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?

 

[TerryR]

Revisiting this issue....

On the advice of the dealer, I removed the safety valve and connected the lines directly to the cylinder, then tested with my spring mowing (delayed this year).

The results are confusing. It takes me five days (at two hours a day) to mow the field. The issue did not appear the first four days, but then did a couple of times on the last day. It was probably the hardest test, the steepest side-hill where I retract and extend the mower to pass trees. And unlike before, I did get it to extend by bouncing the head up and down a little with the other cylinder. So removing the valve seems help, but not fix the issue.

I see that the geometry of the linkage puts the cylinder at the worst advantage when starting to open, and it requires the cylinder to close, the direction it has the least power. It it possible it requires so much hydraulic pressure when trying to push the head uphill that the tractor relief valve is opening?

Here's the cylinder when the mower is in the closed position, which is where it is when it has trouble opening (the safety valve is installed in this photo):

 

[LouNY]

It could be the tractor hydraulics, have you reversed your couplings so the cylinder operated the reverse way as it does when you have issues.

 

[leonz]

Hello Terry,

The valve poppet with the spring controls the metered flow of the relief valve.
The one piece adjustment screw would have a metric Allen wrench hole in the
end of it; is this what you tried to do to adjust the poppet?
The nut on the threaded portion of the metering valve is only there to hold the
poppet in place once it is set.

You need to invest in a pressure gauge fitting for the flail mower if you visit the people
at either of the AFP Industries shops at Mooresville or Johnson city location you should
at least be sure to take the numbers on the hoses which indicate the hose size and
pressure value and show them pictures of the hose sizes and the banjo bolt fittings they used
and clearer pictures of the adjustable relief valve as you are a bit stuck without having a
pressure gauge in the correct hose line or port in the adjustable relief valve that was supplied
with the flail mower.

If either of the piston packings was bad the cylinder would bypass and move on its own.

If the cylinder rod O-ring at the base of the rod stem was bad the cylinder would leak gradually
and the mower head would fall back slowly over time while mowing.

AFP Industries which is the Parker hydraulics representative in your area has 2 stores in
your area one in Mooresville and the other in Johnson City.

If you decide to visit one of them be sure to take the banjo bolts in the top and bottom of
the adjustable relief valve along with the relief valve to make sure that they can give you
the right size metric tapped adjustable relief valve or the correct metric to JIC/SAE fitting
adapters for the correct adjustable relief valve.

Please ask them for a hydraulic pressure gauge port fitting and dust cap for it as well for your
new adjustable relief valve or the correct fitting adapter to install on the valve with a quick coupler
and dust cap as you need this to adjust the pressure on the relief valve with the circuit in operation
to place maximum pressure(dead head)on the cylinder circuit with your tractors hydraulic system.

 

[TerryR]

It could be the tractor hydraulics, have you reversed your couplings so the cylinder operated the reverse way as it does when you have issues.

Sorry, I expected I'd get a notice of a reply, and didn't, so I missed your comment.

That's a good idea, I'll try it.