Hydrolic Valves Open Center

[kennyd]

Another thought, to eliminate the "pump to big" theory, try running the tractor at a lower RPM, that will slow the flow down.

 

[shaley]

I think now you need to do some testing. Remove the hoses from the circuit you show in your highlited schematic and find out if in fact oil will flow when the spool is shifted.

 

[dynasim]

Given that the relief pressure is 2320, I can almost guarantee that the problem is to much flow through the pump.

If a positive displacement pump does not have enough drive torque to pop the safety valve, it will drag the motor down. A 33 hp driver will not drive this pump at full pressure. Since the pressure capability is directly related to the available torque for a given capacity pump, and you are at peak torque at or near the operating RPM, it is a spiralling problem.

However, after the motor drags down to low RPM, you will get some back flow through the pump, and the motor will stay running, but you won't be able to do anything.

To test out your system, I would hook the valve system to the tractor's hydraulics for a bit. I would bet that your system will work as designed.
EDIT: I assumed(possibly incorrectly) that you had a rear hydraulic remote to tie into. You may need to use your FEL's curl circuit.

To use you system as-is, I would significantly lower your safety valve pressure(to say 1700 psi). This would give your tractor a decent operating margin, and you could slow the engine to get the pump capacity to something reasonable(10-12 gpm). Note that the lower pressure will limit your bh's lift capacity, but not its speed.

Best Regards
Chris

 

[dynasim]

I just looked at you flow controller schematic. Because this is a positive displacement pump, the flow can't be "controlled". The flow is going to be essentially dependent only upon the RPM. For a flow controller to work, there must be an alternate path for the oil to bypass.

Chris

 

[JerryG]

I think that everything Chris has said is correct. The valve and the relief combined together can't handle the flow from that pump. The least expensive way to get the hoe to work would be to plumb it into the tractors hydraulic system.

 

[Wern]

I have tried to run the engine at lower RPM to reduce flow, but the engine will stall right away.
Maybe rather than tying the BH into the tractors hydraulic system would be, as dynasim explains, to hook up the flow controller properly, that is to connect the bypass port of the controller to the oil tank,. This way I should be able to reduce flow and test the "pump too big" theory. I am afraid that I might contaminate the tractors hydraulic system with the rudimentary BH oil system (as mentioned earlier, I had debris in the valve set)
I will have to go back to the equipment hook it up again and do more testing. I'll be back, hopefully with facts which leads to resolve the problem.
Thank you all.

 

[kennyd]

to hook up the flow controller properly, that is to connect the bypass port of the controller to the oil tank,. This way I should be able to reduce flow and test the "pump too big" theory. I am afraid that I might contaminate the tractors hydraulic system with the rudimentary BH oil system (as mentioned earlier, I had debris in the valve set)

Wern, The bypass from the divider should go to the tank on the backhoe, not the tractor-so no fear of cross-contamination

 

[shaley]

I can turn my PTO pump by hand without much effort until a valve is actuated, then you are doing work so the effort is greater. If the actuated valve is the stablizer down, the effort is very little. This might be a way to test the circuit with little trouble. I don't think the releif in the BH circuit comes into play until a circuit is overloaded such as the boom trying to lift a tree stump out of the ground that is too heavy.

 

[jinman]

To test out your system, I would hook the valve system to the tractor's hydraulics for a bit. I would bet that your system will work as designed.
EDIT: I assumed(possibly incorrectly) that you had a rear hydraulic remote to tie into. You may need to use your FEL's curl circuit.

Both great ideas... It would be worth the expense of getting the hoses to the FEL curl circuit and show how the system would work.

 

[dynasim]

The only way to make that pump work with that tractor is to lower the relief valve setting. Installing the flow controller properly will not lower the torque/hp required to drive the pump if the pump outlet pressure is held constant.

Diesels are essentially constant torque machines. Lowering the speed will not help with the stalling issue because the tractor just doesn't have the torque to drive the pump at the relief valve pressure(at any rpm).

For a given pump, torque requirement and pump outlet pressure are directly related.

Hope this helps.
Chris