I'm thinking about mounting a thumb to my mini ex. It already has aux hydraulics on the boom for a breaker. I'm wondering the plumbing issues I'll have if I want to use this circuit for the thumb. Do I need a bypass valve that is less than the bucket psi? What keeps the two circuits from damaging either the thumb or the bucket when both are "competing" against each other when the thumb grabs onto something? The last thing I want to do is break something! Yikes! I just want to make sure I do it right and it's something new to me... Forgive a rookie question.
Any thumbs I've seen on the bigger hoes have always had a line relief on the thumb circuit to reduce the pressure to 2250-2500 psi. Main system pressure is usually 4550 to 5000 psi . if you force the bucket against the thumb the thumb should go over relief and fold back.
Not sure how breaker is plumbed on this but a couple of points. Breakers only run 1 way and the return needs zero restriction and generally goes strait to tank. Thumb obviously needs to be 2 way through the valve. If you run a thumb and hammer usually you have 2 manual ball valves at the stick to select which ever and also 1 at the boom foot to return to tank (breaker) or through the valve (thumb). Line relief should already be in the system to lower breaker psi as they don't run at main relief pressure. Check where the breaker return is going. May need 1 line relief and tee the return into the valve. If you have breaker hyd adding a thumb should not be a huge deal.
Thanks guys! I figured it can't be too hard, but I wanted to ask some advice before I break the machine. I think I have the plumbing issues worked out, now I just need to weld together a thumb... Thanks for the help!
I used my blade circuit with an electric shuttle valve to switch between the two, and a 1,850 psi relief valve in the thumb return line. I had my thumb custom built and installed. Good luck to you.
What kind of mini do you have? It may already have 2 way aux hydraulics and might be thumb ready?
The cylinder pressure should be set to 1800 max.The bucket should be stronger that the thumb
This may be a stupid question but here it goes anyway. I have had many thumbs over the years and always made sure the hydraulic thumb was weaker then the bucket. So here is the question, what about the mechanical thumbs that are solid? They're definitely not made to give like a hydraulic thumb would be, so why is it so important to make a hydraulic thumb weak? I realize more hydraulics gives more room for operator error but over crunching of the bucket seems like it'd be just as bad on a solid(mechanical) thumb as a hydraulic....
The only reason is to protect the cylinder rod. Not the structure of the thumb. Normaly the thumb cylinder rod is smaller than the bucket cylinder rod.
DigDirt: thanks for the answer, I always liked the weaker thumb for two reason one like you explained and also so that the stick wouldn't get tweaked out of whack. Seems like with a solid thumb the stick could still get tweaked?
You betcha they can get tweeked.......I welded a mechanical thumb on my Kobelco SK45 with a 3" stick and as I was wrestling a big Poplar tree out of the woods I turned the stick into a corkscrew......Took me 4 hours with a torch & sledge to get it straight again & fix the rest of the thumb..........Poplar tree 1 Dumb Injun 0..........Cheyenne