I talked to four pressure-relief-valve installers today about installing a pressure relief valve on the Kubota U17.
Installer 1 said I didn't need a valve because the thumb cylinder was rated at 3000 lbs. When I told him the bucket curl was rated at 3417 lbs, he wasn't sure if I needed the valve or not.
Installer 2 was the Kubota dealer responsible for installing the thumb in the link I linked above where the thumb appears to be working properly. He said he would install a crossflow valve with a return line to the tank.
Installer 3 said there are two ways to install it. The best is using the crossflow valve with a return to the tank. The other way is a single relief valve on the butt-end of the thumb. He said the problem with the single relief valve method is, when the bucket pushes the thumb back, and then you re-extend the bucket, the thumb will fall back to where it originally was. He said this occurs because the pressure is not equalized in the rod end of the cylinder.
Installer 4 said a relief valve on the butt-end with a return back to the tank was enough. When I asked him about the thumb falling back after having been pushed by the bucket, he back-pedaled a bit and said he wasn't sure if the Kubota U17 was set up in a manner to allow pressure equalization or not. If it was, he said it would prevent the problem. If not, then the bucket would fall back.
I thought I would report my findings here, because nobody brought up the thumb falling back issue that can occur with the single relief valve. Does anyone have any more information about this problem? I'm a bit confused by the different responses I got by the different installers.
Thanks