Help on Aux Valve hook up kubota

[LWF]

One more time on remotes, I have a kubota L3830 with a BH90 backhoe. My hyd block on the side of tractor has 3 ports. The power beyond port goes to the back to the back hoe and loopes( either through the backhoe valve or if taken off the two connect toghether) back to the front and connects to the loader valve to the PB port. The other two hyd ports, pump and ret hook up to the loader valve. I want to hook up an aux valve. Do i disconnect the power beyond hose coming from the backhoe and going to the loader valve and connect it to the PB on the new valve and then run a hose from the PB on the loader valve to the inlet on the new valve and tee the returns together. I am a little confused with the PB going to the backhoe first. Wow got it all out.

Thanks Larry

 

[Farmerford]

Larry:

Are you sure fluid flows first to the backhoe and then to the loader? I think the "Power Beyond" port on your block is labeled that way because it is for "Power Beyond" coming from the device connected to the "Pump Port". That is the typical arrangement.

You didn't mention a connection between the backhoe and the reservoir/tank, which leads me to think that the backhoe is in series with, and downstream of, the loader valve. Fluid flows out of the "Pump" port, into the loader valve inlet, then out of the loader valve power beyond port to the backhoe inlet port, then through the backhoe valve to the "Power Beyond" port on the block. From the block the fluid from the backhoe flows into the three point hitch circuit and ultimately into the transmission case/reservoir.

If that is correct, and if you want an auxillary valve in the same circuit, it will have to be in series with the loader valve and backhoe valve. If the auxillary valve has power beyond, then your proposed plumbing (if I understand it) is correct. That is, the loader valve power beyond connects to the auxillary valve inlet, and the auxillary valve power beyond connects to the backhoe inlet. Then tee the return/outlet port of the auxillary valve into the line from the loader valve outlet to the return port on the block.

Since the auxillary valve is upstream of the backhoe, any relief valve in the aux valve will also control the pressure at the backhoe. So you may need to adjust the relief valve setting in the aux valve to slightly above (50 psi is the rule of thumb) the desired pressure at the backhoe.

 

[LWF]

Farmerford ! It just might be that way as the two hoses from the BH90 per loader assy inst. , one comes from the PB port on the RH side hyd block and the other from the PB port on the loader valve. The other two ports on the loader valve are the pump and tank return both also coming from the hyd block. So you are saying the pressure comes from the pump port in the loader valve and is fed through the PB port on the loader valve back to the BH90 and is returned back via the PB port on the hyd block. I have ordered a brand hyd valve with PB, it is a 2 spool with a joystick and I will mount it right next to my loader valve. The part #is LV22TSTSAB with a LV2-W power beyond kit.The Mfg is Brand BRAND Hydraulics suppliers of hydraulic valves and pumps . So the hook up is as you stated for the new valve?? I am also not sure what you mean about the 50 PSI differance. The new aux valve has an adjustable pressure relief and is set at 2000 PSI

Thanks Larry

 

[Farmerford]

Larry:

Yes, "the pressure comes from the pump port in the loader valve and is fed through the PB port on the loader valve back to the BH90 and is returned back via the PB port on the hyd block".

Relief valve: when valves are in series (as they must be on the typical small tractor open center system) the pressure at any point in the circuit is limited to the lowest setting on the upstream relief valves. Therefore, the 2000 psi relief valve in your new aux valve, which is upstream of the backhoe, will stop the pressure buildup in your backhoe at 2000 psi (actually a little less than that because of friction losses in the valves and lines between the aux valve and the backhoe). That may be enough pressure for your backhoe, but I don't know. Suppose your backhoe is designed for up to 2500 psi and that the system relief on your tractor is also set for 2500 psi. Before you install the aux valve the full 2500 psi is available to the backhoe (assuming no relief valve in the loader valve, or if there is one that it is set at 2500 psi also, or higher), but once you install the aux valve the max pressure at the backhoe will be limited to the aux valve relief setting of 2000 psi.

Unless it will overload an implement attached to the aux valve, you can increase the loader valve relief to 2500 psi (in my example) to get full pressure to the backhoe.

As a further complication, if the system relief is set at, say 2800 psi, and you want to get a full 2500 psi to the backhoe while its cylinders are moving (as opposed to being stalled against a load), you would set the aux valve relief at 2550 psi to offset the losses in the circuit from the aux valve to the backhoe (50psi is probably high in your case, but it is a rule of thumb).