Attaching open center valve on JD closed center hyd sys?

[Tx Jim]

Has anyone seen or utilized this type of hyd oil schematic utilizing an open center valve on a JD closed center hyd system(10-55 series)?? I'm attempting to determine how frt pump won't cavitate as I've been instructed. I've never seen or heard of this configuration until very recently.
Thanks,Jim

 

[buickanddeere]

An internal flow passage diagram of that open centre power beyond valve would be of assistance .
The open centre valve while at rest. the port to tank would have to be closed and the PB outlet to the closed cent would have to be open through to the pump.

 

[Tx Jim]

Glen
You have similar question that I have but I was told it will work but I'm trying to determine how.
Jim

 

[D-]

I'm not sure what the point of the valve is. Perhaps for a gear pump w/o
relief valve.

 

[Destroked 450]

Plumbed as in the diagram it will work but isn't very efficient.
At rest all oil flowing thru a open center valve with PB will flow thru the PB port to the down stream closed center valve which in turn will maintain system pressure.
The only time oil from the open center valve flows to the tank return port is when the open center valve is being functioned.

The down side of that setup is any time the open center valve is being used most if not all oil from the PB port will stop thus making the down stream closed center valve useless until function of the open center valve is stopped.

Example: if a cylinder is operated by the open center valve the down stream CC valve will not work until the function by the OC valve is complete and the valve returned to center.
If a hyd motor is plumbed to the OC valve and it's locked into continuous operation the down stream CC valve would be useless during that time.

A much better setup would be to tee in the OC valve and install a CC conversion plug to make it another CC valve, then all valves could be functioned at the same time providing the pump has enough flow capacity.

 

[Tx Jim]

(quoted from post at 12:14:01 12/01/19)

A much better setup would be to tee in the OC valve and install a CC conversion plug to make it another CC valve, then all valves could be functioned at the same time providing the pump has enough flow capacity.

Which is how a JD 48 frt end loader factory valve was set up for CC operation.

 

[Destroked 450]

That's what we did to a friends JD 2630 when we mounted a Farm Hand loader, it had a dual spool open center valve, swapped in a close center conversion plug and he was good to go.

 

[JD Seller]

Jim what the diagram is not showing is the open center/power beyond valve has a pressure control valve in it. So it keeps the PB port pressurized with zero flow while dumping the flow through the pressure control valve into the return/"T" port. This also results in the supply port/circuit/"P" having pressure all of the time. Thus the two down stream closed center valves have pressurized oil to them. The front pump would not pump any flow IF the pressure control valve pressure was set above the main pump pressure.

That open center power beyond valve would have some "ODD" internal porting to work in a system plumbed like this diagram. I do not see what they are accomplishing by using this valve. Three closed center valves would give you the same thing.

Where I have seen this type of setup is with a open center pump feeding the closed center valves out of a PB port on an open center valve. JD used a circuit similar to this on the JD 6715 tractors. They called it an opened center SUMP supply system. What it gained you was that all the valves could work if used at the same time. Also the pressure control valve keep the supply side at operating pressure at all times. In traditional open center valve stacks the first valve opened closes off all the down stream valves from working. Also there is no pressure until the oil flow hits a resistance like a cylinder lifting some thing. So in some open center system you have a hesitation before they will lift a load.

I wonder if this diagram is misprinted. I can not see any reason for the open center valve. The reason I am saying this is that with a closed center pump you can feed as many closed center valves as you want as long as the supply side is a common circuit. Nothing flows until one or many of the valves are open.

What/were is this being used ??

 

[Destroked 450]

(quoted from post at 21:03:01 12/01/19) Jim what the diagram is not showing is the open center/power beyond valve has a pressure control valve in it. So it keeps the PB port pressurized with zero flow while dumping the flow through the pressure control valve into the return/"T" port. This also results in the supply port/circuit/"P" having pressure all of the time. Thus the two down stream closed center valves have pressurized oil to them. The front pump would not pump any flow IF the pressure control valve pressure was set above the main pump pressure.

I find this statement a little confusing has the pressure control/ pressure relief valve has nothing to do with maintaining pressure thru the power beyond port, and should never dump flow back into the return port unless there's a pressure spike such as a cylinder suddenly reaching the end of it's travel.
A PB plug simply blocks the pumps flow from going to the return port and redirects it to the next down stream valve. In this case the down stream valve is a closed center design thus making both valves act as closed center.

I do agree this is not a good setup and three closed center valves tee'd into the supply line would be a much better system.

 

[WTW]

Sir, You are absolutely correct. Very good explanation! I would also add another inefficiency of this
system / circuit as drawn and that is neither the OC valve or either of the CC valves have compensator
control valve spools which would allow multi-function of two valves at same time to control flow
sharing. If theses valves did have compensator feature, like SCV have, The OC could be used at same
time as the direct fed CC valve. Or the two CC valves could be used at same time preventing all pump
flow going to the valve with lowest working pressure.

If the two CC valves in this schematic are original SCV's then they would have this feature. They would
share flow when used together but, Like you stated, the OC valve will always override the CC valve that
is fed downstream of OC valve. DW

 

[JD Seller]

"I find this statement a little confusing has the pressure control/ pressure relief valve has nothing to do with maintaining pressure thru the power beyond port, and should never dump flow back into the return port unless there's a pressure spike such as a cylinder suddenly reaching the end of it's travel.

A PB plug simply blocks the pumps flow from going to the return port and redirects it to the next down stream valve. In this case the down stream valve is a closed center design thus making both valves act as closed center."

Destroked 450: If you look that open center power beyond valve it also a Selective control valve too. It appears to have outlet A&B ports. If it was a Power beyond valve only then it would not have any flow to a control spool. That is why I am thinking it must have an internal pressure control valve that allows the control spool to have oil flow when it is operated.

This is just a guess without a better diagram of that valve. I can not see any reason for that valve in the first place IF the pump is a closed center one. I have seen a setup like this with an open center pump. When not in operation the pressure control/regulating valve keeps pressure on the inlet circuit but dumps the flow into the return at this point so the pump is not dead headed.

 

[Destroked 450]

Well we're not on the same page but I'm not going to argue about it.
I've installed several valves in series using a power beyond plug on open center hydraulic systems but teeing in another valve on a closed center system is much simpler than plumbing it in series using a power beyond plug.
So we're both in agreement that the way the valves are plumbed in the photo is a bad setup.

 

[JD Seller]

Destroked 450: I am not trying to be argumentative either. I understand what your saying about plumbing in extra valves on a open center system.

I am at a loss on what this setup is trying to do. It looks like the close center pump would go to full flow returning the oil through the open center valve.

Maybe Jim will chime in with what this is on and what it is supposed to do.

Have a good week.

 

[Tx Jim]

Ok fellows there is a similar discussion on another tractor discussion forum that I frequent that was started about operating a wood splitter on a JD 2555. It was mentioned closed center hyd systems & open center wood splitter valves don't get along well. A member drew this schematic. I mentioned on other forum that 1 one fallacy of schematic was that JD piston hyd pump on 10-55 series won't operate correctly unless oil is supplied to it by charge pump. Up until this topic came up my knowledge of currently utilized power beyond control valves was very limited but I understand more now. I was informed that tank port oil outflow is controlled by the valve while I was thinking it PBY outlet were free flow. So I thought I open a topic on this site for another hyd opinion. Tractor by net under hyd section is the website if you care to read the original thread.
Thanks,Jim

 

[Tx Jim]

Correction: Thread on TBN I was referring to is about hyd valve for post pounder/driver not wood splitter.

 

[Destroked 450]

Destroked 450: If you look that open center power beyond valve it also a Selective control valve too. It appears to have outlet A&B ports. If it was a Power beyond valve only then it would not have any flow to a control spool. That is why I am thinking it must have an internal pressure control valve that allows the control spool to have oil flow when it is operated.

Ok I think there's a misunderstanding of the description of the valve in the drawing and possibly the definition of power beyond.
What I see in the photo is in fact a directional control spool valve setup with power beyond capability.

Most of the newer directional control spool valves today have a interchangeable plug to configure the valve to operate has Open Center, Closed Center or Power Beyond.

With this open center plug oil from the pump is allowed to flow freely thru the center of the valve into the return passage and out the end outlet back to the tank.

With this closed center plug oil flow from the pump is blocked is blocked, return oil only flows back to the tank as a result of a valve spool function.

With a power beyond plug installed oil flow from the pump is blocked from the return passage similar to a closed center plug, but the passage thru the plug now directs oil down stream to another valve.

In the drawing the down stream valve is closed centered blocking the oil flow on both valves, thus making both valves closed centered.
If the down stream valve were open centered allowing oil to free flow back to the tank, both valves would function as open centered.

The down side of that setup is whenever the control spool in the upstream valve is moved off center to perform a function, oil flow is redirected to that function and no longer flows to the down stream valve, thus making it inoperable until the up stream function is complete and the control spool is returned to center.

A necessary evil when plumbing multiple valves in series on a open center system, but a total waist of a closed center system where the valves can be plumbed in parallel and all operate simultaneously.

 

[Tx Jim]

Destroked 450
Please go to TBN website & read original thread shown under hyd's section. I think if closed center conversion plug is installed then control valve can no longer be classified as an open center valve.
Jim

 

[Destroked 450]

Read the thread but I'm not a member there so can't respond.
I think the misconception is continuing to call the valve a open center valve.
Once the power beyond adapter (plug) is installed that valve is no longer a true open center valve, it becomes a closed center valve with the capability of flowing oil downstream to another valve.
If I disconnect the plumbing from the PB fitting and screw a plug in that port the valve becomes a true CC valve.
The down stream valve determines what the system will be, in this case the down stream valve is CC so the entire system is CC.
If the down stream valve is OC then that part of the system would be OC and would not work on a JD tractor.

Since these valves are part of the post driver that is powered by the tractors hydraulic system I understand what their doing a little better.

Plumbed like in the diagram it can be operated on a JD tractor with a CC hyd system, should the post driver be mounted on a tractor with OC hydraulics one simply has to replace the CC conversion plug on the down stream valve with a open center plug, then the entire system becomes OC without the need to replumb any of the valves.

That's good thinking on the dealers part.

 

[Tx Jim]

Thanks for reading the tread on the other forum. I agree with you that once CC plug is installed OC valve ceases being an OC valve but I was in the minority on the other site.

 

[Glen D Anderson]

FWIW

I don't have any experience with the application in question(55 series) however I thought I'd throw something out there as food for thought.

According to Jim's first drawing/schematic, the circuit is an open loop design and with that said running an open center valve w/PB would appear to serve no useful purpose unless it has been converted to closed center operation as already stated by others.

However if the circuit were a closed loop, such as a 3020 / 4020, I could see the possible need for running an open center valve w/PB and a dedicated drain to tank. This would be in the case of operating a single acting cylinder that is under a light load. The back pressure that is present on the low pressure side of a closed loop circuit may be enough to prevent the cylinder from retracting in a timely fashion, if at all. So, if you were installing an aftermarket SCV to run a single acting cylinder in this application an open center valve with PB porting may be an option even if other functions are hampered during it's operation...... That said, as I recall our older 20 series tractors, SCVs have provisions(a setting) for running single acting cylinders and the later model 20 series has valving in the SCV adaptor plate the accomplishes the same task.

Thoughts?