I have a bobcat 442 same as Terex HR32. It has a hydraulic thumb that we use all the time. I am installing a manual coupler to make attachment changes easier. Now I am looking to get a mulcher. My machine has just one set of aux lines but two connections coming out of the aux block. The block looks to have a valve to switch the flow to the different connection. I know the thumb are usually set at lower psi to keep from damaging cylinders when bucket it curled. My machine can go up to 4000 psi at 27 gpm. I obviously want to run my mulcher at my max gpm. How can I get the mulcher to be at higher psi and gpm and not cause issues with the thumb cylinder being too high?
I've set a few excavators up by reversing the thumb cylinder plumbing. With it that way you could set your aux relief to match the mulcher in one way flow mode. When switching to 2 way flow to use the thumb you would now be using the other line on the aux circuit to close the thumb and you can set the relief on that side lower so you won't damage the thumb, cylinder or linkage if you overpowered it with the bucket. Just be aware though that the thumb opening side will be seeing whatever pressure you set your mulcher to if you run it over relief when opening the thumb. I don't know if the way I've described is correct or wrong. If anyone else has a better method or can point out a potential issue with how I've done it I'm all ears.
So in your example if closing the thumb pressure is set at 2500 amd opening is at 4000. that would limit the thumb being able to push the bucket back too hard but what about the reverse. If the thumb is close down on a log and the bucket is curled in hard will the thumb still slowly retract to keep the cylinder from bending the thumb cylinder rod?
You'll be pushing against the 2500 psi relief on the extend when you curl the bucket so it should be good. The 4000 psi relief would be on the rod end of the thumb.
That sounds like a briliant idea. Damn.