Noise control of hydraulic station

Hydraulic system has the advantages of large power to weight ratio, easy to achieve various transmission movements, good load characteristics, good rapidity, automatic lubrication, long component life, easy to realize automation, etc., and has been widely used in industrial production. However, the hydraulic system is easy to produce noise pollution, which has been paid more and more attention.

In recent years, with the development of hydraulic technology to the direction of high speed, high pressure and high power, the noise of hydraulic system has become increasingly serious, and has become an important factor hindering the further play of the function of hydraulic system.

As an important part of hydraulic system, hydraulic station is the main source of hydraulic system noise. This paper focuses on the analysis of the causes of hydraulic station noise, and puts forward specific control methods to reduce the noise of hydraulic station from the point of view of hydraulic station design.

1
Composition and work

Common hydraulic station is composed of motor, hydraulic pump, oil filter, check valve, relief valve, accumulator, radiator, electromagnetic water valve, stop valve and pressure, flow, temperature and other indicating devices, typical hydraulic station composition as shown in the following figure.

When the hydraulic station starts, the motor drives the hydraulic pump to work, and the hydraulic pump outputs the high-pressure oil through the one-way valve, oil filter and stop valve. The accumulator is used to absorb the pressure pulsation at the pump outlet, and the relief valve is used to limit the outlet pressure of the hydraulic pump. Oil return through the stop valve, check valve, radiator flow back to the tank.

2
The cause of noise

The motor and hydraulic pump of the hydraulic station are the main sound components, which are themselves a noise source, and some other components such as oil filters, relief valves, fuel tanks and pipelines, etc., do not sound themselves, not independent noise sources, but the mechanical noise and liquid noise generated by the hydraulic pump will stimulate them to produce vibration, thereby producing and radiating a lot of noise.
In the hydraulic system transmission system, the degree of noise generated or transmitted by each component or component is different, and its ranking is shown in the following table.

2.1 Motor noise

The main sources of motor noise are mechanical noise, ventilation noise and electromagnetic noise. Mechanical noise is mainly caused by noise caused by rotor imbalance, high frequency noise caused by defective bearings and improper installation, and noise caused by resonance between the motor bracket and the motor.

2.2 Noise of hydraulic pump

The hydraulic pump is the main noise source in the hydraulic station, and the fluid noise of the hydraulic pump is mainly caused by the periodic change of the pressure and flow rate of the hydraulic pump and the cavitation phenomenon.

In the oil suction and oil injection cycle of the hydraulic pump, the periodic pressure and flow change is generated, and the pressure pulse is formed, which causes the hydraulic vibration to make noise.

In general, the noise of hydraulic pumps increases with the increase of power. The hydraulic power is determined by the output pressure of the hydraulic pump, the displacement, and the speed of these three parameters, they have different degrees of influence on the pump noise, the speed noise has the greatest impact, and the impact of the hydraulic pump displacement on the noise is affected by the pressure change.

In order to obtain the lowest noise level, the lowest practical speed (such as 1 000 to 1 200 r/min) and pressure combination are generally used to provide the desired power. Changes in the power grid voltage will also cause periodic changes in the pressure and flow of the hydraulic pump, resulting in noise.

Therefore, in the process of designing the pumping station, the power grid capacity should be required to be large enough, or the use of voltage regulator electronic equipment.

2.3 Uneven installation noise of hydraulic pump and motor

Hydraulic pump and motor for high-speed rotary body, its rotating part can not be absolutely balanced, hydraulic pump and motor high-speed rotation will produce periodic unbalanced force, this imbalance force caused by bearing bending vibration and noise, when the hydraulic pump or motor fixed unstable or coupling installation of different hearts will cause greater vibration noise.

2.4 Noise of all types of valves

The pressure and flow pulsation of a hydraulic station are determined by its own structure. Pressure pulsation is a kind of exciting force, and all kinds of valves in the hydraulic station will vibrate under the action of this exciting force and produce noise.

In addition, the oil filter is not clean on the high-pressure oil throttling effect and produce fluid noise, the check valve is not reasonable, and the valve in the liquid flow to the check valve is easy to produce vibration and cause noise. The reversing valve suddenly reverses, and the flow rate of hydraulic oil suddenly changes, causing pressure shock, resulting in vibration and noise.

2.5 Noise caused by pipelines

The pipeline itself is not a vibration source, but if the selection and installation of the pipe is unreasonable, under the pressure pulsation of the hydraulic oil, resonance will occur, and the noise emitted at the same time is very large, and such noise must be suppressed and eliminated.
The commonly used method is to set an accumulator or use a high-pressure hose to absorb the pressure pulsation of the hydraulic pump and prevent the transmission of mechanical vibration, which is a simple, easy and effective method.
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3
Noise control measures of hydraulic station

It can be seen from the mechanism of the noise generation of the hydraulic station that although the noise can not be completely eliminated, the hydraulic noise can be greatly reduced by selecting the appropriate Hydraulic Components and the appropriate design scheme during the design.

3.1 Selection of low noise hydraulic components

When selecting Hydraulic Accessories, accessories with low flow resistance, reliable operation and low noise should be selected, such as low-noise cycloidal internal gear pump; Low noise relief valve with damping piston pilot valve structure; Oil immersed solenoid valve, etc.

3.2 Reasonable design of hydraulic station

Whether the design and layout of hydraulic station are reasonable directly affects the size of mechanical noise.

Hydraulic pump and motor connection parts processing, installation accuracy should be strictly required, hydraulic pump and motor connection can use flexible coupling to reduce coupling noise, installation to ensure that fixed; If the space size allows, the hydraulic pump and the motor can be installed on the same foundation and placed separately from the oil tank to isolate the impact of pump vibration on the oil tank.

If the pump is placed on the cover plate of the tank, vibration isolation measures should be taken under the pump base, such as adding a rubber vibration pad to cut off the transmission channel of mechanical noise and prevent the vibration of the tank. The noise generated by the hydraulic pump can be controlled by means of parallel hydraulic pump and unloading loop. In the design of the Fuel Tank, the structural stiffness should be increased if permitted, such as the design reinforcement, so that it is not easy to be excited by other exciting forces; When designing the shape of the tank, the surface area of the tank should be reduced to reduce the radiation noise under the premise of ensuring the heat dissipation requirement.

When designing and installing pipelines, the length of pipelines should be considered to avoid external excitation frequency and resonance point. When the pipe is connected, the oil inlet and outlet of the pump are connected respectively with a hose to cut off the mechanical vibration of the hydraulic pump. In addition, the installation of H-type hydraulic filter on the hydraulic pump outlet pipe can reduce the noise caused by hydraulic vibration.

3.3 Prevent fluid noise

The air mixed into the liquid will produce cavitation phenomenon when the local low pressure or negative pressure occurs in the system. When the cavitation collapses in the high pressure area, the local pressure step will jump higher and accompanied by strong noise.

To prevent cavitation noise, first, to prevent air from entering the system, and second, to eliminate the air that has been mixed into the system.

3.4 Prevent pressure pulsation noise

The periodic flow pulsation of hydraulic pump is the main pressure pulsation source of the system. Due to the pressure fluctuation, the components and pipes in the system will be subjected to periodic vibration, thus stimulating noise. Especially when the pulsation frequency is close to or coincides with the natural frequency of the pipe system, the system resonance will be excited and the noise will be increased.

Therefore, when designing the hydraulic station, the accumulator and buffer bottle instrument are installed at the pump outlet to reduce the pressure pulsation of the system. When designing the pipeline, the pipe length should be avoided as far as possible from the pipe length where resonance occurs. A certain number of pipe clamps are generally configured in the pipeline to improve the connection stiffness of the pipeline. At the same time, the natural frequency of the pipe itself is adjusted by changing the fixed or supporting parts of the pipe clamp to avoid resonance.

In addition, by adding a partial throttle unloading circuit, the pressure pulsation in the working oil circuit can be reduced, thus reducing the noise.

3.5 Use sound absorption and insulation technology to limit noise propagation

To limit noise transmission is to use technical measures such as sound insulation and sound absorption to limit the transmission of noise. The hydraulic pump or oil tank, or the whole hydraulic station can be covered with a sound insulation cover to control the noise in the sound insulation cover and limit the spread of noise.