vacuum pumps of sound and noise reduction measures

Vacuum pump is a kind of variable volume mechanical vacuum pump, which uses the rotary motion of the rotor and the rotator which can slide in the rotor groove to obtain vacuum. When the working fluid is used to lubricate and fill the dead gap of the pump chamber to separate the exhaust valve from the atmosphere, it is commonly known as the oil seal rotary vane vacuum pump. When there is no working fluid, it is a dry rotary vane vacuum pump.

In each kind of pump, there are single-stage and double-stage. In the single-stage pump, due to the different structure and parameters, the ultimate pressure and use of the pump are also different.

Their common characteristics are simple structure, easy to use, can start from atmospheric pressure, can be directly discharged into the atmosphere, small eccentric mass, easy maintenance, the limit pressure of two-stage pump is 6 × 10-2 ~ l × 10-2 PA, one single-stage pump can reach about 4pa, the other is about 50 ~ 200Pa.

At the end of the 1960s, there was a trend of miniaturization of direct coupling and increasing speed in the world. In the early 1970s, a series of direct coupling products appeared. In the early 1980s, improved series products were introduced. There are a variety of accessories for users to choose from, which can protect the pump or the environment. The structure of the pump itself has been improved to improve the reliability.

In terms of pump structure, in order to prevent oil return when the pump is stopped, some are equipped with check valves that can automatically cut off the oil circuit, some are equipped with inlet channel stop valves, and some are equipped with oil pumps and control structures to automatically cut off the gas path to keep the pump port in a vacuum state when the pump is running suddenly.
The noise of the pump can be divided into the following aspects according to the location of the sound:

The details are as follows:

1) The impact of the rotating plate on the cylinder wall. If the design, manufacture or material are not proper, the vane sliding is not smooth, or the blade head cannot always run close to the cylinder wall due to the existence of exhaust dead gap and incompressible oil, which will cause the impact sound of the rotary blade on the cylinder wall. Therefore, it is better to adopt the structure of arc surface to separate the inlet and outlet. The dead gap is eliminated by the exhaust guide groove. When adopting the line separation structure, the distance from the exhaust end point to the tangent point should be shortened as far as possible. For the rotary vane pump below 70L / s, considering the actual thickness of the vane, it is recommended to take 7 ~ 10mm and take the large value for the large pump. When the rotor is too close, because there is only a narrow strip contact between the rotor blade groove and the rotor head, once the sealing effect is not good when the rotating blade turns to the tangent point, the pumping speed and even the limit pressure of the pump will be affected. It can be seen that this structure can not completely eliminate the exhaust dead gap and limit the level of noise reduction. It should be pointed out that too much clearance between the rotor and the slot will reduce the performance. Therefore, it is necessary to ensure reasonable tolerance fit and form and position tolerance value, pay attention to the thermal expansion of the rotor, avoid the scuffing between the rotor and the slot, pay attention to the cold oil viscosity of the oil, and design sufficient vane spring force. When the arc surface is used for separation, the additional eccentricity value of the rotor center should not be too large. Otherwise, when the vane passes through two circular arcs, it will break away from the cylinder wall at the intersection point, which will cause impact noise instead. Generally, the small pump is 0.20 ~ 0.25 mm, and the large pump can be properly increased. Exhaust the sound of pressure oil in dead gap and residual volume. When the pump reaches the limit pressure, the two pressure oil will shoot into the vacuum chamber at high speed when it is connected with the vacuum chamber, and it will collide with the rotor and cylinder wall to produce sound. The size and location of the two volumes are related to the noise.

2) The impact noise of the valve plate on the valve seat and support parts has a large amount of gas, and the amount of circulating oil in the pump, the greater the noise of the valve plate, the higher the valve jump height, the larger the valve area, the greater the noise of the valve plate, and the valve plate material also has a certain impact. The noise of rubber valve should be better than that of steel or laminate. To this end, to control the amount of oil into the valve to close in time, to tight. Pay attention to the material selection and structure of the valve.

3) The noise will increase when the volume of echo and bubble break in the box increases. Therefore, the noise will increase obviously when the air is opened or the atmosphere is opened. If the gas ballast is adjustable, it can be adjusted reasonably.

4) When a large amount of gas and oil are discharged, the noise is generated when the oil baffle and other parts are impacted. If the parts are not rigid enough or not fastened, the vibration and collision will increase the noise. Therefore, the oil retaining plate should not only be sufficiently rigid and fastened, but also need to be rubbed with rubber when contacting with other components, such as fuel tanks, so that the impact noise caused by vibration can be avoided, and the effect of oil blocking can be improved.