Relief Valve - How to Override?

[TerryR]

Hello Terry,

The valve poppet with the spring controls the metered flow of the relief valve.

Not any more. As I said just above, I've removed the valve entirely, so it's no longer part of the problem.

"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..."

Good idea, but neither location is close - about two hours each way. I need an online source.

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

Yes, but they don't move on their own. They are fine until they are asked to push the mower up too steep a hill, then they just do nothing.

"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."

Yes, but it doesn't do that, so that wouldn't seem to be the issue.

 

[LD1]

I know some of this post is older. But it gets confusing with the lingo of extend side and retract side of the cylinder. Because you are also extending and retracting the mower and they are inverse.

Extending the cylinder retracts the mower and retracting the cylinder extends the mower.

Obviously that isnt ideal because the cylinder has alot less power when retracting....yet you are trying to push the weight of the mower...with alot of leverage....up a hill.

That relief valve.....dont look it it as what it protects. Yes, technically it protects the mower head if you hit something. Like mentioned, if you hit an electric pole, tree, etc....that valve would open and allow the mower to swing instead of blowing hoses or breaking something.

But forget that....instead look at that relief as simply protecting the ROD side of the cylinder from over pressurization. So now it becomes as simple as WHAT causes pressure in that rod side port (where the relief valve is/was)

Two things cause pressure there. 1...you are trying to retract the cylinder with the tractors hydraulics. (which would be attempting to extend the mower). And yes....a faulty relief or one set too low would cause your issues. That relief would need set equal to or greater than tractor relief. IF it is set less than your tractor relief....then you arent getting the max power out of that cylinder when trying to retract.
The second case is if some external force tries to EXTEND the cylinder. This would also exert pressure on that rod side port. And trying to FORCE the cylinder to extend is like hitting a tree and trying to force the mower itself to retract.

BUT, since you have removed that valve from the equation and are still having issue, the problem is either with the tractor ofr the cylinder or just the design. First thing you need to do is get a gauge and see what kind of pressure you are getting there at the cylinder. If its within spec of your tractor....it could either be a cylinder problem or a design problem. IF the tractor is on an angle and you are trying to push that mower uphill....the force of that cylinder may simply not be enough. Bad design. Maybe it just barley has enough power as it is to do it on flat surface. Now throw in fighting gravity and the cylinder is simply too small. Take a mini-excavator....large bucket at full extend. IF you are on too much grade they dont swing uphill well either. Simply not enough hydraulic power.

Now the cylinder could still be an issue....as a cylinder at rest can/will only drift in the extend direction if the internal seals are bad. But it cannot and will not retract/collapse on its own even if the piston seals are totally shot.

But honestly this just sounds like a bad design with a cylinder too small. Either that or your tractor doesnt make enough hydraulic pressure. And by modern standards, the 2250psi that the 870 is rated for....even if it still makes it rating...is a little on the low side by 200-300psi

 

[leonz]

Not any more. As I said just above, I've removed the valve entirely, so it's no longer part of the problem.

"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..."

Good idea, but neither location is close - about two hours each way. I need an online source.

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

Yes, but they don't move on their own. They are fine until they are asked to push the mower up too steep a hill, then they just do nothing.

"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."

Yes, but it doesn't do that, so that wouldn't seem to be the issue.

The problem you have is now narrowed down to the tractors hydraulic
system relief pressure setting so the hydraulic systems relief pressure
has to be checked.

Can you have the servicing dealer come and do a service call?
Setting the tractors hydraulic system relief pressure requires the use of a
flow meter to test the system pressure under load and to correctly adjust
the relief valve pressure on the tractor.

 

[TerryR]

BUT, since you have removed that valve from the equation and are still having issue, the problem is either with the tractor ofr the cylinder or just the design. First thing you need to do is get a gauge and see what kind of pressure you are getting there at the cylinder. If its within spec of your tractor....it could either be a cylinder problem or a design problem. IF the tractor is on an angle and you are trying to push that mower uphill....the force of that cylinder may simply not be enough. Bad design. Maybe it just barley has enough power as it is to do it on flat surface. Now throw in fighting gravity and the cylinder is simply too small.

Now the cylinder could still be an issue....as a cylinder at rest can/will only drift in the extend direction if the internal seals are bad. But it cannot and will not retract/collapse on its own even if the piston seals are totally shot.

But honestly this just sounds like a bad design with a cylinder too small. Either that or your tractor doesnt make enough hydraulic pressure. And by modern standards, the 2250psi that the 870 is rated for....even if it still makes it rating...is a little on the low side by 200-300psi

Thanks, LD. I think you are exactly right about the possibilities.

I never run the mower other than in the fully extended (cylinder closed) position for any length of time. The geometry of the swing arms would make it want to partly close without the cylinder holding it open. And I never observe it drifting closed (cylinder opening). So that suggests it's not a cylinder seal issue.

Good question as to whether the 870 still produces the specified pressure. The only clue I have on that is winter before last I got the tractor into a serious ditch while plowing snow, and while trying to work it out with the FEL I burst a seal in the fitting connecting to the bucket curl cylinder. That suggests the pressure hasn't totally fallen off. On the other hand, I never saw the issue with the mower the first couple of years I owned it, suggesting something has changed.

But I think the issue is likely poor design, maybe never taking into account hill side usage, and an older tractor with lower hydraulic pressure than current models.

Still, it might be worthwhile finding out what the hydraulics on the tractor are doing.

 

[TerryR]

Can you have the servicing dealer come and do a service call?
Setting the tractors hydraulic system relief pressure requires the use of a flow meter to test the system pressure under load and to correctly adjust the relief valve pressure on the tractor.

Our nearest dealer is 35 miles away. Don't know if they could do that with a service call. I'll check with them.

They will pickup and return the tractor for $150.

 

[leonz]

Terry, if you decide to have the local dealer pick it up make sure you send the
adjustable relief valve with them as they will need it to test the relief
valves in the tractor as well.

 

[SilentJ]

Sometimes the dealers just know what’s in the parts book. A few decades in the hydraulic components biz here…. I Recognized the logo on the valve you posted. Been doing this too long I guess. A lot of equipment OEM’s buy these kind of parts from external “suppliers”. Anyway, the manufacturer of the valve might have advice. They often work via “distributors” who are like dealers for their parts. There is a contact form here. Being overseas can make communication harder but maybe they have a distributor in your part of the world ?

RELIEF VALVES VMP-1 - OM Group

The relief valve limits the maximum pressure in a circuit to the valve’s setting. When the circuit pressure reaches the setting, the valve opens and stops the circuit pressure going any higher.

www.groupmarchesini.com

 

[rScotty]

SNIP
.........But honestly this just sounds like a bad design with a cylinder too small. Either that or your tractor doesnt make enough hydraulic pressure. And by modern standards, the 2250psi that the 870 is rated for....even if it still makes it rating...is a little on the low side by 200-300psi

I've been following this thread now for a couple of years and have nothing that hasn't already been mentioned. There are already several really knowledgeable people working on ithe problem.

Does anyone think that some pressure gauge info would be helpful? I've been looking at the kits on Amazon and like this one. It has a variety of "T" fittings so that it can be put inline with just about any hydraulic fitting....except it might not fit that short regenerative fitting that between Leonz relief and cylinder.

I'm a believer in the value of hydraulic pressure gauge info & might just order this one for my own use.... $170.00
rScotty