apm
Well-Known Member
OK, I tried this post in the main excavator forum and got no response. Maybe it should be here, instead?
I've got a 1993 Komatsu PC50UU-1 gray market machine. I've got the pdf manual for it. It's got a hydraulic problem that I've been unable to figure out.
This machine is a direct hydraulic machine, no electronics, solenoids, etc. in the hydraulic circuit. I believe it uses a gear pump. The pump is 3 stage and is supposedly brand new (installed by the previous owner). There are two control valves that operate all of the functions. One is a 6 spool valve and one is a 3 spool valve. The first two stages of the pump feed the 6 spool valve, and all functions seem to work as they should. The third stage of the pump feeds the 3 spool valve. this valve controls the blade, the swing motor and the rapid travel function. The blade is weak as well as the swing (slow). The rapid travel functions. I hooked a hydraulic gauge into the line from the pump to the 3 spool valve. There is a test plug there for that purpose. When operating the blade or the swing against the stop pin, the pressure never gets over 1500 psi. Relief is supposed to be about 3100 psi.
I assume I'm bypassing oil either in the pump or the 3 spool valve. The pump is supposed to be brand new. I can hold a function open or against the stop until pressure comes up to 1500 and I'd expect heat to build if I was bypassing oil somewhere. The pump does not seem to get overly hot, nor the valve.
I've swapped out the relief valve from the 6 spool valve (same part number) into the 3 spool valve, and it made no difference. I've had the 3 spool valve out of the machine and totally disassembled and cleaned it. I found nothing wrong, nothing broken, no excessive clearances, etc. There is also a suction and safety valve on the 3 spool that I disassembled and cleaned. It appeared to be fine but I've got no way of testing or swapping that one.
What would you try next?
Thanks,
Greg
I've got a 1993 Komatsu PC50UU-1 gray market machine. I've got the pdf manual for it. It's got a hydraulic problem that I've been unable to figure out.
This machine is a direct hydraulic machine, no electronics, solenoids, etc. in the hydraulic circuit. I believe it uses a gear pump. The pump is 3 stage and is supposedly brand new (installed by the previous owner). There are two control valves that operate all of the functions. One is a 6 spool valve and one is a 3 spool valve. The first two stages of the pump feed the 6 spool valve, and all functions seem to work as they should. The third stage of the pump feeds the 3 spool valve. this valve controls the blade, the swing motor and the rapid travel function. The blade is weak as well as the swing (slow). The rapid travel functions. I hooked a hydraulic gauge into the line from the pump to the 3 spool valve. There is a test plug there for that purpose. When operating the blade or the swing against the stop pin, the pressure never gets over 1500 psi. Relief is supposed to be about 3100 psi.
I assume I'm bypassing oil either in the pump or the 3 spool valve. The pump is supposed to be brand new. I can hold a function open or against the stop until pressure comes up to 1500 and I'd expect heat to build if I was bypassing oil somewhere. The pump does not seem to get overly hot, nor the valve.
I've swapped out the relief valve from the 6 spool valve (same part number) into the 3 spool valve, and it made no difference. I've had the 3 spool valve out of the machine and totally disassembled and cleaned it. I found nothing wrong, nothing broken, no excessive clearances, etc. There is also a suction and safety valve on the 3 spool that I disassembled and cleaned. It appeared to be fine but I've got no way of testing or swapping that one.
What would you try next?
Thanks,
Greg