What solenoid directional control valve for thumb.

Good day
A final thought on omitting relays, should you make the work for revenue and a fire happens insurance company may well pursue a court action for substandard - negligent work. For peace of mind I prefer to stay within normal standards of workmanship.
Kind regards
Uffex

I've worked for many insurance companies and never met anyone working for them that knew anything about machinery. That's why they hired me. I've also never investigated or heard of a fire or electrical problem that caused damage on a machine where an insurance company denied coverage on. Fire is a named peril in the contract so is covered no matter the reason for it. I've also never heard of a subrogation on a loss for a supposed improper install on a machine. I've also never seen or heard of a problem caused from wiring up a thumb circuit directly to the solenoid the way it has been done in the northwest since I've been doing them. I started installing thumbs on Link-Belts back in 1980. I have had problems with micro switches lately on a machine that does have relays installed. For some reason the current flow going through the micro switch to the relay causes a spark inside the micro switch and when there are enough burn marks on the contacts the function they control will no longer work. That would indicate to me that the relays used require more current flow to close than the coil in the solenoid.

Uffex, I certainly appreciate all the information that you provide us on this forum and am in no way trying to insult you but you do have to realize that somethings are done differently in the US than over in the UK. I'm not sure when they began using hydraulic thumbs in the UK but in the US ,our area the Pacific Northwest was one of the first areas to use them and that was about the time that machines switched over from mechanical linkage to pilot operated systems. (late 1980s) John C., myself and many others in our area have been working on these machines since that day and like I said before, the only time I have seen relays is in the logging industry where that little DO3 was cycling every few seconds, all day long. And not using relays has worked great for all this time on a standard hydraulic thumb. Again, thank you for all you do on this site, it is certainly a top notch forum.

It is certainly possible John that the swing motor was the original issue, this one had a #12 hose coming from the thumb relief block down to the swing motor.

Evidently there are many decades of combined experience here so I’m wondering if you guys ever installed or observed some form of in-line shock valve on the cylinder extend line? Or is it just a matter relying on the port relief valve for those rough operators?

Lagwagon said:

Evidently there are many decades of combined experience here so I’m wondering if you guys ever installed or observed some form of in-line shock valve on the cylinder extend line? Or is it just a matter relying on the port relief valve for those rough operators?

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Most higher quality thumb installations had a cushioned cylinder installed. If you Google "cushioned hydraulic cylinder" it gives a pretty good explanation of it.

John C. said:

Just because the valves are capable of handling higher pressures and flows doesn't mean that you can't use them. All the thumbs that I installed over the last thirty years were full on and off. I did have a way of reducing that by installing a subplate under the DO3 valve with a pressure reducing cartridge relief valve to drop the pressure spike when the pilot signals were sent to the main control valve.

You didn't say in your original post if the pedal supplies oil directly to the thumb cylinder or it just supplies pilot pressure to a valve in the main control valve block. Your solenoid valve should be closed center with A/B ports and a drain. The ones I used to get are 1/4" porting for the pilot circuits. I was using the top rocker switch type handle the last time I installed these but most people now days want the trigger switches and buttons. Sure Grip makes a simple handle with a decent cost.

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John, on that relief valve what would you set the pressure to if your pilot pressure would be 500psi? Or did you just dial it down until you had it where you wanted it? Could I just plumb in a relief to the pilot pressure side of my subplate or would that drop my entire system pilot pressure without a check valve?

I just dialed down to suit. Pressure was reduced down stream of the cartridge so you could put any kind of regulator in up stream of the sub plate.