Prince Stack Valve Relief Question

[Cocre]

If a Prince SV stack valve (or any brand I guess) is placed in a hydraulic system that already contains a system relief valve (I am talking about a JD 3320 tractor here) can or should the Prince relief valve plug be removed and replaced with the optional no-relief plug assembly or can the Prince relief valve just be set to relieve at its highest settings thus turning into a no-relief plug?

The Prince valve comes from the factory set to relieve at 2000 psi and the JD valve relieves at 2500. I would think you should have only one system relief valve in the system. Setting the Prince to relieve at 3000 psi should make it to where it would never relieve, effectively turning it into a no relief plug.

Any help in understanding this would be helpful.

 

[kennyd]

Multiple PRV's are common...the one on the valve should be set just below the main PRV setting so you are close.

Let's see what JJ says

 

[J_J]

The first RELIEF valve after the pump, should be set to protect the pump.

I would set the second or any sequential RELIEF valve the same or slightly lower. If you were trying to protect a 1500 psi motor, you would set the valve controlling that motor at around 1450 psi.

 

[Cocre]

I have not tested the factory relief valve pressure setting, but I assume it is OK. I was thinking that setting any other valve at a setting lower than the factory valve would "elevate" that valve to the primary one that controls the entire system pressure. That is why I was thinking either there should be no other relief valve or set all relief valves at a higher setting than the factory relief device. I've got a lot to learn.

Also, the way I currently have my toplink set up the Prince valve really can't relieve anyway. The relief may open, but the excess pressure is not reduced because it is dumping back into an oulet port that is being used as a power beyond port and is not dumping directly back into the tank. Once I get the valve setup with a real power beyond and the outlet connected to the tank return then I can see how the relief can work. But I could be way off here.

 

[Cocre]

On second thought, even relieving to the oulet on an open center system should lower the system pressure on all devices in front of the relief device. I am over thinking this thing again.

 

[Wayne County Hose]

If you could post a schematic of the valve and of your tractor's hydraulics, I could tell you exactly.

 

[AKKAMAAN]

The only problem I see with multiple RV's on the open center cirquit, is that if they all are on the same setting, before they are fully opened, they will start leaking a little at the same pressure. That will make some increase in leakage power losses. I like when the RV stay completely closed all the way up to the opening pressure, then I want it fully opened. Some of these valve I have used have even lowered the pressure a few psi after opening. They are flow compensated. They were common on mobile equipment where operator use throttle (rpm to increase pump flow).

I would, like J_J suggested, choose the one closest to the pump as the prime or main RV, to open first. The others will become extra safety, and I would set them on a slightly higher pressure, up to 150 psi higher at the most. That way the higher set RV should stay fully closed until the main start to open.

It is important that the RV is designed for the flow range it handling. If it is undersized, system pressure will increase if pump flow is increased.

I am probobly "waaaay overthinking" again, but this is my "theory" about it!!

Merry Xmas to you all!! I love this show!!

 

[RickB]

The only problem I see with multiple RV's on the open center cirquit, is that if they all are on the same setting, before they are fully opened, they will start leaking a little at the same pressure. That will make some increase in leakage power losses. I like when the RV stay completely closed all the way up to the opening pressure, then I want it fully opened. Some of these valve I have used have even lowered the pressure a few psi after opening. They are flow compensated. They were common on mobile equipment where operator use throttle (rpm to increase pump flow).

I would, like J_J suggested, choose the one closest to the pump as the prime or main RV, to open first. The others will become extra safety, and I would set them on a slightly higher pressure, up to 150 psi higher at the most. That way the higher set RV should stay fully closed until the main start to open.

It is important that the RV is designed for the flow range it handling. If it is undersized, system pressure will increase if pump flow is increased.

I am probobly "waaaay overthinking" again, but this is my "theory" about it!!

Merry Xmas to you all!! I love this show!!

Following this line of thinking will keep the system functioning up to its maximum design pressure. Good advise.

 

[Cocre]

My crude hydraulic schematics.

Pic 1 is of how it is now. Pic 2 is where I want it to be (Power Beyond feeding Rockshaft).

 

[AKKAMAAN]

If a Prince SV stack valve (or any brand I guess) is placed in a hydraulic system that already contains a system relief valve (I am talking about a JD 3320 tractor here) can or should the Prince relief valve plug be removed and replaced with the optional no-relief plug assembly or can the Prince relief valve just be set to relieve at its highest settings thus turning into a no-relief plug?

The Prince valve comes from the factory set to relieve at 2000 psi and the JD valve relieves at 2500. I would think you should have only one system relief valve in the system. Setting the Prince to relieve at 3000 psi should make it to where it would never relieve, effectively turning it into a no relief plug.

Any help in understanding this would be helpful.

Your new extra valve stack RV setting will basically not affect the RV (2500) in the selective valve because the new valve and rockshaft can not operate while operating the selective valve. For that case, the new valve stack RV can be set below 2500 psi like 2000psi. But then these 2000psi will limit pressure for the rockshaft to 2000psi. So best best is to set the new valve stack RV to like 2600-2700psi, and that way let it just be an extra safety RV.

I agree with you that pic #2 is the right way to plumb it. Pic #1, shows power beyond out from side outlet, which IMO is not good. I would not pressureize the return core of the valve.
Just make sure you have a "POWER BEYOND PLUG", in the power beyond port.

 

[dfkrug]

The only problem I see with multiple RV's on the open center cirquit, is that if they all are on the same setting, before they are fully opened, they will start leaking a little at the same pressure. That will make some increase in leakage power losses. I like when the RV stay completely closed all the way up to the opening pressure, then I want it fully opened. Some of these valve I have used have even lowered the pressure a few psi after opening. They are flow compensated. They were common on mobile equipment where operator use throttle (rpm to increase pump flow).

The RV on one of those Prince stack valves is just a preloaded spring and
an adjustment bolt. I bought those for my CADDigger. It will gradually
open enough to drop the pressure in the system....not flow-compensated.

I agree with the OP, that a second RV in the AUX valve stack is redundant.
When I add a AUX valve or backhoe or whatever, I set the additional RV
right AT the specced system pressure. I want to make the max use of the
design pressure available. If I am happily using my 2500psi tractor, and
I add a hoe or AUX valve or FEL, and set ITS RV at 2450, I have lost some
valuable pressure that was available for ANY implement before.

When a maker sells a valve, they don't know if the user will have
any other RV available in the system, so they offer a RV. Conversely,
if a tractor maker always installs an AUX or FEL valve, they can make do
with only one RV. My Kioti and Bobcat tractors are that way...no system
RV; the RV is in the FEL valve.

Another case can be made for setting the AUX valve RV to the same pressure
as the other RVs in an OC system. If the user goes to relief very often,
as in dirt work, multiple RVs opening simultaneously should reduce the amount
of fluid heating you get. This is minor compared to the above reason,
however.

 

[Cocre]

Thanks for all the info guys. I am going to purchase a gauge and set the pressure to at or slightly above the system setting.

 

[J_J]

Thanks for all the info guys. I am going to purchase a gauge and set the pressure to at or slightly above the system setting.

I would recommend setting the first relief valve after the pump to protect the pump. Then if you install a new valve and cylinders, down stream, and they are lower pressure cyl, then you can adjust the relief valve for that lower pressure. If you select higher relief pressure than the pump, and a QD is not set correctly, then the pump could crack open.

My opinion is that that all reliefs should be set the same, or lower than the pump pressure. The secondary hyd circuit should be set as needed to protect that part of the system. The secondary cyl might be limited to say 2500 psi, and you are running a 3000 psi relief on the first valves.

 

[AKKAMAAN]

I just want to clearify my previous posts!
I agree with J_J!!

 

[dfkrug]

I am going to purchase a gauge and set the pressure to at or slightly above the system setting.

Just realize that any pressure you set above the system relief will be
done blind, since your guage will only show the system relief pressure.
To set your adjustable RV above the system relief, you will gradually
increase it until you are at the system pressure, then add a slight
clockwise turn. This is not my preferred approach, but you won't
hurt anything.

 

[J_J]

Cocre, Thanks for all the info guys. I am going to purchase a gauge and set the pressure to at or slightly above the system setting.


If you do that, then you disable the relief protection for that valve. What if you have lower pressure components in the work ports, that means that the the sys pressure will rise to it's relief pressure, of say 3000 psi, , and perhaps cause some damage to the second valve cylinders, which have a max rating of 2500 psi. If all the cylinders and motors have the same pressure, the one relief would suffice, but that is not a sure thing. The BH may be 2500 psi, and that 500 psi difference represents a lot of force. Perhaps you are trying to squeeze every bit of pressure out of the system. Cracking pressure is always higher than full relief pressure, so when setting the relief, allow the relief valve to operate long enough to set the full open pressure.

 

[Cocre]

All of the components are rated at 3000 psi or higher working pressure. The JD 3320 primary hydraulic relief valve is set to relieve at 2500 psi (not tested but so stated in the factory manual). The backhoe and the new valve used to control the hydraulic top link cannot be on the tractor at the same time. I looked at the technical manual for the hoe and JD says the 447 hoe main system relief is set to relieve at 2250 and no less than 2200. The boom and dipperstick are set to relieve at 2650 +-50. So that gives me some indication as to the proper setting for the new top link control valve. One difference is that the hoe dumps the oil only back to the reservoir, and the top link will use a power beyond port to feed the 3pt hitch. So the closer I set the top link relief to 2500 the better off I will be. Probably 50 psi on either side of that figure will be OK, you think?

I am not the first one to do this and I have not read of any catastrophes from others in their implementations, but I do want to do this thing as right as I can.

 

[J_J]

Where is Sandy Run? My folks are from the Dillon area.

 

[RickB]

All of the components are rated at 3000 psi or higher working pressure. The JD 3320 primary hydraulic relief valve is set to relieve at 2500 psi (not tested but so stated in the factory manual). The backhoe and the new valve used to control the hydraulic top link cannot be on the tractor at the same time. I looked at the technical manual for the hoe and JD says the 447 hoe main system relief is set to relieve at 2250 and no less than 2200. The boom and dipperstick are set to relieve at 2650 +-50. So that gives me some indication as to the proper setting for the new top link control valve. One difference is that the hoe dumps the oil only back to the reservoir, and the top link will use a power beyond port to feed the 3pt hitch. So the closer I set the top link relief to 2500 the better off I will be. Probably 50 psi on either side of that figure will be OK, you think?

I am not the first one to do this and I have not read of any catastrophes from others in their implementations, but I do want to do this thing as right as I can.

There is absolutely no reason that the tractor's main relief (set at 2500psi) will not adequately protect the new valve and the hydraulic top link. Set the new control valve's relief above that of the tractor's main relief valve setting. There would be no harm in using a control valve with no relief at all in this application.
The boom and dipperstick relief settings you reference are circuit relief pressures and should not be confused with system protection. Circuit relief valves protect work ports that are closed and isolated from the system. Circuit reliefs are by definition set above system relief pressure so they will remain closed when the work port is open to pump pressure and flow.

 

[J_J]

RickB ,

Perhaps this will help. It mentions something about the relief valve settings.

Whether the next valve in-line has a relief or not, it will see the main system pressure, and when you activate one of the cylinders, the cyl will see main sys pressure. If it has a relief valve, it should be set at same or lower.