Old Linkbelt 3400 came with a crude hammer circuit installed. There is an electric solenoid valve that diverts oil from one of the control valves to the hammer when you push a button. The piping is 1 inch and there are two accumulators on the return line (I think). I'd like to run a hydro thumb so I need to figure out if I can use whats already installed and determine what I need to buy. If I utilize the current "diverter" valve, the machine is unable to rotate during accessory use. Will this make working with a thumb impossible?
You could add another diverter valve in the hammer circuit to run the thumb, then you'd need to switch it from rotate to thumb, and then use the thumb, then switch back to rotate. You'll never rotate and use the thumb at the same time with this set up as far as I know. Since it's all electric, you could get the right double pole momentary on switch, mount it to the rotate handle, and it would be relatively easy to use the switch to operate the thumb and it would return to rotate in the neutral position.
don't forget pressure relief on a thumb circuit. It needs to yield to curl and not bend things.
 Diverter valve with a couple adjustable things on it?
Accumulators on the hammer return line. Can these remain if I can covert the lines to 2-way functionality?
Antique? Aren't those only ~30 yrs old?
Yes maybe poorly worded but here a car 25 years old is eligible for antique plates. The excavator is a 1985 youngster
Is there a rule of thumb (sorry) to figure out how to tune the thumb pressure relief properly?
Good day Run the bucket cylinder against the thumb you only need enough pressure to hold material, the relief should open and allow the bucket cylinder to win the battle. Kind regards Uffex