How are vacuum pumps classified?

With the application of vacuum technology in the field of production and scientific research, the pressure range of its application is becoming wider and wider Most of the vacuum pumping systems composed of several vacuum pumps are required to pump together to meet the requirements of the production and scientific research process Therefore, there are many cases in which different types of vacuum pumping units are selected for pumping For the convenience of users, these vacuum pumps can be divided into two types according to their working principle or structural characteristics, i.e gas transfer pump and gas capture pump This paper introduces these two types of pumps in detail: 1 Gas transfer pump Gas transfer pump is a kind of vacuum pump which can make gas continuously inhale and discharge, so as to achieve the purpose of pumping There are basically two types of pump: 1 Variable volume vacuum pump Variable volume vacuum pump is a kind of vacuum pump which uses the periodic change of the volume of pump cavity to complete the process of suction and discharge The gas is compressed before it is discharged This kind of pump can be divided into two types: reciprocating and rotary: (1) reciprocating vacuum pump: it uses the piston in the pump cavity to do reciprocating motion, to suction, compress and discharge the gas Therefore, it is also called piston vacuum pump (2) rotary vacuum pump: it uses the piston in the cavity of the pump to do rotary movement, to inhale, compress and discharge the gas There are several types of rotary vacuum pump as follows: ① oil sealed vacuum pump: it is a kind of rotary variable volume vacuum pump which uses oil to seal the gap between moving parts and reduce harmful space This kind of pump is usually equipped with air ballast device, so it is also called air ballast vacuum pump 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 shell with a certain eccentricity and close to the fixed surface of the inner surface of the pump shell Two (or more) rotary discs are installed in the rotor groove When the rotor rotates, the rotary disc can slide back and forth along its radial groove and contact with the inner wall of the pump shell all the time The rotary disc rotates with the rotor, which can divide the pump cavity into several variable volumes B) slide valve type vacuum pump: a slide valve is installed outside the eccentric rotor The rotation of the rotor drives the slide valve to slide and roll along the inner wall of the pump housing The slide valve rod on the upper part of the slide valve can slide in the swinging slide valve guide rail, and the pump cavity is divided into two variable volumes C) fixed vane type vacuum pump: an eccentric rotor close to the inner surface of the pump is installed in the pump housing, and a radial sliding vane which always contacts the surface of the rotor is installed on the pump housing When the rotor rotates, the sliding vane can slide up and down to divide the pump cavity into two variable volumes D) cycloid vacuum pump: a cycloid rotor is installed in the pump chamber eccentrically, which rotates along the inner wall of the pump chamber and divides the pump chamber into two variable volumes E) multi chamber rotary vane vacuum pump: a rotary vane vacuum pump with multiple independent chambers driven by the same motor is installed in parallel in a pump housing ② dry vacuum pump: it is a variable volume vacuum pump without oil (or liquid) seal ③ liquid ring vacuum pump: the rotor with multiple blades is installed in the pump casing eccentrically When it rotates, the liquid (usually water or oil) is thrown to the pump casing to form a concentric liquid ring of the pump casing The liquid ring and the rotor blades form several small volumes with periodic volume changes, so it is also called rotary variable volume vacuum pump ④ roots vacuum pump: the pump is equipped with two double blade or multi blade rotors rotating synchronously in opposite directions, and there is a certain gap between the rotors and between the rotors and the inner wall of the pump housing It belongs to rotary vacuum pump The mechanical booster pump is this type of vacuum pump 2 Momentum transfer pump: this kind of pump relies on high-speed rotating blades or high-speed jets to transfer momentum to gas or gas molecules, so that the gas is continuously transferred from the inlet to the outlet of the pump It can be divided into the following types (1) molecular vacuum pump: it is a vacuum pump that uses a high-speed rotating rotor to transmit energy to the gas molecules to compress and exhaust them It has the following types: ① traction molecular pump: the gas molecules collide with the high-speed rotor to obtain momentum, which is sent to the outlet, so it is a momentum transfer pump ② turbine molecular pump: the pump is equipped with a disk with grooves or a rotor with blades, which rotates between the stator disks (or fins) The linear speed of the rotor circumference is very high This kind of pump usually works in the molecular flow state ③ compound molecular pump: it is a kind of compound molecular vacuum pump which is composed of two kinds of molecular pumps: turbo type and traction type (2) jet vacuum pump: it is a kind of momentum transfer pump that uses the high-speed jet produced by the pressure drop of Venturi effect to deliver the gas to the outlet It is suitable for working in the state of viscous flow and transitional flow This kind of pump can be further divided into the following categories: ① liquid jet vacuum pump: jet vacuum pump with liquid (usually water) as working medium ② gas jet vacuum pump: jet vacuum pump with non condensable gas as working medium ③ steam jet vacuum pump: a jet vacuum pump with steam (such as water, oil or mercury) as working medium (3) diffusion pump: jet vacuum pump with low pressure and high speed steam flow (oil or mercury and other steam) as working medium The gas molecules diffuse into the steam jet and are sent to the outlet The molecular density of the gas in the jet is always very low This kind of pump is suitable for working in the molecular flow state It can be divided into: ① self purification diffusion pump: a kind of oil diffusion pump in which the volatile impurities in the pump liquid are transported to the outlet by special machinery without returning to the boiler ② fractionation diffusion pump: this pump has a fractionation device, which enables the working liquid vapor with low vapor pressure to enter the nozzle with high vacuum working, while the working liquid vapor with high vapor pressure to enter the nozzle with low vacuum working It is a multi-stage oil diffusion pump (4) 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 injection vacuum pump characteristics in series Oil booster pump belongs to this type (5) ion transfer pump: it is a kind of momentum transfer pump that delivers the ionized gas to the outlet under the action of electromagnetic field or electric field 2 Gas capture pump this kind of pump is a vacuum pump which makes gas molecules adsorbed or condensed on the inner surface of the pump, so as to reduce the number of gas molecules in the container and achieve the purpose of pumping It has the following types 1 Adsorption pump is a kind of trapping vacuum pump, which mainly relies on the physical adsorption of adsorbents (such as porous materials) with large surface to pump gas 2 Getter pump: it is a vacuum pump that uses getter to capture gas by chemical combination Getters are usually metals or alloys in the form of lumps or deposited fresh films Sublimation pump belongs to this type 3 Getter ion pump is used to make the ionized gas adsorb on the surface of the material with getter through the action of electromagnetic field or electric field, so as to achieve the purpose of getter It has the following types (1) evaporation ion pump: a vacuum pump in which the ionized gas in the pump is adsorbed on the suction material which is sublimed (or evaporated) in an intermittent or continuous way and covered on the inner wall of the pump to achieve air extraction (2) sputtering ion pump: a vacuum pump in which the ionized gas in the pump is adsorbed on the suction material continuously sputtered from the cathode to achieve the purpose of pumping 4 Low temperature pump: vacuum pump using low temperature surface to trap gas performance parameters and application scope of vacuum pump (1) limit pressure of vacuum pump The ultimate pressure unit of the pump is PA, which means that the pump is equipped with a standard test cover at the inlet and operates according to the specified conditions Under the condition of normal operation without introducing gas, the Zui low pressure tends to be stable (2) air extraction rate of vacuum pump the unit of air extraction rate of the pump is m3 / s or L / s, which refers to the ratio of the gas flow through the test cover to the equilibrium pressure measured at the specified position of the test cover when the pump is equipped with a standard test cover and operates according to the specified conditions Referred to as the pumping speed of the pump (3) air extraction of vacuum pump the unit of air extraction of vacuum pump is pa m3 / s or PA L / s It refers to the gas flow at the pump inlet (4) starting pressure of vacuum pump the unit of starting pressure of vacuum pump is PA, which refers to the pressure when the pump starts without damage and has the function of pumping (5) pressure of the front stage of the pump the unit of pressure of the front stage of the vacuum pump is PA, which means the outlet pressure of the vacuum pump with the exhaust pressure lower than one atmospheric pressure (6) the unit of Zui large front stage pressure at the vacuum pump port is PA, which means that the pressure of the front stage which can damage the pump is exceeded (7) Zui high working pressure of vacuum pump The unit of Zui high working pressure of vacuum pump is PA, which refers to the inlet pressure corresponding to Zui high air extraction Under this pressure, the pump can work continuously without deterioration or damage (8) compression ratio compression ratio refers to the ratio of the outlet pressure of the pump to the inlet pressure of the given gas (9) he's coefficient: the ratio of the actual pumping speed on the pumping channel area to the theoretical pumping speed calculated according to the molecular discharge flow (10) pumping coefficient is the ratio of the actual pumping speed of the pump to the theoretical pumping speed at the pump inlet calculated according to the molecular discharge (11) return flow rate the unit of return flow rate of the pump is g / cm2 S It refers to the pump flow mass flow rate per unit area through the pump inlet when the pump operates under specified conditions (12) allowable quantity of water vapor unit of allowable quantity of water vapor is kg / h, which refers to the mass flow of water vapor that can be pumped out by the gas ballast pump in continuous operation under normal environmental conditions (13) Zui large allowable water vapor inlet pressure Zui large allowable water vapor inlet pressure unit is PA It refers to the Zui high inlet pressure of water vapor that can be pumped out by the gas ballast pump in continuous operation under normal environmental conditions.