Compressors are machines that compress air or other gasses to a given pressure for a variety of applications. These applications include running high-powered tools such as pneumatic drills and nail guns, as well as for filling gas cylinders and running decompression chambers. Compressors are also used in refrigeration and air conditioning. They are used in the automotive industry for inflating vehicle tyres, and compressors also form part of a vehicle’s engine in the form of turbochargers and superchargers. Jet turbine engines are also a type of axial-flow compressor.
Compressors work by using a motor to change the pressure of a given volume of gas. There are many types of compressor, for instance rotary screw compressors use a screw to force a given volume of gas into an increasingly smaller chamber, thereby increasing the pressure. Centrifugal compressors use centrifugal force to compress the gas via an impeller, whilst reciprocal compressors use pistons to achieve this. Axial flow compressors, are an ‚open‘ type of compressor that uses a series of rotating blades to compress gas to different stages of pressure. Diaphragm compressors use a membrane to pressurise gas.
Hermetic compressors, or ‚tin can‘ compressors, are hermetically sealed to prevent the escape of gas or the ingress of any air by using a welded steel casing to house the entire unit. In some types of compressor, the motor is a separate unit, with the compression chamber being the only part that is sealed. With a hermetic compressor, all the parts are in the sealed unit together, with the casing forming the gas pressure envelope. This makes the unit very compact and portable, as well as powerful and efficient, as there is less chance of a pressure loss where motor drive shafts penetrate the casing.
The units are sealed for life, so user servicing is impossible, and failure of any part usually results in the entire unit having to be replaced. Most types of compressor can be hermetic compressors apart from axial-flow types, however, the centrifugal type is often the preferred solution due to the fact that they have fewer moving parts. The lubrication system is sealed in and cannot be topped-up or replaced, so centrifugal compressors usually last longer than other types.
Semi-hermetic compressors use gaskets to form a sealed unit that can be dismantled for servicing, providing a compromise between hermetic and non-hermetic compressors.
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