Testing Relief Pressure

[Tunguska]

I recently installed a PTO pump on my JD 870 to reduce the RPM required when using the wood splitter and still have an acceptable cylinder cycle time as well as adding rear remotes.

The pump is a Prince HC-PTO-2A (~11.1 GPM) feeding a ROPS mounted Prince SVM stack valve. This in turn supplies an LS 3000 valve on the splitter.

I would like to confirm at what pressure each of these valves go into relief. The stack valve should be pretty simple: Pressure side Q.D.>hose>tee with gauge>needle valve>hose>return Q.D. Slowly close the needle valve and note the pressure where the RV pops off.

Where I'm a bit flummoxed is how to test the splitter valve which is in series with the stack valve. For example, say the stack valve is set at 2100 PSI and the splitter valve is 2300, how would you confirm the 2300, short of plumbing it directly to the pump?

(Ideally, I'd like both to be set at 2150 PSI).

Thanks in advance.

 

[J_J]

The first valve relief in line will dictate the relief pressure for the hyd system.

You could/should raise the first relief valve pressure to about 50 to 100 psi below the max pump pressure, and set the other relief valves the same.

 

[Errol]

Some times these valve stacks will have a high pressure carry over where the first valve only controls the pressure in the circuits that are on that valve and direct pump pressure is carried over to the next valve stack where its relief controls that series of circuits on that valve, the best way would be to put a tee piece with a pressure gauge on each cylinder and bottom the cylinder and check the pressure but on hydraulic motors the only way to test is to disconnect from the motor but you will have back pressure from the filter coming back through the motor so you have to take both lines of and cap the return line it gets a bit complicated because there are so many different types of valve arrangement's that it is better to check with someone who know the machine's hydraulic system:confused2:

 

[J_J]

Are you talking about open center circuits with a higher pressure downstream?

You do know open center circuits hyd components are in series.

 

[Errol]

yes but each valve bank can be set to different working pressure either higher or lower like a circuit relief

 

[J_J]

I am still not understanding what you are saying.

After the pump, you have 3 valves in an open center system, and pump pressure of 2600 psi.

If the first valve is set to 2500, what pressure would you set the second and third valve?

If the first valve is set to 2500, how are you going to set the other valve relief to any other higher pressure. Your source is limited to 2500 psi.

If you did set the third valve to say 2899 psi, using an external source, it would never activate.

You could set up the 3pt valve at 2000 psi relief.

 

[Errol]

usually you would have a system relief that would be the highest you want the pump to work at and then you would have circuit reliefs that could be used on hyd motors or cylinders that need controlling to a lower pressure but power can be used at max where you want or lower at say a motor and using high pressure carry over or pressure beyond you can link banks of valves giving you more spools than a single bank can give you and not damage your return system

 

[J_J]

The first valve PRV in a series of valves will limit the pressure.

The other valve reliefs can be set equal or lower to protect each branch circuit.

 

[Errol]

that's right but with high pressure carry over using the first valve doesn't take all the flow from the second valve bank so that you can use both separate banks at the same time and usually the circuit reliefs are lower or you don't put a relief and you rely on the system relief

 

[J_J]

that's right but with high pressure carry over using the first valve doesn't take all the flow from the second valve bank so that you can use both separate banks at the same time and usually the circuit reliefs are lower or you don't put a relief and you rely on the system relief

Actually, the first valve can take all the pump flow and use it on the cyl or hyd motor and leave none for downstream operation.

That is why a priority valve is used with things like power steering. It is located before the first valve. The steering has to have fluid available at all times. If the steering valve was downstream of the FEL valve, and the FEL was using all the fluid, then steering would be dead.

If a valve is only using 5 GPM's of the pumps 10 GPM potential, then 5 GPM is available downstream.