Komatsu pw98 hydraulic pump under load

[salih esati]

Hello i have a komatsu pw98-mr6
The issue is that when the hydraulics get warm the hydraulic pump stays under load even though the joysticks are at neutral position, and it tends to get worse and worse as im working to the point where if i leave the engine at idle it stalls.
Also there is a hissing noise from the valve block when the excavator is warm and it tends to get louder when it get hotter, im guessing these two are related.
None of the commands seem to relieve the pressure of the pump except for the travel pedal.
Is there anyone who knows anything about this problem i would greatly appreciate it.
thank you.

 

[John C.]

I'm thinking with the PW model number that this is an excavator on tires? I haven't seen one in this country for years now.

On the PW90 Dash 3 there was an electrical solenoid somewhere that put the pump on full stroke when in travel mode. I don't have an electrical schematic so that is about the extent of my knowledge of the machine itself. A photo of the pump and main control valve might tell me if you have a OLCC system or a CLCC system.

 

[salih esati]

I'm thinking with the PW model number that this is an excavator on tires? I haven't seen one in this country for years now.

On the PW90 Dash 3 there was an electrical solenoid somewhere that put the pump on full stroke when in travel mode. I don't have an electrical schematic so that is about the extent of my knowledge of the machine itself. A photo of the pump and main control valve might tell me if you have a OLCC system or a CLCC system.

Yes the excavator is on tires.
I will get you a photo of the pump and control valve, in the mean time here's a link of the parts book, it contains some photos of the control valve and pump. https://777parts.org/a1/#?k=!0!1!5276!194!278
also if i lift the excavator off the ground, the tires do not move or anything for that matter, it just keeps the pump under load.
thanks for the reply.

 

[salih esati]

 

[John C.]

Oh my, that's a CLCC or closed center load sensing system. I've never seen one on one of of the PW90-3 machines. I have no access to any schematics or descriptions of how the system works so I'm afraid I can't do you much good. In general all I can say is check out the electrical stuff first? What kind of monitor panel is in the machine. Do you have any fault codes showing? Most malfunctioning components will set an alarm on the monitor panel.

 

[salih esati]

Oh my, that's a CLCC or closed center load sensing system. I've never seen one on one of of the PW90-3 machines. I have no access to any schematics or descriptions of how the system works so I'm afraid I can't do you much good. In general all I can say is check out the electrical stuff first? What kind of monitor panel is in the machine. Do you have any fault codes showing? Most malfunctioning components will set an alarm on the monitor panel.

the monitor panel is very simple, no fault codes are showing.
thanks for the help anyway

 

[Iworkondiggers]

I'd be checking for ls pressure to the pump as this will cause the pump to stroke up loading the engine up causing stall, la standing for load sensing as this is a clss system.
Other option would be check the PC (power constant) epc to ensure that is functioning as that should prevent the pump from stalling the engine.
My first point would be check LS pressure and make sure it's not causing the pump to stroke up and if it fine idleavethay,check pump discharge pressure and unload pressure which will give some direction if you have an LS issue or the pump swash plate is Stuck etc as by the sounds of it no implements are moving on their own so I'd go towards ls pressure, who knows might have 100 bar of ls causing the pump to stroke up

 

[Iworkondiggers]

And check if ls bypass orifice is blocked etc

 

[salih esati]

I'd be checking for ls pressure to the pump as this will cause the pump to stroke up loading the engine up causing stall, la standing for load sensing as this is a clss system.
Other option would be check the PC (power constant) epc to ensure that is functioning as that should prevent the pump from stalling the engine.
My first point would be check LS pressure and make sure it's not causing the pump to stroke up and if it fine idleavethay,check pump discharge pressure and unload pressure which will give some direction if you have an LS issue or the pump swash plate is Stuck etc as by the sounds of it no implements are moving on their own so I'd go towards ls pressure, who knows might have 100 bar of ls causing the pump to stroke up

Hello sorry for the late reply the issue still persists
i bought some hydraulic gauges to check pressure and the ls pressure does rise as high as 80 bar as the excavator warms up
i also replaced the unloading valve but nothing changed

 

[salih esati]

And check if ls bypass orifice is blocked etc

yes i checked the bypass valve and it was clean