Potencias y rendimientos

1. Unload valve 6. Check valve

2. Safety valve 7. Cooler bypass valve

(set pressure: 23.5 MPa {240 kg/cm²}) (cracking pressure: 0.5 MPa {5 kg/cm²}) 3. Pressure compensation valve 8. Lift spool

4. Suction valve 9. Tilt spool

5. Main relief valve 10. Angle spool

(set pressure: 20.6 MPa {210 kg/cm²}) 11. Ripper spool

STRUCTURE AND FUNCTION, MAINTENANCE STANDARD CLSS

2. Unload valve

• In the case of a fixed pump system, the unload valve has functions including those of variable pump and LS valve.

(1) When control valve is at HOLD

Function

• When the control valve is at HOLD, pump dis-charge amount Q is all relieved to the tank cir-cuit. This reduces the pressure loss from the pump to the tank.

Operation

• At the left end of spool (1), pump pressure PP2 (CPP1) is acting on area S1, and at the right end of spool (1), pump pressure PP3 and the force of spring (2) are acting on area S2. In addition, LS pressure PLS is acting on area S3.

• When the control valve is at HOLD, LS pressure PLS is not generated. Piston (3) is set at the left position by spring (4), pressure PP3 is con-nected to TS, and becomes much lower than pump pressure PP1.

• Therefore, pump pressure PP2 (CPP1) is set only by the force of spring (2) to a maximum of 0.53 MPa {5.4 kg/cm²}.

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(2) Control valve operated Function

• When the control valve is operated, an amount of oil corresponding to the opening of the spool flows to the actuator.

• When the control valve is operated, pump dis-charge pressure PP1 is set to LS pressure PLS + 1.5 MPa {15 kg/cm²}.

Operation

• The operation is the same regardless of whether the control valve is being fully operated or used for fine control.

• When more than one actuator is used that the same time, and the condition becomes pump discharge < actuator demand, spool (1) moves further to the left to the end of the stroke.

• As a result, pump circuits PP1 and PP2 and tank circuit T are shut off, and all the pump discharge amount flows to the actuators.

• When the control valve is operated fully, LS pressure PLS is generated and acts on area S1 at the left end of piston (3) and area S3 at the right end of spool (1).

• When LS pressure PLS reaches 0.07 MPa {0.7 kg/cm²}, piston (3) overcomes the force of spring (4) and moves fully to the right.

• As a result, the connection between the spring chamber of spring (2) and port TS is cut off and the condition becomes PP1 = PP2.

• Spool (1) moves to the left so that the difference in pressure between pump pressure PP1 and LS pressure PLS becomes 1.5 MPa {15 kg/

cm²}.

• In addition, when the control valve is at neutral, the oil being drained to the circuit T all flows to the actuators.

STRUCTURE AND FUNCTION, MAINTENANCE STANDARD CLSS

3. Work equipment operated (1) When lift is operated to LOWER

• When the lift is operated to LOWER, spool (1) moves to the right from the HOLD position, and the oil from the pump enters bridge circuit C, passes through cylinder port B, and enters the cylinder bottom.

• When this happens, the oil at the cylinder head passes through cylinder port A and is drained.

(2) When lift is operated to FLOAT

• When the lift is operated to FLOAT, spool (1) moves further to the right. The oil from the

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4. LS bypass plug

Function

• It releases the residual pressure of LS pressure PLS.

• It makes the speed of the rise in pressure of LS pressure PLS more gentle. In addition, with this discarded throttled flow, it creates a pressure loss in the throttled flow of the spool or shuttle valve, and increases the stability by lowering the effective LS differential pressure.

Operation

• The pressurized oil for LS circuit PLS passes from clearance filter a (formed by the clearance between LS bypass plug (1) and the valve body) through orifice b and flows to seal drain circuit TS.

PP : Pump circuit PLS : LS circuit TS : Seal drain circuit A : To each valve

STRUCTURE AND FUNCTION, MAINTENANCE STANDARD CLSS

5. Introduction of LS pressure For lift, tilt, angle, ripper valve

Function

• The LS pressure is the actuator load pressure at the outlet port end of the control valve.

• It actually reduces pump pressure PP at pres-sure reducing valve (3) of the prespres-sure compen-sation valve to the same pressure as actuation circuit pressure A, and sends it to the LS circuit PLS.

Operation

• When spool (1) is operated, pump discharge pressure PP flows from flow control valve (2) and notch a in spool (1) through bridge passage b to actuator circuit A.

• At the same time, pressure reducing valve (3) also moves to the right, so pump pressure PP has its pressure reduced by the pressure loss at notch C. It is introduced to LS circuit PLS, and

• Actuator circuit pressure PA (=A) acts on the left end of pressure reducing valve (3); the reduced pump discharge pressure PP acts on the other end.

• As a result, pressure reducing valve (3) is bal-anced at a position where actuator circuit pres-sure PA and the prespres-sure of spring chamber PLS1 are the same. Pump discharge pressure PP is reduced at notch C, becomes actuator cir-cuit pressure A, and is taken to LS circir-cuit PLS.

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6. Pressure compensation valve

Function

• During compound operations, if the load pres-sure becomes lower than the other actuator and the oil flow tries to increase, compensation is received. (When this happens, the other actua-tor being used for compound operation (right side) is at a higher load than the actuator on this side (left side).)

Operation

• If the load pressure of the other actuator (right side) becomes higher during compound opera-tions, the oil flow in actuator circuit A on this side (left side) tries to increase.

• If this happens, the LS pressure PLS of the other actuator acts on spring chamber PLS1, and pressure reducing valve (1) and flow control valve (2) are pushed to the left.

• Flow control valve (2) throttles the area of open-i ng betwe en pump c open-ir cuopen-i t P P and s pool upstream PPA, and pressure loss is generated between PP and PPA.

• Flow control valve (2) and pressure reducing valve (1) are balanced in position where the dif-ference in pressure between PLS and PA acting on both ends of pressure reducing valve (2) and the pressure loss between PP and PPA on both sides of flow control valve (2) are the same.

• In this way, the pressure difference between upstream pressure PPA and downstream pres-sure PA of both spools used during compound operations is the same, so the pump flow is divided in proportion to the area of opening of notch a of each spool.