Relief valve

[lumberjack1986]

The pressure relief setting is entirely dependent on his setup.

Unless your bucket circuit has work reliefs, you want the thumb weaker than the bucket. Put the thumb ~90* to the stick, install a pressure gauge on the thumb's extend port, and run the bucket into the thumb full power and watch the pressure gauge. Stop if you hit the cylinders rated psi, otherwise there's your max pressure setting.

 

[Bob Rooks]

The pressure relief setting is entirely dependent on his setup.

Unless your bucket circuit has work reliefs, you want the thumb weaker than the bucket. Put the thumb ~90* to the stick, install a pressure gauge on the thumb's extend port, and run the bucket into the thumb full power and watch the pressure gauge. Stop if you hit the cylinders rated psi, otherwise there's your max pressure setting.

The bucket circuit uses the system relief which is around 2,500 psig. There is no "bucket work relief". The OP already blew a hose curling back into the thumb. With the thumb relief set around 1,900 psig he will be able to allow the bucket to curl against the thumb without breaking anything and still have substantial clamping force. If the OP feels he needs more he can simply tweak the relief valve up. But be advised this also loads the pins more.

 

[Greg9504]

The bucket circuit uses the system relief which is around 2,500 psig. There is no "bucket work relief". The OP already blew a hose curling back into the thumb.

Are you basing that on fact or the observation that a hose blew? Just curious.

I'm no expert on Takeuchi excavators but looking at the parts manual

page 8-2, the valve block has ORV on both the bucket and the aux circuit.





It looks like the aux circuit is the third valve, see above parts diagrams (verify it covers your serial number), and verify that the hoses do go to the aux/thumb.

On my backhoe the aux circuit relief was set at 3500 PSI when I got it, when I put a thumb on I adjusted it down to 2200 PSI, which allowed my bucket to over come it.

If you want to get an idea of what the valve may look like and how to set it, check out this video I made of my thumb install on my JCB 212S backhoe. It gets to the hydraulic specifics around 3:40 into the video

http://youtu.be/cEjhr2V3GXA

Your valve may be adjusted differently, but my guess is that it is very similar to my JCB. Remove the cap nut, back off the lock nut, turn clockwise increases pressure, opposite to decrease pressure. Adjust with engine off, reassemble between tests or you may leak fluid.

Greg.

 

[J_J]

The extra relief valve should go into the base end of the cyl as that side of the cyl is being compressed by the bucket, maybe.

The relief out will go to a return line.

Then you have the mechanical advantage of the bucket and /or the thumb cyl.

You want the thumb cyl to give, maybe.

 

[Greg9504]

Umm why are you continuing to tell him to add an extra relief valve when the parts diagram shows a factory installed relief valve? Adjusting the factory one will be much easier than installing an external one with the added hoses.

 

[Bob Rooks]

Umm why are you continuing to tell him to add an extra relief valve when the parts diagram shows a factory installed relief valve? Adjusting the factory one will be much easier than installing an external one with the added hoses.

Very well Greg. If his valve stack has a separate relief valve in the auxiliary circuit it is most likely on the pressure side, not the return side, between the cylinder and the valve stack..
Some trivia: Neither JCB or Takeuchi manufacture hydraulic components.
I will watch your video when time permits.

 

[lumberjack1986]

Of course it's in the pressure side, that makes no sense.


There is NO NEED for the bucket to be able to over power the thumb. What is REQUIRED is that both the bucket circuit and the thumb circuit are kept at or below their respective rated max pressures. My excavator has work reliefs on everything on the boom. In some areas of rotation, the bucket overpowers the thumb, in some areas the thumb overpowers the bucket. EZPZ, no ifs, ands, nor buts.

If the thumb and bucket don't have work reliefs, it is possible or even likely that one will over pressurize the other, regardless of any relief in the supply side if the system.

 

[Greg9504]

If his valve stack has a separate relief valve in the auxiliary circuit it is most likely on the pressure side, not the return side, between the cylinder and the valve stack

His aux circuit is clearly two way (it operates the thumb), there is no such thing as a pressure side vs return side in that case. Both sides are equally capable of generating pressure depending on which way the valve is operated.

I posted the pages from the parts manual which clearly shows that the aux valve has relief valves on both sides of the valve. Here it is again with the valve section and relief marked:

There are two relief valves, one for each side of the valve.

lumberjack1986, FWIW every install document that I've read from manufacturers of hydraulic thumbs recommend that the bucket over powers the thumb. I think probably in most cases this keeps the pressure below the max rating of the cylinder used for the thumb. Also regardless of what the relief on the side used to extend the thumb is set to, you need to set the relief on the side used to retract the thumb as well. Otherwise you could be over the max rating of the cylinder when you retract the thumb.

 

[Bob Rooks]

I will leave it for the OP to decide. I digress.

 

[J_J]

You are correct in the fact that if there is a work port relief valve, the no additional valve is required.

My statement was for a spool with no work port relief.

You are also correct the set the retract pressure relief to less than the bucket extend pressure relief.

We are both thinking on how to keep the bucket pressure from blowing the hose cyl seals.