Discussion on reducing the noise of hydraulic valve
Discussion on reducing the noise of hydraulic valve
1. Introduction
The noise problem of hydraulic system has become one of the main factors hindering its further use. The international organization for Standardization (ISO) Regulations on the noise level of hydraulic transmission generally do not exceed 70 ~ 80dB. Therefore, the noise problem should be taken into account in both system design and component selection. Hydraulic valve is an important component that directly affects the working process and working characteristics of the hydraulic system. When designing the hydraulic system, non professionals often choose it simply according to its working parameters, nominal pressure and nominal flow under rated working state. As a result, the best effect can not be achieved in use and adjustment, and some phenomena such as impact, vibration and noise even affect the work of the system. The following discusses how to reduce noise and improve the use quality of common hydraulic valves in application, in order to remind users to pay attention and ensure the correct and reasonable use of valve components.
2. Noise of overflow valve
(1) The performance of the pilot valve is unstable. On the one hand, the cone valve of the pilot valve is excessively worn due to frequent opening during use, resulting in poor contact between the cone surface of the cone valve and the valve seat, resulting in unstable flow of the pilot valve and noise caused by pressure fluctuation. At this time, the cone valve should be repaired or replaced in time. If the main valve is not damaged, remove the adjusting nut and push the guide rod several times to make it in good contact. In addition, the pilot valve spring may be deformed, skewed or invalid, resulting in large pressure fluctuation and noise. At this time, the spring should be replaced.
(2) Air intrusion creates cavitation. The overflow valve is used as a constant pressure valve in the hydraulic system. In order to keep the system pressure close to constant, part of the oil overflows at a high flow rate through a small valve port under a certain pressure difference. Therefore, a high-speed jet will be caused near the valve port. According to Bernoulli equation, the liquid pressure at this place decreases. When the pressure is lower than the air separation pressure of this kind of oil, the air dissolved or mixed in the oil will separate and produce bubbles. When the oil containing a large number of bubbles flows into the oil return chamber of the valve body, the bubbles collapse due to the increase of pressure, resulting in cavitation and high-frequency noise. The main reason for cavitation of overflow valve is the change of liquid flow pressure and velocity caused by the change of valve port and valve body oil cavity shape.
In order to eliminate cavitation and noise at the valve port, the overflow section of the valve port should be designed with a long conical gap to reduce the sudden contraction and sudden diffusion of oil. Some small holes can also be added on the valve seat to guide the downstream oil that has recovered pressure back to the retracted part to prevent negative pressure.
(3) Overflow valve resonance. As shown in Figure 190 (a), the specifications and setting values of overflow valves a and B are the same. When two pumps supply oil in parallel, sometimes the overflow valve will make a strong noise. When the setting pressures of the two overflow valves are staggered from each other, the noise can be basically eliminated. This shows that two relief valves with the same setting value are easy to produce resonance, which should be avoided as much as possible. If another overflow valve is selected and connected to point C, as shown in Figure 190 (b), the above noise problem can be solved.
(4) Improper piping. As shown in Figure 191 (a), two hydraulic pumps supply oil to different actuators respectively. When only one hydraulic pump works, the overflow valve has no noise. When the two hydraulic pumps are close to each other and work at the same time, the overflow valve has a lot of noise and the pointer of the pressure gauge swings badly, which is caused by improper piping. Connect the oil return pipes of the two overflow valves back to the oil tank respectively, as shown in Figure 191 (H), and the noise can be eliminated.
3. Noise of directional valve
(1) The valve core moves too fast. When the valve core moves too fast to produce hydraulic impact, the instantaneous pressure peak of the system is several times higher than the normal working pressure, resulting in equipment vibration and noise.
The reduction measures can be considered from the following aspects: ① set a one-way throttle valve in the hydraulic directional valve to adjust the action speed of the valve core by changing the opening of the throttle valve; ② Extend the commutation time; ③ Reasonably select the transition and centering function of slide valve; ④ Control the reversing thrust.
Specific practices; ① The soft switching valve is adopted to control the oil discharge speed of the end face of the valve core by adjusting the size of the orifice, so as to limit the moving speed of the valve core; ② The moving speed of the main valve core is controlled by machining a throttling groove on the edge of the valve core or using a superimposed double one-way throttle valve; ③ The proportional electromagnet is used to change the thrust of the valve core to prolong the commutation time.
(2) The actual flow through the directional valve is too large. For the electromagnetic directional valve, the maximum flow rate shall generally be within the rated flow rate and shall not exceed 120% of the rated flow rate, otherwise it is easy to cause excessive pressure loss and cause heating and noise. If there is no suitable directional valve, the one with larger pressure and flow can also be selected, but the economy is poor. When the flow exceeds 63L / min, the electromagnetic directional valve cannot be selected.
4. Noise of hydraulic control check valve
(1) Improper model selection. The hydraulic control check valve in the system shown in Figure 192 is of internal leakage type. When the change-over valve works in the left position, the load moves downward. From the principle analysis, the working principle is correct. But in actual work, when the load drops, it will always send out rhythmic morning, with serious vibration. After analysis, the reasons are as follows: when the load moves downward, the a port of the hydraulic control check valve produces a quite high pressure due to the action of the throttle valve, and at this time, the control oil port of the hydraulic control check valve is still the original set pressure. Because the pressure action area of port a of the internal discharge check valve is not different from that of the control chamber, the check valve will be closed under the action of port a pressure. At this time, the pressure of port a decreases and the check valve will be opened again. This process is repeated, resulting in rhythmic vibration and noise.
The solution can be considered from the following aspects: ① increase the control oil pressure; ② Set the throttle valve on the hydraulic control check valve; ③ Select the leakage type hydraulic control check valve.
(2) Short term negative pressure. As shown in Figure 193 (a), the gravity load of the hydraulic system is large, resulting in discontinuous jumping and oscillation noise of rapid drop and stop alternation of the load during the descent process. This is mainly due to the large load. When running downward, due to the high speed, the oil supply of the hydraulic pump has no time to supplement the volume formed in the upper chamber of the hydraulic cylinder for a moment, so a short-term negative pressure is generated in the whole oil inlet circuit. At this time, the control pressure of the right check valve decreases, the check valve closes, and the return oil circuit of the system is suddenly closed, so that the hydraulic cylinder stops suddenly. When the pressure in the oil inlet circuit rises, the check valve on the right side opens and the load drops rapidly again... The above process is repeated, resulting in system oscillation and noise intermittently.
One of the solutions to this problem is to install a one-way throttle valve on the falling oil return circuit, as shown in Figure 193 (b), so as to prevent the generation of negative pressure. In addition, if the intermediate function of the directional valve is changed to unloading type, such as "H", the locking effect will be better and the noise problem will be basically eliminated.
5. Noise of sequence valve
According to the structure, the sequence valve is divided into direct acting type and pilot type, internal control type and external control type. If the selected structure is inappropriate, it will lead to out of control pressure and noise. The specific reason is that the oil pressure in the pressure regulating spring chamber is equal to the outlet pressure, the valve core closes the valve port under the action of hydraulic pressure, and the sequence valve becomes a normally closed valve. On the contrary, it is also possible that when the system does not reach the set pressure of the sequence valve, the pressure oil flows out from the secondary oil outlet, which will cause large system pressure fluctuation, out of control and noise.
The above hydraulic valves also have the problem of noise caused by resonance in use, because the hydraulic valve is mainly composed of valve body and valve core in structure. When working, the valve core of the hydraulic valve is supported on the spring. When its frequency is close to the pulsation frequency of the oil delivery pipe of the hydraulic pump or other vibration source frequency, it will cause vibration and noise. At this time, it is necessary to change the natural frequency of the pipeline system, change the position of the hydraulic valve or appropriately increase the accumulator, which can prevent vibration and reduce noise.
Through the above analysis, we realize that it is far from enough to meet the requirements of a single component when designing the system and selecting components. We should also pay attention to mutual coordination and compatibility to improve efficiency, which also saves a lot of trouble in the later debugging process.
