air borne

How to Reduce Noise Emission

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How to reduce noise emission from hydraulic machines

It is to be noted that in many industrialized nations, there are rules and regulations that restrict noise levels in the factories and workplace. The regular activities in the industrial areas using hydraulic machines and the resulting high noise emission of hydraulic components means that it is warning the machine operator to do something to reduce the noise of the machine in the working area. To do that you should know, “what exactly is the cause of the noise?”

Three Main Causes

Fluid Borne Noise

Structure Borne Noise

Air Borne Noise

The dominant cause of noise in hydraulic systems is the pump. The hydraulic pump produces fluid-borne noise and structure-borne noise into the system and radiates air-borne noise. All hydraulic pumps have a fixed number of pumping chambers, which operate in a continuous cycle like as opening closing of fluid inflow. The continuous process leads to a corresponding sequence of pressure pulsations, which cause the fluid-borne noise. This results in the downstream components to vibrate. The structure-borne noise is produced by exciting vibration in any component. The transfer of fluid and structure induced vibration to the nearby air mass results in air-borne noise.

How to reduce fluid-borne noise?

While the main cause of fluid-borne noise is pressure pulsation, it can be reduced through hydraulic pump design, though the problem cannot be fully eliminated. In large hydraulic systems or noise-sensitive applications, the fluid-borne noise emission can be reduced by the installing a silencer. The most simple form of silencer is the reflection silencer. This is widely used in hydraulic systems and it reduces sound waves by inducing a second sound wave of the same amplitude and frequency at a 180-degree phase angle to the first.

How To reduce structure-borne noise?

The structure-borne noise is caused by the vibrating mass of the power unit (this includes the hydraulic pump and its prime mover). This can be reduced through the elimination of sound bridges between the the power unit and valves and the power unit and tank. This is normally attained by using flexible connections like rubber mounting blocks and flexible hoses. In some cases it is necessary to introduce additional mass, the force of which reduces the transmission of vibration at bridging points.

How to reduce air-borne noise?

The force of noise radiation from an object is proportional to its area. This force is inversely proportional to its mass. Hence to reduce air borne noise, you can reducing an object’s surface area or increase its mass. For example, build the hydraulic reservoir from thicker plate. The magnitude of air-borne noise created directly from the hydraulic pump can be reduced by mounting the pump inside the tank. If the noise from hydraulic system remains outside the required level even after all the above noise reduction measures have been tried, encapsulation or screening must be considered.

Hydraulic Fluid Energy Storage

Another cause of noise in hydraulic systems is due to the storage and subsequent release of energy in the hydraulic fluid. Hydraulic fluid is not perfectly rigid. When the fluid is compressed, it results in energy storage. However if this compression is not properly controlled, the stored energy dissipates instantaneously. This sudden release of energy moves the fluid very fast, and this creates noise. So while handling hydraulic system, it is necessary to control the energy storage in hydraulic fluid.

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