Relief Valve - How to Override?

[TerryR]

Thanks, ptsg. That makes sense. So it's only supposed to protect against over-pressure on the extend side. Since my issue is with the retract side, the valve could only be the cause if it were held open for some reason.

But a bad piston seal could cause retract action to fail under load as you say. It would also cause the extend action to fail, would it not? But maybe it's never loaded as much to notice? Or could a bad piston seal leak in only one direction?

 

[ptsg]

Thanks, ptsg. That makes sense. So it's only supposed to protect against over-pressure on the extend side. Since my issue is with the retract side, the valve could only be the cause if it were held open for some reason.

But a bad piston seal could cause retract action to fail under load as you say. It would also cause the extend action to fail, would it not? But maybe it's never loaded as much to notice? Or could a bad piston seal leak in only one direction?

Depends on what kind of seals they used on that cylinder.

I have some cylinders where they used two opposing piston seals, instead of a single one that seals in both directions.

The thumb cylinder I'm my backhoe is that way and I have a bad seal on the retract side but works fine while extending. I haven't fixed because it still manages to retract the thumb and hold it there somewhat.

Not saying it's the issue but a possibility, giving that you tried just about everything else.

 

[TerryR]

Thanks, ptsg. Given no other apparent cause I'll have to look at that.

I've recognized that retracting the cylinder, which is the direction it fails, requires higher pressure to achieve the same force because of the smaller piston area being acted upon. So that could in part explain a failure in one direction.

 

[ericm979]

This happens with the tractor stopped and the head lifted off the ground. If I do it while moving with the head on the ground it does eventually move out, but then I have to lift the mower off the ground and back up to the tree or whatever that caused me to retract the head in the first place.

When it does move out while the tractor is moving, is the tractor engine rpm higher than when you're try to move the head with the tractor stopped?

 

[TerryR]

When it does move out while the tractor is moving, is the tractor engine rpm higher than when you're try to move the head with the tractor stopped?

No, it is in both cases operating at PTO speed, which is full throttle on my machine.

 

[ptsg]

I'm wondering another thing. That cutter requires 2 spools right? One to extend/retract and another to till the head. Have you tried swapping the two functions on the remotes and sit it changes anything?