SBS120 Hydraulic Pump for E320C E320D E323D E321D Excavators
The SBS120 hydraulic pump is a main hydraulic piston pump specifically designed for E320C, E320D, E323D, and E321D excavators. Compatible with part numbers 272-6955, 173-3381, 200-3366, and 244-8483.
Common Failure Modes
1. Internal Wear & Excessive Internal Leakage
Symptoms: Weak digging force and slow machine movements; performance degrades significantly after warming up. High hydraulic oil temperature, hot pump housing, and excessive case drain flow. Metal debris (copper/iron particles) found in filter elements.
Cause: Scuffing and wear of pistons, slippers, valve plate, cylinder block, and failed seals.
2. Regulator (Boost Unit) Failure
Symptoms: Engine lugging and speed drop under load. Erratic movement speeds and power mismatch. Improper flow adjustment causing engine lugging or slow movements.
Cause: Stuck proportional solenoid valve, jammed spool, and worn ball joint.
3. Cavitation / Air Ingestion
Symptoms: Continuous high-pitched whining noise from pump compartment.
Cause: Air suction through aged pipelines, clogged suction strainer, or low oil level. Bubble impact causes pitting corrosion on valve plate.
4. Seal Leakage
Symptoms: Oil leakage at front pump shaft end and seepage at housing O-rings. Severe case pressure rise may blow out seals.
5. Pilot Pump Wear
Symptoms: Low pilot pressure, stiff joystick, and slow response. Main pump pressure and flow remain normal but insufficient driving force for main control valve.
6. Bearing Damage & Mechanical Noise
Symptoms: Metallic knocking or grinding noise inside pump. Increased bearing clearance. Severe cases may cause rotor-stator rubbing and pump destruction.
7. Swash Plate Wear & Scoring
Symptoms: Unstable flow, pressure fluctuation, and jittery movements under load.
Cause: Wear and scoring on swash plate and thrust plate.
Procurement Recommendations
- Require factory hydraulic bench testing for all new or remanufactured pumps, including test reports with dual-pump pressure, flow rate, and case drain internal leakage data
- Prioritize quality verification of the regulator (boost unit), which is the highest failure component in 320D models
- For remanufactured pumps, confirm complete replacement of pistons, valve plate, and slippers - refuse products with only simple polishing and repairs
- Inspect port seals and shaft seals before delivery, and ensure proper protection during transportation to prevent contamination
- Clean hydraulic tank and pipelines before installation, and replace all hydraulic filter elements to prevent contaminant-induced damage to new pumps
Komatsu Hydraulic Pump Assembly Technical Diagram
Hydraulic Pump Assembly Component Details and Specifications
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