Closed circuit charge pressure problem

[Eng.Mohamed.ALi]

hello guys .

I have an equipment working with ( two ) hydraulic motors ( HAGGLUNDS CB 840), pump SP 355 axial piston pump working in a closed circuit , the problem is the charge pressure is fluctuated and tripped the system, I replaced the pump and the problem still not solved , kindly please I need any supports or ideas, the circuit drawing is attached.

 

[HPost]

Is this a mobile machine, driven by an engine? Or is the input speed constant?

When you changed the pump, what exactly did you change? The complete hydrostatic pump or just the charge pump?

When you say the pressure fluctuated, you mean the pressure dropped off and the pressure switch saw the drop and was tripped?

It could be that the flushing valve is stuck open and allowing too much oil to flow out through the low side of the loop. Does the pressure drop off when the motors are running forwards and backwards, or just in one direction?

It could also be that the flushing relief is jammed or stuck open, so when the flushing valve opens, there is too much flow in the low side of the loop and so the pressure drops off.

You need to answer the above so that help can be given...

 

[Eng.Mohamed.ALi]

thank you HPost for reply

here you are the answers:

The machine is stationary and the drive is electrical motor.
The pump I replaced is axial piston pump and the charge pump is built-in so , that is mean both pumps have been replaced.( Please see the drawing attached )
Yes , the charge pressure drop could be observed clearly on the pressure gauge ( just the pump take angle and the motors start rotating )
The application is only in one direction rotating

 

[HPost]

Can you put a pressure gauge on the test ports, the items labelled 27? Does that pressure also drop?

The pressure is dropping because there is excess flow from the charge pump to the tank. From what you have said, it would seem that the "leak" must be in the motors somewhere.

Check the pressure at the test ports. When the motors are running, one will show loop pressure and the other will show charge pressure. Let us know what you see and also let us know what happens as the system heats up. Does the pressure drop get worse?

 

[73lafuite]

The pressure should be about E2 35bar pressure in ME3 about 20bar and 15bar MK4 when the pump is at zero flow. When the motors are running and ME3 MK4 should fall by about 3 bar.
If you do not lose the boost pressure when the oil is cold, and it falls over when the oil is hot and high torque engines: there is a good chance that the motors are used look paragraph A.
If the boost pressure drops suddenly without direct relation to the temperature or high pressure look paragraph B.
A) If you find the pollution in the filter 207 or in the tank and the pump is new: it is serious and it is likely that the engines are concerned. Put your ear against the crankcase engine and listen for the sound is normal. Drain the tank and inspect the interior keep the particles for analysis and clean.
B) That he should know that the pressure relief 3 (15bar) and 6 (also 15bar) are poorly designed. These are pressure limiters to direct action. They are really too sensitive to pollution. They are easy to disassemble, check that the anti vibration nozzle is not clogged, clean the spool/check and not to hesitate to remove any scratches with sandpaper.

 

[Eng.Mohamed.ALi]

Thank you all.