Hydraulic over heating with load sensing pump

[WezTec]

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

 

[hydtools]

If the relief valve, item 15, is set to a pressure less than the compensator set pressure, the pump will not push fluid through the relief valve wasting power and creating heat.
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

 

[hydromech]

I am tending to think that pump is not running at low pressure when in stand by or its not sensing the load correctly.

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

 

[hydtools]

Here is a description of how a load sensing system works.

http://www.pirate4x4.com/tech/billa...ad sensing systems principle of operation.pdf

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

 

[WezTec]

The pump is inside the tank so i cannot feel if it is hot. The pressure gauge reads 100Bar when in standby, when the cylinder moves the pressure drops then raise to 100Bar like a pressure compensated pump. When i adjust the relief i can take it up to 160Bar then the motor starts to stall.

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?

 

[hydromech]

This all makes sense, the pump is always under load, so that is why the system is getting hot. The load sensing compensator measures the differential across the valve. If the valve gets a voltage it will start to open and the pump will see a load and respond. 100 bar is the max pressure to lift the load. I think you will need to pull the pump to check the compensator. The stand by load should be much lower.

 

[Bert542]

To help understand loadsensing think of these facts:
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."

 

[kcj]

I can't open the schematic, so I may be down the wrong path but I have seen this before:

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.

 

[hydtools]

The high standby pressure would indicate that the directional valve is partially open or leaking sending a presssure signal to the load/flow compensator causing the pump to stroke for flow but, since the piston is stopped at the end of its stroke the pump pressure compensator is taking over and setting the pump to run at high standby pressure. The closed-center valve should not be the wrong valve. The load compensator should adjust the pump to run run at the low standby pressure against the blocked 'P' port.

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

 

[hydtools]

Follow up question. What is the standby pressure of the other identical power pack?

Ted