How various vacuum pumps work

A vacuum pump is a device that creates, improves, and maintains a vacuum in a closed space in a variety of ways. A vacuum pump can be defined as a device or device that uses a mechanical, physical, chemical, or physicochemical method to evacuate a pumped container to obtain a vacuum. With the development of vacuum applications, the types of vacuum pumps have been developed in many ways, with pumping speeds ranging from a few tenths per second to hundreds of thousands and millions of liters per second. According to the working principle of the vacuum pump, the vacuum pump can basically be divided into two types, namely a gas transfer pump and a gas trap pump. With the application of vacuum application technology in the field of production and scientific research, the requirements of the pressure range are wider and wider. Most of them need to be vacuum pumped by several vacuum pumps to meet the requirements of production and scientific research process. The vacuum application department covers a wide range of working pressures, so any type of vacuum pump cannot be fully applied to all working pressure ranges. It can only be used according to different working pressure ranges and different working requirements. Vacuum pump. For ease of use and the needs of various vacuum processes, various vacuum pumps are sometimes combined according to their performance requirements for unit type applications.

How various vacuum pumps work

Water ring vacuum pump / liquid ring vacuum pump working principle

The water ring vacuum pump (referred to as the water ring pump) is a rough vacuum pump. The ultimate vacuum that can be obtained is 2000~4000Pa, and the series atmospheric injector can reach 270~670Pa. The water ring pump can also be used as a compressor, called a water ring compressor, which is a low pressure compressor with a pressure range of 1 to 2 x 105 Pa gauge.

The water ring pump was originally used as a self-priming pump and was gradually used in many industrial sectors such as petroleum, chemical, machinery, mining, light industry, medicine and food. In many processes of industrial production, such as vacuum filtration, vacuum water diversion, vacuum feeding, vacuum evaporation, vacuum concentration, vacuum regain and vacuum degassing, water ring pumps are widely used. Due to the rapid development of vacuum application technology, water ring pumps have been paid attention to in the acquisition of rough vacuum. Since the gas compression in the water ring pump is isothermal, the flammable and explosive gas can be removed, and the dusty and water-containing gas can be removed. Therefore, the application of the water ring pump is increasing.

An appropriate amount of water is contained in the pump body as a working fluid. When the impeller rotates clockwise in the figure, the water is thrown around by the impeller. Due to the centrifugal force, the water forms a closed ring of approximately equal thickness depending on the shape of the pump chamber. The inner surface of the lower portion of the water ring is just tangent to the impeller hub, and the upper inner surface of the water ring is just in contact with the tip of the blade (actually the blade has a certain depth of insertion within the water ring). At this time, a crescent-shaped space is formed between the impeller hub and the water ring, and this space is divided by the impeller into a plurality of small cavities equal to the number of blades. If the lower part of the impeller is 0°, the volume of the small cavity becomes smaller from 180° before the rotation, and it communicates with the suction port on the end face. At this time, the gas is sucked in, and when the inhalation is finished, the cavity is small. It is isolated from the suction port; when the impeller continues to rotate, the small cavity becomes larger and smaller, so that the gas is compressed; when the small cavity communicates with the exhaust port, the gas is discharged outside the pump.

In summary, the water ring pump relies on the change of the volume of the pump chamber to achieve the suction, compression and exhaust, so it belongs to the variable displacement vacuum pump.

How does the Roots pump work?

The Roots pump is in the pump chamber, and two "8"-shaped rotors are mounted perpendicularly to each other on a pair of parallel shafts, and a pair of gear belts having a transmission ratio of 1 are operated in opposite synchronous rotational motions. Between the rotors, there is a certain gap between the rotor and the inner wall of the pump casing to achieve high speed operation. Since the Roots pump is a vacuum pump without internal compression, the compression ratio is usually low, so the high and medium vacuum pumps require a foreline pump. The ultimate vacuum of the Roots pump depends on the structure and manufacturing accuracy of the pump itself and on the ultimate vacuum of the foreline pump. In order to increase the ultimate vacuum of the pump, the Roots pump can be used in series.

The Roots pump works like a Roots blower. Due to the continuous rotation of the rotor, the pumped gas is sucked from the intake port into the space v0 between the rotor and the pump casing, and then discharged through the exhaust port. Since the v0 space is fully closed after inhalation, the gas is not compressed and expanded in the pump chamber.

However, when the top of the rotor turns over the edge of the exhaust port and the v0 space communicates with the exhaust side, since the gas pressure on the exhaust side is high, a part of the gas is returned to the space v0, so that the gas pressure suddenly increases. When the rotor continues to rotate, the gas exits the pump.

Rotary vane vacuum pump working principle

The rotary vane vacuum pump (referred to as the rotary vane pump) is an oil-sealed mechanical vacuum pump. Its working pressure range is 101325~1.33×10-2(Pa), which belongs to low vacuum pump. It can be used alone or as a foreline pump for other high vacuum pumps or ultra high vacuum pumps. It has been widely used in the production and scientific research departments of metallurgy, machinery, military, electronics, chemical, light industry, petroleum and medicine.

The rotary vane pump can remove the dry gas in the sealed container, and if a gas ballast device is attached, a certain amount of condensable gas can be removed. However, it is not suitable for the removal of gases that are too high in oxygen, corrosive to metals, chemically reactive to pump oil, and contain particulate dust.

The rotary vane pump is one of the most basic vacuum acquisition devices in vacuum technology. Rotary vane pumps are mostly small and medium pumps. Rotary vane pumps are available in single and double stages. The so-called two-stage is to connect two single-stage pumps in series. Generally, it is made into two stages to obtain a higher degree of vacuum.

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

The rotary vane pump is mainly composed of a pump body, a rotor, a rotary vane, an end cover, a spring and the like. A rotor is eccentrically mounted in the cavity of the rotary vane pump, the outer circumference of the rotor is tangent to the inner surface of the pump chamber (there is a small gap between the two), and two rotor blades are mounted in the rotor slot. When rotating, the top end of the rotary vane is kept in contact with the inner wall of the pump chamber by the centrifugal force and the tension of the spring, and the rotation of the rotor drives the rotary vane to slide along the inner wall of the pump chamber.

The two rotary vanes divide the crescent-shaped space enclosed by the rotor, the pump chamber and the two end caps into three parts A, B and C. When the rotor rotates in the direction of the arrow, the volume of the space A communicating with the suction port is Gradually increasing, is in the process of inhalation. The volume of the space C communicating with the exhaust port is gradually reduced, and is in the process of exhausting. The volume of the centered space B is also gradually decreasing and is in the process of compression. Since the volume of the space A is gradually increased (i.e., expanded), the gas pressure is lowered, and the external gas pressure at the inlet of the pump is stronger than the pressure in the space A, so that the gas is sucked. When space A is isolated from the suction port, that is, to the position of space B, the gas begins to be compressed, the volume is gradually reduced, and finally communicates with the exhaust port. When the compressed gas exceeds the exhaust pressure, the exhaust valve is pushed away by the compressed gas, and the gas is discharged to the atmosphere through the oil layer in the oil tank. Continuous operation of the pump achieves the purpose of continuous pumping. If the exhausted gas passes through the air passage and is transferred to another stage (low vacuum level), it is pumped away by the low vacuum stage, and then compressed by the low vacuum stage and discharged to the atmosphere, which constitutes a two-stage pump. At this time, the total compression ratio is borne by two stages, thereby increasing the ultimate vacuum.

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