Open Center Hydraulics and Valve

[dmccarty]

I just bought a log splitter the runs off the tractor hydraulics. It works fine and I'm happy with it since its splits the ugly wood I could not split by hand.

The manual said to make sure that the high/low hydraulic hoses where connected to the proper ports on the value. I have a Power Beyond kit on my tractor to run the backhoe and I know which port is high pressure and which is low pressure.

The scary thing for me is that the manual says if the hoses are not connected correctly I could burn out my tractor's hydraulic pump!

I sent a note to the splitter company and of course no answer to my questsions....

I have two concerns/questions.

Can you really burn out a pump by switching which port the hoses go to on the splitter valve? I thought the value was real simple, fluid comes into the port, lever is moved and the cylinder goes one way or the other. If the hoses where switched would not the cylinder just do the opposite of what it did before?

And not hurt the tractor's pump?

In effect I did this on my 4n1 bucket when I replaced a busted hose. I put the disconnects on the opposite hoses so my closing and opening of the bucket is now reversed at the joy stick.

I'm surprised that I could hurt the pump by moving hoses.

The other concern I have is that the splitter value does not work they way I would like. To split wood the lever goes to the right which causes the cylinder to close. This just seems opposite to me. Furthermore I can release the lever and the ram continues to close. This seems like a safety issue to me. I would rather the value work like a dead man switch. When I'm splitting my hand is on the lever anyway so I can minimize the closing of the cylinder.

When I open the cylinder, if I let go of the lever, it stops. This stinks and messes up the work flow. After the log is split I want the ram to open while I move the split wood and/or adjust the log for another split. Having to hold the lever means I'm wasting some time.

The obvious solution is to switch the hydraulic hoses and the value should work in reverse. But I'm afraid of killing the hydraulic pump.

Is this really a concern?

Later,
Dan

 

[MadReferee]

You are confusing two important points, first is that the valve has a pressure inlet and pressure outlet, second is that the valve also has 2 work ports that connect to the cylinder. That's 4 connections on the valve. Fluid will flow from the inlet to the outlet whenever the spool is in the neutral position. When the spool is activated fluid will flow from the inlet into one of the work ports and then to the cylinder and exhaust fluid from the cylinder will go to the other work port and out via the pressure outlet.

The work port hoses are only energized when the spool lever is actuated. Switching these two work port hoses will cause the cylinder to act in the opposite way so if the lever forward was cylinder extend it will now be cylinder retract.

Switching the pressure inlet and outlet lines may or may not have an effect. It all depends on the valve's internal design.

Switching the pressure inlet/outlet with the work port lines would be catastrophic for either the pump or the valve or the cylinder or any/all of them.

Some log splitter specific valves have pressure releases on the work ports that may cause the spool lever to return to neutral when the cylinder has fully extended or retracted. For these valves, the works ports must be connected as per manufacturers directions in order for the valve to work properly.

 

[Dirthog]

If you switch the hoses from the valve to the cyl you should be alright the problem comes when you try and change the pressure and return hoses on the valve you take the relief valve out of the system also if the valve has a one way check in it you could block the oil flow all together. and burn out the pump rather quick

 

[dmccarty]

If you switch the hoses from the valve to the cyl you should be alright the problem comes when you try and change the pressure and return hoses on the valve you take the relief valve out of the system also if the valve has a one way check in it you could block the oil flow all together. and burn out the pump rather quick

Well since I have not burned out the pump I guess I have it right. Why would there be a check valve in an open center circuit?

The splitter comes with a kit to convert the valve to a close closed center circuit.

And the hoses I'm talking about, are from the tractor to the value. Not valve to cylinder. So switching them could be badness.

But you make sense regarding my 4n1 switch. The hoses are past the joystick/valve... Hmmm. That removes a worry.

Thanks,
Dan

 

[Dirthog]

so that the oil will only flow one way some attachments will only work with the flow one way

 

[dmccarty]

so that the oil will only flow one way some attachments will only work with the flow one way

That makes sense. Would that apply to a simple hydraulic cylinder?

Thanks!
Dan

 

[MadReferee]

That makes sense. Would that apply to a simple hydraulic cylinder?

A simple double acting cylinder has no internal check valves. Fluid must be able to flow in both directions or the cylinder would lock up.

Cylinders normally used on top links have double pilot operated check valves. These valves require a specific pilot/cracking pressure to be applied before the check valve will open to allow fluid flow.

Some spools have load check valves. These check valves prevent the initial jerky motion due to the forces of gravity. When the spool is activated the load check closes monentarily preventing gravity from dropping the load until the pressure has built up enough for the hydraulics to carry the load.

 

[dmccarty]

A simple double acting cylinder has no internal check valves. Fluid must be able to flow in both directions or the cylinder would lock up.

That is how I thought the cylinder works. So I could switch the hoses on the log splitter without blowing up my pump?

Why would the manual warn about getting these hoses connected to the correct port on the valve?

Thanks!
Dan

 

[MadReferee]

That is how I thought the cylinder works. So I could switch the hoses on the log splitter without blowing up my pump?

Yes.

Why would the manual warn about getting these hoses connected to the correct port on the valve?

If they were talking about the work ports then there may be a pressure relief on one of the work ports that controls the spring back to center when ram is fully extended or retracted.

In any case, swapping work port hoses will not hurt your pump. Swapping the inlet and outlet hoses may or may not work. Swapping the inlet/outlet with the work ports will definately cause failure of something and it may be expensive. The real bottom line is that each connection on the valve has a specific function and they should be connected correctly or you may cause damage.