Ultra-high vacuum units operating above 10-5pa include diffusion pump, molecular pump ultra-high vacuum unit and oil free ultra-high vacuum unit. The unit has the following characteristics:
The maximum vacuum degree of main pump is higher than 10-7~10-8pa.
(2) can endure the high temperature of 200 ~ 450 ℃ baking;
The partial pressure of return gas of the main pump is low.
For the main pump with high selectivity, it shall be equipped with a sufficiently large auxiliary pump.
(1) ultra-high vacuum unit of diffusion pump
The ultimate vacuum of ultra-high vacuum units with diffusion pumps as the main pumps is 10-7~ 10-8pa.
In order to reduce the influence of the reverse diffusion of gas from the front stage of the diffusion pump and the reverse diffusion of mechanical pump oil on the ultimate vacuum degree, a diffusion pump with a lower pumping speed can be used at the front stage of the diffusion pump to reduce the compression ratio and reverse diffusion. If a titanium sublimation trap is added to the inlet of the diffusion pump, the nitrogen partial pressure from the diffusion pump can be further reduced, and a super-high vacuum of 10-11pa can be obtained.
(2) ultra-high vacuum unit of molecular pump
The maximum vacuum of ultra-high vacuum units, which mainly use molecular pumps, is 10-8pa, which is characterized by quick start and low oil pollution.
The pumping speed can be increased by adding liquid nitrogen cold trap in the unit. The outlet of the mechanical pump is provided with a water cold trap to prevent oil vapour from entering the system.
(3) oil free ultra-high vacuum unit
The vacuum unit that does not use oil to make working liquid and does not seal with organic material is called the super-high vacuum unit without oil. The commonly used main pumps include cryogenic pump, titanium pump, sputtering ion pump, etc. Compared with the oil vacuum unit, it has the following advantages:
Clean vacuum and no pollution source can be obtained.
When the oil free vacuum pump is started, the pre-pump can be isolated.
If the ventilation stops suddenly, the system will not be polluted;
It has no oil, no noise and no vibration, which improves the working environment.
The terminal vacuum degree is high, the pumping speed is high, and the pumping time is short.