I am working on a Komatsu WB146-5 backhoe which has no loader boom or backhoe function at all. This machine has steering so there is hydraulic pressure from the pump. There is absolutely no movement on the boom and backhoe so they are not receiving any hydraulic pressure. This machine has excavator style backhoe controls. The main solenoid valve block has 475 psi and when the pilot controls are activated for a function, it puts 450 psi to the to the correct valve on the main valve bank. But since the hydraulic pressure does not reach the loader or boom valves on the main control valve, nothing happens. Komatsu uses a very complicated system to control the pump pressure and volume which includes load sensing and more which makes it extremely difficult to troubleshoot. Bottom line...I have hydraulic pressure entering the main control valve and the priority valve sends pressure to the steering when used. The rest of the time this oil is sent to the return and ends up in the hydraulic tank. This oil is not available to the other hydraulic valves on the main control valve block. The main relief valve looks good as well as the priority valve, the unloading valve, LS bypass valve and the sequential reducing valve. But one of these valves has to be the culprit for sending the oil to return. Any ideas?
A lot of Komatsu's had a series of lighted switches located near the real control panel. One of those safety switches made the hydraulics to the backhoe go active, another would activate the maximum flow via the squash plate. Does your model have these?
The wiring on this machine is a rats nest. I assume those switches operated the solenoids in the main solenoid valve. Those do have 12 volts to them and the controls are sending hydraulic pressure to the main control valve so that does not seem to be the problem.
did you find the issue on this?
No, I went through the whole rear valve block, found a number of issues, but that did not fix the problem. Since individual Komatsu parts are so expensive, we opted to buy a complete used rear valve block and that fixed the issue.