How Does an Air Compressor Work?

An air compressor’s main function is to convert power into pressurised air.

When air is compressed, it becomes stronger, making it useful for different workshop applications or to power tools.

Today, air compressors are used anywhere pneumatic tools are running or in places where products are assembled and serviced, such as workshops, factories, auto mechanic or petrol stations and at home.

Compared to using a centralised power source, air compressors are much smaller in size and don’t require a massive motor to run. They’re also highly portable, quieter and more durable.

By understanding how an air compressor works, you can better determine the right air compressor for the job. Here’s what you need to know.

Air Compressors – The Basics

Air stored under pressure creates potential energy that can be held in the tank until needed.

Air compressors work by absorbing air and circulating it through the system by different methods, depending on the type of compressor you’re using. It’s then filtered and returned direct to the outlet at a desired pressure.

The basic components are:

1. Drive: Either belt-driven, which uses the moving belt to activate the system’s pump, or direct-drive system, where the motor is attached directly the crankshaft of the compressor. Belt-driven is the most economical option, whereas direct-drive systems allow for smaller designs and few maintenance requirements
2. Pump: Uses the energy from the drive to absorb air and compress it, which is sent through a tube into the storage tank
3. Storage Tank: Equipped with a one-way valve (check valve) to stop compressed air from putting back pressure on the pump. It acts as a buffer to eliminate running the compressor continuously for less pump wear and motor damage

Most air compressors are powered by an electric motor or gas engine.

Screw Air Compressors

Rotary screw air compressors are the most commonly used types.

These machines have two interlocking helical rotors, male and female, which rotate in opposite directions to draw air in between them.

Air is then trapped between the rotors. As the screws turn, the pressure of the air increases as the space between the rotors decreases. The speed of this process can be adjusted according to the application in variable speed drive rotary compressors.

Rotary screw air compressors can also come with one screw. However, single-screw rotary types are rarely used for compressing air, as they’re seen more in refrigerant applications.

Best Uses: Designed for heavy-duty applications and can work at high speeds and large flow rates. If there’s a high demand for air in your workshop, rotary screw compressors can keep up without wasting energy or creating unnecessary noise.

Oil Lubricated Air Compressors vs Oil Free

Rotary screw compressors can either be oil lubricated or oil free.

Oil lubricated compressors work by bathing the walls and bearings within the cylinder with oil. The oil also provides a hydraulic seal between the rotors to transfer mechanical energy.

In oil free air compressors, male and female rotaries are controlled by timing gears to ensure they maintain alignment.

These gears and their bearings need oil to work and are treated with lasting lubrication. Whilst there is oil in an oil free air compressor, the difference is that it’s separated from the compressed air side, making applications oil free. The compression is done without oil, only air, resulting in very hot compressed air.

Piston Air Compressors

Piston air compressors are oil lubricated.

They work by using the tool’s crankshaft to force air into the compression chamber. The crankshaft drives the piston closed before pushing the compressed air into the storage tank. As the piston opens again, more air is drawn into the tank.

Reciprocating piston air compressors contain the following parts:

• Crankshaft
• Piston
• Cylinder
• Connecting rod
• Valve head

There are two types of piston compressors, single-stage and dual.

Single-stage uses a piston to compress the air in one stroke, a full rotation of the crankshaft. Dual-piston air compressors have two stages. The compressor uses one piston to compress air in a single stroke, before moving that compressed air to a smaller cylinder for a second stroke from a second piston, doubling the air pressure stored in the tank.

For more information about which air compressor is right for your job, contact our team or follow our blog for the latest tips.