Posted by JerryCPP(WA) on December 30, 2019 at 19:25:24 from (66.172.99.31):
I just got a very old Komatsu PC05 mini excavator. It had a new thumb installed before I got it. They got pressure for the thumb by cutting and welding a cap on the ¾” pipe return line, taking pressure from that line, running it to the thumb valve with 3/8” hose, and back to the filter and tank, effectively making the main return line 3/8” hose. I don’t think restricting the return line is good. I want to put a T in the main pressure line (manual says main line max is 2489 pounds,) install a Prince R1850H relief valve in the new line, set it to 1000 pounds, and run that hose to the thumb valve. Then when you activate the thumb, it will only get 1000 pounds pressure. When you curl the bucket, the thumb cylinder will over-pressurize, causing the Prince valve to relieve pressure to 1000 pounds, with the blown-off oil going back to the tank. I will restore the original main return line to ¾”. Am I off base here? Suggestions?
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