I have a pin on thumb going on to my SK130. I see that lots of people are doing the same thing and there has been lots of comment on the welding issues involved and the need for good hardened bushings in all links. These are very helpful. However, I haven't seen any comments on valving/regulator issues. Should the thumb cylinder operate at the same max 5000 psi as the bucket cylinder? Is it desirable to put some kind of pressure regulation on the thumb pressure line to prevent damage to the thumb/dipper stick or the lines? As the thumb cyl is smaller than the bucket cyl it strikes me that it could be under a lot of stress and some kind of automatic regulation could be useful in preventing damage. Also I see that some operate with the thumb cyl direct linked to the thumb but others use dogbone links to the bucket link pin. Any advantage one way or the other? Thx.
hi, i cannot recall...is your machine already factory plumbed with aux nibbler/breaker hydraulics? if so there are 3 ball valves marked with an " N " and " B ". the setting of these valves allow one or two way oil flow plus either one or two pump oil flow too. i have info on these i can forward to you. normally hydraulic thumbs will have the aux hydraulics set up to operate as one pump and 2-way flow. larger 3-way ball valve on " N " the other 2 on " B " the aux port reliefs set around 2250 psi - 2500 psi. the piston side of the hyd thumb must be set as so it can hold when the bucket moves against the hyd thumb but not solid it must relieve so you do not brake or bend the rod of the thumb cylinder. one pump flow is all you need speed wise and enough to generate the horsepower of cyl - if 2 pump flow you will most definitely risk bending the rod of the hyd thumb like a banana. if you plan on running other attachments such as a tamper or hammer down the road, i'd hook the cab side line to the rod port of thumb cyl and the piston side to the hyd tank side (generally larger line - less back pressure when moving thumb parked against the arm dumping larger volume of oil quicker to tank) when running tamper say on "one pump one way flow "B", the cab side is also the feed oil. it will help keep the thumb parked in place, less drifting. although you'll still need to add another shut-off valve. cheers!
Thanks Adam. I set the 3 valves according to the service item you sent, to one pump and 2 way flow. The piece I was missing was setting the relief pressure on that circuit to as you suggest 2400 psi or so. That I will do. Then if the bucket is closed hard on the thumb the relief opens and the thumb backs off hopefully avoiding bending anything. This machine has the full breaker/nibbler option but I think the thumb is going to be permanent. Excellent - thx for the help.