PC56 main valve

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Product details

Komatsu PC56 Excavator Main Relief Valve Specification

Basic Information

Applicable Model: Komatsu PC56-7

Other Names: Main Safety Valve, Two-stage System Relief Valve

Mounting Position: Installed on both ends of main control valve, one piece for front pump and one for rear pump separately.

Core Functions

1. Limit maximum system pressure to protect main hydraulic pump, cylinders and high-pressure hoses from overpressure damage.

Factory standard setting: Primary pressure 32.5 MPa, boost secondary pressure 35.5 MPa.

2. Two-stage pressure shift with power boost function:

Light-load condition (pilot off): 32.5 MPa for energy saving;

Heavy-load digging (pilot on): 35.5 MPa to boost digging force by around 10%.

3. Stabilize system pressure and prevent engine lugging and hose burst under overload.

Structure & Operating Principle

- Construction: Direct-acting poppet type, composed of poppet, compression spring, adjusting screw, O-ring and fixed orifice.

- Normal status: Pressure below set value, poppet kept closed by spring force, full hydraulic oil flows to actuators.

- Overpressure status: Hydraulic force lifts poppet, surplus oil drains back to tank to cap system pressure.

- Two-stage logic: Pilot oil feeds into spring chamber to compress spring and raise relief setting for high-power digging.

Key Technical Data

- Primary set pressure: 32.5 MPa

- Boost secondary set pressure: 35.5 MPa

- Cracking pressure: approx. 31.5 MPa

- Mount thread: M14×1.5

- Material: Hardened steel poppet, carbon steel valve body, alloy steel spring

Common Defects & Performance Issues

1. Low pressure below 30 MPa: Weak overall power, slow working speed, poor compound movement performance.

2. Overpressure over 37 MPa: Engine lugging, pipeline vibration, abnormal noise and hose burst risk.

3. Stuck poppet or clogged orifice: Unstable pressure, excessive oil temperature, irregular operation speed.

4. Internal leakage or worn seals: Fast idle pressure drop and cylinder drifting.

5. Failed boost function: Insufficient digging power under heavy load.

Pressure Adjustment

- Clockwise rotation = increase pressure; Counter-clockwise rotation = decrease pressure.

- Standard setting: Primary 32.5 MPa, secondary boost 35.5 MPa.

- Recommended lock nut torque: 20~25 N·m.

Glossary

Main Relief Valve

Main Safety Valve

Two-stage Relief Valve

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