Piston compressors: How they work

Piston compressors take regular air in, but expel it as compressed air. Learn how these air compressors work and find out about the different models.

Estimated time to read: 7 minutes

March 8, 2023

How piston compressors compress air

The first recorded reference to a piston compressor (also known as a ‘reciprocating compressor’) was made towards the end of the 18th century. While the technology has improved dramatically since then, the basic concept behind the piston compressor remains the same:

1.    When the piston in the piston compressor descends, it creates a vacuum, drawing air into the compressor via the inlet.

2.    This air passes through inlet valves into the cylinder. While these inlet valves are currently open, the discharge valves are closed. In other words, air travels in, but is unable to get out.

3.    When the cylinder is full of air, the piston ascends, compressing the air.

The discharge valves usually open at a certain level of pressure. As the piston ascends, it pushes the compressed air out through the open discharge valves. 

Different types of piston compressors

In theory, all piston compressors work according to the same principle. However, there are major differences in how the compressor puts this principle to use. The main difference is based on the number of stages in which the compression takes place. 

There are single-stage, double-stage, and multi-stage compressors. Dividing the compression over a number of different stages means the compressor doesn’t need to work as hard. The temperature of the air is also lower at output. 

Of course, to fully benefit from multi-stage compression, the air needs to be cooled between the different stages, allowing even greater compression. This can be done with the help of an intercooler. There are also oil-injected and oil-free piston compressors that have specific benefits and uses. 

Alup compressor

Oil-injected piston compressors

Oil-injected piston compressors lubricate the cylinders, pistons and cranks by circulating oil throughout the compressor. A tiny amount of residual oil ends up in the compressed air. It’s nothing to worry about – depending on what you’re using your compressed air for. 

Oil-free piston compressors

In the electronics, food-and-beverage and medical industries, even trace amounts of oil in compressed air pose a major problem. As such, these industries frequently use oil-free piston compressors, with permanently lubricated bearings and grease-free piston rings. While this means oil-free compressed air, it unfortunately also means extra maintenance.

Oil-injected vs oil-free piston compressors

With no restrictions on lubrication, oil-injected piston compressors usually have more moving parts than their oil-free cousins. This means they’re heavier, more expensive and more powerful, with a longer lifespan. They’re the most commonly used piston compressors. 

Wondering whether you need a piston compressor or a different type of air compressor? Would you like to know whether you need an oil-free or an oil-injected model? Or would you like the opinion of experts who spend their days working with compressors and their nights dreaming about them? The team at ALUP is at your service.

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See also

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