Common terminology of vacuum

1.Definition of vacuum 2.Degree of vacuum 3.Unit of vacuum 4.Conversion of Torr and par 5.Mean free path
6.Flow 7.Conductance 8.Pressure or intensity of pressure 9.Standard atmospheric pressure 10.Limit vacuum
11.Suction speed 12.Thermocouple vacuum gauge 13.Ionization gauge 14.Compound vacuum gauge 15.Cold cathode ionization gauge
16.Resistance vacuum gauge 17.McGraw gauge 18.B-A gauge 19.Water ring vacuum pump 20.Reciprocating vacuum pump
21.Oil-sealed mechanical vacuum pump 22.Roots pump 23.Turbo-molecular vacuum pump 24.Oil diffusion vacuum pump 25.Low temperature vacuum pump
26.Cold trap 27.Gas ballast valve 28.Vacuum freeze-drying 29.Vacuum evaporation 30. Vacuum drying


  1, Definition of vacuum

  The vacuum system refers to the thin air condition of the atmospheric pressure in the area.

  2,Vacuum degree

  Gas dilution degree in the vacuum state, usually use high and low vacuum degree to express. High degree of vacuum refers to good vacuum degree; while low degree of vacuum refers to poor vacuum degree.

  3,Vacuum degree Unit

  Commonly used unit is Torr, but in recent years, Pa is used as the unit internationally.

  1 Torr = 1/760 atmospheric pressure = 1 mm Hg

  4, The conversion of Torr and Pa

  1 Torr = 133.322 PA or 1 Pa = 7.5 x 10-3 Torr

  5,Mean free path

  As the gas particles in irregular heat movement, mean free path is the average distance of gas particles’ two successive collisions expressed by the symbol "λ".


  It indicates to the gas volume flowing through any section in unit time, symbol: Q, with unit of Pa.L/s or Torr.L/s.

  7,Flow guide

  It indicates the capability of the vacuum pipe through gas, in unit of L/s; in the steady state, the pipeline flow is equal to the pipe flow divided by the pressure difference between the two ends of the pipe, symbol: U, U = Q/ (P2- P1)

  8,Pressure or intensity of pressure

  It indicates force of gas molecules acting on the wall of a container, symbol: "P".

  9,Standard atmospheric pressure

  The pressure is atmospheric pressure 101325 dynes per square centimeter, symbol: A

  10,Ultimate vacuum

  If vacuum vessel is fully pumped gas, it has stable vacuum degree, which is said as the ultimate vacuum. Usually the vacuum vessel shall be 12 hours gas forming, again pump vacuum after 12 hours, and measure every 10 minutes during the final one hour; take the 10 times of average value as the ultimate vacuum.

  11,Air suction rate

  At a certain pressure and temperature, gas volume pumped from the pump air intake in unit time is called the pumping rate, referred to as the suction rate. That is, Sp = Q/ (P -P0)

  12,Thermocouple vacuum gauge

  The electric potential of the thermocouple is related to the temperature of the heating element, and the temperature of the component is related to the principle of the heat conduction of the gas to measure the vacuum degree of the vacuum gauge.

  13, Ionization vacuum gauge (also called as hot cathode ionization meter)

  Consist of a cylinder shaped collection pole, grid and filaments located in the grid center. Cylindrical collection poles are outside the grid. Hot cathode emits electron ionization gas molecules; ions have been collected by collection poles. The vacuum meter measures gas pressure according to the size of collected ion flow.

  14,Compound vacuum gauge

  By the thermocouple vacuum gauge and the hot cathode ionization vacuum gauge, the measurement range is from atmospheric pressure to~10-5Pa。

  15,Cold cathode ionization gauge

  At the two ends of the anode tube are provided with a pair of cathode plate, in which the external magnetic field function, the formation of penning discharge in the anode tube produces ions. The vacuum meter measures air pressure according to the size of collected ion flow.

  16, Resistance vacuum gauge

  The resistance of the heating element is related to the temperature, the temperature of the component is related to the principle of the gas conduction, and the vacuum gauge is used to measure the vacuum degree.

  17,Macraw vacuum gauge (compression type vacuum gauge)

  The gas to be measured is pressed to very small volume via mercury (or oil) compression; compare open tube and closed tube’s liquid column difference, and directly calculate the gas pressure with the Boyier’s law.

  18, B-A gauge

  This is a cathode collector and collector cathode ionization gauge. Collector is a filament, placed in the center of the grid, the filament on the outside of the grid, so as to reduce the impact of soft X rays, extend the lower limit of measurement, can be measured ultra-high vacuum.

  19,Water ring vacuum pump

  It is a mechanical vacuum pump, whose impeller rotor rotates to produce water ring, and is used for pumping the air through the eccentric rotation of the rotor and the volume of the water ring and the blade.

  20,Reciprocating vacuum pump

  It is a mechanical vacuum pump using the reciprocating motion of the piston.

  21,Oil seal mechanical vacuum pump

  It is a mechanical vacuum pump to keep seal via oil, and can be divided into fixed type, rotary type, valve type, trochoidal type and so on.

  22,Roots vacuum pump

  It is a mechanical vacuum pump with a pair of rotors in synchronous high-speed rotation, the pump cannot pump separately; its front stage needs to be equipped with oil seal and water rings etc., which can directly discharge air.

  23, Turbo molecular vacuum pump

  With a high-speed rotation of impeller, when the gas molecules and high-speed rotation of the turbine blade clash was driven to the gas outlet again by the first stage pump pumping.

  24,Oil-diffusion vacuum pump

  Diffusion pump nozzle jet of high speed steam flow. In the molecular flow conditions, gas molecules continue to diffuse into the steam flow, and the steam was brought to the pump outlet is compressed and then removed by the former pump.

  25,Low temperature vacuum pump

  Utilize the low temperature surface to condense adsorption gas below 20K.

  26,Cold trap (water cooled baffle)

  A device that is placed between a vacuum vessel and a pump for adsorption of gas or for collecting oil vapor.

  27,Gas ballast valve

  Oil sealed mechanical vacuum pump compression chamber is opened a hole, and fitted with a regulating valve, when the valve is opened and regulation into the gas, rotor to go to a certain location, air is through the hole of the incorporation of compression chamber to reduce the compression ratio, so that most of the vapor by condensation and the incorporation of gas together were excluded from the pump outside the role of valve said the gas ballast valve.

  28,Vacuum freeze drying

  Vacuum freeze drying is also known as sublimation drying. Its principle is to freeze the material, so that its contained moisture changes into ice, and then make the ice sublimation in vacuum to achieve the purpose of drying

  29,Vacuum evaporation

  In a vacuum environment, the material is heated and deposited onto a substrate called vacuum evaporation, or vacuum coating.

  30,Vacuum drying

  A method of drying an article by utilizing the characteristics of low boiling point in a vacuum environment.

  31, Names commonly used in the vacuum system

  (1)Main pump:in the vacuum system, used to obtain the required vacuum to meet the specific requirements of the vacuum pumps, such as vacuum coating machine oil diffusion pump is the main pump.

  (2)Pre-stage pump:to maintain a vacuum pump of pressure is below the critical level of pressure before the vacuum pump, such as the Roots pump configuration of the rotary vane or piston pump is pre pump.

  (3)Crude oil pump:It starts to suction from atmospheric pressure, and draw the system pressure to another vacuum pump and start working. Such as the slide valve pump in the vacuum coating

  (4)Maintenance pump:in the vacuum system, backing pump cannot be effectively used if gas volume is very small. This configuration a small capacity auxiliary pump to maintain the work of the main pump, this pump is said to maintain the pump. Such as a small rotary vane pump at the diffusion pump outlet.