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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.

UNIT CONVERSION TABLE

 

From
To
Pa (N / m2 ) Torr ( mmHg ) atm mbar psi ( bf / in2 ) kgf / cm2 mH2O(15o )
1Pa ( N / m2 ) 1 7.50 x 10-3 9.87 x 10-6 10-2 1.45 x 10-4 1.02 x 10-5 1.02 x 10-4
1Torr ( mmHg ) 133.32 1 1.316 x 10-3 1.33 1.93 x 10-2 1.359 x 10-3 1.36 x 10-2
1 atm 1.013 x 105 760 1 1.013 x 103 14.696 1.033 10.34
1 mbar 100 0.750 9.87 x 10-4 1 1.45 x 10-2 1.02 x 10-3 10.206 x 10-3
1 psi ( bf / in2 ) 6.89 x 103 51.71 6.8 x 10-2 68.9 1 7.031 x 10-2 0.703
1 kgf / cm2 9.8 x 104 735.56 0.968 9.81 x 10-2 14.223 1 10
1 mH2O 9.8 x 103 73.49 9.68 x 10-2 98.0 1.421 0.1 1