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
These include the valve
This leftover parcel of air
| Some amount of air
pressure is necessary
to open the check
valves in a typical air
There is plenty
There is not enough
The same goes for diaphragm pumps. Next page---->