Adding Valve to Closed Center Post Pounder

[RickB]

The CC valve would stop the flow through the OC valve except when any valve spool was stroked.

First valve will have a PB plug feeding the second valve. The second valve will then have a Closed center plug, therefore making both valves closed center. The pressure side will be blocked no matter how many valves are behind (ahead of?)the last one (fitted with a CC plug).

Here are a couple explanations Jim.

 

[aczlan]

Rick
I'm just attempting to determine how it's designed to work. I'm still attempting to understand how CC valve can block oil to the added OC valve. I suppose from what you stated that you have actually seen this type of setup utilized on a JD CC hyd system.
Thanks,Jim

A Open Center Power Beyond valve sends all high pressure flow that is not used by the A and B work ports out the PB port. In the schematic I drew, that flow then goes on to the Closed Center valve which stops it unless it needs the flow for it's A and B work ports.
Where you run into trouble is when you use a Open Center valve that does NOT have Power Beyond on a Closed Center system as the Open Center valve will send all flow not used by the A or B ports to the tank.

As for the missing charge pump, I was drawing a simplified schematic, so it wasn't drawn in.

Aaron Z

 

[aczlan]

Please explain this part of schematic because I can't determine how a CC valve is blocking the OC valve.

Normal flow for a Open Center Power Beyond valve in neutral position (handle at rest) is high pressure fluid into the P port and out the PB port. The Tank and A/B ports are closed.
As such, the high pressure fluid flows out the PB port, if you feed it into the P port on a Closed Center valve, the Closed Center valve will block the flow.

Plus I'm not buying into the return oil(green line) will be low pressure. I've never measured it but when one sends 2250 psi to return line I think it won't be low pressure in return line.

Low pressure is relative, if you aren't sending full pump flow through the tank line, it's the same size line as the pressure line, and there are no obstructions in it, why wouldn't it be a lower pressure?
If it wasn't a lower pressure, you would greatly reduce the amount of work that the hydraulics could do with a double acting cylinder or a hydraulic motor.
It's probably still a couple hundred PSI, but if there is no obstruction and less flow, there will be less pressure.
Here is a return line filter, it's rated for 70 GPM and 200PSI: 1-1/4" NPT 7 GPM Zinga Return Filter | Zinga | Brands | www.surpluscenter.com

Another fallacy to that schematic not functioning on a JD closed center hyd system is the blue arrow(suction) because JD piston pumps are incapable of sucking oil & requires oil to be supplied to them via a charge pump. The blue suction might be fine IF large hyd reservoir was mounted above CC pump but it won't operate correctly with smaller reservoir because many JD tractors have a smaller reservoir & had hyd problems

Again, it's a simplified drawing focusing on the fluid flow after it leaves the high pressure pump and how it goes to the valves, then back to the tank, where the charge pump is located (or if there is one) is immaterial to this discussion as the fluid has to go through the high pressure pump to get to the valves.

Aaron Z

 

[Tx Jim]

First valve will have a PB plug feeding the second valve. The second valve will then have a Closed center plug, therefore making both valves closed center. The pressure side will be blocked no matter how many valves are behind the last one (fitted with a CC plug).

Sorry I was typing while both were posting.


Thank you for your reply BUT IMHO once closed center plug is installed in the open center valve then open center valve ceased actually being open center & becomes a closed center valve. JD utilized the same CC plug(key 21) on FEL such as the model 48 in the late 1960's. I learned back in the 70's on a valve similar in photo how JD CC hyd system will act(cavitation) if seal(key 19) has failed. Valve from schematic with orifice with green line(arrow) concerns me as to what keeps oil from continuously returning oil while pump is pumping.

 

[RickB]

The green line calls out the return from the work ports. If the spool is not stroked, there is no flow. Which I previously stated.

 

[Tx Jim]

aczlan
I wasn't unaware you drew the schematic but you did a nice job. My knowledge of the power beyond control valves is very limited to non existent because they weren't utilized when I served as a dealer service manager. Thanks for being gracious to answer BUT I'll bet I'm not the only one who doesn't understand the concept.
Jim

 

[Tx Jim]

Rick
Sorry I didn't comprehend your reply about how the tank orifice is controlled. As I age my reading comprehension seems to get less. Thanks for your replies & I think I'm beginning to understand.
Jim

 

[buickanddeere]

Tank ? Where is this tank ? Is this the tank ahead of the tractor radiator, under the hood and above the front pump ? I don’t recall of any mention of a ported transmission filter cover in these conversations.
As for the dealer insisting on an open Center valve. He is either clueless, stubborn or miserable.

 

[Zebrafive]

Tank ? Where is this tank ? Is this the tank ahead of the tractor radiator, under the hood and above the front pump ? I don’t recall of any mention of a ported transmission filter cover in these conversations.
As for the dealer insisting on an open Center valve. He is either clueless, stubborn or miserable.

Tank is considered to be transmission case. The tank above the front pump is a reservoir to supply oil to the front pump by gravity. Some transmission pumps (charge pumps) stop when the clutch is pushed in. The reservoir will supply the front pump as long as it has oil to supply.


It's my understanding a ported filter cover is a less restrictive oil return than to "tank/sump"

 

[buickanddeere]

Tank is considered to be transmission case. The tank above the front pump is a reservoir to supply oil to the front pump by gravity. Some transmission pumps (charge pumps) stop when the clutch is pushed in. The reservoir will supply the front pump as long as it has oil to supply.


It's my understanding a ported filter cover is a less restrictive oil return than to "tank/sump"

the ported filter is designed for applications where there is at least 175psi pressure on the return line . As in a hydraulic motor or return lines from a loader etc .
The oil is returned to a location past the transmission pump discharge but prior to the filter element .
The line to the front pump is usually supplied with what ever oil the transmission pump has left over . After the transmission bearings are lubricated, the high/low clutch and the PTO clutch/brake .
What oil the front pump does not take flows through the oil cooler into the reserve tank . When the reserve tank is full the extra oil is routed back to the transmission case .
During continuous high demand hydraulic loads the transmission pump can not keep up with the demands of the front pump. The gallon or two of oil in the oil cooler and front reserve tank is used to supply the front pump. Then the front pump cavitates.
Retuning hydraulic oil via a ported filter cover vs just dumping the return oil into the transmission case will supply the front pump with all the return oil plus what ever the transmission pump can send .
Otherwise the 23gpm front pump is only going to pump 5-6gpm continuous.