How does a vacuum pump work?

Question

when using dual head motor, especially diaphragm motor.

Answer 1

The most basic vacuum pump is a piston in a cylinder with two valves. In one stroke with one valve open and the other closed the piston draws a volume of air from the tank where we need vacuum. It expels the air using the other valve with the first valve open. There is your basic vacuum pump.

Practically were have vacuum pumps that use impellers, ejectors which use fast steam to draw vacuum and many more

Answer 2

There are two categories of vacuum pumps: transfer pumps and trapping pumps.  

The transfer pumps are also called kinetic pumps since they impart the momentum to the gas which is being pushed in a such a way that the gas is transferred continuously from the inlet of the pump to the outlet. This is usually done by mechanical moving parts of the pump, as shown in Figure 5. The moving (usually rotating) part of the pump accelerates the molecules of the gas and makes the region of lower pressure. Therefore, the molecules from the tank will start moving towards the region of lower static pressure, with the procedure continuously repeating until all (or most) of the molecules are taken from the container where we would like to have a vacuum. When we get the wanted level of vacuum we isolate the tank by a high vacuum valve. This valve stops any exchange of gas between the container and the pump.