My pc50 has a manual thumb, stationary pinned in place, we are converting the manual thumb to a hydraulic thumb. What size hydraulic cylinder is best suited for this? We are using a selector valve and the boom off set plumbing and pedal to operate the thumb. I have read that if you use too small of a thumb, the pressure from bucket curl will damage it, or atleast depress it, and if you over power you bucket curl you run into issues there. thanks
with mine thumb, its a tag thumb on a takeuchi tb53, when I installed the thumb, I also adjusted the relief settings on the auxilary circuit. Factory said to knock it back to 1800 psi. from 3000. If you go off cylinder size you may get down to a rod size that will bend too easily. I'd have to measure mine but the cylinder looks small compared to the others and its 1.5" or 2". At factory relief settings it was way overpowering the bucket curl.
Ive heard of relief valves specifically on the thumb hydraulics itself, very very important.
If I will be powering the thumb off the hydraulics that are used operate the boom off set function, using a selector valve, do I need to install relief valve also? Thanks
I know with mine the relief valve is adjustable for different attachments. Without a relief your going to be limited as to what your boom offset is set at. Reliefs are a safety feature, they are intended to keep you from damaging your machine. For instance, if you had a large thumb cylinder and no relief protection on your bucket circuit, the strength of the metal would be the limit. Bent cylinder rods, torn welds, blown hoses, and other more expensive problems could occur. Talk to a hydraulic shop, they may be able to put an adjustable relief in the hydraulic cylinder, or one in your switching valve.
cool thanks, so If I am running a smaller size hyd cylinder on the thumb then the cylinder that the relief is set for currently (the off set cylinder) I could damage the cylinder on the thumb or blow a hydraulic line or ..... Thanks for the help,
The relief valves fitted to the boom swing circuit will only protect whichever function (boom swing or thumb) the selector valve/s are switched to. The problem then is that the reliefs need to be set at factory pressure (3000 or so) for the boom swing, but lower (1500-1800) for the thumb. I would be fitting another crossline relief (4 or 5-port) between the selector valve and the thumb cylinder. This would then be set to a pressure which will let the bucket curl push the thumb cylinder back in. Have you checked that the machine hasn't already got a service valve fitted? Most of the jap import PC50MR's we get here have a slice fitted, but no pilot or arm hoses/piping.
Hello, I work for an attachment manufacturer and for a thumb we would build for the PC50 the largest cylinder bore you would want to use would be about 3.5" and 3" would probabaly be best. Our installation manual would specify the relief for the system operating the thumb be set about 1,800PSI. The intention is for the bucket curl system to always be able to overpower the thumb system. If this does not happen you make us very happy because we get to sell you all repair parts when you break your equipment. We do see installers tie into extendahoe systems, Off Set systems and even hammer systems (converted to 2 way flow) to operate thumbs but again you need to work to limit the pressure going to the thumb. Good Luck