Working principle and fault analysis of excavator LS valve

LS pressure is a very critical parameter in CLSS (closed load Sensing System). LS oil pressure refers to the load of the actuator

Stress. In normal operation, the LS pressure is slightly less than the load pressure of the actuator. At overflow, the LS pressure is equal to the actuator load pressure.

First, LS pressure generation

PPC oil pressure acts on the left end of the main spool, and the main spool moves to the right.

Main pump pressure PP through the main spool, top open valve flow to the actuator.

At the same time, the main pump pressure PP enters the LS generation loop through the throttle hole of the main spool.

When the actuator loop pressure (that is, the load pressure) rises to the required pressure, the pump pressure PP also rises, one-way in the main spool

The valve opens to the right and the actuator loop is connected to the LS loop.

Accordingly, the PLS pressure of the LS loop is almost equal to the pressure of the actuator loop (load pressure). Therefore, the LS pressure reflects the size of the actuator load pressure.

At this time, the PLS oil pressure generated by the LS circuit enters the LS circuit of the hydraulic system through the LS shuttle valve.

Note: Neutral: PLS=0

When working: PLS is slightly less than the main pump pressure PP

When overflow: PLS= main pump pressure Pp

Second, fault diagnosis

Fault phenomenon: low bucket rod speed.

Check result: The orifice with PLS pressure in the spool of the main control valve is blocked.

Fault analysis: According to the customer's reflection that the machine has never changed the hydraulic oil for 8000 hours, and the oil is too dirty to the spool of the bucket rod main control valve

The hole is blocked, the oil flow is not smooth, the PLS pressure drops, and the pump flow decreases (refer to the LS valve).

Troubleshooting: Take out the spool of the main control valve of the bucket rod and clean it, replace the hydraulic oil and hydraulic oil filter, and clean all the oil pipes and oil tanks.

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