Composition and type of low vacuum unit
The low vacuum unit consists of different main pumps, reciprocating vacuum pumps, oil seal vacuum pumps, water vapor injection pumps, water ring pumps, molecular sieve adsorption pumps, oil vapor injection pumps, roots pumps and other vacuum components of the front pumps (oil vapor injection pumps, roots pumps), valves and pipes. Its main characteristics are high working pressure, large amount of exhaust gas, low pumping speed.
The low vacuum unit can be divided into the following types according to the different characteristics of the purpose, the main pump and the vacuum components.
1. Low vacuum units for industrial use
FIG. 1 shows the metal low vacuum system for ultra-high vacuum coating machine.
FIG. 1 metal low vacuum system
1- machine sealing pump; 2- air vent valve; 3- pipe valve; 4- oil trap; 5- thermocouple gauge; 6- pipe valve; 7- electromagnetic valve.
2. Low vacuum unit of root pump main pump
It is used in a vacuum drying system to remove a large amount of water vapor and require high limit vacuum degree.
(1) the principle of low-vacuum unit of primary roots pump is shown in FIG. 2.
FIG. 2 schematic diagram of low vacuum unit of primary roots pump
L-lutz pump; 2 - the valve; 3- air injection pump; 4- water ring pump; 5- pneumatic mechanical pump.
(2) when the two-stage roots pump and the first-stage water ring pump (ultimate vacuum degree 7x103Pa) and the pneumatic mechanical pump are used together, as shown in FIG. 3. The working pressure can reach 10-1pa. When a large amount of water vapor is needed, close the valve 2 and use the water ring pump as the front stage pump. When the water vapor pressure drops to 3x102~1x103Pa, close valve 1, open valve 2, and use the pneumatic mechanical pump as the front stage pump.
FIG. 3 schematic diagram of low vacuum unit of two-stage roots pump
1-lotz pump; 2- pneumatic mechanical pump; 3- water ring pump.
(3) the primary roots pump is directly used in tandem with the atmospheric jet pump and water ring pump (extreme vacuum P=3x103Pa), and the minimum working pressure can reach 3x102~1x103Pa).
FIG. 1-61 of the roots pump and water ring pump is used in series of two roots pumps. The double water ring pump serves as its front stage pump, which can improve the ultimate vacuum degree of the unit.
When considering the water saturation vapor pressure is the theoretical limit vacuum of water ring pump and the gas backflow, the limit vacuum of the front stage pump should be increased. The ultimate vacuum can reach 3x103~5x103Pa.