Rotary vane vacuum pump

The rotor installed eccentrically inside the rotary vane vacuum pump is tangent to the fixed surface of the stator, and two (or more) rotary vanes slide in the rotor slot (usually radially) and make contact with the inner wall of the stator, dividing the pump chamber into several variable volume rotary variable volume vacuum pumps. Usually, the gap between the rotary vane and the pump chamber is sealed with oil, so rotary vane vacuum pumps are generally oil sealed mechanical vacuum pumps.

Application

Its working pressure range is 101325-1.33 × 10-2 (Pa), which belongs to low vacuum pumps. It can be used alone or as a pre pump for other high vacuum pumps or ultra-high vacuum pumps. It has been widely used in production and scientific research departments such as metallurgy, machinery, electronics, chemical industry, light industry, petroleum, and medicine.

Structure

Rotary vane vacuum pumps can remove dry gases from sealed containers, and if equipped with gas ballast devices, they can also remove a certain amount of condensable gases. But it is not suitable for extracting gases with high oxygen content, corrosive to metals, chemical reactions to pump oil, and containing particulate dust.

Rotary vane vacuum pump is one of the most basic vacuum acquisition equipment in vacuum technology. Rotary vane pumps are mostly small and medium-sized pumps. There are two types of rotary vane vacuum pumps: single-stage and two-stage. The so-called two-stage refers to connecting two single-stage pumps in series structurally. Generally, it is made into a two-stage configuration to achieve a higher vacuum degree.

The relationship between the pumping speed and inlet pressure of a rotary vane pump is specified as follows: at inlet pressures of 1333Pa, 1.33Pa, and 1.33 × 10-1 (Pa), the pumping speed values shall not be lower than 95%, 50%, and 20% of the nominal pumping speed of the pump, respectively.

The rotary vane pump is mainly composed of pump body, rotor, rotary vane, end cover, spring, etc. Install a rotor eccentrically in the cavity of the rotary vane pump, with the outer circle of the rotor tangent to the surface inside the pump cavity (with a small gap between the two), and two spring equipped rotary vanes installed in the rotor slot. When rotating, the top of the rotor is kept in contact with the inner wall of the pump chamber by centrifugal force and spring tension, and the rotor rotates to drive the rotor to slide along the inner wall of the pump chamber.

Working principle

1. Working principle of liquid ring vacuum pump:

The commonly used liquid ring vacuum pumps include water ring vacuum pumps and Naxi pumps. It is mainly used for suctioning gases, especially when suctioning corrosive gases.

Install an appropriate amount of water as the working fluid in the pump body. When the impeller rotates clockwise, water is thrown around by the impeller. Due to the centrifugal force, the water forms a closed ring of approximately equal thickness determined by the shape of the pump chamber. The lower inner surface of the water ring is exactly tangent to the impeller casing, and the upper inner surface of the water ring is just in contact with the top of the blade (in fact, the blade has a certain insertion depth inside the water ring). At this point, a crescent shaped space is formed between the impeller casing and the water ring, and this space is further divided into several small chambers equal to the number of blades by the impeller. If the lower zero degree of the impeller is taken as the starting point, the volume of the small chamber increases from small to large when the impeller rotates 180 degrees before, and it is connected to the suction port on the end face. At this time, gas is sucked in, and when the suction is completed, the small chamber is isolated from the suction port; When the impeller continues to rotate, the small chamber becomes smaller, compressing the gas; When the small chamber is connected to the exhaust port, the gas is further discharged outside the pump. The water ring pump relies on changes in the pump chamber volume to achieve suction, compression, and exhaust, therefore it belongs to the variable volume vacuum pump.

2. Working principle of slide valve vacuum pump:

Another typical rotary vacuum pump is a slide valve vacuum pump, which is equipped with an eccentric rotor inside the pump casing. There are several slots on the rotor, and there are sliding blades inside the slots that can slide. The sliding blades in the rotor groove extend outwards and do not come into contact with the pump casing. Gas is drawn in on the side where the space enclosed by the slide and pump casing expands, and discharged on the other side where the space enclosed by the two shrinks. The low pressure generated by the sliding vane vacuum pump can reach 0.06Pa. Compared to rotary vane vacuum pumps, it operates more stably and has stronger durability.

3. Working principle of jet vacuum pump:

Jet pumps use the principle of converting kinetic energy and static pressure energy during flow to suction and transport fluids. The working fluid can be steam or liquid.

The jet pump consists of a working nozzle, a diffuser, and a mixing chamber connected together. The working nozzle and diffuser form a special airflow duct with varying cross-sections. The working steam is sprayed from the nozzle at a high speed under high pressure. During the spraying process, the airflow can convert static pressure energy into kinetic energy through the nozzle. The pressure difference between the working steam pressure and the outlet pressure of the pump causes the working steam to flow in the pipeline.

In this special pipeline, steam passes through the outlet of the nozzle to the inlet of the diffuser in this area (mixing chamber), creating a negative pressure zone due to the high-speed steam flow. The negative pressure here is much lower than the working steam pressure and the maximum pressure (back pressure) that the pump outlet can withstand. At this time, the extracted gas is sucked into the mixing chamber, and the working steam and the extracted gas mix with each other and exchange energy, transferring the kinetic energy converted from the static pressure energy of the working steam to the extracted gas. The mixed gas flow expands in the diffuser and generates a positive shock wave. The velocity of the mixed gas flow after the wave decreases to subsonic, and the pressure of the mixed gas flow increases. Subsonic airflow is slowed down and pressurized during the gradual expansion flow of the diffuser. The mixed airflow increases in pressure and decreases in velocity at the outlet of the diffuser, and is then discharged from the pressure outlet. Therefore, the jet pump is also a gas compressor.

Characteristics of rotary vane vacuum pump

The advantages include fast pumping speed, small size, light weight, low noise, easy maintenance, and high ultimate vacuum degree.