Relief Valve - How to Override?

[TerryR]

I have a Peruzzo Fox Cross 1600 ditch and bank flail mower with an issue the dealer doesn't recognize - they seem to think it's working as designed.

The cylinder that swings the mower head out to the side and back has a "safety" valve that is supposed to keep it from swinging into an obstacle. The problem is when I try to swing the head out while heading down hill, or on a side hill where the head swings up the hill, the valve opens and the weight of pushing the head up the hill keeps it from swinging out. The valve functions and it either doesn't move or actually moves the other way.

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.

Here's a photo of the cylinder and valve, and one of the under side of the valve:

I've tried adjusting the screw under the covered nut, tightening it down all the way thinking that would keep the valve from releasing, but it doesn't seem to help. Neither did backing it off.

Am I doing this wrong? Is the valve defective? Is there any way to plumb it out of the system?

Any ideas welcome.

 

[ptsg]

From you description, almost seems that the relief valve is stuck open. Tightening the set screw all the way in should pretty much make that valve irrelevant and being that you did that with no success, leads me to believe that there is something stuck in the cartridge that keeps the valve open.

Have you tried pulling the cartridge out and inspect to see if there anything obvious.

The idea of the valve is to protract the implement if you happen to hit a tree or something, it will swing out of the way.

 

[oldnslo]

Did turning the adjustment screw either way seem to make any difference at all? Normally turning clockwise will increase setting. If no apparent change then ptsg is correct there is something wrong with that valve. I would suggest having that valve over a hard surface before trying to remove it since there may or may not be loose parts under that valve.

 

[TerryR]

Thanks. It hadn't occurred to me I could open the valve and look for issues. To do that I back out the hex "nut" closest to the valve body, the one the adjusting screw goes into?

 

[nyone]

If none of that works maybe use some kind of spring to help the arm?

 

[ptsg]

Thanks. It hadn't occurred to me I could open the valve and look for issues. To do that I back out the hex "nut" closest to the valve body, the one the adjusting screw goes into?

Pull the entire cartridge which is the big hex near the body of the valve.

The reason I think it's stuck open is because this valve should work as a check valve when you move the cutter out. If it can even do it facing uphill, then it's bypassing when it shouldn't.

It could be trash holding the poppet open or bad o-ring too.

 

[TerryR]

Thanks, ptsg, I'll give that a try this morning.

 

[TerryR]

I took it apart today. It's pretty simple. The spring bears on the end of a spool, I suppose you call it, about 50-60 mm long. It has a head that the spring bears on, which also seems to be the valve. It has a shank around 8mm in diameter, which has thinner sections. I didn't find an O-ring, but it's hard to see into so I might have missed it.

There was nothing obvious that was amiss. I put it back together and in a short trial found no issues, but didn't exercise it enough to really know. I'll be mowing tomorrow so should be able to give it a proper test.

 

[TerryR]

Well, the issue isn't fixed, and after looking at it more closely, I'm more confused than ever. Here's a shot of the cylinder in question. The mower head is fully retracted here, which is means the cylinder is fully extended:

I have always thought the relief valve, which you can see attached to the cylinder above, was supposed to stop the mower head from extending when it hit an obstacle. But best I can see, it can't work that way.

Here's a detail of the valve, overlaid with a photo of the internal parts:

Best I can figure out, the valve releases over-pressure in the chamber on the left, letting oil out the port on the bottom in the photo. The left chamber seems to be connected to the hose from the tractor that extends the cylinder (retracts the mower), the one on top of the valve in the photo. It seems to also connect to the hose to the base of the cylinder, the one attaching below the valve. So when extending the cylinder, oil flows through the upper hose, through left side of the valve, and out the lower hose to the base of the cylinder.

The port on the bottom in the photo, which the oil flows into when the valve releases, is connected to the hose to the top of the cylinder (which when pressurized extends the mower). Thus it seems like the relief valve protects the mower when it is being closed, not while it is being opened.

Getting back to my original issue, the mower refuses to open when doing so requires it to move up hill. I had thought that was caused by the valve was opening too easily. But now it appears the valve does not release from excessive pressure while opening the mower, but only while closing it.

This makes no sense to me. I had the adjustment tightened all the way down, which as ptsg noted above, should keep the valve from releasing at all.

It was also suggested that something was keeping the valve from closing properly. Maybe, but I don't think so. I found nothing that might do that when I opened the valve. And, when mowing with the mower is fully extended it naturally wants to move to a partly closed position, with pressure from the cylinder keeping it from doing that. If the valve were leaking it should move back from the fully extended position, but it doesn't.

I've considered that the relief valve on the tractor might be opening, not this one. But when I extend any cylinder fully until it stops I hear the engine governor open a bit as the engine works against the load. But I get no engine reaction when I try to open the mower and it refuses.

Any ideas welcome, because I'm out of them.

 

[ptsg]

That idea of that safety valve is to protect the mower, the tractor and whatever it hits.

The only time that valve comes into play is when you have the mower extended all the way out and lets say you hit a telephone pole with it. This will push mower in and the extend side of the cylinder will have a lot of pressure. This safety valve will release this pressure sending it to the rod side and let the mower retract without breaking stuff.

Another issue I'm thinking is bad piston seals on that cylinder. That could cause your issue as well.