Thumb Valve Leak Mystery

[wdchyd]

I am thinking someone, awhile back, rebuilt one of these relief cartridges. I believe he opened it up and did some machine work and replaced something, and put it back together and it worked. Does anyone else remember that post.

Yes, I remember commenting on this subject before.........these cartridge valves are not suppose to come apart but can be unscrewed by using the jaws of a lathe to grab the area where the oring is......them loosen the hex to expose a hidden oring internally in the cartridge.....it's the oring on that stem that is leaking......

Regarding the perpetual leaks that the OP'r is running into, there is an elevated return pressure downstream of this valve......it needs to be a power beyond type valve to deliver downstream pressure to the next valve, separate from return to tank flow.....

the orings on his valve and the oring in the PRV cartridge is seeing the high pressure from a restriction or the next valve inline.....resulting in oring failure every time......these orings are not suppose to see high pressure, only low pressure from return flows to tank......

NEEDS PB VALVE......

 

[J_J]

If all else fails he could seal up the relief port and install an external relief valve before the FEL valve.

 

[wdchyd]

Yes, that could be done but the high return pressure oil leaving the valve housing is what's causing the root problem here, the high pressure oil in the PRV does not see that oring, only the return pressure, ......and the orings will still develop leaks at the valve spools in time if the PRV is plugged off.....

IIRC in this thread it has been a recurring problem, I think the valve has too much downstream pressure on the return side......PB valve needs to be installed and plumbed in or there is a restriction in the return side (fitting too small) if a PB valve is in use.....

My bet would be this is a regular valve installed inline with another valve (3PH, BH )or something else downstream..........:confused2:

 

[mmranch]

Thanks to all for the ideas! This is getting a bit complex for me to understand but I understand the basic concept that maybe high pressure fluid is getting to where it should be low pressure fluid.

A few more tidbits.

When I spoke with my dealer, I mentioned that I had turned the PRV adjustment screw 1/4 turn and the leak had stopped (the leak has not leaked since). He mentioned that he had spoke with a tech at Prince and that person said that sometimes if there's not enough pressure on that spring in the PRV, it will leak and that tightening it a bit can fix the leak (not very scientific I know).

I also found in the valve docs a cutaway drawing of the internals of the PRV cartridge itself and it seems very simple. Adjustment screw presses against a plunger (my term), which presses against the spring, which presses against another plunger which is where the relief happens. The first plunger appears to have an o-ring which seems to be where the fluid would be passing to leak down the adjustment screw.

This is my crude understanding of how the valves are setup: two hoses connect from the rear remotes of the tractor to the BH control valve (I assume that maybe there's a PRV for the BH on this valve inside the BH console). There are hoses that come from the BH control valve to the thumb valve and this thumb valve is mounted on the outside of the BH console (it is enclosed in a bracket and only it's spool and PRV are really accessible without unbuilding the bracket and BH console). The Prince RD4100 thumb valve has a number of options including a power beyond port but it is plugged.

So as far as I understand, it's tractor>BH valve>thumb valve.

I recently received my pressure gauge but have not used it yet. If I plug it into the output rear remote, won't that give me the pressure that the tractor is putting out? Do I need to do something to make the pressure go to the max or is just plugging in the gauge enough to read the max pressure?

If I plug in the gauge at the thumb cylinder, won't that show me the pressure that the thumb valve is putting out?

These two places and the FEL connections are the only places I have QDs to plug in the gauge.

Got to get to work.

Thanks again!

 

[wdchyd]

So as far as I understand, it's tractor>BH valve>thumb valve.

After the thumb valve does the flow go directly to tank or into the 3PH..??

My theory is that the return pressure coming out of the thumb valve is too high....resulting in premature seal failure....Yes/No..??

 

[J_J]

wdchyd,

If the fluid from the BH is going to the 3pt, then when the 3pt is is fully stressed out, lifting max load, then there is a good chance that there is high back pressure being felt on all the valves.

 

[wdchyd]

JJ,

That's exactly what I'm saying.......the max pressure on the 3PH will show its ugly face to those seals that are failing from back pressure.......:thumbsup:

Of course that's assuming it's going directly to the 3PH w/o PB......:confused2:

 

[wdchyd]

another thought is my BH for example doesn't use the 3PH cuz it's locked out when the BH is mounted on the back......

so in my case there's no need for PB on a BH valve bank if the 3PH is not in use.....thus no back pressure to the BH valve......

I just wonder if the OP'r has his thumb valve upstream of the BH control valve.....it might be a good thing to confirm or deny......

 

[J_J]

mmranch,

You said:

The Prince RD4100 thumb valve has a number of options including a power beyond port but it is plugged.

So as far as I understand, it's tractor>BH valve>thumb valve.


Why are you not using the PB from the thumb valve to go to the 3pt. You seem to be using the OUT/TANK port to send fluid to the 3pt, and if that is true, you are providing the thumb valve with to much back pressure whenever you use the 3pt. That is not good for the spools and the relief valve, depending on the thumb PRV setting. I would set all the relief valve the same.

You should have a series connection like this. Pump, FEL, BH, THUMB, 3pt. You should be using any PB port available to feed the next valve, as this port can handle the high pressure. .

 

[mmranch]

Thanks for all the ideas on this!

After getting my tractor out of the bog it was stuck in today (I hate when that happens), I finally can now upload some photos which may shed better light on the situation (see attached images of BH console).

I opened the BH console today to see how things were setup. It turns out that it is setup like this:

tractor rear remote > thumb valve input > thumb valve output > BH control valve input > BH control valve output > tractor rear remote.

So the thumb valve is first, then BH valve. My dealer set things up this way. At the moment, the thumb valve PRV has not been leaking... but I haven't put sustained heavy use on the BH since I slightly turned the adjusting screw.

Thanks again.