Low pressure piston compressors are reliable and cheap
A basic low pressure piston compressor can be thought of as being an internal combustion engine working backwards. It is a reliable, effective and very well proven technology. Low pressure piston compressors can have single or multiple cylinders, with multiple cylinders creating greater volume throughput. At the top of each cylinder are2 simple spring operated valves, which open when or close as the piston moves up or down in the cylinder. There are usually two valves per cylinder, one intake valve, one exhaust valve.
Below the cylinders is a basic crank case with crankshaft & connecting rods in a similar configuration as an internal combustion engine. Bearings are usually ball or roller bearings with splash lubrication from an oil sump.
High pressure piston compressors are also available. These multi stage compressors generate high pressure air up to 400 bar across 4 stages. (See article on High pressure compressors)
Low pressure piston compressors are effective and low cost. However they are only really suitable for comparatively low volume, they are also really only suitable for intermittent use, typically less than 30 minutes running per hour. They also do tend to be noisy and require regular servicing. A final issue for consideration is that the air produced will have quite high pulse level, resulting in the requirement for air to be pumped into a large receiver to damp the air before use.
Benefits – Low initial costs, simple construction, simple engineering
Downsides – Intermittent use only, tend to be noisy, air needs to be damped, high servicing requirements