Prince stack valve leaking off

[number9L]

So, been out of town since getting the Prince SV valve and TnT setup installed. When the 3ph is lifted, my BB will leak down about 1/16" per 2 seconds on the tilt cylinder and about 1/16" per 5 seconds on the top link cylinder. I've isolated the cylinders (unplugged the hoses at the QC) and the BB doesn't move when the 3ph is lifted.

I have no visible signs of leaks on any of the hoses or fittings or around the valve body. Guess its leaking off internally back the the outlet or PB port?

Is this a common trait with stack valves? Or Prince SV series valves?

Gonna be frustrating trying to regrade some land this week with the BB position drifting on the move.


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[number9L]

So I've got 3 sets of QCs. I tested with the tilt cylinder in each set of QCs and each time the BB drops 1/2" in 22 seconds. I then tested and had my 2 boys set on the RH side of the BB and it dropped 1/2" in 13 seconds (they weigh about a combined 90#).

Is this amount of leak off to be expected? I can't see all 3 work sections being faulty. Is there something I'm missing somewhere else?

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[medic0648]

Both sections of my sv valve leak also. With the engine running on the jd the loader arms go up and the bucket dumps. The jd is CC though. it actually does a decent job staying in place when turned off though.

 

[J_J]

So I've got 3 sets of QCs. I tested with the tilt cylinder in each set of QCs and each time the BB drops 1/2" in 22 seconds. I then tested and had my 2 boys set on the RH side of the BB and it dropped 1/2" in 13 seconds (they weigh about a combined 90#).

Is this amount of leak off to be expected? I can't see all 3 work sections being faulty. Is there something I'm missing somewhere else?

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Everyone would like a 0 leak down, but it just ain't going to happen. Some valves, cyl, hyd systems are just better than others.

You will have to verify if the 3pt will leak down before the following check is done.

You do know there is a leak down rate associated with each model valve, and it is hard to find the correct answer as to when the leak rate is good enough for a replacement. Might even have to be verified by a dealer.

It could be something like 10 drops a minute, etc. If you got the valve from Surplus, call them and asked what the leak down rate is for replacement.

So if you want to see what the leak down rate on the remote valve is, then raise a load on the 3pt, and turn the transport knob clockwise to lock the 3 pt. and then remove the return/out hose and then let it drip in to a jar/bucket. Time the drops or volume or both.

A heavy load could force fluid past cyl seals and valve spools.

You can use needle valves to isolate cyl and valves.

 

[number9L]

I am going to call Surplus, but am going to start with Prince first. I'm going to ask what the leak down rate is and if they think 1/2" in 22 seconds is acceptable. It's NOT to me. That's nearly 1-1/2" a minute. I spent a lot of money on that **** valve and if that's "normal" and I have to live with it I guess I'll look into needle valves to be able to set the implement in position and lock it in place. Be a PITA working that way though.

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[Leejohn]

That is way to much, maybe over night I could live with.

 

[medic0648]

I can see why I have bypass on mine. Between the tractor being cc running about 2850psi and the bucket cylinders needing to be rebuilt in the not too distant future stuff is bound to creep.

 

[J_J]

medic0648,

If you have a hyd gage on the hyd system, does the pressure stay that high with all valves in neutral, or does it decrease down to a stand down pressure?



In both CC and open center hyd system, and no flow from the pump, the load on the cyl will determine the leak down rate.

The cyl should not be bypassing to measure the leak down on the valve. The amount of the load will also dictate the leak down rate.

Using a CC hyd system, with pump running, standby pressure might give a certain leak down rate and full pressure might give another leak down rate, plus the weight of the load.

What you might not know is where is the valve leaking the fluid to, to base end of cyl, to rod end of cyl, or to return port.

 

[Tx Jim]

I can see why I have bypass on mine. Between the tractor being cc running about 2850psi and the bucket cylinders needing to be rebuilt in the not too distant future stuff is bound to creep.

If your closed center system is operating a 2850 psi that's 500 psi TOO HIGH and it's no wonder you have hyd problems.

 

[Tx Jim]

medic0648,

If you have a hyd gage on the hyd system, does the pressure stay that high with all valves in neutral, or does it decrease down to a stand down pressure?




Using a CC hyd system, with pump running, standby pressure might give a certain leak down rate and full pressure might give another leak down rate, plus the weight of the load.

J_J
There should be very minimal difference in stand-by pressure & operating pressure on a CC system on a JD. Actually except for a brief moment the pressures will be identical.

 

[medic0648]

Actually per the service manual it's within spec. I made sure to check the pressures after having to replace the loader valve.My bucket cylinders are bypassing across the internal seals combined with some additional fluid bypassing the valve. The loader arms move 1-2in in about 10min. I just don't currently have the time/money to rebuild or have the cylinders rebuilt right now. It's on my list after getting a rebuilt injector pump and installing it.

 

[number9L]

I called and talked to technical support and an engineer at Prince on conf call today. Explained the situation and the leak rate I've measured. They said the valve is metal - metal blockage across the spool and the allowable leak rate is 12cc / min max. We discussed ways I could test in my shop and came up with, I lift the BB and support it, then disconnect the Outlet hose (can also test with the opposite work port) and put the hose in a measuring cup, then remove the support and measure the leak rate for 1 min. If its above 12cc then I'd need to return the valve to Surplus for replacement or forwarding to Prince for tests in their lab.

I am going to do the test later this week after I finish regrading the area around my shop - which has been a challenge with the BB drifting out of position on the fly. I am guessing that I will find the valve leak to be in spec, just too much for what I'd like or need it to be.

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[MtnViewRanch]

I am going to be very interested in what you come up with. It's late and I'm tired, but based on what you had said about the side link drop rate, I think you are over 50 CCs per minute.

 

[oldnslo]

number9L,
Did prince state at what pressure and temperature this leakage is measured at? If not you need to find out since leakage rate is a combination of pressure and oil viscosity.

12cc = .73 cubic inch


Are you measuring the cylinder movement or end of arm movement on the side link?

 

[MtnViewRanch]

number9L,
Did prince state at what pressure and temperature this leakage is measured at? If not you need to find out since leakage rate is a combination of pressure and oil viscosity.

12cc = .73 cubic inch


Are you measuring the cylinder movement or end of arm movement on the side link?

I believe that his measurements were taken at the rod and it is leaking down at a rate of 30/16" per minute. (1/16" in 2 seconds per 1st post) That is with a 2" dia cylinder with a 1 1/4" dia rod. Some one want to do the math? I come up with 59.1 cc. :confused3: Just a wee bit more than the allowable leakage rate.

 

[J_J]

There are several kinds of leak.

Static leak might be a hyd component at rest.

Dynamic leak would be a leak under pressure, and even that varies.

Is the leak caused by weight/load?

Is the leak caused by highly pressurized source.

As oldnslo mentioned, viscosity would cause a difference.

Heat may make a difference. Maybe heat will swell the seal and not leak when hot, but when cooled, the seal starts leaking.

No matter why it is leaking, they have their rules for pass or fail.

This is Surplus warranty.

Warranty Information
Products we regularly stock that are purchased directly from the manufacturer are covered by that manufacturers warranty.

We warrant all other products, only to the original purchaser, to be free from defects in materials and workmanship for a period of 90 days from date of shipment.

 

[oldnslo]

I believe that his measurements were taken at the rod and it is leaking down at a rate of 30/16" per minute. (1/16" in 2 seconds per 1st post) That is with a 2" dia cylinder with a 1 1/4" dia rod. Some one want to do the math? I come up with 59.1 cc. :confused3: Just a wee bit more than the allowable leakage rate.

Double checking the math.
Presume To allow the implement to lower the cylinder must extend.

Rod end area = 3.1416 minus the rod area of 1.2272 = Rod end area of 1.9144 inches squared

1.9144 times 1.875 inches of travel = 3.5895 cubic inches or 58.821 cc

I would our math is pretty darn close.

 

[number9L]

Sorry for the confusion guys. The spot I put a tape measure on and timed was the rear, RH edge of the BB, the rear blade corner. That was an easily distinguishable spot that was easy to put a tape measure against while based on the concrete floor and most importantly, keep my head and limbs in the clear. At this spot, it leaks 1/2" in 22 sec. I connected the tilt cyl to all 3 sets of remotes and each one had the same leak rate.

What does this translate to at the rod? I don't know, I'll check and reply with that value.

The leakage is when the rod is under tension, obviously, when I have the BB (or whatever else I attach) picked up with the 3ph. I had my boys (about 90# total) sit on the corner of the BB and it leaked 1/2" in 13 sec, so weight / pressure does add to the rate of leak.

I am running Kubota Super UDT2 fluid, with about 40hr on the fluid since I did the 50hr service (changed everything but the coolant).

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[J_J]

I really don't think it is the valve, after you said you had the same readings on all three work ports..

When they select spools for a valve, they may go through many spools for one that will have the lowest leakage, and to find three spools that have the same leakage rate, makes great odds.

Did you test the cyl for leakage. Use a needle valve in between the work port and the cyl. This will isolate the valve.

Retract the cyl and close off the needle valve, and shut off the engine. With the needle valve closed off, tell me if the cyl is leaking.

 

[number9L]

JJ, I tested the cyl in that I raised the 3ph, got the BB level and disconnected both hoses to the cyl at the QCs. The BB didn't move over several minutes while sitting watching the tape measure at the same spot as I had before.

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