Generation of LS pressure

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Generation of LS pressure


1. Definition


LS pressure is a very critical parameter in CLSS (Closed Load Sensing System). In normal working, 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.


2. Generation


LS阀.jpg


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

                                                             ↓↓↓

The main pump pressure PP flows to the actuator through the main spool (2) push valve (4).

                                                             ↓↓↓

At the same time, the main pump pressure PP enters the LS generate circuit C through the orifice (a) of the main spool (2).

                                                             ↓↓↓

When the actuator circuit pressure A (that is, the load pressure) rises to the required pressure, the pump pressure PP also rises, the check valve (5) in the main spool (2) opens to the right, and the actuator circuit A and LS circuit C Connected.

                                                             ↓↓↓

Accordingly, the PLS pressure of the LS circuit C and the pressure (load pressure) of the actuator circuit A are almost equal. Therefore, the LS pressure reflects the load pressure of the actuator.

                                                             ↓↓↓

At this time, the PLS oil pressure generated by LS circuit C enters the LS circuit of the hydraulic system through the LS shuttle valve (6).

Note:

When neutral: PLS = 0

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

Overflow: PLS = main pump pressure Pp


3. Fault Diagnosis


Ls阀.png


Symptom: The joystick speed is too low.

Inspection result: Throttle orifice (a) is blocked by PLS pressure generated in the main control valve spool of the joystick.

Failure analysis: According to customer reports, the machine has never changed its hydraulic oil after 8000 hours of operation.

The small hole (a) is blocked, the oil flow is not smooth, the PLS pressure is reduced, and the pump flow is reduced (see LS valve)

Troubleshooting: take out the main control valve spool of the bucket for cleaning, replace hydraulic oil, hydraulic oil filter element, clean all oil pipes and fuel tank.