I’ve got an early 790 excavator that is acting like it has air in the system. I replaced many lines from the hydraulic tank to the pumps, filters have been changed, screen in tank is clean. I blew a hose and shut it down before it lost much oil and ever since then it’s been acting up. It only does it when the oil gets warm. Plus it’s not constant. If it starts chattering I can stop movement and then it will be ok for a few minutes. Oil is new. Bled air from system also. Gonna try a new pilot pump as that was suggested. But looking for more insight on this headache. Thanks for now!
What oil are you using in the machine?
When you say you bled air from system, how did you do it?
It’s chevron iso 46. Meets hygard standards
The two hex nuts on top of the pumps with the engine running
Good day Check the tank pressure, you may have no pressure forcing the fluid into the pumps. Kind regards Uffex
Thanks for the reply. Should’ve noted that but I also checked that earlier. Would it act that way if the control valves move too far?
Good day A low or no tank pressure normally makes for noise from the pumps and lack of performance, full stroke the cylinders a few times then press the button on top of the tank - you should hear air escaping. I'm not too sure of what you mean by control valves moving too far. Kind regards Uffex
I’m talking about the control arms on top of both pumps. I believe they are called regulating valves?
The 790 has an air compressor that is used to pressurize the tank. Make sure it is operational. The tank should have 12-20 psi of air pressure. There should be a gauge in the cab to indicate if the pressure is in the green zone.
Good day I'm not so sure what reaction the pump regulation would have, I suggest start with basics first. Before you change the servo pump, check it out, no point to spend if you get not further forwards. Kind regards Uffex
I’m not sure what else to check that would be basic. Air pressure is good, new oil and filters, clean suction screen, many new suction lines. Checked the arm adjustments. Unless it could be sucking air from someplace?? Clamps are tight but I’ll retorque them again.
The plugs on top of pumps to bleed is correct with engine running. Also what others have said about air compressor. There is a air relief valve on top of cover plate where you fill hyd tank. If that valve leaks, pressure wont build in tank. There should be another air gauge on inside wall of hyd tank under big hinged access cover. That gauge has a regulator on it that sets pressure for dash gauge and tank.
Also, are you aware that in order to check hyd level, the boom down and stick o fully extended and bucket full curl on the ground.
Everything checks out. Might try the charge pump tomorrow. It actually sounds like a dry bushing when it starts making the noise. But it’s on all the controls. Could it be a relief valve?
Do you have one of those stethoscope things like a Dr has around his neck to listen for sounds? I have an electronic version that lets me really pinpoint odd noises on machines. The regular ones are cheap, worth a try.
So I went to drain the oil today and it was excessively foamy. Machine hasn’t ran in 24 hours.
It was the oil all along
oil was contaminated with water? or wrong oil.
It was brand new iso 46 oil. But didn’t like it. Switched back to hygard