A modern"Vacuum pump" in the classroom.

 A "vacuum pump" is so named for its function. It is really an air pump that is
specifically designed to reduce the air pressure of a connected chamber.

 You may have seen the use of such a pump in class as part of a classical physics demonstration.

 The problem with the use of such a pump is that its process is hidden deeply within an iron
casing, no knowledge imparted to the class during physics demonstrations as to its specific operation.
 Because it is an expensive and delicate piece of scientific equipment, instructors often do not
allow students to touch or operate the machine.

 It is very important to introduce newcomers to both the concept and the feel as what it
takes to create this kind of reduced pressure in a connected vessel.


     What the vacuum service air pump isn't.

  It is a common misconception that a lab vacuum pump is nothing more than an air compressor  that is used to "suck" air out of things.

Such reciprocating piston machines are quite unsuitable for the low pressures necessary for
modern physics demonstrations like electrical discharges in rarefied air and other gases.
 There are spaces in a 
typical piston-type air 
compressor that are not 
part of the volume that is 
displaced or swept by 
the piston. 

 These include the valve 
passages, pockets and the annular spaces 
around the piston above 
the sliding ring seals. 

 This leftover parcel of air 
cannot be expelled, stays 
in the fixed volume of the pump and is uselessly 
reworked over repeatedly. 

 Some amount of air 
pressure is necessary 
to open the check 
valves in a typical air 

  There is plenty 
of pressure to open the 
valves in  pressure 

 There is not enough 
force by the lowered 
pressure air of vacuum 
service to open 
the spring loaded 



   The same goes for diaphragm pumps.         Next page---->