I have a HitachiEX 120-3 that was leaking at the top coupler On the oil cooler. I purchased a new coupler from the dealer, installed it and it leaks when the machine is at peak acceleration. I have the coupler as tight as it will go. Any suggestions As to how to stop the leaks? *The Coupler is about 4“ long with rubber inserts on either end and then collars that go over them.
check that the coupling is the right type by the Hitachi part number (4067834). Remove the coupling and check that there is no possible cracks or splitting around the pipes that the rubbers seal on. inspect the rubber seals on the coupling for any nicks or defects and that they are a snug fit to the pipe before the clamps go on. check where the rubber seals are positioned that there is no fretting marks or paint edges on the pipes that the rubber is trying to seal on. check there is nothing restricting the bypass valve that is retained inside the pump directly below the coupling. ensure that the top and bottom pipes and coupling are all aligned before installing the union clamps, sometimes loosening pipe to frame clamps and mounting brackets can help with alignment issues.
I had an alignment problem with the coupling…corrected it and the coupling works fine. Leak fixed.