According to the working principle of imported vacuum pumps, vacuum pumps can be basically divided into two types, namely gas transfer pumps and gas capture pumps. But with the increasing demand for the pressure range of vacuum application technology in the fields of production and scientific research, it is mostly necessary to use several types of vacuum pumps to form a vacuum pumping system to jointly pump air in order to meet the requirements of production and scientific research processes. Therefore, there are many cases of using vacuum units composed of different types of vacuum pumps for pumping. Below, we will briefly introduce some types of gas transmission vacuum pumps.
Gas transfer pump is an imported vacuum pump that can continuously inhale and expel gas to achieve the purpose of pumping. There are basically two types of pumps:
The first major type is variable volume vacuum pump: Variable volume vacuum pump is a type of vacuum pump that uses the periodic changes in pump chamber volume to complete the suction and exhaust processes. The gas is compressed before discharge. This type of pump is divided into two types: reciprocating and rotary:
⑴ Reciprocating vacuum pump: It uses the piston in the pump chamber to perform reciprocating motion, suck in, compress, and discharge gas. Therefore, it is also known as a piston vacuum pump (diaphragm vacuum pump is also a reciprocating vacuum pump).
⑵ Rotating vacuum pump: It uses the rotor inside the pump chamber to rotate and suck in, compress, and discharge gas. There are several types of rotary vacuum pumps:
① Oil sealed vacuum pump: It is a rotary variable volume vacuum pump that uses oil to seal the gaps between moving parts and reduce harmful space. This type of pump usually comes with an air ballast device, so some are also called air ballast vacuum pumps. According to its structural characteristics, it can be divided into the following five types:
a) Rotary vane vacuum pump: The rotor is installed in the pump casing with a certain eccentricity and is close to the fixed surface of the pump casing. Two (or more) rotary vanes are installed in the rotor groove. When the rotor rotates, the rotary vanes can slide back and forth along its radial groove and always contact the inner wall of the pump casing. This rotary vane rotates with the rotor and can divide the pump chamber into several variable volumes.
b) Slide valve vacuum pump: A slide valve is installed outside the eccentric rotor, and the rotor rotates to drive the slide valve to slide and roll along the inner wall of the pump casing. The slide valve rod on the upper part of the slide valve can slide in the swinging slide valve guide rail, dividing the pump chamber into two variable volumes.
c) Fixed plate vacuum pump: There is an eccentric rotor located near the inner surface of the pump inside the pump casing, and a radial sliding plate that always contacts the surface of the rotor is installed on the pump casing. When the rotor rotates, the sliding plate can slide up and down to divide the pump chamber into two variable volumes.
d) Cycloidal vacuum pump: A rotor with a cycloidal profile is eccentrically installed in the pump chamber, which rotates along the inner wall of the pump chamber and divides it into two variable volumes.
e) Multi chamber rotary vane vacuum pump: a rotary vane vacuum pump with multiple independent chambers driven by the same electric motor in parallel within a pump casing.
② Liquid ring vacuum pump: A rotor with multiple blades is eccentrically installed inside the pump casing. When it rotates, it throws liquid (usually water or oil) towards the pump casing to form a concentric liquid ring. The liquid ring and rotor blades form several small volumes with periodic volume changes. When the medium is water, it is also called a water ring vacuum pump.
③ Roots vacuum pump: The pump is equipped with two double or multi bladed rotors that rotate synchronously in opposite directions, and there is a certain gap between the rotors and between the rotor and the inner wall of the pump casing. It belongs to the rotary variable capacity vacuum pump. The mechanical booster pump is this type of vacuum pump.
④ Screw vacuum pump: an air extraction equipment that utilizes a pair of screws to synchronously rotate at high speed in the pump casing, generating suction and exhaust effects. It is an updated product of oil sealed vacuum pumps and can remove gases containing a large amount of water vapor and a small amount of dust. It is widely used in major pharmaceutical and chemical enterprises in China.
⑤ Claw type vacuum pump: The principle of a claw type vacuum pump is similar to Roots, using two claw shaped rotors and the pump chamber to form a suction volume. During the rotation process, the rotor can automatically open and close.
⑥ Vortex vacuum pump: Vortex vacuum pump is an oil-free vacuum pump evolved from a vortex compressor.
Among them, screw vacuum pumps, claw vacuum pumps, and vortex vacuum pumps can also be called dry vacuum pumps, which can achieve oil-free sealing.
The second major category is momentum transfer pumps. This imported vacuum pump relies on high-speed rotating blades or high-speed jets to transfer momentum to gas or gas molecules, allowing gas to be continuously transmitted from the pump inlet to the outlet. It can be specifically divided into the following types:
Molecular vacuum pump: It is a vacuum pump that uses a high-speed rotating rotor to transfer energy to gas molecules, causing them to compress and exhaust. It has the following types:
① Traction molecular pump: Gas molecules collide with a high-speed moving rotor to obtain momentum, which is sent to the outlet. Therefore, it is a momentum transfer pump.
② Turbomolecular pump: The pump is equipped with a slotted disk or a rotor with blades, which rotates between the stator disks (or fixed blades). The linear velocity of the rotor circumference is very high. This type of pump typically operates in a molecular flow state.
③ Composite molecular pump: It is a composite molecular vacuum pump composed of two types of molecular pumps, turbine and traction, which are connected in series.
⑵ Jet vacuum pump: It is a momentum transfer pump that uses the high-speed jet generated by the pressure drop of the Venturi effect to transport gas to the outlet, suitable for working in viscous and transitional flow states. This type of pump can be further divided into the following types in detail:
① Liquid jet vacuum pump: a jet vacuum pump that uses liquid (usually water) as the working medium.
② Gas jet vacuum pump: a jet vacuum pump that uses non condensable gases as the working medium.
③ Steam jet vacuum pump: a jet vacuum pump that uses steam (such as water, oil, or mercury) as the working medium.
⑶ Diffusion pump: a jet vacuum pump that uses low-pressure and high-speed steam flow (such as oil or mercury vapor) as the working medium. Gas molecules diffuse into the vapor jet and are sent to the outlet. The density of gas molecules in the jet is always very low, and this imported vacuum pump is suitable for working in a molecular flow state. It can be divided into:
① Self purification diffusion pump: An oil diffusion pump in which volatile impurities in the pump liquid are transported by specialized machinery to the outlet without returning to the boiler.
② Fractional diffusion pump: This type of pump has a distillation device, which allows working liquid vapor with lower vapor pressure to enter the nozzle for high vacuum operation, while working liquid vapor with higher vapor pressure enters the nozzle for low vacuum operation. It is a multi-stage oil diffusion pump.
Diffusion jet pump: It is a momentum transfer pump composed of a single-stage or multi-stage nozzle with diffusion pump characteristics and a single-stage or multi-stage nozzle with jet vacuum pump characteristics in series. The oil booster pump belongs to this type.
