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This post was last edited by foam_ZPTK on 2019-7-11 05:28. A vacuum pump is a device or apparatus that uses mechanical, physical, chemical, or physicochemical methods to evacuate a container in order to create a vacuum. In simple terms, a vacuum pump is a device that uses various methods to improve, create, and maintain a vacuum in a closed space. Based on the working principle of vacuum pumps, they can basically be divided into two types: gas capture pumps and gas transfer pumps. It is widely used in industries such as metallurgy, chemicals, food, and electronic coating. With the development of vacuum applications, a wide variety of vacuum pumps has been developed, with pumping speeds ranging from a few tenths of a liter per second to hundreds of thousands or even millions of liters per second. As the requirements for the pressure range in which vacuum technology is applied in production and scientific research become increasingly wider, it is often necessary to use a vacuum pumping system composed of several different vacuum pumps in order to meet the needs of these processes. Given the wide range of working pressures encountered in vacuum applications, no single type of vacuum pump can be suitable for all such pressure ranges; instead, different types of vacuum pumps must be used depending on the specific working pressure and requirements. For ease of use and to meet the requirements of various vacuum processing processes, different vacuum pumps are sometimes combined based on their performance characteristics and used in the form of units. Commonly used vacuum pumps include dry screw vacuum pumps, water ring pumps, reciprocating pumps, slide valve pumps, rotary vane pumps, Roots pumps, and diffusion pumps. These pumps are the essential main types of pumps utilized in various sectors of China’s national economy where vacuum processes are employed. In recent years, driven by the continuous rapid economic development of our country, the downstream industries related to vacuum pumps have maintained a fast growth trend. Coupled with the ongoing expansion of applications for vacuum pumps, China’s vacuum pump industry has achieved sustained, stable, and rapid development. Pump body structure: The layout of the pump body in a vacuum pump determines the overall structure of the pump. In the vertical structure, the air inlet and outlet are arranged horizontally, which facilitates the assembly and connection of pipelines. However, the pump has a high center of gravity, resulting in poor stability at high speeds; therefore, this type is mostly used in small pumps. The air inlet of a horizontal pump is at the top, and the exhaust outlet is at the bottom. Sometimes, for the convenience of installing and connecting the pipes in the vacuum system, the exhaust port can be arranged horizontally, meaning that the inlet and exhaust directions are perpendicular to each other. At this time, the exhaust port can open in either the left or right direction; apart from the end connected to the exhaust pipe, the other end is either blocked or connected to a bypass valve. This pump design has a low center of gravity, ensuring good stability during high-speed operation. This structure is commonly used in large and medium-sized pumps. The two rotor shafts of the pump are installed perpendicular to the horizontal plane. The assembly clearance of this structure is easy to control, the rotor is convenient to assemble, and the pump occupies a small area. However, the pump has a high center of gravity, the gears are difficult to disassemble and assemble, and the lubrication mechanism is also relatively complex. Drive method of the pump ⑴ Whether the vibrations generated during the operation of the vacuum pump have any impact on the process and the environment. If the process does not permit it, a vibration-free pump should be selected or vibration prevention measures should be taken. ⑵Determine the composition of the gas to be drawn, whether it contains condensable vapors, particulate dust, or is corrosive, etc. When selecting a vacuum pump, it is necessary to know the gas composition and choose an appropriate pump for the gas to be evacuated. If the gas contains vapors, particles, and corrosive gases, it is advisable to consider installing auxiliary equipment such as condensers and dust collectors on the inlet pipeline of the pump. ⑶At its operating pressure, the vacuum pump should be capable of removing all the gas generated during the process in the vacuum equipment. ⑷Combine the vacuum pump correctly. Due to the selective pumping capability of vacuum pumps, sometimes a single pump cannot meet the pumping requirements; thus, several pumps must be used in combination and complement each other to fulfill those requirements. For example, titanium sublimation pumps have a high pumping speed for hydrogen but cannot pump helium, while triode-type sputter ion pumps (or diode-type asymmetric cathode sputter ion pumps) have a certain pumping speed for argon; by combining the two, a better vacuum level can be achieved in the vacuum system. Additionally, some vacuum pumps cannot operate at atmospheric pressure and require pre-evacuation ； Some vacuum pumps have an outlet pressure lower than atmospheric pressure, requiring a pre-pump; therefore, these pumps need to be used in combination. ⑸Requirements for oil contamination in vacuum equipment. When the equipment requires absolutely oil-free operation, various oil-free pumps should be selected, such as water ring pumps, molecular sieve adsorption pumps, sputter ion pumps, cryopumps, etc. If the requirements are not very stringent, one can opt for a pump with an oil pump, along with certain oil-contamination prevention measures—such as adding a cold trap, baffles, or oil traps—to also meet the requirements for a clean vacuum. ⑹Select the operating point of the vacuum pump correctly. Each type of pump has a certain operating pressure range. For example, the operating pressure range of the 2BV series water ring vacuum pumps is from 760 mmHg to 25 mmHg (absolute pressure). Within such a wide pressure range, the pumping speed of the pump changes with pressure (for detailed variations, refer to the pump’s performance curve); its stable operating pressure range is 760–60 mmHg. Therefore, it is more appropriate to select the pump’s operating point within this range, rather than allowing it to operate at 25–30 mmHg for an extended period of time. ⑺What is the environmental impact of the oil vapor discharged by vacuum pumps? If the environment does not permit pollution, an oil-free vacuum pump can be used, or the oil vapor can be vented outside. ⑻The operating pressure of the vacuum pump should meet the requirements for ultimate vacuum and operating pressure of the vacuum equipment. For example, if a certain vacuum drying process requires an operating vacuum level of 10 mmHg, the ultimate vacuum capacity of the vacuum pump selected must be at least 2 mmHg; ideally, it should be able to reach 1 mmHg. Typically, the ultimate vacuum capacity of the pump chosen should be half to an order of magnitude higher than the operating vacuum level of the vacuum equipment. ⑼Prices, operating, and maintenance costs of vacuum pumps. Mechanical installation of vacuum pumps ⑴ Vacuum pumps should be installed in a solid and stable area on the ground, with sufficient space around them to facilitate inspection, maintenance, and upkeep. ⑵The foundation beneath the vacuum pump base should be level; it is recommended to use shock-absorbing rubber pads at the four corners of the base or to install it using bolts, in order to ensure smooth operation of the vacuum pump with minimal vibration. ⑶The connection pipes between the vacuum pump and the system must be securely sealed. For small vacuum pumps, metal pipes with oil-resistant rubber gaskets can be used; vacuum hoses are also an option for such pumps. The diameter of the pipes must be at least equal to the suction port diameter of the vacuum pump, and the pipes should be short with as few bends as possible. (When welding pipelines, slag in the pipes must be removed; it is strictly prohibited for slag to enter the vacuum pump chamber.) ) ⑷ In the connecting piping, users can install a valve and a vacuum gauge above the inlet of the vacuum pump, allowing them to check the ultimate pressure of the vacuum pump at any time. ⑸Connect the power supply as specified on the motor’s nameplate, and install a grounding wire along with fuses and thermal relays of appropriate specifications. ⑹When testing the vacuum pump under power, the motor belt must be removed, and it is necessary to confirm that the pump rotates in the correct direction before putting it into use, in order to prevent oil spraying due to reverse rotation of the vacuum pump. (Turn towards the direction indicated by the protective shield) ⑺ For vacuum pumps with cooling water, connect the cooling water as specified. ⑻When installing a solenoid valve at the vacuum pump outlet, the valve and the vacuum pump should operate simultaneously. ⑼When the gas discharged by the vacuum pump affects the working environment, a pipe can be installed at the exhaust port to direct it away, or an oil mist filter can be fitted. In terms of the pump body structure, the two rotors of the vacuum pump are made to rotate synchronously relative to each other by means of a pair of high-precision gears. The drive shaft is connected to the motor via a coupling. There are mainly two types of arrangements for the transmission structure: one is where the motor and gears are located on the same side of the rotor, as shown in the figure. The driven rotor is driven directly by the gear at the motor end, which results in minimal torsional deformation of the drive rotor shaft. As a result, the gap between the two rotors does not change due to excessive torsional deformation of the drive shaft, thereby maintaining a uniform gap between the rotors during operation. The biggest drawback of this drive method is: a. There are three bearings on the driving shaft, which increases the difficulty of machining and assembly of the pump; it also makes it inconvenient to disassemble, assemble, and adjust the gears ； b. The overall structure is unbalanced, with the pump’s center of gravity leaning towards the motor and gearbox side. Feature (1): High pumping speed over a wide pressure range ； (2) The rotor has good geometric symmetry; therefore, it generates little vibration and operates smoothly. There are gaps between the rotor and the housing, as well as between the rotors themselves; no lubrication is required. Frictional losses are minimal, which can **reduce the driving power, thereby enabling higher rotational speeds** ； (3) There is no need for oil sealing or lubrication in the pump chamber, which reduces the contamination of the vacuum system by oil vapors ； (4) There is no compression in the pump chamber, and no exhaust valve. It has a simple and compact structure, and is not sensitive to dust and water vapor in the gas being drawn in ； (5) The compression ratio is relatively low, resulting in poor hydrogen pumping efficiency ； (6) The rotor surface is a curved cylindrical surface with a relatively complex shape, making it difficult to machine and inspect. A gas transfer pump is a type of vacuum pump that enables continuous intake and exhaust of gas in order to achieve pumping action. There are basically two types of such pumps: variable-volume vacuum pumps, which use periodic changes in the volume of the pump chamber to carry out the intake and exhaust processes, with the gas being compressed before it is exhausted. This type of pump comes in two varieties: reciprocating and rotary vane: (1) Reciprocating vacuum pump: It utilizes a piston within the pump chamber to move back and forth, thereby drawing in, compressing, and expelling gas. Therefore, it is also known as a piston-type vacuum pump. (2) Rotary vane vacuum pump: It uses a piston moving in a rotational motion within the pump chamber to draw in gas, compress it, and discharge it. Rotary vacuum pumps come in the following types: ① Oil-sealed vacuum pump: It is a rotary displacement vacuum pump that uses oil to seal the gaps between moving components, thereby reducing unwanted spaces. This type of pump usually comes with a gas ballast device; hence, it is also known as a gas-ballasted vacuum pump. Based on their structural characteristics, they are divided into the following five forms. A rotary vane vacuum pump: The rotor is mounted within the pump casing at a certain eccentric distance, close to the fixed surface on the inner wall of the casing. Two (or more) vanes are placed within the rotor slots; as the rotor rotates, these vanes can slide back and forth along their radial slots while remaining in constant contact with the inner wall of the pump casing. These vanes rotate together with the rotor, thereby dividing the pump chamber into several chambers with variable volumes. b. Slide valve vacuum pump: A slide valve is mounted outside the eccentric rotor. As the rotor rotates, it causes the slide valve to slide and roll along the inner wall of the pump casing. The slide valve rod located above the slide valve can move within a pivotable slide valve guide rail; meanwhile, the pump chamber is divided into two chambers with variable volumes. c. Fixed-vane vacuum pump: An eccentric rotor located close to the inner surface of the pump chamber is installed within the pump casing; a radial vane that remains in constant contact with the rotor’s surface is attached to the casing. As the rotor rotates, the vane moves up and down, thereby dividing the pump chamber into two chambers with variable volumes. d. Epicyclic vacuum pump: An eccentric rotor with an epicyclic profile is installed within the pump chamber; it rotates along the inner wall of the chamber, dividing it into two volumes that can change. e. Multi-chamber rotary vane vacuum pump: A rotary vane vacuum pump in which multiple independent working chambers driven by a single motor are mounted in parallel within one pump housing. ②Dry screw vacuum pump: It is a variable-volume vacuum pump that does not use oils (or liquids) for sealing. ③Liquid-ring vacuum pump: It has a multi-bladed rotor that is eccentrically mounted inside the pump casing. As it rotates, it throws liquid (usually water or oil) onto the inner wall of the casing, forming a liquid ring concentric with the casing. This liquid ring and the rotor blades create several small volumes whose sizes change periodically; hence, it is also known as a rotary variable-volume vacuum pump. ④Roots vacuum pump: It contains two lobed or multi-lobed rotors that rotate synchronously in opposite directions. A certain clearance is maintained between the rotors as well as between each rotor and the inner wall of the pump casing. It belongs to the rotary variable-volume vacuum pump. A mechanical booster pump is a vacuum pump of this type. Momentum transfer pumps operate by using rapidly rotating blades or high-speed jets to transfer momentum to gases or gas molecules, thereby continuously transferring the gas from the pump’s inlet to its outlet. It can be specifically divided into the following types. (1) Molecular vacuum pump: It is a type of vacuum pump that uses a rapidly rotating rotor to transfer energy to gas molecules, thereby compressing and exhausting them. It comes in the following types: ① Molecular pump driven by traction: Gas molecules gain momentum by colliding with a high-speed rotating rotor and are then sent to the outlet; therefore, it is a type of momentum-transfer pump. ②Turbomolecular pump: The pump contains grooved disks or bladed rotors that rotate between stator disks (or stators). The linear velocity at the rotor’s circumference is very high. This type of pump usually operates in a molecular flow regime. ③Composite molecular pump: It is a composite molecular vacuum pump formed by connecting a turbomolecular pump and a drag molecular pump in series. (2) Jet vacuum pump: It is a momentum transfer pump that uses the pressure drop resulting from the Venturi effect to generate a high-speed jet for transporting gas to the outlet, and is suitable for operating in viscous and transitional flow conditions. This type of pump can be further divided into the following categories: ① Liquid jet vacuum pumps: Vacuum pumps that use a liquid (usually water) as the working medium. ②Gas jet vacuum pump: A jet vacuum pump that uses a non-condensable gas as the working medium. ③Steam jet vacuum pump: A jet vacuum pump that uses steam (water, oil, or mercury vapor) as the working medium. Diffusion pump: A jet vacuum pump that uses a low-pressure, high-speed stream of steam (such as oil or mercury vapor) as the working medium. Gas molecules diffuse into the steam jet and are sent to the outlet. The density of gas molecules in the jet is always very low; such pumps are suitable for operating in a molecular flow regime. They can be classified as follows: ① Self-purifying diffusion pump: An oil diffusion pump in which volatile impurities in the pumping fluid are mechanically transported to the outlet and do not return to the boiler. ② Fractionating diffusion pump: This type of pump is equipped with a fractionation device that allows vaporized working fluid with a lower vapor pressure to enter nozzles designed for operation in high vacuum conditions, while vaporized working fluid with a higher vapor pressure enters nozzles designed for operation in low vacuum conditions; it is a multi-stage oil diffusion pump. (4) Diffusion jet pump: It is a momentum transfer pump consisting of single-stage or multi-stage nozzles with the characteristics of diffusion pumps in series with single-stage or multi-stage nozzles with the characteristics of jet vacuum pumps. Oil booster pumps fall into this category. (5) Ion transport pump: It is a momentum transfer pump that transports the ionized gas to the outlet under the action of an electromagnetic field or an electric field. A gas capture pump is a type of vacuum pump in which gas molecules are adsorbed or condensed on the inner surface of the pump, thereby reducing the number of gas molecules inside the container and achieving the purpose of evacuation. There are several types of such pumps. Adsorption pump: It is a type of capture vacuum pump that relies on the physical adsorption effect of adsorbents with large surfaces (such as porous materials) to evacuate gas. Absorber pump: It is a vacuum pump that uses an absorber to capture gases through chemical bonding. Absorbers are usually metals or alloys in the form of blocks or freshly deposited thin films. Sublimation pumps belong to this type. Getter ion pump: It uses an electromagnetic field or electric field to cause the ionized gas to be adsorbed on the surface of a getter material, thereby achieving the purpose of vacuum pumping. It comes in the following types. (1) Evaporation ion pump: A type of vacuum pump in which the ionized gas inside the pump is adsorbed onto a pumping material coated on the inner wall of the pump and sublimating (or evaporating) in a intermittent or continuous manner, thereby achieving vacuum pumping. (2) Sputtering ion pump: A type of vacuum pump in which the ionized gas inside the pump is adsorbed onto the pumping material continuously sputtered from the cathode, thereby achieving evacuation. Cryopumps: Vacuum pumps that use cryogenic surfaces to capture gases can be classified into three categories based on their vacuum level: rough vacuum, high vacuum, and ultra-high vacuum. The rough vacuum system is mainly used to remove air and other gases that are somewhat corrosive, insoluble in water, and may contain a small amount of solid particles. It is widely used in processes such as vacuum evaporation, concentration, impregnation, and drying in industries including food, textiles, pharmaceuticals, and chemicals. This type of pump features a high vacuum level, simple structure, ease of use, reliable operation, and convenient maintenance. Mainly used for rough vacuum. In processes with high gas extraction rates. It is primarily used to remove air and other gases that are non-corrosive, insoluble in water, and contain a small amount of solid particles, in order to create a vacuum inside a sealed container. A small amount of liquid is allowed to be mixed in the inhaled gas. It is widely used in industries such as machinery, pharmaceuticals, food, and petrochemicals. It is one of the main vacuum devices used to achieve a rough vacuum. It is widely used in industries such as chemicals, food, and building materials, and is particularly suitable for processes such as vacuum crystallization, drying, filtration, and evaporation. The oil-free (corrosion-resistant) vertical reciprocating vacuum pump is an upgraded version of the horizontal vacuum pump, and it is the main equipment used to achieve a rough vacuum. Thanks to the fully sealed design, complete isolation between the crankcase and the cylinders is achieved ； Together with the use of self-lubricating materials in the piston rings, advanced oil-free lubrication is achieved. Due to the absence of wastewater discharge, this type of vacuum pump is particularly suitable for processes such as vacuum distillation, vacuum evaporation, vacuum drying, vacuum concentration, and vacuum impregnation in industries like chemicals, pharmaceuticals, and food processing. High-vacuum rotary piston vacuum pumps are widely used in the production and development of new materials, new technologies, and new processes such as vacuum crystal pulling, vacuum coating, vacuum metallurgy, vacuum heat treatment, vacuum impregnation, vacuum drying, vacuum distillation, vacuum slurry preparation, and aerospace simulation tests. The slide valve vacuum pump can be used alone or as a forepump for rotary vane vacuum pumps, oil booster pumps, and oil diffusion pumps. When pumping gases that are corrosive to ferrous metals, cause chemical reactions with vacuum oil, or contain large amounts of steam and dust, additional equipment is required. Advantages: It has several times higher durability compared to rotary vane vacuum pumps, as well as a higher pumping speed; however, its price is relatively higher. One of the basic devices used to remove gas from a sealed container. It can be used alone or as a pre-pump for booster pumps, diffusion pumps, and molecular pumps. This type of pump is widely used in industries such as metallurgy, machinery, electronics, chemicals, petroleum, and pharmaceuticals for processes such as vacuum smelting, vacuum coating, vacuum heat treatment, and vacuum drying. The sliding vane rotary vacuum pump features a compact structure, small size, light weight, low noise, and minimal vibration. Therefore, it is suitable as a pre-pump for diffusion pumps, and is even more appropriate for use in precision instruments and laboratories. For example: mass spectrometers, refrigerator production lines, vacuum freeze-dryers, etc. The Roots vacuum pump is a rotary variable-volume vacuum pump that requires a pre-pump in order to be used over a wide pressure range. It has a high pumping speed and is not sensitive to dust and water vapor present in the gas being evacuated. It is widely used in industries such as metallurgy, chemicals, food, and electronic coating. Primarily used as the main pump in vacuum systems, and requires assistance from a pre-pump. Such as: water ring vacuum pumps, slide valve vacuum pumps, vertical oil-free vacuum pumps, molecular vacuum pumps, etc. The record for the largest rotary vane vacuum pump in China is 20,000 L/S.