The reason for the vibration of Hitachi ZX690LCH-5A hydraulic system and some noise!
The main reasons for the vibration and noise of the hydraulic system:
(1) Vibration and noise caused by cavitation in hydraulic pumps and suction lines
When the resistance of the suction pipeline is great, the oil is too late to fill the pipeline and the pump cavity, resulting in a partial vacuum and forming a low pressure. When the pressure is as low as the air separation pressure, the air dissolved in the working fluid (usually 9% (volume fraction)) is decomposed in large amounts, forming cavities and bubbles. When the bubbles are compressed and broken in the high-pressure zone, they will produce high-frequency shocks. The pressure can sometimes be as high as 10 times the system pressure. At this time, the system will cause cavitation, accompanied by shock vibration, noise and high temperature. Elimination methods are:
①Increase the diameter of the oil pipe, reduce or avoid the bending of the oil suction pipe, and reduce the pipe resistance.
②Clean the oil filter frequently.
③The oil suction height of the hydraulic pump should be as small as possible (not more than 0.5m).
(2) Vibration and noise caused by oil trapping in hydraulic pumps
The hydraulic pump is trapped in oil. The high-pressure oil part causes some parts in the pump to be hit by high-frequency, and the load increases and produces noise. The partial vacuum part causes the air dissolved in the hydraulic oil to generate cavitation bubbles, causing uneven flow and pressure. Vibration, thereby generating noise. Remedy: Mainly check the size and position of the unloading groove on the end cover of the gear pump. If they are similar, they can be repaired with a knife, otherwise the end cover needs to be replaced. For the vane pump, it is mainly to check whether the triangular groove is processed too short, and it can be repaired with a triangular knife.
(3) Noise caused by regulating valve
①The pressure regulating spring is damaged. Replace the spring.
②Poor sealing of valve seat. Replace the steel ball or repair the sealing joint surface of the valve seat so that the joint surface of the steel ball and the valve seat is in good contact.
③The spool valve does not move flexibly in the valve body. Polish the slide valve with metallographic sandpaper and remove the dirt.
④ The spool valve orifice is blocked. Clean and unblock the orifice.
⑤ The throttle valve opening is too small, and the flow rate is high to produce jets. Reduce the hydraulic pressure difference between the inlet and outlet of the throttle valve, or use a small size throttle valve to make the throttle valve open larger when the flow is small.
⑥The electromagnetic reversing valve switches quickly, causing hydraulic shock. A buffer device is installed in the oil circuit of the electromagnetic reversing valve.
(4) Mechanical noise of hydraulic system
①The coaxiality error of the prime mover and pump coupling is too large or loose or the bearing is damaged. Ensure that the coaxiality error is within 0.1mm, and replace the damaged bearing.
②The pipeline is poorly installed, and the distance between the oil inlet pipe and the oil return pipe is too close. Properly extend the distance between the oil inlet pipe and the oil return pipe, and the main pipe should be positioned with a pipe clamp device.
