Hydraulic system noise and its elimination methods

In mechanical processing, the noise and vibration of the hydraulic system directly affect the accuracy of the workpiece.

Noise is a vibration wave from a certain sound source. There are many reasons for noise in the hydraulic system, such as noise caused by voltage fluctuations, noise from mechanical systems, noise caused by load and flow changes, noise caused by cavitation caused by air entering, noise caused by trapped oil and fluid vortex, etc.

1. hydraulic pump is a major noise source

Changes in grid voltage, load changes, pressure fluctuations and flow pulsations can all cause noise and vibration in the hydraulic pump. Grid voltage fluctuations will cause flow pulsation in the hydraulic pump, causing pressure fluctuations at the pump outlet and pipeline. This is fluid noise caused by flow and pressure fluctuations caused by external factors.

Due to pressure shocks in the trapped oil area, Hydraulic Pumps can also generate fluid noise. For example, when the cylinder of a swash plate type directional piston pump is at the top dead center during rotation, the liquid pressure in the piston cavity suddenly rises to the discharge pressure at the moment it is connected to the discharge cavity, generating a large pressure shock. Similarly, when it is at the bottom dead center, pressure shocks are also generated, which are the main noise sources of the hydraulic pump.

To minimize the noise of the hydraulic pump, the grid capacity should be large enough; when selecting a hydraulic pump, try to choose a hydraulic pump with a low speed while ensuring the required power and flow rate; you can also use a compound pump, increase the sensitivity of the overflow valve, and add a load-unloading path to reduce noise.

2. The control valve is another noise source

The cavitation effect of the control valve produces fluid noise. This is because the oil flow through the valve body produces a ☆ flow effect, which produces a very high flow rate at the throttle port. The pressure also changes with the flow rate. When the pressure is lower than the atmospheric pressure, the air dissolved in the oil is separated and a large number of bubbles are generated. The noise frequency at this time will be very high.

In addition, in the jet state, the oil flow velocity is uneven and eddy currents occur, or noise is also generated due to the oil flow being cut off. The solution to this type of noise is to increase the back pressure on the downstream side of the throttle port to make it higher than the boundary value of the air separation pressure. The multi-stage pressure reduction method can be used to prevent the occurrence of cavitation. Generally, when the oil flows through the throttle port of the control valve, the ratio of the upstream pressure to the downstream pressure should be 3 to 6.

The pressure fluctuation of the hydraulic pump causes the valve parts to resonate, thus increasing the noise. In the control valve, especially the throttle valve, the throttle opening is small and the flow rate is high, which is easy to generate vortex. Sometimes the valve core hits the valve seat and vibrates greatly. When this phenomenon occurs, a small-sized control valve can be replaced, or the throttle opening can be opened wider.

When the directional control valve is closed or opened, vibration and noise will be caused by hydraulic shock. For example, when the electromagnetic reversing valve is switched quickly. The hydraulic shock will cause the pressure in the pipe to fluctuate violently and spread along the pipeline. When it is transmitted to the hydraulic pump and the oil cylinder, it will cause vibration and noise in these links. To reduce this vibration and noise, the reasonable setting of valves and pipelines should be used to minimize hydraulic shock.

3. Hydraulic pump suction phenomenon generates noise

The hydraulic pump suction phenomenon refers to the oil pump directly sucking in air or the air mixed in the sucked oil. This phenomenon not only affects the oil quality and increases noise, but also affects the volumetric efficiency of the hydraulic pump, which is not allowed to occur in the hydraulic system. The main reason for this phenomenon is that the oil tank and the oil suction pipe are set unreasonably. In order to prevent this phenomenon, the following measures should be adopted:

① The oil tank should be reasonably designed and have a large enough volume. A long oil tank with a partition can be used, which can be divided into a return tank and an oil suction tank;

② The oil in the oil tank should be added to the specified height, and the oil suction pipe must be 3/5 deep in the oil pool;

③ The hydraulic oil specifications should meet the requirements of the instructions. All joints should be strictly sealed to prevent the pump from sucking air into the pump for a short time. All relevant settings should be cleaned regularly to prevent blockage.

4. Noise generated by vibration of mechanical parts in the hydraulic system

Due to errors in design, manufacturing, installation, etc., the relevant parts of the hydraulic system will vibrate and output noise when working. Attenuators and isolation methods can be used to eliminate or reduce this noise.

① Attenuators are used to prevent noise from spreading, and attenuators are of two types: absorption type and reflection type;

② Reasonable layout of pipelines and setting accumulators in pipelines can attenuate periodic vibrations in the system;

③ Connecting filters in series in the pipeline can eliminate noise caused by pressure fluctuations in the system.