Choose a vacuum pump to understand the type and working principle of vacuum.
Complete set of vacuum pump types
According to the working principle of vacuum pump, vacuum pump can be basically divided into two types, namely gas transmission pump and gas capture pump. With the increasing demand of vacuum application technology for its application pressure range in the fields of production and scientific research, most vacuum pumping systems composed of several vacuum pumps need to be pumped together to meet the requirements of production and scientific research. Therefore, vacuum pump groups composed of different types of vacuum pumps are often selected for pumping. For convenience, it is necessary to classify these pumps in detail according to their working principle or structural characteristics. Now described as follows:
First, the gas pump
Air pump is a kind of vacuum pump that can continuously inhale and exhaust gas, so as to achieve the purpose of pumping air. There are basically two types of pumps:
1) variable displacement vacuum pump
Variable displacement vacuum pump is a kind of vacuum pump which uses the periodic change of pump cavity volume to complete the suction and exhaust process. The gas is compressed before it is discharged. This kind of pump is divided into reciprocating and rotary types:
⑴ Piston vacuum pump: The reciprocating motion of the piston in the pump cavity is used to suck, compress and discharge gas. Therefore, it is also called piston vacuum pump.
⑵ Rotary vacuum pump: The piston in the pump cavity rotates to suck, compress and discharge gas. Rotary vacuum pump has the following types:
① Oil-sealed vacuum pump: it is a rotary variable displacement vacuum pump, which 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 a gas 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 casing with a certain eccentricity and close to the fixed surface of the inner surface of the pump casing. Two (or more) rotating blades are installed in the rotor slot. When the rotor rotates, the rotating blade can slide back and forth along its radial groove and always contact with the inner wall of the pump casing. The rotating blades rotate with the rotor to divide the pump chamber into several variable volumes.
B) Slide valve vacuum pump: A slide valve is installed outside the eccentric rotor, and 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 at the upper part of the slide valve can slide in the swingable slide valve guide rail, thus dividing the pump chamber into two variable volumes.
C) Fixed vane vacuum pump: an eccentric rotor close to the inner surface of the pump is installed in the pump housing, and a radial slider is installed on the pump housing, which is always in contact with the surface of the rotor. When the rotor rotates, the slider can slide up and down to divide the pump cavity into two variable volumes.
D) Subcycloidal vacuum pump: a rotor with a subcycloidal profile is eccentrically installed 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-cavity rotary vane vacuum pump: A pump shell is equipped with a plurality of rotary vane vacuum pumps with independent working chambers which are driven in parallel by the same motor.
② Dry vacuum pump: variable displacement vacuum pump without oil (liquid) seal.
③ Liquid ring vacuum pump: The multi-blade rotor is eccentrically installed in the pump housing. When it rotates, liquid (usually water or oil) is thrown into the pump casing to form a concentric liquid ring. The liquid ring and rotor blades form several small volumes with periodic volume changes, so it is also called rotary variable displacement vacuum pump.
④ Roots vacuum pump: This pump is equipped with two Shuang Ye or multi-blade rotors rotating synchronously in opposite directions, and a certain gap is maintained between the rotors and between the rotors and the inner wall of the pump housing. It belongs to a rotary variable vacuum pump. 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 gas can be continuously transported from the inlet to the outlet of the pump. Specific can be divided into the following categories.
⑴ Molecular vacuum pump: It is a kind of vacuum pump that uses a high-speed rotating rotor to transfer energy to gas molecules and make them compress and exhaust. It has the following types:
① Traction molecular pump: gas molecules collide with a high-speed moving rotor to gain momentum and are sent to the outlet, so it is a momentum transfer pump.
② Turbo-molecular pump: The pump is equipped with a rotor with grooved disks or blades, and the rotor rotates between stator disks (or stators). The linear velocity of the rotor circumference is very high. This kind of pump usually works in the state of molecular flow.
③ Composite molecular pump: it is a composite molecular vacuum pump composed of two kinds of molecular pumps: turbine pump and traction pump.
⑵ Jet vacuum pump: It is a momentum transfer pump which uses high-speed jet generated by Venturi effect pressure drop to transport gas to the outlet, and is suitable for working in viscous flow and transitional flow. This kind of pump can be divided into the following types:
① Liquid jet vacuum pump: a jet vacuum pump with liquid (usually water) as the 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 the working medium.
⑶ Diffusion pump: Jet vacuum pump with low pressure and high speed steam flow (steam such as oil or mercury) as working medium. Gas molecules diffuse into the steam jet and are sent to the outlet. The molecular density of gas in jet is always very low, so this pump is suitable for working in molecular flow state. Can be divided into:
① Self-purification diffusion pump: an oil diffusion pump in which volatile impurities in the pump liquid are transported to the outlet through special machinery without returning to the boiler.
(2) Fractionation diffusion pump: This pump has a fractionating device, so that the working liquid vapor with low vapor pressure enters the nozzle working under high vacuum, and the working liquid vapor with high vapor pressure enters the nozzle working under low vacuum. This is a multi-stage oil diffusion pump.
⑷ Diffusion jet pump: It is a momentum transfer pump composed of a single-stage or multi-stage nozzle with diffusion pump characteristics and a single-stage or multi-stage nozzle with jet vacuum pump characteristics in series. Oil booster pump belongs to this type.
5. Ion pump: It is a momentum pump that transports ionized gas to the outlet under the action of electromagnetic field or electric field.
Second, the gas capture pump
This kind of pump is a vacuum pump that makes gas molecules adsorb or condense on the inner surface of the pump, thus reducing the number of gas molecules in the container and achieving the purpose of pumping air. There are the following types.
1) adsorption pump
Air is pumped mainly by physical adsorption of adsorbents with large surface area (such as porous substances).
2) Suction pump
It is a vacuum pump that uses getter to capture gas through chemical combination. Getters are usually metals or alloys in the form of blocks or deposited fresh films. Sublimation pump belongs to this type.
3) Inspiratory ion Pump
It is through the action of electromagnetic field or electric field that ionized gas is adsorbed on the surface with getter material, so as to achieve the purpose of pumping air. It has the following types.
⑴ Evaporative ion Pump: A vacuum pump in which the ionized gas in the pump is adsorbed on the getter material that sublimates (or evaporates) intermittently or continuously and covers the inner wall of the pump, so as to realize air pumping.
⑵ Sputtering ion pump: a vacuum pump in which the ionized gas in the pump is adsorbed on the getter material continuously sputtered by the cathode to achieve the purpose of pumping air.
4) Cryogenic pump
Vacuum pump using low temperature surface to capture gas
3. 1.3 Performance parameters and application scope of vacuum pump
3. 1.3. 1 vacuum pump performance parameters
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 entrance and works according to the specified conditions. Without introducing gas, the minimum pressure tends to be stable and normal.
2) Pumping rate of vacuum pump
The pumping 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 designated position of the test cover when the pump is equipped with a standard test cover and works under specified conditions. Short for suction speed of pump.
3) Pumping capacity of vacuum pump
The pumping unit of vacuum pump is Pa m3/s or pal/s. Refers to the gas flow at the pump inlet.
4) Starting pressure of vacuum pump
The starting pressure of vacuum pump is Pa, which refers to the pressure when the pump is started without damage and has pumping effect.
5) Pre-pressure of the pump
The pre-pressure unit of vacuum pump is Pa, which refers to the outlet pressure of vacuum pump whose exhaust pressure is lower than one atmosphere.
6) Maximum back pressure of vacuum pump
The maximum backing pressure unit of the vacuum pump port is Pa, which means that it exceeds the backing pressure that will damage the pump.
7) Maximum working pressure of vacuum pump
The maximum working pressure of vacuum pump is Pa, which refers to the inlet pressure corresponding to the maximum pumping capacity. Under this pressure, the pump can work continuously without degradation or damage.
8) Compression ratio
Compression ratio refers to the ratio of outlet pressure to inlet pressure of a given gas.
9) Ho's coefficient
The ratio of the actual pumping speed on the pumping channel area of the pump to the theoretical pumping speed calculated by molecular exudation.
10) pumping speed coefficient
The ratio of the actual pumping speed of the pump to the theoretical pumping speed calculated by molecular exudation at the pump inlet.
1 1) reflux rate
The reflux rate of the pump is g/cm2.s, which refers to the mass flow of pump flow per unit area through the pump inlet when the pump works under specified conditions.
12) allowable amount of water vapor
The allowable unit of water vapor is kg/h, which refers to the mass flow of water vapor that can be pumped by the gas ballast pump under normal environmental conditions.
13) Maximum allowable steam inlet pressure
The maximum allowable steam inlet pressure is Pa. Refers to the highest inlet pressure of water vapor that can be pumped out when the gas ballast pump works continuously under normal environmental conditions.
According to your requirements, I think it is better to choose oil-sealed vacuum pump.
Reason:
1, its vacuum can be pumped to a very low level, which can be selected according to the type. The lowest vacuum can be pumped to zero.
2, it is sealed with oil to ensure your humidity.
It doesn't need water circulation system, so it is much smaller.