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VACUUM PUMPS' MAIN APPLICABLE INDUSTRIES AND ACCESS PATCH
Mariotte law
If the volume of a given quantity of gas is Increasing, its pressure decreases.
This method can be used to produce a Vacuum, In the following chapter we are going to talk about th "vacuum generator" of a 3 vances rotary vacuum pump and the "oil casing" necessary in rough vacuum pumps.
Vacuum Generator
An eccentric rotor turns in a housing(stator) equipped with an inlet and an outlet with exhaust valve. 3 vanes, sliding In the rotor and forced against th housing, divide the space in three compartiment of variable volume.
Gas pumping
Phase 1
The volume A is in communication with a vessel in which vacuum is desired.
Gases are sucked into the volume A as there is a depression caused by its increasing volume.
This is the Suction phase.
Phase 2
The volume A is isolated from the vessel and the outlet. The volume A decreasing, acompression of gases occurs.
This is the Compression phase.
Phase 3
The voulme A is in communication with the outlet. The volume is still decreasing and we have an overpressure, which is not enough to open the exhausr valve.
This is the Overpressure phase.
Phase 4
The volume A is still decreasing and pressure reaches atmospheric pressure the exhaust valve opens and the gas is exhausted.
This is the Exhaust Phase.
Pumping condensable vapours
Note:
At a given temperature vapours can be only compressed up to saturation pressure. For example at 70C(working teamperature of the SOGEVAC pumps) the saturation pressure of water is 320 mbar; this means that water vapours can be compressed up to 320 mbar, after which water begins to condense. In a vessel containng water, the air is rapidly pumped out the pressure in vessel is the one of water vapour.
Phase 1
The volume A is in communication with vessel, and the volume increasing, suction of vapours occurs.
This is the Suction phase.
Phase 2
Volume A is isolated form the vessel and exhaust outlet. The Volume A decreases and vapours are compressed. But as pressure during this phase is generally over 320 mbar condensation begins.
There is no compression but Condensation.
Phase 3
The volume A is in communication with exhaust outlet and pressure does not exceed 320 mbar. Water stays in the pump under liquid phase and mixes with oil.
Consequently:water from an emulsion with oil which loses its lubrication qualities. The oil filter can clog and pump can be demaged.
Conclusion:Vapours cannot be pumped. To prevent this problem a Gas Ballast Valve must be used.
