What causes insufficient pressure in an excavator's hydraulic pump?

I. Internal Faults of the Hydraulic Pump Unit (Root Causes)

1. Internal Wear and Leakage in Moving Parts
Axial piston pumps are the standard configuration for excavator main pumps. Common wear points include: excessive clearance between pistons and cylinder bores; wear or scoring on the valve plate and cylinder face; and wear on the contact surfaces between slippers and the swashplate. Such wear leads to cross-flow between high- and low-pressure chambers and a significant drop in volumetric efficiency, manifesting as an inability to build pressure, rapid oil temperature rise, and the presence of metal debris in the oil. In severe cases, the breakage of the return plate or detachment of slippers results in a total loss of displacement.

2. Failure of the Variable Displacement Mechanism
Sticking of the servo piston or blockage in control oil passages/damping orifices causes the swashplate to remain at a shallow angle, resulting in insufficient displacement; symptoms include normal low-pressure readings but a rapid drop in pressure under load. Additionally, spring fatigue or setting drift in the pressure cut-off valve or power regulator can cause the pump to enter an unloading state prematurely, limiting the system's maximum pressure.

3. Structural and Seal Damage
Damage to the pump shaft oil seal (leading to air intake), sand holes or cracks in the pump housing, and wear or slipping of the input splines all cause power or pressure loss, ultimately resulting in insufficient output pressure.

II. Hydraulic Oil and Suction-Side Faults (Most Frequent Triggers)

1. Poor Suction and Cavitation: Low reservoir oil levels, clogged suction filters, or air leaks at suction pipe fittings cause the pump to ingest air, leading to cavitation. This results in significant fluctuations in output flow and pressure, accompanied by abnormal noise; in severe cases, pressure cannot be built at all.

2. Oil Deterioration: Using the wrong grade of hydraulic oil, oil with excessively low viscosity, or high oil temperatures caused by cooling system failures reduces the oil's sealing capability, exacerbates internal leakage, and hinders pressure buildup.

3. Oil Contamination: Impurities not only accelerate internal pump wear but also clog damping orifices in valve assemblies, indirectly causing pressure regulation failures.

Quick Troubleshooting Strategy

1.First, connect a pressure gauge directly to the main pump outlet and briefly block the discharge line to conduct a test: if the pressure reaches the rated value, the pump itself is functioning correctly, and the fault lies in the downstream valve assembly, piping, or actuators; if the pressure remains below the rated value, then inspect the pump body and the suction side.

2.Follow the principle of proceeding "from the easiest to the most difficult": first check easily accessible items such as the oil level, filter element, oil temperature, and main relief valve, before disassembling the pump to inspect for internal wear, thereby avoiding unnecessary or blind disassembly.

Tip: Contact Belparts for solutions to insufficient hydraulic pump pressure in excavators.