How to analysis on the generation and elimination of vibration in fluid hydraulic system?

Vibration is a phenomenon that often occurs in the working of hydraulic systems. It mainly comes from two aspects: the vibration generated by the movement of the mechanical system and generated during the working process of the fluid.

Most of the vibrations are very harmful to the hydraulic system, of course except for the hydraulic equipment that uses the principle of vibration.

Vibration directly affects the performance of the main engine and the hydraulic system, causing damage to the hydraulic components, accessories and pipelines. Then thereby it will shorten the system service life.

1. Causes of fluid vibration

  • Vibration of hydraulic pump

The flow pulsation of a hydraulic pump is an inherent characteristic of the pump. During the process of sucking and pressing oil, the pressure and flow periodically change will form a pressure pulse.

This pulsation will inevitably cause pressure pulsation in the outlet pipe of the hydraulic pump and spread to the entire system, produce fluid vibration. In addition, the pressure shock in the trapped area of the hydraulic pump, the back flow of the plunger pump, and the inability of the variable pump to reduce the oil delivery in time when the oil pressure rises, all will cause hydraulic vibration.

  • Vibration caused by bubbles

The oil is generally mixed with about 2% to 5% of air, and the mixed air is suspended in the hydraulic oil in the form of bubbles with a diameter of 0.05 to 0.5 mm.

When the partial pressure of the oil mixed with air drops to the air separation pressure, the dissolved air in the oil will separate and precipitate, forming a large number of bubbles (this phenomenon is called cavitation).

When the oil with a large number of bubbles flows again to a higher pressure at high places, the bubbles are instantly crushed to form local high pressures, causing large pressure fluctuations and causing the system to vibrate.

  • Vibration caused by hydraulic valve switching

In the hydraulic system, when the load inertia is large, if the directional control valve is suddenly closed or opened, the flow rate of the liquid flowing in the pipeline will change suddenly. At this moment, the conversion of the kinetic energy of the liquid will cause pressure shock and cause vibration.

  • Forward rush phenomenon and vibration caused by impact load

When the load change causes the hydraulic actuator to suddenly change from the working state to the unloaded state, due to the inertia of the system, a forward thrust will occur, causing hydraulic shock and vibration.  When the hydraulic actuator is suddenly loaded from the no-load state, due to the shock load causes the liquid pressure to rise suddenly, causing pressure shock and vibration.

2. Measures to eliminate fluid vibration

  1. Reduce the influence of air bubbles
  • Reasonable selection of hydraulic components will help reduce the influence of air bubbles on the system

When selecting an oil suction filter, you can choose an out-of-box self-sealing oil suction filter with a signaling device, such as the TF series out-of-box self-sealing oil suction filter. When the filter element is blocked by contaminants, the vacuum degree of the oil outlet is 0.018, then the transmitter will send out an alarm signal to remind the operator to replace the filter element in time to avoid clogging of the filter element. Or it will result in poor oil suction of the oil pump and partial vacuum at the oil inlet and air suction.

  • Reasonably design the structure of hydraulic components to help reduce the influence of air bubbles in the system

Set up pressure measuring joints with exhaust devices at each high point of the hydraulic pipeline, and regularly discharge the gas mixed into the pipeline through the exhaust device of the pressure measuring joints.

When designing the oil tank, set the oil filter and the oil suction filter respectively arranged at both ends of the oil tank to increase the stroke of the oil flowing in the oil tank, so that the oil has as much time as possible to precipitate bubbles during the bypass process.

The pipeline connection is well sealed , Choose a combined sealing gasket with better sealing performance at the junction of the pipe joint and the integrated block to avoid air infiltration.

2. Reduce the impact of hydraulic valves

The reversing valve and the overflow valve in the hydraulic valve are easy to cause fluid impact, and then cause vibration. So this point should be considered when selecting the model.

Selecting the directional valve, when the pressure is high and the flow is large, choose the elector-hydraulic directional valve with better commutation stability. When selecting the directional valve’s neutral function, if the load inertia is large, you can choose Y type Function to ensure that there is still a certain buffer effect after the valve is closed. If the hydraulic motor of the large inertia system is not allowed to continue to rotate after the reversing valve being closed, you can choose the O-type or M-type function.

And before the reversing valve is closed, it is best to first unload the hydraulic pump and close the reversing valve after a certain delay. If select the overflow valve, when the pressure is high and the flow is large, use the pilot-operated overflow valve.

3. Appropriate dynamic compensation

If an overload supplement valve and a back pressure valve are installed in the system, the dynamic performance of the system will be greatly improved and hydraulic shock will be reduced.

In addition, setting a back pressure valve can also increase the minimum working pressure of the system, avoid the generation of bubbles. And at the same time it will slow down the front-shooting phenomenon caused by changes in working conditions, thereby reducing system vibration.

4. Other measures

In order to reduce pipeline vibration, when designing hydraulic pipelines, pipe clamps can be installed according to the design specifications and sharp turns of the pipeline should be avoided as much as possible.

Accumulators should be installed at the inlet and outlet of hydraulic actuators to relieve hydraulic shock.

3. Conclusion

Vibration is an inseparable physical phenomenon of the hydraulic system. Correctly analyzing the causes of vibration and taking reasonable and effective control measures are important to improve the efficiency of the system and extend the life of the system.

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