In mechanical processing, noise and vibration from the hydraulic system can have a direct impact on the accuracy of the processed part.
Noise refers to a vibratory wave produced by a specific sound source.
There are numerous causes of noise in hydraulic systems, including voltage fluctuations, mechanical systems, changes in load and flow, cavitation caused by air and oil ingress, and trapped fluids.
The hydraulic pump is an important source of noise
Variations in mains voltage, changes in load, pressure fluctuations and flow pulsations can contribute to noise and vibration in hydraulic pumps.
Fluctuations in mains voltage will result in flow pulsations in the hydraulic pump, leading to fluctuations in pump output and piping pressure, resulting in fluid noise caused by changes in flow and pressure.
Pressure buildup in trapped areas in the oil system can also generate fluid noise in the hydraulic pump. For example, when the cylinder block of a tilted axial piston pump reaches top dead center during rotation, the sudden increase in suction pressure to discharge pressure when the liquid pressure in the piston cavity connects to the discharge cavity of oil creates a large pressure shock.
Similar pressure shocks occur when the cylinder block is located at bottom dead center. These pressure shocks are the main source of noise in the hydraulic pump.
To minimize the noise produced by the hydraulic pump, the capacity of the electrical network must be sufficient.
When choosing a hydraulic pump, it is important to prioritize low speed, ensuring the necessary power and flow.
An alternative solution is to select a composite pump, which increases relief valve sensitivity and incorporates a discharge circuit to reduce noise.
The control valve is another source of noise
Control valve cavitation creates fluid noise as oil flow through the valve body generates air flow, resulting in a high flow velocity at the regulator orifice.
As the flow rate changes, the pressure also changes. When the pressure drops below atmospheric pressure, the air dissolved in the oil separates, producing a large number of air bubbles and causing high-frequency noise.
In addition, vortices generated by irregular oil flow speeds or interruption of oil flow in the jet state can also cause noise.
To resolve this type of noise, the back pressure on the downstream side of the regulator orifice must be increased to exceed the air separation pressure.
Using multistage decompression can prevent cavitation. In general, the ratio of upstream pressure to downstream pressure at the control valve orifice should be between 3 and 6.
Hydraulic pump pressure fluctuations can cause valve resonance, leading to increased noise. The butterfly valve, in particular, with its small throttling opening and high flow velocity, is prone to generating vortices.
Sometimes the valve core can press against the valve seat, causing significant vibration.
In these cases, the butterfly valve can be replaced with a smaller control valve or the butterfly orifice can be enlarged.
When a directional control valve is opened or closed, it can cause vibration and noise due to hydraulic shock. For example, when a directional control solenoid valve is switched quickly, it creates a hydraulic shock that causes violent fluctuations in pipeline pressure, which spread throughout the pipeline. When these fluctuations affect hydraulic pumps and cylinders, they result in vibration and noise in these components.
To minimize this type of vibration and noise, hydraulic shock must be reduced through appropriate valve and piping configurations.
Hydraulic pump suction generates noise
Suction in a hydraulic pump refers to the direct intake of air through the pump or the presence of air in the sucked oil.
This phenomenon not only degrades the quality of the oil, increases noise and affects the volumetric efficiency of the hydraulic pump, which is unacceptable in a hydraulic system.
The main cause of this phenomenon is inadequate fuel tank and suction tube settings. To avoid suction, the following measures must be taken:
- Reasonably design the fuel tank with a suitable volume. A long tank with dividers can be used, dividing it into a crankcase oil tank and a suction tank.
- Make sure the oil in the fuel tank is at the specified height and the suction tube is inserted into the oil tank to a depth of 3/5.
- Use hydraulic oil that meets manual specifications and make sure all joints are well sealed to prevent air from entering the pump for a short period. Regularly clean all relevant equipment to avoid clogging.
Mechanical parts in the hydraulic system generate noise due to vibration
Errors in the design, manufacture and installation of a hydraulic system can result in vibration and noise from its components during operation.
To eliminate or reduce this noise, attenuators and isolation techniques can be used:
- Attenuators can be used to prevent noise diffusion and come in two forms: absorption and reflection.
- Proper arrangement of piping and the use of accumulators can reduce periodic vibrations in the system.
- Installing filters in series in the pipes eliminates noise caused by pressure fluctuations in the system.
