Case DH4B Trencher/Backhoe Won't Spin Trenching Chain

[MTGreen]

Which relief valve, I do not know how to identify a/the relief valve

Every high pressure hydraulic circuit has a relief valve for over pressure built in and you may have more than one. If you trace the circuit from the tank to the pump to the valve to your hydraulic motor/cylinder and back to your tank, there will be a relief valve somewhere in the circuit that opens when the pressure gets too high to short circuit the fluid back to the tank and relieve the pressure. If that valve is stuck open it will be continuously short circuiting and you'll never get anywhere close to working pressure at your motor/cylinder regardless of what your pressure pump is putting out.

There's definitely one in the circuit and you may have an additional one on your valve as well

The surest way to rule this out is to measure the pressure at your actuator (in your case hydraulic motor) when your valve is open. If you have full system pressure here you do not have a relief valve problem and you either have a bad hydraulic motor or a blockage somewhere in the motor output to the tank or incorrect plumbing. If you don't then it could be a number of things like blockages on the input side or incorrect plumbing or relief valve stuck open.

 

[r8f1k]

If you look at the second photo I posted, there are two small caps that are on the bottom of each spool. I pulled those two out and you can push on a rod that makes the levers move. However, they are sticky and don't always return to the home position. I have solvent siting in the caps now and I am working the rods a little at a time until they free up. Hopefully this will do it.

 

[laurencen]

if it were me I would take the valve totally apart and give it a good cleaning, you mentioned water in the system, the valve body is cast iron and spool chromed steel, it will rust together sitting in water, they need to be taken apart and cleaned

 

[r8f1k]

Any recommendations on what chemicals to NOT use?

 

[laurencen]

we use diesel fuel, Varasol is good but ut takes oil out the cast, get some brass brushes, they sell ones for bores work great in cavities holes

 

[r8f1k]

I let the spools soak in HOT water and degreaser. I took as much apart as I could, the longer it sat, the looser it got. 2 out of the 3 will return with ease to the 'home' position. One is still a little sticky, so I have it sitting overnight in degreaser again. Lots of compressed air and moving the valves seems to have made a difference. I plan on dipping it again in the solvent tank and giving it a good cleaning in there. I think I will give it run tomorrow sometime in the afternoon. I will report.

 

[r8f1k]

I let the spool soak, took as much of it apart as I could, no change. Nothing. No hum, no shudder, not a thing. Must be something else. Not sure what to do.......I am also not sure what to do about the trencher pump/motor situation. I am tempted to pull the console again and remove the pump entirely and see if the roll pins, as mentioned, are broken or fell out. Another thought I have is, are the control cables adjusted properly? Is there the potential that the actuator cables are misadjusted and things are not being pulled or pushed as they should?

 

[r8f1k]

Any ideas? I had the thought of removing the existing pump and putting in a new unit. Just a regular direct drive pump and plumbing it to another spool. Use a spool for chain direction. Any thoughts?

 

[r8f1k]

Something like this.

 

[oldnslo]

R8
Picture in post 89 looks like a low speed high torque geroler or gerotor style motor. Is this what is on the trencher?

Have you done any testing on the trencher pump? Don’t recall who posted them but there were some suggestions on how to isolate and test the pump.