Vacuum Knowledge | Technical Terms | Vacuum Pump Classifications

  1. Definition of vacuum

A vacuum system refers to a state of dilute gas below the atmospheric pressure in the area.


  1. Vacuum degree

The degree of dilution of the gas in a vacuum state is usually expressed as "high vacuum" and "low vacuum". High vacuum means "good" vacuum, and low vacuum means "poor" vacuum.


  1. Vacuum unit

Usually use Torr as the unit, in recent years, Pa is used internationally.

1 Torr = 1/760 atmosphere = 1 mm Hg


  1. Tor and Pa conversion

1 Torr = 133.322 Pa or 1 Pa = 7.5×10-3 Torr


  1. Flow rate

The amount of gas flowing through any section per unit time, the symbol is represented by "Q", and the unit is Pa·L/s or Tor·L/s.


  1. Pressure

The force of gas molecules acting on the unit area of the container wall, denoted by "P".


  1. Standard atmospheric pressure

The pressure is the air pressure of 101325 dynes per square centimeter, symbol: (Atm).


  1. Ultimate vacuum

After the vacuum container is fully evacuated, it is stabilized at a certain degree of vacuum, which is called the ultimate vacuum. Usually, the vacuum container needs to be refined for 12 hours, then evacuated for 12 hours, and measured every 10 minutes for the last one hour, and the average value of the 10 times is taken as the ultimate vacuum value.


  1. Pumping speed or capacity

Under a certain pressure and temperature, the gas pumped from the pump inlet per unit time is called the pumping speed, or capacity. That is, Sp=Q/(P-P0)


  1. Water ring vacuum pump

The water ring is created by the rotation of the impeller rotor of the pump. Due to the eccentric rotation of the rotor, the volume between the water ring and the impeller is periodically changed and the mechanical vacuum pump is pumped.


  1. Reciprocating vacuum pump

A mechanical vacuum pump that uses the reciprocating motion of the piston to pump air.


  1. Oil-sealed mechanical vacuum pump

The mechanical vacuum pump that uses oil to keep the seal can be divided into rotary vane type vacuum pump, piston vacuum pump, trochoid type vacuum pump, etc.


  1. Roots vacuum pump

It is a mechanical vacuum pump with a pair of sole-shaped rotors that rotate synchronously at high speed. This pump cannot be used alone. The backing pump needs to be equipped with a vacuum pump such as oil sealed vacuum pump or water ring vacuum pump.


  1. Turbo molecular vacuum pump

There is a high-speed rotating impeller. When the gas molecules collide with the high-speed rotating turbine blades, they are driven to the gas outlet and then pumped out by the backing pump.


  1. Oil diffusion vacuum pump

A high-speed steam flow is ejected from the nozzle of the diffusion pump. Under the condition of molecular flow, the gas molecules are continuously diffused into the steam flow, and are carried by the steam to the pump outlet to be compressed step by step and then discharged by the backing pump.


  1. Cryogenic vacuum pump

A vacuum pump that uses a low-temperature surface below 20 to condense and adsorb gas.


  1. 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 intake is adjusted, the rotor turns to a certain position, and the air is mixed into the compression chamber through this hole to reduce the compression ratio, so that the large part of the steam will not be condensed and will be excluded from the pump together with the mixed gas. The valve that plays this role is called a gas ballast valve.


  1. 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 sublime the ice under vacuum to achieve the purpose of drying.


  1. Vacuum evaporation

In a vacuum environment, heating and coating the material on the substrate is called vacuum evaporation, or vacuum coating.


  1. Vacuum drying

A method of drying items by utilizing the low boiling point in a vacuum environment.


  1. Common vacuum pumps of vacuum systems

  • Main suction pump: in the vacuum system, the vacuum pump used to obtain the required vacuum degree to meet the specific process requirements, such as the oil diffusion pump in the vacuum coating machine, is the main pump.

  • Backing 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 vacuum pump or piston pump configured in front of the roots pump is the backing pump. (3) Rough suction pump: a vacuum pump that starts to pump from atmospheric pressure and pump the system pressure to another vacuum pump to start working. For example, the piston pump in the vacuum coating machine is the rough suction

  • Maintenance pump: in the vacuum system, the air volume is very small, and the backing pump cannot be effectively used. To this end, an auxiliary pump with a smaller capacity is configured to maintain the main suction pump, which is called a maintenance pump. For example, a small rotary vane vacuum pump is equipped at the outlet of the diffusion pump, which is a maintenance pump.


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