What is a Vacuum Pump?
A vacuum pump refers to a device or equipment that uses a mechanical, physical, chemical, or physical-chemical method to evacuate the pumped container to obtain a vacuum. Generally speaking, a vacuum pump is a device that uses various methods to improve, generate, and maintain a vacuum in an enclosed space.
- Chinese name
- Vacuum pump
- Foreign name
- Vacuum pump
- Industry
- Machinery manufacturing
- Category
- Water ring pump, reciprocating pump, slide valve pump, etc.
- A vacuum pump refers to a device or equipment that uses a mechanical, physical, chemical, or physical-chemical method to evacuate the pumped container to obtain a vacuum. Generally speaking, a vacuum pump is a device that uses various methods to improve, generate, and maintain a vacuum in an enclosed space.
- According to the working principle of vacuum pumps, vacuum pumps can basically be divided into two types, namely gas capture pumps and gas transfer pumps. It is widely used in metallurgy, chemical industry, food, electronic coating and other industries.
Development history of vacuum pump
- 2SK water ring vacuum pump
- 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 essential main pumps in the application of vacuum processes in various industries in our national economy Species. In recent years, with the sustained and rapid development of China's economy, vacuum pump-related downstream application industries have maintained rapid growth momentum. At the same time, driven by factors such as the continuous expansion of vacuum pump applications, China's vacuum pump industry has achieved sustained, stable and rapid development.
Structural features of vacuum pump
- (1) The overall structure of the pump
- The arrangement of the pump body of the vacuum pump determines the overall structure of the pump.
- The inlet and exhaust ports of the vertical structure are set horizontally, and the assembly and connection of the pipes are relatively convenient. However, the pump has a high center of gravity and poor stability at high speeds, so this type is mostly used for small pumps.
- The inlet of the horizontal pump is on the top, and the exhaust is on the bottom. Sometimes in order to facilitate the installation and connection of the vacuum system pipes, the exhaust port can be connected 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 one end connected to the exhaust pipe, the other end is blocked or connected to a bypass valve. This pump has a low center of gravity and good stability at high speeds. Generally large and medium-sized pumps adopt this structure.
- The two rotor shafts of the pump are mounted perpendicular to the horizontal plane. The structure assembly gap is easy to control, the rotor assembly is convenient, and the pump covers a small area. However, the center of gravity of the pump is high, the gears are difficult to assemble and disassemble, and the lubrication mechanism is relatively complicated.
- (2) Transmission mode of pump
- The two rotors of the vacuum pump operate relatively synchronously through a pair of high-precision gears. The drive shaft is connected to the motor through a coupling. There are mainly two types of drive structure arrangements: 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 at the end of the motor. In this way, the torsional deformation of the driving rotor shaft is small, and the gap between the two rotors will not change due to the large torsional deformation of the driving shaft, so the gap between the rotors is running. The process is even. The biggest disadvantages of this transmission method are: a. There are three bearings on the drive shaft, which increases the processing and assembly difficulties of the pump, and the disassembly and adjustment of the gear is inconvenient; b. The overall structure is uneven, and the center of gravity of the pump is biased to the motor and gear Box side.
- Features
- (1) There is a large pumping speed in a wide pressure range;
- (2) The rotor has good geometric symmetry, so the vibration is small and the operation is stable. There is a gap between the rotors and between the rotor and the casing, no lubrication is required, and the friction loss is small, which can greatly reduce the driving power, so that a higher speed can be achieved;
- (3) There is no need to seal and lubricate with oil in the pump cavity, which can reduce the pollution of vacuum system by oil vapor;
- (4) There is no compression in the pump cavity, and there is no exhaust valve. 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 gas is poor;
- (6) The surface of the rotor is a curved cylinder with a complicated shape, which is difficult to process and inspect.
Vacuum pump mechanical selection
- Does the vibration produced by the vacuum pump affect the process and the environment? If the process is not allowed, a vibration-free pump should be selected or anti-vibration measures should be taken.
- Understand the composition of the gas to be pumped. The gas contains no condensable vapor, whether there is particulate dust, and whether it is corrosive. When selecting a vacuum pump, you need to know the gas composition and select the appropriate pump for the gas being pumped. If the gas contains vapor, particles, and corrosive gases, you should consider installing auxiliary equipment such as condensers and dust collectors on the pump's inlet pipe.
- (3) Under its working pressure, the vacuum pump should be able to remove all the gas generated during the vacuum equipment process.
- Combine the vacuum pump correctly. Due to the selective pumping of vacuum pumps, sometimes a pump cannot be used to meet the pumping requirements. Several pumps need to be combined to complement each other to meet the pumping requirements. For example, the titanium sublimation pump has a high pumping speed for hydrogen, but cannot pump helium, while a tripolar sputtering ion pump (or a bipolar asymmetric cathode sputtering ion pump) has a certain pumping speed for argon, both Combined, the vacuum device will get better vacuum. In addition, some vacuum pumps cannot work at atmospheric pressure and require pre-vacuum; some vacuum pumps have outlet pressures lower than atmospheric pressure and require foreline pumps, so they need to be used in combination.
- Vacuum equipment requirements for oil pollution. If the equipment strictly requires no oil, you should choose various oil-free pumps, such as: water ring pumps, molecular sieve adsorption pumps, sputtering ion pumps, cryogenic pumps, etc. If the requirements are not strict, you can choose to have an oil pump, plus some oil pollution prevention measures, such as adding cold traps, baffles, oil traps, etc., can also meet the requirements of clean vacuum.
- Select the working point of the vacuum pump correctly. Each pump has a certain working pressure range, such as: 2BV series water ring vacuum pump working pressure range 760mmHg ~ 25mmHg (absolute pressure), in such a wide pressure range, the pumping speed of the pump changes with the pressure (for details, please refer to the pump Performance curve), its stable working pressure range is 760 ~ 60mmHg. Therefore, the working point of the pump should be selected within this range, which does not allow it to work for a long time under 25 ~ 30mmHg.
- What is the impact of the oil vapor from the vacuum pump on the environment. If the environment does not allow pollution, you can choose an oil-free vacuum pump or exhaust oil vapor to the outside.
- The working pressure of the vacuum pump should meet the requirements of the ultimate vacuum and working pressure of the vacuum equipment. For example, a vacuum drying process requires a working vacuum of 10mmHg, and the ultimate vacuum of the vacuum pump selected should be at least 2mmHg, and preferably 1mmHg. Usually, the ultimate vacuum of the pump is selected to be half to one order of magnitude higher than the working vacuum of the vacuum equipment.
- The price, operation and maintenance cost of vacuum pump.
- Mechanical installation
- The vacuum pump should be installed in a place with a strong and solid ground, and there should be sufficient room around it for easy inspection, maintenance, and maintenance.
- Installation schematic
- (3) The connecting pipeline of the vacuum pump and the system should be sealed reliably. For small vacuum pumps, metal pipeline connection gaskets can be used for oil-resistant rubber. For small vacuum pumps, vacuum rubber hoses can be used for connection. The pipe diameter must not be less than the suction diameter of the vacuum pump. And less elbows. (When welding the pipeline, the welding slag should be removed from the pipeline, and it is strictly prohibited to enter the vacuum pump cavity.)
- In the connecting pipeline, the user can install a valve and a vacuum gauge above the vacuum pump inlet, and can check the ultimate pressure of the vacuum pump at any time.
- Connect the power supply according to the motor label, and connect the ground wire and fuses and thermal relays of appropriate specifications.
- When the vacuum pump is turned on for trial operation, the motor belt must be removed, and the vacuum pump must be turned in accordance with the specified direction before being put into use to prevent the vacuum pump from injecting fuel in the reverse direction. (Turn the direction indicated by the protective cover)
- For vacuum pumps with cooling water, connect the cooling water according to regulations.
- If a solenoid valve is installed at the vacuum pump port, the valve and vacuum pump should operate simultaneously.
- When the exhaust gas of the vacuum pump affects the working environment, the exhaust pipe can be connected to the pipeline to lead away or attach an oil mist filter.
Vacuum pump classification
| Vacuum pump | Divided by working principle | Gas delivery pump | Variable capacity vacuum pump | Reciprocating | ||
| Rotary vane | Oil seal | Rotary vane | ||||
| Slide valve | ||||||
| Fixed slice | ||||||
| Cochoid | ||||||
| Multi-chamber rotary vane | ||||||
| Dry screw | ||||||
| Liquid ring | ||||||
| Roots vacuum pump | ||||||
| Momentum transfer pump | Molecular vacuum pump | Traction molecular pump | ||||
| Turbo molecular pump | ||||||
| Compound molecular pump | ||||||
| Jet vacuum pump | Liquid jet vacuum pump | |||||
| Gas jet vacuum pump | ||||||
| Steam jet vacuum pump | ||||||
| Diffusion pump | Self-purifying diffusion pump | |||||
| Fractional Diffusion Pump | ||||||
| Diffusion jet pump | ||||||
| Ion transport pump | ||||||
| Gas capture pump | Adsorption pump | |||||
| Getter pump | ||||||
| Getter ion pump | Evaporative ion pump | |||||
| Sputtering ion pump | ||||||
| Cryopump | ||||||
| Divided by vacuum degree | Rough vacuum | |||||
| High vacuum | Slide valve vacuum pump | |||||
| Rotary Vane Vacuum Pump | ||||||
| Roots vacuum pump | ||||||
| Ultra-high vacuum |
- Gas transfer pump
- Gas transfer pump is a vacuum pump that can continuously suck and discharge gas to achieve the purpose of pumping. There are basically two types of this pump:
- Variable capacity vacuum pump
- A vacuum pump that uses the periodic changes in the volume of the pump cavity to complete the suction and exhaust processes. 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: It uses the piston in the pump cavity to make a rotary motion to suck, compress and discharge the gas. The rotary vacuum pump has the following forms:
- Oil-sealed vacuum pump: It is a rotary variable-capacity vacuum pump that uses oil to seal the gap between moving parts and reduce harmful spaces. This pump usually has a gas ballast device, so it is also called a 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 eccentric distance and is close to the fixed surface of the inner surface of the pump casing. Two (or more) rotary vanes are installed in the rotor groove. It can slide back and forth along its radial groove and always contact the inner wall of the pump casing. This rotary blade rotates with the rotor to divide the pump cavity into several variable volumes.
- b. Spool valve vacuum pump: A spool valve is installed on the outside of the eccentric rotor. The rotation of the rotor drives the spool to slide and roll along the inner wall of the pump casing. The spool rod on the upper part of the spool can slide in the swingable spool valve guide. The cavity is divided into two variable volumes.
- c. Fixed vane vacuum pump: an eccentric rotor close to the pump's inner surface is installed in the pump casing, and a radial sliding blade which is always in contact with the rotor surface is mounted on the pump casing. When the rotor rotates, the sliding blade can slide up and down to pump The cavity is divided into two variable volumes.
- d. Yu cycloid vacuum pump: A eccentric 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: In a pump casing, there are multiple rotary vane vacuum pumps driven by the same motor in parallel.
- Dry Screw Vacuum Pump: It is a variable capacity vacuum pump that is not sealed with oil (or liquid).
- Liquid ring vacuum pump: A 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 circular liquid in the pump casing. The vanes form several small volumes whose volume changes periodically, so they are also called rotary variable capacity vacuum pumps.
- Roots vacuum pump: The pump is equipped with two double-lobed or multi-lobed rotors that rotate simultaneously in opposite directions. A certain gap is maintained between the rotors and between the rotors and the inner wall of the pump casing. It belongs to rotary variable capacity vacuum pump. A mechanical booster pump is a vacuum pump of this form.
- Momentum transfer pump: This 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 transmitted from the pump's inlet to the outlet. 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 gas molecules to compress and exhaust them. It has the following types:
- Traction molecular pump: The gas molecules collide with the rotor moving at high speed to obtain power and are sent to the outlet. Therefore, it is a momentum transfer pump.
- Turbo molecular pump: a slotted disc or a rotor with a blade is installed in the pump, and it rotates between the stator discs (or stators). The linear velocity of the rotor circumference is high. Such pumps usually operate in a molecular flow state.
- Compound molecular pump: It is a compound molecular vacuum pump which is composed of two turbo-pump and traction-type molecular pumps connected in series.
- (2) Jet vacuum pump: It is a momentum transfer pump that uses high-speed jets produced by the pressure drop of the Venturi effect to transport gas to the outlet, and is suitable for working in viscous retention and transient flow conditions. This pump can be divided into the following types in detail:
- Liquid jet vacuum pump: Jet vacuum pump with liquid (usually water) as working medium.
- Gas jet vacuum pump: Jet vacuum pump with non-condensable gas as working medium.
- Steam jet vacuum pump: Hungry jet vacuum pump with steam (water, oil or mercury vapor) as working medium
- (3) Diffusion pump : Jet vacuum pump with low-pressure high-speed steam flow (steam such as oil or mercury) as the working medium. The 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, and this pump is suitable for working in the state of molecular flow. It can be divided into:
- Self-purification diffusion pump: an oil diffusion pump that is volatile impurities in the pump liquid and is transported to the outlet by special machinery without returning to the boiler.
- Fractional diffusion pump: This pump has a fractional distillation device, which allows the working fluid vapor with lower vapor pressure to enter the high vacuum working nozzle, and the working fluid vapor with higher vapor pressure to enter the low vacuum working nozzle. Grade oil diffusion pump.
- (4) Diffusion jet pump: It is a momentum transfer 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. Oil booster pumps belong to this form.
- (5) Ion transfer pump: It is a momentum transfer pump that transfers ionized gas to the outlet under the action of electromagnetic field or electric field.
- Gas capture pump
- This pump is a 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. There are the following types.
- Adsorption pump: 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 chemically capture gas. The getter is usually a metal or alloy in the form of a lumpy or deposited fresh film. The sublimation pump belongs to this form.
- Getter ion pump: It is used to make the ionized gas adsorbed on the surface of getter material through the action of electromagnetic field or electric field, so as to achieve the purpose of pumping. It has the following types.
- (1) Evaporation ion pump: A vacuum pump in which the ionized gas in the pump is adsorbed on a suction material that sublimates (or evaporates) in a discontinuous or continuous manner and covers the inner wall of the pump.
- (2) Sputtering ion pump: A vacuum pump in which the ionized gas in the pump is adsorbed on the getter material scattered by the continuous sputtering of the cathode to achieve the purpose of pumping.
- Cryogenic pumps: vacuum pumps that capture gases using cryogenic surfaces
- According to the degree of vacuum, it can be divided into three categories: rough vacuum, high vacuum, and ultra high vacuum.
- Rough vacuum system
- It is mainly used to remove air and other gases that are corrosive, insoluble in water, and allow 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. During the process of large air extraction. It is mainly used to remove air and other non-corrosive, water-insoluble, 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 in the inhaled gas. It is widely used in machinery, pharmaceutical, food, petrochemical and other industries.
- Is one of the main vacuum equipment to obtain rough vacuum. Widely used in chemical, food, building materials and other sectors, especially in vacuum crystallization, drying, filtration, evaporation and other processes are more suitable.
- The oil-free (corrosion-resistant) vertical reciprocating vacuum pump is a replacement product of the horizontal vacuum pump and is the main equipment for obtaining rough vacuum. Due to the use of a fully sealed device, complete isolation of the crankcase and the cylinder is achieved; coupled with the use of self-lubricating materials for the piston rings, 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
- Slide valve vacuum pump
- (Rotary Piston Vacuum Pump)
- It is widely used in the production and development of new materials, new technologies, and new technologies 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.
- Sliding valve vacuum pump can be used alone or as a foreline pump of Roots vacuum pump, oil booster pump, oil diffusion pump. When pumping gas that is corrosive to ferrous metals, chemically reacts on vacuum oil, contains a large amount of steam and a large amount of dust, additional equipment is required. Advantages: Compared with rotary vane vacuum pumps, the durability is several times higher, the pumping rate is larger, and the price is relatively higher.
- One of the basic equipment used to extract gas from 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, petroleum, pharmaceutical and other industries.
- Rotary Vane Vacuum Pump
- Vacuum pump (2 photos)
- (Sliding Vane Rotary Vacuum Pump)
- It has the advantages of compact structure, small size, light weight, low noise and small 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 spectrometer, refrigerator assembly line, vacuum freeze dryer, etc.
- Roots vacuum pump
- (Roots Vacuum Pump)
- It is a rotary variable capacity vacuum pump. It must be used in conjunction with a foreline pump. It can be used in a wide pressure range. It has a large pumping speed and is not sensitive to the dust and water vapor contained in the pumped gas. 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 a 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 in China maintains a record of 20000L / S.
Vacuum pump performance parameters
| parameter name | Parameter definition |
|---|---|
| Ultimate pressure of vacuum pump | The unit of the ultimate pressure of the pump is Pa, which means that the pump is equipped with a standard test cover at the inlet and works according to the specified conditions. Without the introduction of gas to work normally, the minimum pressure tends to be stable. |
| Pumping rate of vacuum pump | The pumping rate unit of the pump is m3 / s or l / s, which means that when the pump is equipped with a standard test cover and works according to the specified conditions, the gas flow rate from the test cover and the equilibrium pressure measured at the specified position of the test cover Ratio. Referred to as the pumping speed of the pump. |
| Pumping capacity of vacuum pump | The vacuum pump unit is Pam3 / s or Pal / s. Refers to the gas flow at the pump inlet. |
| Starting pressure of vacuum pump | The starting pressure unit of the vacuum pump is Pa, which refers to the pressure when the pump starts without damage and has the effect of pumping. |
| Foreline pressure of vacuum pump | The front pressure unit of the vacuum pump is Pa, which refers to the outlet pressure of the vacuum pump whose exhaust pressure is lower than one atmosphere. |
| Maximum foreline pressure of vacuum pump | The vacuum pump port's maximum foreline pressure unit is Pa, which means that it exceeds the foreline pressure that can damage the pump. |
| Maximum working pressure of vacuum pump | The maximum working pressure unit of the vacuum pump is Pa, which refers to the inlet pressure corresponding to the maximum pumping volume. At this pressure, the pump can work continuously without deterioration or damage. |
| Compression ratio of vacuum pump | Compression ratio is the ratio of the pump's outlet pressure to the inlet pressure for a given gas. |
| Hoh's coefficient of vacuum pump | The ratio of the actual pumping speed over the area of the pumping channel to the theoretical pumping speed calculated here based on molecular effusion. |
| Pumping speed coefficient of vacuum pump | The ratio of the actual pumping speed of the pump to the theoretical pumping speed calculated by molecular effusion at the pump inlet. |
| Vacuum pump recirculation rate | The unit of the reflux rate of the pump is g / cm2.s. It refers to the mass flow rate of the pump flow through the unit area of the pump inlet when the pump works according to the specified conditions. |
| Allowable amount of water vapor | The permissible unit of water vapor is kg / h, which refers to the mass flow of water vapor that can be removed by the gas ballast pump during continuous operation under normal environmental conditions. |
| Maximum allowable water vapor inlet pressure | The maximum allowable water vapor inlet pressure unit is Pa. It refers to the maximum inlet pressure of water vapor that can be removed by the gas ballast pump during continuous operation under normal environmental conditions. |
- Pressure range
- Vacuum pump type Working pressure range (Pa) Starting pressure (Pa)
- Piston vacuum pump 1 × 105 1.3 × 102 1 × 105
- Rotary vane vacuum pump 1 × 1056.7 × 10-1 1 × 105
- Water ring vacuum pump 1 × 1052.7 × 103 1 × 105
- Roots vacuum pump 1.3 × 1031.3 1.3 × 103
- Turbo molecular pump 1.31.3 × 10-5 1.3
- Water vapor jet pump 1 × 1051.3 × 10 -1 1 × 105
- Oil diffusion pump 1.3 × 10-21.3 × 10 -7 1.3 × 10
- Oil vapor jet pump 1.3 × 101.3 × 10 -2 <1.3 × 105
- Molecular sieve adsorption pump 1 × 1051.3 × 10 -1 1 × 105
- Sputtering ion pump 1.3 × 10-31.3 × 10 -9 6.7 × 10-1
- Titanium sublimation pump 1.3 × 10-21.3 × 10 -9 1.3 × 10-2
- Zirconium aluminum getter pump 1.3 × 101.3 × 10 -11 1.3 × 10
- Cryogenic pump 1.31.3 × 10-11 1.31.3 × 10-1
Vacuum pump terminology explained
- Definition of vacuum
- Vacuum system refers to the state of rare gas below atmospheric pressure in the area
- Degree of vacuum
- The degree of gas thinning under vacuum is usually expressed by "high vacuum" and "low vacuum". A high vacuum degree means that the vacuum degree is "good", and a low vacuum degree means that the vacuum degree is "poor".
- Vacuum degree unit
- Torr is usually used as the unit, and internationally, Pa is used as the unit.
- 1 Torr = 1/760 atmosphere = 1 mmHg
- Tow and Pa
- 1 Torr = 133.322 Pa or 1 Pa = 7.5 × 10-3 Torr
- Mean free path
- The average distance over which gas particles that make random thermal movements fly over two consecutive collisions is represented by the symbol "".
- flow
- The amount of gas flowing through an arbitrary cross section per unit of time. The symbol is represented by "Q". The unit is Pa · L / s or Torr · L / s.
- Conductance
- Represents the ability of a vacuum pipe to pass gas. The unit is liters per second (L / s). Under steady state, the pipeline conductance is equal to the pipeline flow divided by the pressure difference between the two ends of the pipeline. The symbol is written as "U". U = Q / (P2- P1)
- Pressure or pressure
- The force of a gas molecule acting on a unit area of the container wall is represented by "P".
- Standard atmospheric pressure
- The pressure is 101325 dyne per square centimeter, and the symbol is (Atm).
- Ultimate vacuum
- After the vacuum container is fully evacuated, it is stabilized at a certain degree of vacuum, which is called the ultimate vacuum. Generally, the vacuum container must be refined for 12 hours, and then evacuated for another 12 hours. The last hour is measured every 10 minutes, and the average value of 10 times is used as the ultimate vacuum value.
- Pumping rate
- At a certain pressure and temperature, the gas drawn from the pump inlet at a unit time is called the pumping rate, or pumping speed for short. That is Sp = Q / (PP0)
- Cold trap ( water-cooled baffle)
- A device placed between a vacuum container and a pump for adsorbing gas or trapping oil vapor.
- Gas ballast valve
- A small hole is opened in the compression chamber of the oil-sealed mechanical vacuum pump, and a regulating valve is installed. When the valve is opened and the air volume is adjusted, the rotor is turned to a certain position. A part of the steam does not cause condensation and is excluded from the pump together with the mixed gas. The valve that plays this role is called a gas ballast valve.
- Vacuum freeze-drying
- Vacuum freeze-drying, also known as sublimation drying. The principle is to freeze the material so that the water contained in it becomes ice cubes, and then sublimate the ice under vacuum to achieve the purpose of drying.
- Vacuum evaporation
- In a vacuum environment, heating and plating materials on a substrate is called vacuum evaporation, or vacuum coating.
- Vacuum drying
- Method for drying articles by utilizing the characteristics of low boiling point under vacuum environment.
- Common names for vacuum systems
- Main pump: In a vacuum system, a vacuum pump used to obtain the required degree of vacuum to meet specific process requirements, such as the oil diffusion pump in a vacuum coating machine is the main pump.
- Foreline pump: A vacuum pump used to maintain the pressure of the foreline of a vacuum pump below its critical foreline pressure. For example, the rotary vane or slide valve pump configured in front of the roots pump is the foreline pump.
- Coarse pump: A vacuum pump that starts pumping at atmospheric pressure and pumps the system pressure to another vacuum pump. For example, the slide valve pump in the vacuum coating machine is the crude oil pump.
Application of vacuum pump
| Liquid ring pump | Although liquid ring pumps are rough vacuum pumps, they still have a large market in China's petroleum, chemical, power, light textile, paper, pharmaceutical and other fields. In foreign countries, sales of liquid ring pumps account for 14% of the total vacuum pump market, second only to dry pumps. Because liquid ring pumps are mostly castings, and their processing requirements are not high, they are labor-intensive products. There is a competitive advantage in price. The key is to improve the design, reduce the size, reduce weight, improve efficiency, and reduce energy consumption. |
|
| Spool valve pump | As the slide valve pump is more durable and reliable, various vacuum furnaces, coating machines and drying and dipping equipment at home and abroad use the slide valve pump as the foreline pump. However, the slide valve pump has a heavy casting and a large amount of processing work. Each vacuum plant is looking for partners in China. In order to make domestic slide valve pumps enter the international market, it is necessary to further reduce the pump's vibration noise, eliminate fuel injection and oil leakage, and improve the long-term reliability of the slide valve pump. |
|
| Directly connected rotary vane pump | With the continuous expansion of vacuum technology in various application fields, the demand for direct-connected rotary vane pumps is increasing. Due to the large number of such pumps, the large amount of processing and assembly work, and the low price, some foreign vacuum manufacturers have established professional factories in China. The domestic small and medium-sized direct-connected rotary vane pumps have technically passed the customs and the price is much cheaper than foreign pumps. Therefore, domestic pumps still have a competitive advantage. The key is to solve the problem of shaft seal leakage and the performance and quality of rotary vane materials and vacuum pump oil In order to ensure the stable performance and reliable operation of the direct-connected pump at high speed and high temperature, the domestic direct-connected rotary vane pump's ability to remove water vapor must be further improved. |
|
| Roots pump |
|
|
| Molecular pump |
| |
| Dry pump | The continuous growth of the foreign dry pump market is mainly driven by the rapid development of the semiconductor industry, chemical industry, and thin film industry. In Japan, the semiconductor industry has replaced oil-sealed mechanical pumps with dry vacuum pumps, and more than 45% of the European and American semiconductor industries have replaced oil-sealed mechanical pumps with dry vacuum pumps, which has greatly improved product performance and quality. In order to meet the requirements of different application fields and different working conditions, there are multi-stage Roots vacuum pumps, multi-stage claw vacuum pumps, screw vacuum pumps, scroll vacuum pumps, reciprocating piston vacuum pumps, and turbo oil-free vacuum pumps. The ultimate pressure is from 10Pa to 10-2Pa, and the pumping speed is from 20m3 / h to 500m3 / h. | |
| Water ring pump |
|
- In summary, the water ring pump relies on the volume change of the pump cavity to achieve suction, compression and exhaust, so it belongs to a variable capacity vacuum pump.
- Compared with other types of mechanical vacuum pumps, water ring pumps have the following advantages
- The structure is simple, the manufacturing accuracy is not high, and it is easy to process.
- The structure is compact and the pump has a high number of revolutions. Generally, it can be directly connected to the motor without the need for a speed reduction device. Therefore, with a small structure size, a large exhaust volume can be obtained, and the footprint is small.
- The compressed gas is basically isothermal, that is, the temperature change of the compressed gas process is small.
- Because there is no metal friction surface in the pump cavity, there is no need to lubricate the pump, and the wear is very small. The seal between the rotating member and the fixed member can be directly completed by a water seal.
- Even suction, stable and reliable work, simple operation and convenient maintenance.
- Water ring pumps also have their disadvantages:
- Low efficiency, generally around 30%, better up to 50%.
- The degree of vacuum is low, not only because of structural limitations, but more importantly, due to the saturated vapor pressure of the working fluid. With water as the working fluid, the ultimate pressure can only reach 2000 ~ 4000Pa. Use oil as working fluid, up to 130Pa.
- In short, because the gas compression in the water ring pump is isothermal, it can pump out flammable and explosive gases. Because there is no exhaust valve and friction surface, dusty gas, condensable gas and gas-water mixture can be removed. With these outstanding features, despite its low efficiency, it is still widely used.
Vacuum pump measurement method
| measurement method | definition |
|---|---|
| Thermocouple Vacuum Gauge | A vacuum gauge that uses the principle that the potential of a thermocouple is related to the temperature of the heating element, and the temperature of the element is related to the heat transfer of the gas. |
| Ionization vacuum gauge | It consists of a cylindrical collector, a grid and a filament located in the center of the grid. The cylindrical collector is outside the grid. The hot cathode emits electrons to ionize gas molecules, and the ions are collected by the collector. The vacuum gauge measures the gas pressure according to the collected ion current. |
| Composite vacuum gauge | It consists of a thermocouple vacuum gauge and a hot cathode ionization vacuum gauge, and the measurement range is from the atmosphere to 10-5Pa. |
| Cold cathode ionization meter | There are a pair of cathode plates at the two ends of the anode cylinder. A magnetic field is applied to generate a Penning discharge in the anode cylinder to generate ions. A vacuum gauge for measuring the gas pressure according to the magnitude of the ion current collected by the cathode plate. |
| Resistance vacuum gauge | Using the principle that the resistance of the heating element is related to temperature, and the temperature of the element is related to gas conduction, a vacuum gauge is used to measure the degree of vacuum through a bridge circuit. |
| McLaugh vacuum gauge | It also becomes a compression type vacuum gauge, which uses mercury (or oil) to compress the gas to be measured to a very small volume, and then compares the liquid column difference between the open and closed tubes, and uses the Boyle's law to directly calculate the absolute gas pressure Vacuum gauge. |
| Capacitive film vacuum gauge | This is a hot cathode ionization gauge with the cathode and collector inverted. The collector is a thin wire, placed in the center of the grid, and the filament is placed outside the grid, thereby reducing the impact of soft X-rays, extending the lower measurement limit, and measuring ultra-high vacuum. Capacitive film vacuum gauges combine three different regulations in a small, economical regulation, measuring process pressure and basic pressure from 5x10-10 to 1500 mbar. Capacitive thin-film vacuum gauges have been paid more and more attention due to a series of advantages such as high measurement accuracy, fast dynamic response, measurement results that are independent of gas components, and resistance to corrosion and air pressure. Use it to replace mercury pressure gauge, oil pressure gauge, resistance vacuum gauge, thermocouple vacuum gauge and even partly replace ionization gauge. |
Selection of vacuum pump
- The function of the vacuum pump is to remove gas molecules from the vacuum chamber, reduce the gas pressure in the vacuum chamber, and make it reach the required vacuum degree. In summary, there is a large range from the atmosphere to extremely high vacuum, and so far no vacuum system can cover this range. Therefore, in order to meet the process specifications of different products, work efficiency and equipment working life requirements, different vacuum sections need to choose different vacuum system configurations. To achieve the best configuration, the following points should be considered when selecting a vacuum system:
- The vacuum required for each process must first be determined. Because each process has its own vacuum range, it must be carefully studied and determined.
- Check the ultimate vacuum degree of the vacuum pump system on the basis of determining the required vacuum degree of the process, because the ultimate vacuum degree of the system determines the optimal working vacuum degree of the system. Generally speaking, the ultimate vacuum of the system is 20% lower than the working vacuum of the system and 50% lower than the ultimate vacuum of the foreline pump.
- Check to determine the type and volume of extraction required by the process. Because if the type of gas being pumped reacts with the liquid in the pump, the pump system will be contaminated. At the same time, it must be considered to determine the appropriate exhaust time and the amount of gas generated during the extraction process.
- Check to determine the time required to reach the required degree of vacuum, the flow resistance and leakage of the vacuum pipe. Consider the required pumping rate to maintain the vacuum under certain process requirements after reaching the required vacuum.
- s = 2.303 (v / t) lg (p1 / p2)
- among them:
- s is the vacuum pumping rate (l / s)
- v is the volume of the vacuum chamber (l)
- t is the time required to reach the required vacuum (s)
- p1 is the air pressure in the initial container
- p2 is the pressure in the container after pumping
- Influencing factors
- It is the size of the product. The higher the pumping volume request, the larger the product volume, and the higher the motor power required.
- It is to decide what kind of structure the product adopts. The vacuum degree has two kinds of readings: gauge pressure and absolute pressure. Absolute pressure means that the reading is an absolute value, that is, the closer the reading is to '0 \', the higher the vacuum. On the other hand, the closer the gauge pressure is to 760mmH, the higher the degree of vacuum. If the absolute pressure (limit vacuum) you requested is close to '0 \', then only the vacuum pump can meet this demand.
Vacuum pump maintenance
- The quality of the vacuum pump depends on its mechanical structure and the quality of the oil. It must be protected when using the vacuum pump. If a more volatile organic solvent is distilled, the organic solvent will be absorbed by the oil, which will increase the vapor pressure and reduce the evacuation efficiency. If it is an acid gas, it will corrode the oil pump. If it is water vapor, the oil will become milk. The turbid liquid sucked out the vacuum pump.
- Therefore, the following points must be paid attention to when using a vacuum pump:
- An absorption device must be installed between the distillation system and the vacuum pump.
- Before distillation, the organic solvent vapor must be completely removed from the system with a water pump.
- If it can be pumped by a water pump, try to use a water pump. If the volatile substances are contained in the distilled material, you can first use the pump to reduce the pressure and then use an oil pump.
- The pressure reducing system must be airtight. All rubber plugs must be of the proper size and channel. Rubber tubes must be vacuum rubber tubes. The ground glass is coated with vacuum grease.
- Vacuum pumps can be divided into three categories according to the scope of use and the efficiency of extraction:
- (1) For general water pumps, the pressure can reach 1.333 ~ 100kPa (10 ~ 760mmHg) as a "rough" vacuum.
- (2) Oil pump, the pressure can reach 0.133 ~ 133.3Pa (0.001 ~ 1mmHg) as "second high" vacuum.
- (3) Diffusion pump, pressure can reach below 0.133Pa, (10-3mmHg) is "high" vacuum.
- If you want lower pressure, you need to use an oil pump. A good oil pump can pump below 133.3Pa (1mmHg).
- There are two types of pressure reducing pumps commonly used in organic chemistry laboratories: water pumps and vacuum pumps. If low pressure is not required, water pumps can be used. If the pump is well-structured and the water pressure is high, the evacuation efficiency can reach 1067 ~ 3333Pa (8 ~ 25mmHg). The minimum pressure that the pump can pump theoretically corresponds to the water vapor pressure at the time of the water temperature. For example, when the water temperature is 25 ° C, 20 ° C, and 10 ° C, the pressure of water vapor is 3192, 2394, and 1197Pa (8-25mmHg), respectively. When pumping with a water pump, a safety bottle should be installed in front of the pump to prevent the water pressure from falling and the water flow to be sucked back up; before stopping the pumping, deflate and then turn off the pump.
Vacuum pump lubricant
- In the vacuum pump, the vacuum pump oil is not only used as a medium to obtain vacuum, but also plays a role in lubrication, cooling and sealing of mechanical friction points.
- This is the most important performance of vacuum pump oil. Because the vacuum pump requires a high degree of vacuum, paraffin-based narrow cut lubricants are generally used. For diffusion vacuum pumps, silicone oil or other synthetic oils with very low vapor pressure can also be used.
- The internal volume of the vacuum pump cavity changes continuously to form an exhaust effect, and the lubricating oil is required to have appropriate viscosity and viscosity-temperature characteristics.
- Vacuum pumps continue to develop at a high speed. Due to the high-speed friction between the sliding vane and the pump body, the oil temperature rises, and the oil is easily oxidized and decomposed. Especially the diffusion pump often works in a very high temperature environment, which increases the vapor pressure in the system. The degree of vacuum is reduced, so vacuum pump oil is required to have good thermal oxidation stability.
- If the vacuum pump sucks corrosive gas, it will chemically react with the oil and corrode the parts inside the pump; the suction air often contains water vapor condensation water, which causes the emulsification of the vacuum pump oil and corrodes the metal. Sex.
- The main requirement is that the vacuum pump does not carry light components, so as not to affect the saturated vapor pressure of the oil.
- Ultimate pressure is an important performance indicator of vacuum pump oil to understand the ultimate pressure of the vacuum pump at the lowest vacuum ultimate pressure.
Vacuum pump motor temperature is high
- Each company's 300MW unit is equipped with two mechanical vacuum pumps, one of which is in operation and the other is standby. The vacuum pump is used to evacuate the unit when it starts, and to extract the uncondensed gas in the condenser during normal operation. The pump is equipped with a motor of 160kW, a speed of 590r / min, a rated current of 330A, a voltage of 380V, and Class B insulation, and the current is 220 ~ 230A during normal operation. Every summer, the motor temperature will exceed the limit, and it is forced to install a temporary cooling fan, but the effect is not great. Long-term high temperature operation of the motor will cause insulation aging and shorten its service life. The reason for the high temperature of the vacuum pump motor is as follows.
- Cause Analysis
- (1) The motor has a large power, a large working current, and a large amount of heat.
- (2) Low fan speed, low wind pressure and small air volume.
- (3) The number of fan blades is small, and the amount of wind generated is small.
- (4) Dust and oil are attached to the motor, which reduces heat dissipation.
- (5) The voltage of the bus where the vacuum pump motor is located is 380V. Due to the cable voltage drop and uneven load distribution, the actual voltage applied by the motor is only 365V, which causes a large running current due to the low voltage.
- Countermeasure
- The motor power and speed are matched with the vacuum pump and cannot be changed. The fan is installed on the motor shaft. The speed of the motor determines the speed of the fan and cannot be replaced. Although increasing the number of fan blades can play a certain role, after the number of blades is increased, the dynamic balance is not easy to find. If it is not correctly aligned, it will cause the motor vibration to increase.
- (1) Extend the original fan cover by 40cm, and install an axial flow fan with the same diameter as the fan cover. The power of the axial flow fan motor is 850W, the speed is 1489r / min, and the voltage is 380V. The original fan remains. The axial flow fan is provided with another power control, and the axial flow fan and the main motor are not interlocked. After the vacuum pump is started, the axial flow fan will be started in time, and the axial flow fan will be shut down 30 minutes after the vacuum pump is stopped, so that the main motor is fully cooled;
- (2) Regularly remove dust from the motor, keep the heat sink of the motor clean, and increase its heat dissipation capacity;
- (3) Adjust the voltage of the bus where the vacuum pump is located to 400V.
- effect
- (1) Due to the high speed of the axial flow fan, the large wind pressure and volume, and the cooling effect is greatly enhanced. Under the same ambient temperature and load current, the temperature of the main motor has decreased by 12 ° C. The main motor temperature did not exceed the limit in summer.
- (2) The axial flow fan can be controlled manually. After the main motor is stopped, the axial flow fan can still run, which can fully cool the main motor.
- (3) Try to balance the load distribution of the two sections of the bus as much as possible to prevent a certain section of the bus from causing excessive voltage drops due to excessive load.
- (4) After the voltage is adjusted, the operating current of the vacuum pump is reduced to 210A, and the heat generation is relatively reduced.
- (5) It slows down the insulation aging speed of the main motor and prolongs its service life.
Wear of vacuum pump shaft bearings
- title
Vacuum pump corrosion
- Polymer composite repairs vacuum pump corrosion
Vacuum pump casing crack
- Polymer composites repair shell cracks
Vacuum pump smoke and injection
- 1. Smoke, if the pump has just started to smoke, it is normal, if it has been smoking for a long time, it is abnormal. The solution: Smoke indicates that there are repairs to the pump's air inlet, including pipes, valves, and containers. After leak detection is dealt with, smoking will end. Vortex flowmeter 2. Fuel injection, indicating that there are a large number of leak points outside the air inlet, and even the air inlet is exposed to the atmosphere. Solution: Seal the air inlet of the pump to make the pump run, if there is no fuel injection, there are leaks; the exhaust valve disc is damaged, check whether the exhaust valve disc is damaged, and replace the defective exhaust valve.