First of all, the noise generated by the hydraulic system may be the noise of the relief valve, the noise of the plunger pump or motor, or the noise of the hydraulic cylinder. The reasons are as follows.

1.溢流阀噪声

1. Noise of relief valve

阀的噪声主要是由先导阀性能不稳定引起的。原因是空气混入油中，先导阀前腔内的高频压力振荡导致空气振动，从而产生高频噪音。空气必须及时排出，防止再次进入。在使用过程中，针阀因频繁开启而过度磨损，导致锥面和阀座不能紧密贴合，导致先导流量不稳定，压力波动产生噪音。先导阀弹簧应及时修理或更换。先导阀弹簧的疲劳变形导致压力调节功能不稳定、压力波动大、噪音大。应该更换弹簧。

The noise of safety valve is mainly caused by the unstable performance of pilot valve. The reason is that the air is mixed into the oil, and the high frequency pressure oscillation in the front chamber of the pilot valve leads to the air vibration, resulting in high-frequency noise. Air must be discharged in time to prevent re-entry. In the process of use, the needle valve is excessively worn due to frequent opening, which causes the cone surface and the valve seat not to fit tightly, which leads to the instability of pilot flow and the noise caused by pressure fluctuation. The spring of pilot valve should be repaired or replaced in time. The fatigue deformation of pilot valve spring results in unstable pressure regulation function, large pressure fluctuation and high noise. The spring should be replaced.

2.液压缸噪声

2. Hydraulic cylinder noise

如果油与空气混合或液压缸中的空气没有完全排出，在高压作用下会发生气穴现象，造成高噪音，必须及时排出空气。如果气缸盖油封过紧或活塞杆弯曲，在运动过程中会因其他力产生噪音，必须更换油封或及时调整活塞杆。

If the oil is mixed with air or the air in the hydraulic cylinder is not completely discharged, cavitation will occur under high pressure, resulting in high noise, so the air must be discharged in time. If the cylinder head oil seal is too tight or the piston rod is bent, noise will be generated due to other forces during the movement. The oil seal must be replaced or the piston rod must be adjusted in time.

3.柱塞泵或马达的噪音

3. Noise of plunger pump or motor

如果空气混入液压泵吸入的油中，气穴噪声很容易在高压区产生，并以压力波的形式传播，造成油振荡。原因:液压泵的滤油器和进油管堵塞或油的高粘度会导致泵进油口真空度高和空气渗透；液压泵和先导泵轴端的油封损坏，进油管密封不良，也会导致空气进入。油箱油位过低，使液压泵的进油管直接排空。

If air is mixed with the oil inhaled by the hydraulic pump, cavitation noise is easily generated in the high pressure area and propagates in the form of pressure wave, causing oil oscillation. Causes: the oil filter and oil inlet pipe of the hydraulic pump are blocked or the oil viscosity is high, resulting in high vacuum at the oil inlet of the pump and air penetration; the oil seal at the shaft end of the hydraulic pump and pilot pump is damaged, and the poor sealing of the oil inlet pipe will also lead to air entering. The oil level in the oil tank is too low, so that the oil inlet pipe of the hydraulic pump is drained directly.

液压泵内部部件过度磨损，如“柱塞泵缸体、配流盘、柱塞、柱塞孔等磨损。使泵内部泄漏严重。当泵输出高压小流量油时，会产生流量脉动，造成较高的噪音。此时，可以适当增加先导系统可变机构的偏转角，以改善内部泄漏对泵输出流量的影响。液压泵伺服阀的阀芯和控制流量的活塞也会受到局部磨损。当活塞移动时，会产生脉动，流量和压力的波动会导致泵出口产生更大的振动和噪音。此时，可以对磨损严重的部件进行刷镀、研磨或更换。

The internal parts of the hydraulic pump are excessively worn, such as "plunger pump cylinder body, port plate, plunger, plug hole, etc. The internal leakage of the pump is serious. When the pump outputs high-pressure and small flow oil, it will produce flow pulsation and cause high noise. At this time, the deflection angle of the variable mechanism of the pilot system can be appropriately increased to improve the influence of internal leakage on the pump output flow. The valve core of the hydraulic pump servo valve and the piston controlling the flow rate will also be locally worn. When the piston moves, it will produce pulsation. The fluctuation of flow and pressure will lead to greater vibration and noise at the pump outlet. At this time, the severely worn parts can be brush plated, ground or replaced.

液压泵配流盘的磨损在使用过程中，由于卸载槽开口处的表面磨损或污泥沉积，卸载槽会缩短，卸载位置会改变，导致积油，从而导致噪音增大。通过平面研磨修复的分配板也将具有缩短卸载槽的结果。如果不及时适当延长，将会产生更高的噪声。装配时，分配板的大卸荷槽必须安装在泵的高压室内，其锐角方向必须与缸体的旋转方向相反，否则也会给系统带来较大的噪音。

Wear of valve plate of hydraulic pump in the process of use, due to the surface wear or sludge deposition at the opening of the unloading tank, the unloading tank will be shortened and the unloading position will be changed, resulting in oil accumulation and noise increase. The distribution plate repaired by plane grinding will also have the result of shortening the unloading groove. If it is not extended properly in time, it will produce higher noise. During assembly, the large unloading groove of the distribution plate must be installed in the high-pressure chamber of the pump, and its acute angle direction must be opposite to the rotation direction of the cylinder block, otherwise, it will bring large noise to the system.