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Basic overview
Introduction
The vacuum pump is a rotary variable-volume gas delivery pump. The vacuum pump must be matched with the fore-stage pump before it can be used in a wide pressure range. It has a large pumping speed and is insensitive to the dust and water vapor contained in the gas being pumped. Widely used in metallurgy, chemical industry, food, electronic coating and other industries.
development of
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 indispensable main pumps in the application of vacuum technology in various industries of our national economy. . In recent years, with the sustained and rapid development of China's economy, the vacuum pump related downstream application industry has maintained a rapid growth momentum. At the same time, due to the continuous expansion of vacuum pump application fields and other factors, China's vacuum pump industry has achieved sustained and stable development.
According to the "2013-2017 in-depth investigation and investment forecast analysis report of China's vacuum pump manufacturing industry" data shows [1]
In the vacuum pump market of China, the entry and success of foreign companies have become an indisputable fact. The Japanese vacuum is distributed around the world, the German Leybold is expanded in China, the United States Taisell Group, South Korea Youcheng and other international famous manufacturers have also sought partners in the China builds a manufacturing base. Their appetite is very big, and it is likely to be the market for whale swallowing vacuum pumps. In recent years, although some domestic companies have gradually emerged and occupied a leading position in the vacuum pump market, most companies have poor R & D capabilities, and high-end products are still technically inferior to foreign counterparts.
Features
(1) There is a larger pumping speed in a wider pressure range;
(2) The rotor has good geometric symmetry, so the vibration is small and the operation is stable. There are gaps between the rotors and between the rotor and the casing, no lubrication is needed, and the friction loss is small, which can greatly reduce the driving power and thus achieve a higher speed;
(3) There is no need to seal and lubricate with oil in the pump cavity, which can reduce the pollution of the oil vapor to the vacuum system;
(4) There is no compression and no exhaust valve in the pump cavity. Simple and compact structure, insensitive to dust and water vapor in the pumped gas;
(5) The compression is relatively low, and the effect of pumping hydrogen is poor;
(6) The surface of the rotor is a curved cylindrical surface with a complicated shape, which is difficult to process and inspect.
structure
(1) The overall structure of the pump
The layout of the pump body of the vacuum pump determines the overall structure of the pump.
The vertical structure of the inlet and exhaust ports are set horizontally, and it is more convenient to assemble and connect the pipelines. However, the center of gravity of the pump is high and the stability is poor during high-speed operation, so this type is mostly used for small pumps.
The intake port of the horizontal pump is on the top, and the exhaust port is on the bottom. Sometimes, to facilitate the installation and connection of the vacuum system, the exhaust port can be taken out from the horizontal direction, that is, the inlet and exhaust directions are perpendicular to each other. At this time, the exhaust port can be opened from both left and right directions, except for connecting one end of the exhaust pipe, the other end is blocked or connected to the bypass valve. This pump has a low center of gravity and good stability during high-speed operation. Generally, large and medium-sized pumps adopt this structure.
The two rotor shafts of the pump are installed perpendicular to the horizontal plane. The assembly gap of this structure is easy to control, the rotor is easy to assemble, and the pump covers a small area. However, the center of gravity of the pump is high and the gears are inconvenient to disassemble, and the lubrication mechanism is relatively complicated.
(2) The transmission mode of the pump
The two rotors of the vacuum pump are operated relatively synchronously through a pair of high-precision gears. The driving shaft is connected to the motor through a coupling. There are two main types of transmission structure layout: one is that the motor and gear are placed on the same side of the rotor as shown in the figure. The driven rotor is directly driven by the gear on the motor end, so that the torsional deformation of the active rotor shaft is small, the gap between the two rotors will not change due to the large torsional deformation of the drive shaft, so the gap between the rotors is running Even in the process. The biggest shortcomings of this transmission method are: a. There are three bearings on the driving shaft, which increases the difficulty of processing and assembly of the pump, and it is also inconvenient to disassemble and adjust the gear; b. The overall structure is uneven, and the center of gravity of the pump is biased toward the motor and gear Box side.
classification
According to its working principle, it is basically divided into two types: gas delivery pump and gas capture pump. Gas delivery pumps include: 1, liquid ring vacuum pump (water ring vacuum pump) 2, reciprocating vacuum pump 3, rotary vane vacuum pump 4, fixed vane vacuum pump 5, sliding valve vacuum pump 6, trochoidal vacuum pump 7, dry screw Vacuum pump 8, Roots vacuum pump 9, molecular vacuum pump 10, traction molecular pump 11, compound vacuum pump 12, water jet vacuum pump 13, gas jet pump 14, steam jet pump 15, diffusion pump, etc. Gas trap pumps include: adsorption pumps and cryopumps, etc.
Gas transmission pump
The gas transmission pump is a vacuum pump that can continuously suck and discharge gas to achieve the purpose of pumping. There are basically two types of pumps:
Variable volume vacuum pump
A vacuum pump that uses the periodic change of the volume of the pump cavity to complete the suction and exhaust process. The gas is compressed before being discharged. This pump is divided into two types: reciprocating and rotary vane:
(1) Reciprocating vacuum pump: the piston in the pump cavity is used for reciprocating motion to suck, compress and discharge gas. Therefore, it is also called piston vacuum pump.
(2) Rotary vane vacuum pump: the piston in the pump cavity is used for rotary motion to suck, compress and discharge the gas. Rotary vacuum pumps have the following forms:
â‘ Oil-sealed vacuum pump: It is a rotary variable volume vacuum pump that uses oil to seal the gap between moving parts and reduce harmful space. This kind of pump usually has a gas ballast device, so it is also called gas ballast vacuum pump. According to its structural characteristics, it is divided into the following five forms.
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 inner surface of the pump casing. Two (or more) rotor blades are installed in the rotor groove. When the rotor rotates, the rotor blades It can slide back and forth along its radial groove and is always in contact with the inner wall of the pump casing. This rotor rotates with the rotor and can divide the pump cavity into several variable volumes.
b. Spool valve vacuum pump: A spool valve is installed outside the eccentric rotor. The rotation of the rotor drives the spool valve to slide and roll along the inner wall of the pump casing. The spool valve stem above the spool valve can slide in the swingable spool guide rail. The cavity is divided into two variable volumes.
c. Fixed-blade vacuum pump: an eccentric rotor close to the inner surface of the pump is installed in the pump housing, and a radial sliding vane is always in contact with the rotor surface. When the rotor rotates, the sliding vane can slide up and down to move the pump The cavity is divided into two variable volumes.
d. Cycloid vacuum pump: A rotor with a trochoid is installed eccentrically in the pump cavity, which rotates along the inner wall of the pump cavity and divides the pump cavity into two variable volumes.
e. Multi-chamber rotary vane vacuum pump: Multiple independent working chamber rotary vane vacuum pumps driven by the same motor are installed in parallel in one pump housing.
â‘¡Dry type screw vacuum pump: It is a variable volume vacuum pump that is not sealed with oil (or liquid).
â‘¢ Liquid ring vacuum pump: The rotor with multiple blades is eccentrically installed in the pump casing. When it rotates, the liquid (usually water or oil) is thrown into the pump casing to form a concentric ring liquid in the pump casing. The ring liquid is the same as the rotor The blades form several small volumes with periodic changes in volume, so they are also called rotary variable volume vacuum pumps.
â‘£Roots vacuum pump: The pump is equipped with two double-lobed or multi-lobed rotors rotating synchronously in opposite directions, and a certain gap is maintained between the rotors and the rotor and the inner wall of the pump casing. It belongs to the rotary variable volume vacuum pump. The mechanical booster pump is this form of vacuum pump.
Momentum transmission pump: This pump relies on high-speed rotating blades or high-speed jets to transmit momentum to gas or gas molecules, so that gas is continuously transmitted from the pump inlet to the outlet. It can be divided into the following types.
(1) Molecular vacuum pump: It is a kind of vacuum pump that uses a high-speed rotating rotor to transmit energy to gas molecules to compress and exhaust. It has the following types:
â‘ Traction molecular pump: Gas molecules collide with the rotor moving at high speed to obtain power, and are sent to the outlet. Therefore, it is a momentum transmission pump.
â‘¡Turbo molecular pump: The pump is equipped with a slotted disk or a rotor with blades, which rotates between the stator disks (or stators). The linear velocity of the rotor circumference is high. Such pumps usually work under molecular flow.
â‘¢ Compound molecular pump: It is a compound molecular vacuum pump connected in series by two molecular pumps of turbo type and traction type.
(2) Jet vacuum pump: It is a kind of momentum transmission pump that uses high-speed jet produced by the pressure drop of Venturi effect to deliver gas to the outlet. It is suitable for working in the state of viscous retention and transitional flow. This pump can be divided into the following types in detail:
â‘ Liquid jet vacuum pump: Jet vacuum pump with liquid (usually water) as the working medium.
â‘¡ Gas jet vacuum pump: Jet vacuum pump with non-condensable gas as working medium.
â‘¢ Steam jet vacuum pump: a steam jet vacuum pump with steam (water, oil or mercury vapor) as the working medium
(3) Diffusion pump: a jet vacuum pump that uses low-pressure high-speed steam flow (steam such as oil or mercury) 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, this pump is suitable for working in the state of molecular flow. It can be divided into:
â‘ Self-purifying diffusion pump: A kind of oil diffusion pump in which the volatile impurities in the pump liquid are transported to the outlet through a special machine without returning to the boiler
â‘¡ Fractionation diffusion pump: This pump has a fractionation device, so that the working fluid vapor with low steam pressure enters the nozzle for high vacuum operation, and the working fluid vapor with high steam pressure enters the nozzle for low vacuum operation. Grade oil diffusion pump.
(4) Diffusion jet pump: it is a momentum transmission pump composed of a single-stage or multi-stage nozzle with the characteristics of a diffusion pump and a single-stage or multi-stage nozzle with the characteristics of a jet vacuum pump. The oil booster pump belongs to this form.
(5) Ion transmission pump: It is a momentum transmission pump that transports ionized gas to the outlet under the action of electromagnetic field or electric field.
Gas trap pump
This pump is a kind 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 in the container to achieve the purpose of pumping.
Adsorption pump: It is a trapping vacuum pump that mainly relies on the physical adsorption of an adsorbent (such as a porous substance) with a large surface
Getter pump: It is a vacuum pump that uses a getter to capture gas in a chemically combined manner. Getters are usually metals or alloys in the form of lumps or deposited fresh films. Sublimation pumps belong to this form.
Getter ion pump: It is to make the ionized gas adsorbed on the surface of the getter material by the action of electromagnetic field or electric field to achieve the purpose of pumping. It has the following types.
(1) Evaporating ion pump: A vacuum pump in which the ionized gas in the pump is adsorbed on the getter material that sublimates (or evaporates) in a discontinuous or continuous manner and covers the inner wall of the pump to achieve pumping.
(2) Sputtering ion pump: a vacuum pump in which the ionized gas is adsorbed on the getter material continuously sputtered from the cathode to achieve the purpose of pumping.
Cryogenic pumps: vacuum pumps that use low-temperature surfaces to capture gas
According to its vacuum degree, it can be divided into three categories: rough vacuum, high vacuum and ultra high vacuum.
Coarse vacuum system
It is mainly used to evacuate air and other gases that are corrosive, insoluble in water, and contain a small amount of solid particles. Widely used in vacuum evaporation, concentration, impregnation, drying and other processes in food, textile, pharmaceutical, chemical and other industries. This type of pump has the characteristics of high vacuum, simple structure, convenient use, reliable work and convenient maintenance.
Mainly used for rough vacuum. In the process of large air extraction. It is mainly used to evacuate air and other non-corrosive, insoluble in water, gas containing a small amount of solid particles in order to form a vacuum in a closed container. A small amount of liquid is allowed to be mixed in the sucked gas. It is widely used in machinery, pharmaceutical, food, petrochemical and other industries.
It is one of the main vacuum equipment to obtain rough vacuum. It is widely used in chemical, food, building materials and other departments, especially in vacuum crystallization, drying, filtration, evaporation and other processes.
The oil-free (corrosion-resistant) vertical reciprocating vacuum pump is a replacement product of the horizontal vacuum pump and the main equipment for obtaining rough vacuum. Due to the use of a fully sealed device, complete isolation of the crankcase and cylinder is achieved; coupled with the use of self-lubricating materials for the piston ring, advanced oil-free lubrication is achieved. Because there is no sewage discharge, this type of vacuum pump is especially suitable for vacuum distillation, vacuum evaporation, vacuum drying, vacuum concentration, vacuum impregnation and other processes in the chemical, pharmaceutical and food industries.
High vacuum system
Spool valve vacuum pump
(Rotary Piston Vacuum Pump)
It is 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 mud training, and aerospace simulation tests.
The spool valve vacuum pump can be used alone or as the foreline pump of the roots vacuum pump, oil booster pump, and oil diffusion pump. When pumping a gas that corrodes ferrous metals, chemically reacts with vacuum oil, contains a lot of steam, and a lot of dust, an additional device is required. Advantages: Compared with the rotary vane vacuum pump, the durability is several times higher and the pumping rate is larger, and the price is relatively higher.
One of the basic equipment used to evacuate the gas in a closed container. It can be used alone or as a foreline pump for booster pumps, diffusion pumps, and molecular pumps. This type of pump is widely used in vacuum smelting, vacuum coating, vacuum heat treatment, vacuum drying and other processes in metallurgy, machinery, electronics, chemical industry, petroleum, medicine and other industries.
Rotary vane vacuum pump
(Sliding Vane Rotary Vacuum Pump)
It has the advantages of compact structure, small size, light weight, low noise and low vibration. Therefore, it is suitable for use as a foreline pump for diffusion pumps, and is more suitable for supporting precision instruments and laboratory use. For example: mass spectrometers, refrigerator lines, vacuum freeze dryers, etc.
Roots vacuum pump
(Roots Vacuum Pump)
It is a rotary variable volume vacuum pump. It must be matched with the fore-stage pump before it can be used in a wide pressure range. It has a large pumping speed and is insensitive to the dust and water vapor contained in the gas being pumped. Widely used in metallurgy, chemical industry, food, electronic coating and other industries. It is mainly used for the main pump of the vacuum unit and needs to be assisted by the foreline pump. Such as: water ring vacuum pump, slide valve vacuum pump, vertical oil-free vacuum pump, molecular vacuum pump, etc. The largest Roots vacuum pump maintains a record of 10000L / S.
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