Noise in hydraulic systems and methods to eliminate it

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In machining, the noise and vibration of hydraulic systems directly affect the accuracy of the workpieces. Noise is a vibration wave originating from some sound source. There are many causes of noise in hydraulic systems, such as noise caused by voltage fluctuations, noise from mechanical systems, noise resulting from changes in load and flow rate, noise generated by air entering and causing cavitation, and noise due to oil entrapment and fluid vortices. 1. The hydraulic pump is a major source of noise. Changes in grid voltage, variations in load, as well as pressure fluctuations and flow pulsations can all cause noise and vibration in the hydraulic pump. Voltage fluctuations in the power grid cause flow pulsations in the hydraulic pump, leading to pressure fluctuations at the pump’s outlet and in the pipelines; this is fluid noise resulting from flow and pressure fluctuations caused by external factors. 　　Hydraulic pumps can also generate fluid noise due to pressure surges in the oil trapping area. In swashplate-type variable displacement piston pumps, when the cylinder block is at the top dead center during rotation, the liquid pressure in the piston chamber suddenly rises to the discharge pressure at the moment it connects with the discharge chamber, resulting in a significant pressure shock. Similarly, pressure shocks are also generated at the bottom dead center, and they are the main sources of noise in liquid diaphragm pumps. To keep the noise of the hydraulic pump at its lowest, the power grid capacity must be sufficient ； When selecting a hydraulic pump, try to choose one with a low rotational speed, provided that the required power and flow rate are met ； A composite pump can also be used to improve the sensitivity of the relief valve, and additional unloading circuits can be added to reduce noise. 2. Control valves are another source of noise; cavitation in control valves generates fluid noise. This is due to the flow of oil through the valve body, which creates a ☆flow effect; a very high flow velocity is generated at the throttle opening. As the flow velocity changes, so does the pressure. When the pressure drops below atmospheric pressure, the air dissolved in the oil separates out, forming numerous bubbles. At this point, the noise frequency will be very high. Furthermore, in a jet state, uneven oil flow speeds cause vortices, or noise is generated due to the interruption of the oil flow. To address this type of noise, it is necessary to increase the back pressure on the downstream side of the throttle opening, making it higher than the threshold value for air separation pressure; multi-stage pressure reduction can be used to prevent cavitation from occurring. Generally, when oil flows through the throttle orifice of a control valve, the ratio of the pressure on the upstream side to the pressure on the downstream side should be 3 to 6. Pressure fluctuations in the hydraulic pump cause resonance in the valve components, thereby increasing noise. In control valves, especially throttle valves, the throttle opening is small and the flow velocity is high, which facilitates the formation of vortices; sometimes the valve spool presses against the valve seat, resulting in significant vibration. When this phenomenon occurs, it can be resolved by replacing it with a control valve of a smaller size or by widening the throttle opening. When the direction control valve is closed or opened, vibration and noise are caused by hydraulic shock. Such as when the electromagnetic directional control valve switches rapidly. Hydraulic shock causes severe pressure fluctuations within the pipe, which propagate along the pipeline; when they reach the hydraulic pump and cylinders, they induce vibration and noise in these components. To reduce such vibration and noise, hydraulic shock should be minimized through proper design of valves and piping. 3. Noise is generated by cavitation in the hydraulic pump. Cavitation in a hydraulic pump refers to the situation where the oil pump draws in air directly, or where air is mixed in with the oil being drawn in. This phenomenon not only affects the quality of the oil and increases noise, but it also impacts the volumetric efficiency of the hydraulic pump; it is not acceptable in hydraulic systems. The main reason for this phenomenon is the improper placement of the fuel tank and the fuel suction pipe. To prevent this phenomenon, the following measures should be taken: ① The fuel tank should be designed properly with sufficient capacity; a long fuel tank equipped with partitions can be used, dividing it into a return fuel tank and a suction fuel tank ； 　　②The oil level in the tank must be raised to the specified height, and the oil suction pipe must be inserted 3/5 of its length into the oil pool ； ③The hydraulic oil specifications must meet the requirements specified in the manual. All joints must be tightly sealed to prevent air from being drawn into the pump for short periods of time. All relevant settings should be cleaned regularly to prevent blockages. 4. Noise generated by mechanical components in the hydraulic system due to vibration. Due to errors in design, manufacturing, installation, etc., the relevant components in a hydraulic system vibrate during operation, resulting in noise; this noise can be eliminated or reduced using attenuators and isolation methods. 　　①Attenuators are used to prevent noise from spreading, and there are two types of attenuators: absorptive and reflective ； 　　②Properly arranging the pipelines and installing accumulators within them can reduce the periodic vibrations in the system ； 　　③Connecting a filter in series in the pipeline can eliminate the noise caused by pressure fluctuations in the system.