The physics of air pumps designed
                   for real vacuum service

 The mechanical requirements for air pumps for vacuum service are the following:

 ( 1 )  Flow of already very thin air should not be impeded by any pump inlet check valves.

 ( 2 )  The machine must have the ability to capture, compress and exhaust the air away from the
          chamber being evacuated.

  First lets find out what is so special about a traditional "vacuum pump".

Here is a more complete diagram of a traditional rotary vane pump used for vacuum service.

 Illustrations of such machines abound in many books relating the use of vacuum in
various scientific and industrial applications.

 Those diagrams are often overly simplified and fail to show the role that the oil plays in
the pump's operation.


  Diagram that shows how the oil seals and lubricates 
working parts. 

The oil not only serves to lubricate the  
machine, but also forms the dynamic  
seals that prevent the air from leaking around  
the rotor, stator and the vanes of the pump. 

 Another important detail often left out is the 
role  that the oil plays in displacing the air in the 
passage that leads to the flap valve.  

The function of the reed flap valve is  
grossly understated in many texts.  

 This valve prevent the oil from being sucked 
( surging )  
back into each arriving crescent of rarefied  
air space and ramming the approaching vane.  

 Also, if the space in front of the  
arriving vane was completely filled with  
oil,  the pump would be vary hard to turn  
owing to the fact that oil is thicker than air.  

 The oil would have to be squeezed back out  
that small hole.


  A precise amount of oil is feed into each rotation 
of the vacuum pump rotor.

  A separate oil pump that is driven from the main shaft of the machine feeds 
channels in the end plates that cover the 
pump cavity pass the oil to the stator 
and rotor parts. 

    Understanding of the physics of traditional "vacuum pump" operation allowed the design
of a viable alternative.                 <---- Back to main page     <-- Back to previous page    Next page-->