There are basically two types of air compressors: those which compress air through positive displacement, and compressors which compress air by negative displacement. Positive displacement compressors fall generally into three categories: rotary screw, vane, and reciprocating. Positive displacement compressors are ones which are found in small and medium sized industries. There are two types of negative displacement compressors: centrifugal flow, and axial. These are fundamentally for large industrial uses and even for use in jet engines. Care and research will determine the best type to purchase.
Positive Displacement Compressors
Rotary screw compressors work most commonly by mating two rotors which are meshed together. They trap the air and compress it along the rotors. They are available in lubricated or oil free types. They have an advantage over reciprocating types because they can be operated continuously at full load while reciprocating types must be used in a start/stop mode and only at 60% or below. They are also quieter and the air produced is easier to dry but this compressor may not be the best choice.
Reciprocating compressors are smaller in horsepower, are driven by an electric motor, and are most often used to feed air to building systems. Large compressors of this type have generally gone out of use and are not commercially manufactured any more.
Vane compressors are less efficient than reciprocating compressors and also are smaller than the rotary screw compressors. They are usually used where floor space is at a minimum.
Negative Displacement Compressors
Centrifugal compressors have fewer rubbing parts than reciprocating compressors of the same size and give higher airflow while being more energy efficient. They need several stages to achieve the higher compression ratio and that is a drawback. Their best uses are ones that require high volume but little pressure increase. Industry uses these compressors to increase oil production in oil fields and in smaller turbojet aircraft powered by gas turbine engines.
Axial air compressors have turning and non turning foils powered by a turbine which work together to both guide and increase the pressure of air flow. Jet engines are one application for this type of compressor.
Safety Considerations Related To The Operator Of Smaller Compressors
- Reading the instructions are the first step to safely operate any air compressor.
- If it is powered by gasoline, remember that gasoline is highly flammable so let the engine cool at least two minutes before adding more fuel.
- Wear both safety glasses and ear plugs.
- Maximum pressure for the compressor is set by the manufacturer so don't increase it.
- Be sure the pressure safety-valve ring is in a grounded receptacle.
- Never point the air stream at yourself or others.
- Release the remaining compressed air from the tank when finished.
- Before servicing the compressor shut off the motor, unplug the unit, and turn off the regulator valve.
- Finally, always follow the manufacturer's safety rules.