Why Does a Hydraulic System Make Noise During Operation?

A hydraulic system—also referred to as a hydraulic power unit (HPU), hydraulic station, or hydraulic pump station—typically consists of two major components: hydraulic elements (including power, actuator, control, and auxiliary components) and working fluid.

Hydraulic systems can be categorized by motor mounting orientation: vertical, horizontal, or side-mounted. Below is the basic composition of a typical hydraulic power unit.

Possible Causes of Noise in Hydraulic Systems

The two primary noise-generating components in a hydraulic station are the electric motor and the hydraulic pump. While other components don’t generate noise directly, the vibrations caused by pump operation can cause overflow valves, hydraulic hoses, and other parts to resonate, creating additional noise.

1. Motor Noise

Motor noise is mainly caused by rotor imbalance or issues with the motor bearing quality or installation. Resonance between the motor and its mounting frame can also contribute to noise.

2. Hydraulic Pump Noise

The hydraulic pump is the main source of noise in a hydraulic system. The noise it generates typically stems from two key factors:

• Cyclic fluctuations in pressure and flow

• Cavitation

During the suction and discharge cycle, the hydraulic pump’s internal structure and working principles prevent perfectly smooth flow, leading to pressure pulsations. These pulsations cause fluid vibrations, resulting in noise throughout the hydraulic circuit.

Additionally, poor suction or air ingestion can lead to cavitation—when air bubbles collapse under high pressure, they produce intense impact and loud noise, further worsening the system’s sound levels.

In general, a pump’s noise level is proportional to its power output. The power depends on pressure (P), displacement (Q), and speed (n). Among these, speed has the most significant impact on noise, followed by displacement and pressure. For noise control, it's recommended to:

• Reduce pump speed

• Optimize displacement and pressure

A typical recommended pump speed range is 1000–1200 rpm, striking a balance between performance and sound.

Unstable power supply can also lead to noise. Voltage fluctuations affect pump performance and lead to inconsistent flow/pressure, so it's essential to ensure sufficient electrical capacity or voltage regulation for noise control.

3. Installation Issues

Both motors and pumps operate at high speeds and generate imbalance forces, which can cause shaft vibration and noise—especially if the installation is not stable. Loose mounting will amplify vibration and noise significantly.

How to Reduce Noise in Hydraulic Stations

Although noise can’t be completely eliminated in a working hydraulic system, it can be significantly reduced. Here's how:

✅ Use Low-Noise Hydraulic Components

Select components with low flow resistance and designed for quiet operation, such as:

• Low-noise hydraulic pumps

• Damping piston-type valves

• Pilot valves with noise-reduction design

✅ Design a Well-Engineered Hydraulic Station

The overall layout has a major influence on both performance and sound.

• Ensure precision alignment between pump and motor; use flexible couplings to absorb vibration.

• If possible, mount pump and motor on a rigid base and separate them from the tank to minimize structure-borne noise.

• If the pump must be mounted on the tank lid, place rubber dampers under the base to reduce noise transmission.

Tank design should also focus on noise suppression:

• Use reinforcing ribs to increase rigidity

• Reduce tank surface area (while maintaining cooling capacity)

• Avoid flat, vibrating surfaces that radiate noise

For piping:

• Prevent resonance by avoiding lengths that match the system’s natural frequency

• Use high-strength hoses for inlet and outlet ports to isolate vibration

✅ Control Fluid Noise & Prevent Cavitation

Air in the hydraulic fluid can cause cavitation and bursting bubbles, leading to high-impact noise. Prevention strategies include:

• Prevent air entry: Optimize return oil path, set correct oil return pipe depth, and avoid suction loss.

• Remove air quickly: Use air bleed valves or vent structures at system high points to maintain fluid continuity.

✅ Minimize Pressure Pulsations & Resonance

Cyclic flow output from pumps causes pressure ripple, which can lead to resonance when matching pipe lengths align with natural frequencies.

To mitigate:

• Install accumulators or dampeners at the pump outlet

• Use proper pipe clamps to enhance stiffness

• Adjust support point locations to avoid resonance lengths

• Optimize piping layout to avoid excessive length or sharp changes