I first start the machine all functions meet spec pressure (about 3000psi on these machines) As I operate the machine for a while the fluid will heat up. I believe iv taken temp readings on the warm fluid to be around 120-140 degF. At this temperature the tested pressure is reduced to around 1800 psi in both the loader and hoe functions and the machine is noticeably weaker. Some things I have tried: -Replaced Hydraulic return filter -Replaced Fluid -Replaced suction screen in tank -Removed and inspected relief valve (didn't see any obvious problems) -Maxed out relief valve adjustments I fear that the pump may have seen its day and is no longer operating efficiently. When I opened up the tank ports I did find a lot of garbage. Chewed up bits of old seals I assume. I was sad to see there was no suction screen installed. No way of knowing how long it was like that. Have I covered all the bases before a pump replacement or am I missing something? Thanks!
Can you open up the pump to inspect it? It's pretty simple to do.
Check the hydraulic cylinders for excessive heat buildup. There might be a couple with leaking piston seals. That would explain the garbage in the system.
Yes I could. I'll have to drain the tank. Iv never opened a gear pump before. I assume the seals and wear plates can be replaced but scoring on the casting walls would be bad. Maybe if I get time in the future I'll have at it.
So iv always wondered how hot is too hot for a cylinder. They say seals can be damaged beyond 180 degrees but I assume they should not even be close to that hot. Iv gotten readings of 140 after working the ho hard on hot days.
These pumps are either a single or tandem pump which are cast iron they wear internally and there is no spare parts to repair so it will be a new pump .I would firstly carry out a flow test with a flow meter in-between pump and valve block to measure what your machine is actually putting out before condemning anything.
Yes i have the double pump. When you say no spare parts you mean no housing parts or castings right? I have seen seal & pressure plate kits for sale that are designated for 3cx/1400b applications. Even if the housing is worn new plates might help if they are also worn. A flow test would be a good idea though. I just have to get my hands on a 30gpm/3000psi flow gage. They don't seem to come cheap.
So I would need a flow meter and a valve right? Thanks for the info.
Oh and a pressure gage of course
Yes and if you connect into the 1" pipe from pump to front loader block remember that you will not have the main relief valve protecting the circuit. So make sure you don't exceed the mrv pressure when caring out the test or you will blow hose , split pump, blow burst disc or hurt yourself.
Right. Thank you for that. Iv only had the machine a year and im still getting into it. I will do this if I can get my hands on a meter soon. So there is what I assume to be another relief valve or some kind of flow controller mounted in the Engine bay. Correct me if im wrong but I think it has to do with the Aux Roadbreaker circuit. I would just like to verify that it would affect on the whole machine pressure. Have you seen this before? Thanks.
Alright, Where are all the gear pump gurus? I took the pump apart today. The Auxiliary chamber was in pretty good shape but I wasn't having pressure problems with the extradig. The main Chamber looked like it had a little more wear but I really don't see any deep scoring on the chamber walls despite the fact that there was some buildup on the crown of the gear teeth. The gap between the gear and wall was around .003 - .004. I did see some wear on the pressure plates but I'm not familiar with how much is too much wear. I priced a seal kit with plates for this pump but the quote was more than the cost of a new pump!
Upon further inspection the wear plate seal is in very poor condition. If my research serves me right, I think this could allow fluid to leak from the high pressure side of the chamber to the low pressure side.
You are correct but your end plates are junk.
Good to Know. Thank you
Pump is rebuilt. I got new plates and seals. JCB Jeff was right though, there are no replacement parts available for these roller bearing pumps. I got lucky and a company in the UK was willing to sell me these parts out of a new old stock pump they had on hand. Just have to get some fluid in her to see if shes got her strength back!