A compressor is a mechanical pump that compresses gas. They range from small 12 Volt emergency compressors with relatively high pressure but very low volume, to shop compressors with large air tanks for storage, and scuba compressors that can deliver thousands of psi to fill high pressure cylinders.
Pros/Cons of each type
12 Volt Emergency Compressor:
- Quite cheap to buy
- Theoretically capable of 200-300 psi
- Low flow
- Poor duty cycle - as low as 20% (the other 80% is for rest) is not uncommon.
- Prone to malfunction and often have a very short life.
- Requires power source (Car battery, car battery charger, or Mains to cigarette socket transformer)
- Reasonably cheap to run
- Won't run out, unlike gas bottles.
- Can provide a mobile pressure supply if gasoline powered.
- Requires power socket (if electrical).
- Requires fuel (if gasoline powered).
- Typically limited to 8 bar/120 psi but 10 bar/145 psi types are available.
- Can be costly to buy initially.
- Very high pressure (typically 2500-4500 psi)
- Can be used to fill gas bottles.
- Moderate flow
- Very large.
- Very expensive.
- Power socket required.
Types of compressors
- Reciprocating - Uses a reciprocating piston to draw gas in through a valve and force the drawn gas into a storage tank or through a smaller orifice. They are available with single or multiple cylinders, depending upon the pressure and volume required. Reciprocating compressors are referred to as positive displacement compressors. (1)
- Rotary Screw - Two intermeshing helical rotors in a twin bore case are used to compress between one convex and one concave rotor. The trapped volume of gas is decreased while the pressure is increased. Rotary screw compressors are referred to as positive displacement compressors. (1)
- Centrifugal Compressor - Unlike the reciprocating and rotary screw compressors, centrifugal compressors do not make use of positive displacement. Gas enters the center of rotation of an element and is forced outward. The element can use curved blades, radial blades, or backward blades. The acceleration of the gas causes the pressure to rise. (1)