The vacuum system is under thin air condition which is lower than the local ATM.

　　The air thin degree under the vacuum state, it is represents by "the vacuum degree is high" and "the vacuum degree is low". The vacuum degree is high to represent the good vacuum degree,the vacuum degree is low meaning the bad vacuum degree.

　　Usally use "Torr" as the unit，also use the Pa in the international world resently.

　　1Tor＝1/760ATM＝1mmHg

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

　　The air granules meet each other the twice while they doing the irregular movement to fly the average distance. It is expressed by“λ”.

　　The air capacity passing across any random cross in the unit time is expressed by “Q”，the unit is Pa·L/s or Torr·L/s.

　　It expresses the vacuum pipe's ability of passing the air through.The unit isL/s，at the steady condition,the flow conductor of the pipe is equal to flow capacity divides the difference of the two sides pressure intensity. With the sign“U”express. 　　U＝Q/(P₂- P₁)

　　The force in unit area of the container wall is acted by the air molecule.It is expressed by sign "P".

　　The pressure intensity is 101325dyn/cm2 indicates the atmosphere. The sign is Atm.

　　After the completely pumping, the container inside keeps in a definite vacuum degree steadily.This vacuum degree is limit vacuum. In general, the container must be refined for 12 hours, then pumped for 12 hours,at the final hour measure the vacuum degree once per 10 minutes.Choose the average date of the 10 times as the limit vacuum.

　　Under the definite pressure intensity and temperature,the pumping air capacity from the intake port in unit time is called suction capacity:S_p＝Q/（P－P₀）

　　The vacuum meter is making use of the thoery about the thermocouple force is relative with the heating components,and the components temperature also ties in the air heat conduct to measure the vacuum degree.

　　It is composed by the cylindraceous collection pole, web and the filament in center of web, the cylindraceous pole is out of the web.The hot cathod sends the electrons to ionizate the air molecule, the ions are collected by the collection pole. On the foundation of the ions current's big or small to measure the air pressure, this kind of vacuum meter is ionizaion vacuum meter.

　　It is composed by the thermocouple vacuum meter and the hot cathod ionization vacuum meter.The measure scope is from ATM to 10^-5Pa。

　　At the both sides of the anode canister has a pair of cathod boards, under the effect of the outside magnetic field，the inner anode canister forms Paning to discharge then comes into being the ions, according to the ions current's big or small to measure the air pressure intensity, this kind of meter is called cold cathod inization vacuum meter.

　　By way of the thoery that the resistance of the heating components is tied in the temperature,and the components temperature is also tied in the air transmission conductor and using the electrical bridge circuit to measure the vacuum degree, this kind of vacuum meter is resistance vacuum meter.

　　Using the Hg (or oil)to compress the measured air into very small volume,then compare the liquid columnation of open pipe and close pipe.By way of the Boyier Law to calculate the absolute pressure of the air. This kind of vacuum meter is Mcload vacuum meter.

　　It is a hot cathod ionization gauge that converted by the cathod and the collected pole. The collected pole is a thread which is set in the centre at the web, and the filament is out of the web, this can reduce the influence to the X-ray, then expand the measure lowe limit. Thus can measure the ultrahigh vacuum.

　　The impeller's rotation of the pump to form the water ring. Owing to the Rotor rotates ecentrically to make the volume between the water ring and vanes changed periodically. The mechnical vacuum pump using this kind to pump air is called water ring pump.

　　This mechnical vacuum pump is using the piston's to and pro movement to pump the air.

　　This mechnical vacuum pump is using the oil to keep seal. It can class the Statory type, Rotory type, Rotary Piston etc.

　　It has a pair of shoes shape Rotor which rotates high speed.This pump can not use alone, the fore stage must assemble the oil seal pump or water ring pump that can aspirate the air directly.

　　It has a high speed impeller,when the air molecule meets the high speed turbo vanes to push to the outlet, then is pumped by the fore pump.

　　The high speed steam current is spouted out from the outlet port of the diffusion. Under the molecule current, the air molecule diffuses into the steam current continually, and carries by the steam to the outlet, then is pumped by the next stage in turn, at last, is pumped out by the fore pump.

　　The vacuum pump is using the low temperature surface that under the 20K to absorb the air.

　　It is set between the container and pump. Using as the device to absorb the air and collect the oil steam.

　　To open a hole in the compressed room of the oil seal vacuum pump and install a adjust valve.When turn on the valve and adjust the intaking volume, the Rotor turns a definite position, the air passes the hole to enter the compressed room, then the compressure rate is reduced. So that most of the steam can not coagurate to pump outside of the pipe with the aerifed air. Possess the function above valve is called gas ballast valve.

　　Freezing dry in vacuum is also called sublimation dryness. Its thoery is freezing the material to make the water contained becomes ice, then sublimate the ice in vacuum to dry.

　　In vacuum condition, the process of heating the material and plating them on the basic sheets is called vaporizing and plating in vacuum, or also called vacuum plating.

　　It is a method by way of the boiling point is low under the vacuum condition to dry the material.

　　(1)main pump：In vacuum systems, it is used for abtaining the required vacuum degree to satisfy the definite process. Such as the oil diffusion pump is the main pump which used in the vacuum plating machine.

　　(2)fore pump：It is used for keeping the fore pressure of a pump is lower than the fore critical pressure. Such as the fore set Rotary pump or Rotary piston pump are also the fore pump.

　　(3)rough pump：To pump air under the ATM, and make the system pressure to achieve the vacuum pressure that the next pump begins to aspirate. Such as the rotary piston pump in the plating vacuum machine is the rough oil pump.

　　(4)maintain pump：In vacuum system, when the suction capacity is very small, so the fore pump isn't used efficiently. Then install a lower volume assistant pump to maintain the main pump's working.This kind of pump is maintain pump.For example: install a small rotary vane pump at the diffusion vacuum pump's outlet port.