Hydraulic over heating with load sensing pump
Hydraulic over heating with load sensing pump
(OP)
Hi, we have two identical power packs. One has an overheating problem and the other is working okay.
I have a schematic (please see attachment), it has a load sensing pump. I have worked with standard compensated pumps but l am not to familiar with load sensing so I have a few questions
Does a load sensing pump drop to low pressure (standby pressure) when the valve is closed, what pressure would it be? is this set by the factory ?
On the schematic the relief valve is on the tank lid, which I think is a remote relief as the pump is submerged. When I adjust the relief on the tank it adjust the pressure, this is when the valve closed. I assume this is a problem so we have checked the proportional valve and we have -0.25V which means the valve is delivering oil to the remote relief this is why we can adjust the pressure which will be the compensator on the pump?
I thought this was the problem and that the valve should be at 0V but when we checked the other unit it was the same.
If I had to put the valve at 0V I assume that the load sensing compensator should take over and drop to standby pressure as the system doesn't operated all the time!
Or the load sensing compensator is set to high?
Please feel free to correct me and help with troubleshooting with the overheating problem
Regards
Wesley
I have a schematic (please see attachment), it has a load sensing pump. I have worked with standard compensated pumps but l am not to familiar with load sensing so I have a few questions
Does a load sensing pump drop to low pressure (standby pressure) when the valve is closed, what pressure would it be? is this set by the factory ?
On the schematic the relief valve is on the tank lid, which I think is a remote relief as the pump is submerged. When I adjust the relief on the tank it adjust the pressure, this is when the valve closed. I assume this is a problem so we have checked the proportional valve and we have -0.25V which means the valve is delivering oil to the remote relief this is why we can adjust the pressure which will be the compensator on the pump?
I thought this was the problem and that the valve should be at 0V but when we checked the other unit it was the same.
If I had to put the valve at 0V I assume that the load sensing compensator should take over and drop to standby pressure as the system doesn't operated all the time!
Or the load sensing compensator is set to high?
Please feel free to correct me and help with troubleshooting with the overheating problem
Regards
Wesley





RE: Hydraulic over heating with load sensing pump
The relief valve should be set to a pressure high enough to allow the compensator to work and low enough to prevent catastrophic failure of any circuit component.
The relief valve may be at fault, not working properly.
Do you know what these pressure settings should be?
Ted
RE: Hydraulic over heating with load sensing pump
The schematic does not show a pressure compensator on the pump?
The pump should run at about 10-20 BAR in stand by, possibly less.
The general idea is that the signal from the shuttle valve will bring the pump off stand by and the pump will create enough pressure to do the work required and nothing more. When the relief valve spills, the signal to the pump is lost and that will limit the pressure.
Excess pressure generation will turn directly to heat.
You need to look at the pressure gauge (11), that will tell you what the pump is doing.
What is the pump doing in stand by?
What is the pump doing when the cylinder is moving?
Put your hand on the pump casing drain...is it hot?
What should the counter balance/over centre valve (13) be set at?
Hydromech
RE: Hydraulic over heating with load sensing pump
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Excess internal pump leakage could result in increased temperature. The pump would be generating more standby flow than normal near-zero standby flow to maintain standby pressure. Like Hydromech asked, does the pump feel hotter than the rest of the system.
Ted
RE: Hydraulic over heating with load sensing pump
Should the proportional valve be set to 0V, i am assuming that the valve is giving oil to the load sensing compensator which is closing it off, wont this make the pump run like a standard compensated pump?
Or can you adjust the load sensing on the pump could that be set to high or faulty?
When adjusting the counter balance valve the cylinder just drops down as it has a load on it.
The schematic shows that the P port is blocked, this is why I think maybe the proportional valve should be at 0 you shouldn't be able to adjust the pressure when the valve is closed?
RE: Hydraulic over heating with load sensing pump
RE: Hydraulic over heating with load sensing pump
When the loadsense line is left open the pump will only deliver standby pressure. When the loadsense line is plugged the pump behaves like a normal pressure compensated pump and will deliver to it's compensator setting.
Looking at your circuit, when the valve is in it's centre position the loadsense line is able to drain from C to A at the shuttle valve through the A port of the valve to tank. The gauge should read only 10-20bar (as previously mentioned above).
You should check:
1 - The circuit is actually connected like the diagram.
2 - Is the directional valve configuration as shown. ie have you been supplied with a blocked centre valve by mistake. (Blocked centre valves are the most common).
Bert542
"Of all the things I have lost, I miss my mind the most."
RE: Hydraulic over heating with load sensing pump
When you say proportional valve, do you mean prop directional control of the load? If this is a closed loop control (position or force measured, fed back to valve controller) then the error signal will usually keep the valve spool slightly off neutral to balance the forces applied by the load. The load sense line is then always seeing load pressure and pump stanys on load pressure.
Even then, if the pump compensates properly it should not be significant heat.
I am guessing RV malfunction or set too low.
If you take motor amps reading it will give an idea of the magnitude of the heat generated and that might point to a source.
RE: Hydraulic over heating with load sensing pump
Perhaps the load compensator is mis-adjusted or faulty and does not function correctly leaving the pressure compensator to be the only functioning control. I suspect that the load compensator is mounted on the pump next to the pressure compensator and the tank will have to be opened to access the load compensator.
The relief valve shown mounted external on the tank may not be the load compensator. It may be there to adjust return line pressure, for some reason. It does affect the gage reading when adjusted indicating it is in the flow path of the standby flow.
Ted
RE: Hydraulic over heating with load sensing pump
Ted