Vibrations in Variable Displacement Pump Systems

Category: Troubleshooting and causes of errors

Did you know that the suction line can be a source of vibration in hydraulic systems?

If the oil column in the suction hose of a hydraulic variable displacement pump is constantly accelerating and decelerating — meaning it flows in a pulsating or oscillating manner — this can cause a number of serious issues. The variable displacement pump can suffer damage in several ways:

1. Cavitation

Cause: Acceleration and deceleration can cause a vacuum in the suction hose that falls below the vapor pressure of the oil.
Effect: Vapor bubbles (cavitation) form, which then collapse, producing locally very high pressures and temperatures.
Damage: Erosion damage on vanes, pistons, control edges, and inside the pump (pitting, material loss).

2. Increased Load on Bearings and Seals

Cause: Uneven flow creates pressure spikes and vibrations that affect the housing and internal moving parts.
Effect: Higher radial and axial forces on bearings and seals.
Damage: Bearing failure, leakage, premature wear of seals.

3. Inadequate Lubrication

Cause: Irregular suction can cause the pump to occasionally draw in air or result in highly fluctuating flow rates.
Effect: The pump’s internal lubrication (hydrodynamic via the oil) is disrupted.
Damage: Increased metal contact, higher wear, potential scoring.

4. Vibration-Induced Material Wear or Fatigue

Cause: Mechanical vibrations (e.g. from resonance effects in the oil column) can be transferred to the pump housing or attachments.
Effect: Continuous loading over many cycles.
Damage: Microcracks, fatigue fractures in housings, brackets, or connections.

5. Reduced Service Life Due to Dynamic Loads

Cause: Constant pressure and flow fluctuations act like load cycles.
Effect: Higher fatigue stress on moving components.
Damage: Premature failure due to material fatigue.

Remedies / Measures:

Optimize suction line: As short as possible, large diameter, and avoid tight bends.
Use suction dampers or pulsation dampers
Ensure positive inlet pressure: e.g. via charge pump or elevated tank.
Conduct vibration analysis: Check and adapt resonance behavior of the suction line.
Optimize control/regulation to enable smoother load transitions.