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- sarious industrial, manufacturing, and building processes require compressed air to
power pneumatic tools;
- in the manufacturing and blow moulding of PET plastic bottles and containers;
- some types of jet engines—such as turbojets and turbofans - compress the air
required for fuel combustion;
- in hyperbaric oxygen therapy and other life support devices, compressors put
breathing gas into small volume containers, such as diving cylinders;
- submarines use compressors to store air for later use in displacing water from
buoyancy chambers to adjust depth;
- turbochargers and superchargers are compressors that increase internal combustion
engine performance by increasing the mass flow of air inside the cylinder, so the engine
can burn more fuel and hence produce more power;
- rail and heavy road transport vehicles use compressed air to operate rail vehicle or
road vehicle brakes—and various other systems (doors, windscreen wipers, engine,
gearbox control, etc.);
- service stations and auto repair shops use compressed air to fill pneumatic tires and
power pneumatic tools.
In the United States, there were 300 gas compressor manufacturers in 2011 producing
compressors for all of these uses. Although these factories were classified as small
business, the total 2011 sales for gas and air compressors was over $9 billion.

5.2 Reciprocating compressors
Figure 5.2 shows the schematic of a reciprocating compressor. Reciprocating
compressors consist of a piston moving back and forth in a cylinder, with suction and
discharge valves to achieve suction and compression of the refrigerant vapor. Its
construction and working are somewhat similar to a two-stroke engine, as suction and
compression of the refrigerant vapor are completed in one revolution of the crank. The
suction side of the compressor is connected to the exit of the evaporator, while the
discharge side of the compressor is connected to the condenser inlet. The suction

Fig. 5.2 - The schematic of a reciprocating compressor.

(inlet) and the discharge (outlet) valves open and close due to pressure differences
between the cylinder and inlet or outlet manifolds respectively. The pressure in the inlet
manifold is equal to or slightly less than the evaporator pressure. Similarly the pressure

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