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1. When control valve is at HOLD

Function

• When the control valve is at HOLD, pump dis-charge amount Q disdis-charged by the minimum swash plate angle is released to the tank circuit.

At this time, pump discharge pressure PP1/PP2 is set at 2.45 MPa {25.0 kg/cm²} by spring (2) in the valve. (LS pressure PLS1/PLS2: 0 MPa {0 kg/cm²})

• Since the pump merge-divider valve is at the merge position, pump discharge pressures PP1 and PP2 are merged. LS pressures PLS1, PLS2, and PLS3 are also merged.

Operation

• Pump discharge pressures PP1 and PP2 are

• When the control valve is at HOLD, LS pres-sures PLS1 and PLS2 are not generated, so only pump discharge pressures PP1 and PP2 act, and PP1 and PP2 are set by only the load of spring (2).

• As pump discharge pressure PP1/PP2 rises and reaches the load of spring (2) (2.45 MPa {25.0 kg/cm²}), spool (1) is moved to the right. Pump discharge pressures PP1 and PP2 are con-nected to tank circuit T through the cut of spool (1)

• As a result, pump discharge pressure PP1/PP2 is set to 2.45 MPa {25.0 kg/cm²}.

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2. During fine control of work equipment valve Work equipment valve: Boom, arm, bucket, boom swing, or attachment.

Function

• During fine control of the work equipment valve, when the demand flow for the actuator is within the amount discharged by the minimum swash plate angle of the pump, pump discharge pres-sure PP1/PP2 is set to LS prespres-sure PLS1/PLS2 + 2.45 MPa {25.0 kg/cm²}. When the difference between pump discharge pressure PP1/PP2 and LS pressure PLS1/PLS2 reaches the load of spring (2) (2.45 MPa {25.0 kg/cm²}), unload spool (1) opens, so LS differential pressure EPLS becomes 2.45 MPa {25 kg/cm²}.

• Since the pump merge-divider valve is at the merge position, pump discharge pressures PP1 and PP2 are merged. LS pressures PLS1, PLS2, and PLS3 are also merged.

Operation

• When fine control is carried out on the work equipment valve, LS pressures PLS1 and PLS2 are generated and act on the right end of spool (1) (PP1 = PP2, PLS1 = PLS2). When this hap-pens, the area of the opening of the work equip-ment valve spool is small, so LS pressures PLS1 and PLS2 are very different from pump dis-charge pressures PP1 and PP2.

• When the difference between pump discharge pressure PP1/PP2 and LS pressure PLS1/PLS2 reaches the load of spring (2) (2.45 MPa {25.0 kg/cm²}), spool (1) moves to the right, and pump discharge pressures PP1 and PP2 are con-nected to tank circuit T.

• In other words, pump discharge pressure PP1/

PP2 is set to the spring force (2.45 MPa {25.0 kg/cm²}) + LS pressure PLS1/PLS2, and LS dif-ferential pressure DPLS becomes 2.45 MPa {25.0 kg/cm²}.

CLSS

3. When work equipment valve is operated Work equipment valve: Boom, arm, bucket, boom swing, or attachment

Function

• When any work equipment valve is operated if the demand flow for the actuator becomes greater than the pump discharge from the mini-mum swash plate angle, the oil flow to tank cir-cuit T is cut off, and all pump discharge amount Q flows to the actuator circuit.

• Since the pump merge-divider valve is at the merge position, pump discharge pressures PP1 and PP2 are merged. LS pressures PLS1, PLS2, and PLS3 are also merged.

Operation

• When any work equipment valve is operated for a long stroke, LS pressures PLS1 and PLS2 are generated and act on the right end of unload spool (1) (PP1 = PP2, PLS1 = PLS2). When this happens, the area of the opening of the work equipment valve spool is large, so LS pressures PLS1 and PLS2 are not so different from pump discharge pressures PP1 and PP2.

• For this reason, the difference between pump discharge pressure PP1/PP2 and LS pressure PLS1/PLS2 does not reach the load of spring (2) (2.45 MPa {25.0 kg/cm²}), so spool (1) is pushed to the left by spring (2).

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4. During fine control of both travel valves

Function

• During fine control of both travel valves, when the demand flow is below the maximum pump discharge amount, pump discharge pressure PP1/PP2 is set to LS pressure PLS1/PLS2 + 2.45 MPa {25.0 kg/cm²}.

• When the difference between pump discharge pressure PP1/PP2 and LS pressure PLS1/PLS2 reaches the load of spring (2) (2.45 MPa {25.0 kg/cm²}), unload spool (1) opens, so excessive oil (maximum pump discharge mount - demand flow) flows into the tank circuit.

• Since the pump merge-divider valve is at the separate position, pump discharge pressures PP1 and PP2 are separated. LS pressures PLS1 and PLS2 are also separated.

• The swash plate angle of the pump becomes maximum, so the pump discharge amount becomes maximum. (For details, see the sec-tions on the pump merge-divider valve and logic valve.)

Operation

• When fine control is carried out on both travel valves, LS pressures PLS1 and PLS2 are gener-ated and act on the right end of spool (1) (PP1, PP2, PLS1, and PLS2 are separated).

• When this happens, the area of the opening of both travel valve spools is small, so LS pres-sures PLS1 and PLS2 are very different from pump discharge pressures PP1 and PP2.

• When the difference between pump discharge pressure PP1/PP2 and LS pressure PLS1/PLS2 reaches the load of spring (2) (2.45 MPa {25.0 kg/cm²}), spool (1) moves to the right, and pump discharge pressures PP1 and PP2 are con-nected to tank circuit T and the excessive oil (maximum pump discharge mount – demand flow) flows.

• In other words, the excessive oil (maximum pump discharge mount – demand flow) above the strokes of both travel valves flows into tank circuit T.

CLSS

5. When both travel valves are operated

Function

• During operation of both travel valves, when the demand flow becomes maximum, the oil flow to tank circuit T is cut off, and all pump discharge amount Q flows to both travel circuits.

• Since the pump merge-divider valve is at the separate position, pump discharge pressures PP1 and PP2 are separated. LS pressures PLS1 and PLS2 are also separated.

• The swash plate angle of the pump becomes maximum, so the pump discharge amount becomes maximum. (For details, see the sec-tions on the pump merge-divider valve and logic valve.)

Operation

• When both travel valves are operated to the stroke ends, LS pressures PLS1 and PLS2 are generated and act on the right end of unload spool (1) (PP1, PP2, PLS1, and PLS2 are sepa-rated).

• When this happens, the area of the openings of both travel valve spools is large, so LS pressures PLS1 and PLS2 are not so different from pump discharge pressures PP1 and PP2.

• For this reason, the difference between pump discharge pressure PP1/PP2 and LS pressure PLS1/PLS2 does not reach the load of spring (2) (2.45 MPa {25.0 kg/cm²}), so spool (1) is pushed to the left by spring (2).

• As a result, pump discharge pressures PP1 and

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6. When either travel valve is operated

Function

• The demand flow decided by the valve stroke is sent to the travel circuit on the operated travel valve side and the all pump discharge amount is sent to the tank circuit on the non-operated travel valve side.

• Since the pump merge-divider valve is at the separate position, pump discharge pressures PP1 and PP2 are separated. LS pressures PLS1 and PLS2 are also separated.

• The swash plate angle of the pump becomes maximum, so the pump discharge amount becomes maximum. (For details, see the sec-tions on the pump merge-divider valve and logic valve.)

Operation

When left travel valve is operated to stroke end and right one is at HOLD.

• When the left travel valve is operated to the stroke end, LS pressure PLS1 is generated and acts on the right end of unload spool (1).

• When this happens, the area of the openings of both travel valve spools is large, so LS pressures PLS1 is not so different from pump discharge pressures PP1.

• For this reason, the difference between pump discharge pressure PP1 and LS pressure PLS1 does not reach the load of spring (2) (2.45 MPa {25.0 kg/cm²}), so spool (1) is pushed to the left by spring (2).

• As a result, pump discharge pressures PP1 and tank circuit T are shut off, and all pump dis-charge amount QP1 on the P1 side flows to the left travel circuit.

• Since the right travel valve is at HOLD, LS pres-sure PLS2 is not generated, so only pump dis-charge pressure PP2 acts.

• When pump discharge pressure PP2 reaches the load of spring (4) (2.45 MPa {25.0 kg cm²}), spool (3) moves to the right, and all pump dis-charge amount QP2 on the P2 side flows into tank circuit T.

CLSS