How a Compressor Works

What does a compressor do?


A compressor is the motor that pumps things around. In this case it is moving the refrigerant round in a loop or circuit. In some places the refrigerant is being squeezed by the compressor - we say it is under high pressure. These areas are shown in red in the animation below.  The blue areas are where the pressure is under low pressure.

Keeping the refrigerant fluid at a high pressure is difficult. Just as a bicycle tyre needs pumping up to make it firm enough to be able to ride comfortably,  so that part of our fridge circuit needs constant pumping to create high pressure.

It needs the constant pumping not because the refrigerant is leaking (like air leaking from your bicycle tyre) but because it’s being moved into something called an expansion valve and into a section of the circuit which is at a lower pressure.

The low pressure side of our circuit requires a continuous supply of liquid so that it can evaporate and create a cooling effect (in order to keep your food cool).

It is also the compressor’s job to pump the gas back from the low pressure to the high pressure side so that it can be turned back to liquid and the whole process can start again in a continuous cycle.

How is gas pressure raised by the compressor? Remember the Gas Laws - Boyle’ Law says ‘as the volume goes down, pressure goes up.’ The compressor is made up of a piston in a cylinder which moves up and down -  just like when you are pumping your bike tyre pump.

Refrigeration Loop


There are many different types of compressor but they all use the basic mechanism of a piston and cylinder to create a pumping action.  But they all have the same job – increasing the volume of a gas so that the pressure increases.

Below we see a Rotary Mechanism. It's called rotary because the piston, shown by the label "cylinder block" in this diagram, is rotating within the chamber.  The rotary mechanism is considered simple and suitable for small compressors used in things like frozen cabinets in shops or restaurants.




What does a compressor look like when it is working?

The video runs through all of the different parts inside a compressor similar to one you would find in your fridge at home:

Cooling Science Homepage

Careers in refrigeration