Hydraulic System Noise Source and Elimination Method

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

Hydraulic System

Noise is a vibration wave from a certain sound source.

There are many reasons for causing noise in hydraulic systems.

Such as the noise caused by voltage fluctuations, by mechanical systems, by the changes in load and flow, by air entry to generate cavitation, by trapped oil and fluids, etc.

Hydraulic pump is a major noise source

Hydraulic pump

Changes in power grid voltage, changes in load, pressure fluctuations, and flow pulsations all can cause noise and vibration in hydraulic pumps.

The grid voltage fluctuation will cause the flow pulsation of the hydraulic pump, causing the pump outlet and pipeline pressure to fluctuate.

This is the fluid noise caused by the flow and pressure fluctuation. And all caused by external factors.

Due to the pressure shock in the oil trapped area, the hydraulic pump can also generate fluid noise.

For example, when the cylinder block of the slanting axial piston pump is at the top dead center during the rotation, at the moment when the liquid pressure in the piston cavity is connected to the oil discharge cavity, suction pressure will suddenly rise to the discharge pressure, and produce a large pressure shock.

In the same way, when they are located at the bottom dead center, pressure shocks also occur.

They are the main noise source of the hydraulic pump.

To minimize the noise of the hydraulic pump, the grid capacity must be large enough.

When selecting a hydraulic pump, under the premise of ensuring the required power and flow, try to choose a hydraulic pump with a low speed.

You can also choose a compound pump to increase the sensitivity of the relief valve and add an unloading circuit to reduce noise.

Control valve is another noise source

Control valve

The cavitation of the control valve creates fluid noise.

This is because the oil flow generates air flow through the valve body, which generates a high flow velocity at the regulator orifice.

As the flow rate changes, so does the pressure.

When the pressure is lower than atmospheric pressure, the air dissolved in the oil will be separated out, and a large number of air bubbles are generated, at this time, the noise frequency will be very high.

In addition, in the jet state, vortices are generated because of the uneven velocity of the oil flow or due to the oil flow is cut off, will all produce noise.

The solution to this kind of noise is to increase the back pressure on the downstream side of the regulator orifice, making it higher than the bound of air separation pressure.

Multi-stage decompression can be used to prevent cavitation.

In general, when the oil flow passes through the orifice of the control valve, the ratio of the upstream side pressure to the downstream side pressure should be 3 to 6.

Pressure fluctuations of the hydraulic pump cause resonance in the valve, thereby increasing noise.

Among the control valve, especially the throttle valve, its throttling opening is small and the flow velocity is high, which is easy to produce vortex.

Sometimes, the valve core presses against the valve seat, causing great vibration.

When this happens, the throttle valve can be replaced by a small size control valve, or widen the throttle orifice.

When the directional control valve is closed or opened, it will cause vibration and noise due to hydraulic shock.

For example, when the solenoid directional control valve is rapidly switched, the hydraulic shock will cause the pressure in the pipe to fluctuate violently and the fluctuation will spread along the pipeline.

When transmitted to hydraulic pumps and cylinders, vibration and noise will be generated in these links.

To reduce this kind of vibration and noise, the hydraulic shock should be minimized through reasonable setting of valves and pipelines.

The suction of the hydraulic pump generates the noise

The suction phenomenon of a hydraulic pump means that the oil pump directly sucks in the air or the sucked oil is mixed with air.

This phenomenon not only affects the oil quality and increases the 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 the improper setting of the fuel tank and suction pipe.

To prevent this, the following measures should be taken:

① The fuel tank should be designed reasonably and its volume should be large enough. Can use a long tank with a partition, divided into the sump oil tank and the suction tank;

② The oil in the fuel tank must be added to the specified height, and the suction pipe must be inserted into the oil tank at a depth of 3/5;

③ The specifications of hydraulic oil should meet the requirements of the manual. All joints must be tightly sealed to prevent short-term suction of air into the pump. All relevant equipment should be cleaned regularly to prevent clogging.

Mechanical parts in hydraulic system generate noise due to vibration

Due to errors in design, manufacturing, and installation of the hydraulic system, relevant parts generate vibration and output noise when they work.

Attenuators and isolation can be used to eliminate or reduce this kind of noise.

① The attenuator can be used to prevent noise diffusion, and the attenuator has two types: absorption and reflection;

② The reasonable arrangement of pipelines and the installation of accumulators in pipelines can attenuate the periodic vibration in the system;

③ Filters can be connected in series in pipelines to eliminate noise caused by pressure fluctuations in the system.

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