Mini excavator thumb - relief valve question

[ROcHE1234]

Hi,

I'm new around here

I'm adding a hydraulic thumb to my Volvo EC25. It does not have relief valves on the AUX ports from the factory and they are very pricey from the dealer. So I went with the external relief valve route.

Installed it on the extend side of the cylinder and plumbed to tank. Everything appears to work OK but I've read confusing threads about the need for a relief valve on BOTH sides of the cylinder. If I push the thumb against the bucket, I can hear the relief valve do its job and the bucket will not move. However, if I do the opposite (bucket against thumb), the thumb will retract and it does not feel like the valve is actually doing anything but I could be wrong.

Do I need to have relief valves on BOTH sides of the cylinder (extend & retract) in this scenario ?

Pic of the current setup. The line on the other side of the stick is plumbed straight to the retract side of the cylinder, no valve or anything.

 

[nyone]

I think the way you have it on the non rod side of the cylinder is best if you only have 1. More often than not your going to be hitting the relief with the cylinder wanting to retract.

But no the way its plumbed it's not going to have a relief on the other side of the cylinder.

 

[Rich B1]

I would have a relief on both sides of a cylinder circuit. It is possible to over power the unprotected side of a cylinder using other machine functions

 

[ROcHE1234]

Thanks for the quick reply.

I was under the impression that curling the bucket against the extended thumb would generate pressure on the "extend side" of the cylinder which is the one with the relief. This is the confusing part.

 

[pjbci]

For what its worth, my ec140el was fitted new at the dealer with hyd thumb and no relief valves. I asked two techs about it, both said it didnt need them as the system recyles pressurized oil. I dont like the idea of no relief valves but I watch my guys often over power the thumb with the bucket and no lines bust or cylinders leak. The thumb just retracts until they quit pushing on it and it stays at that point.

 

[oldnslo]

Pjb
Your ec140 might have work port relief valves in the directional valve for the thumb since if the thumb cylinder is moving that oil is going somewhere.

 

[ptsg]

Thanks for the quick reply.

I was under the impression that curling the bucket against the extended thumb would generate pressure on the "extend side" of the cylinder which is the one with the relief. This is the confusing part.

And it does. You have the relief valve in the right place and you don't need a second one, unless you're using another attachment that may indeed need a another relief valve.

From your description, looks like it's also doing its job just fine. When you curl the bucket and push against the thumb, the thumb will give. That means the relief valve opened and it's relieving the pressure.

By the way, that's a very nice and clean install!

 

[Tarnold]

What brand is that relieve valve, where to get? I need one on my kubota 61. Just added a thumb and shattered a rock about the size of a big watermelon with too much pressure. My thumb requires 1800 psi per instructions.

 

[ROcHE1234]

And it does. You have the relief valve in the right place and you don't need a second one, unless you're using another attachment that may indeed need a another relief valve.

From your description, looks like it's also doing its job just fine. When you curl the bucket and push against the thumb, the thumb will give. That means the relief valve opened and it's relieving the pressure.

By the way, that's a very nice and clean install!

Thank you!

 

[ROcHE1234]

What brand is that relieve valve, where to get? I need one on my kubota 61. Just added a thumb and shattered a rock about the size of a big watermelon with too much pressure. My thumb requires 1800 psi per instructions.

It's from Walvoil and I bought it at a local hydraulics shop here in Canada. I think any good shop will have something similar on the shelf.