Types of Air Compressors

The three basic types of air compressors are:

Reciprocating: Positive displacement machines using a piston within a cylinder
Rotary Screw: Positive displacement compressors with two rotors within a casing
Rotary Centrifugal: Dynamic compressors depending on transfer of energy from a rotating impeller

Key Specifications

All compressor types are further specified by:

Number of compression stages
Cooling method (air, water, oil)
Drive method (motor, engine, steam, other)
Lubrication (oil, Oil-Free)
Packaged or custom-built

Compressor Type	Mechanism	Cooling Method	Lubrication	Maintenance	Applications
Reciprocating	Piston in cylinder (single/double acting)	Air or Water cooled	Lubricated or Oil-Free	Regular valve maintenance	70-250 psig range applications
Rotary Screw	Two rotors in casing	Oil cooled (air/water cooled oil coolers)	Oil flooded or Oil-Free	Low maintenance, easy operation	High volume, continuous duty
Centrifugal	Rotating impeller (dynamic)	Air or Water cooled	Oil-Free by design (sealed)	Minimal air-oil contact	High capacity, high speed operation

Detailed Type Descriptions

Reciprocating Air Compressors

Mechanism: Positive displacement machines that increase pressure by reducing volume. Use a piston within a cylinder as the compressing element.

Configurations:

Single-stage: 70-100 psig pressure range
Two-stage: 100-250 psig pressure range
Single-acting: Compression on one side of piston
Double-acting: Compression on both sides of piston

Typical Range: 1-50 HP (~4 CFM at 100 psi per HP)

Advantages: Wide range of pressure and capacity selections, available in lubricated and non-lubricated configurations

Rotary Screw Compressors

Mechanism: Positive displacement compressors with two rotors that compress air internally (no valves). Most common type is the single-stage helical/spiral lobe oil-flooded screw compressor.

Characteristics:

Oil seals internal clearances
Cooling occurs inside the compressor
Continuous duty, compact size
Smooth, pulse-free air output

Capacity Control: Variable speed and variable displacement (slide valve technique)

Configurations: Oil-flooded and Oil-Free variants (air or water cooled)

Typical Range: 100+ HP

Centrifugal Compressors

Mechanism: Dynamic compressors that transfer energy from a rotating impeller to air, converting angular momentum to pressure.

Characteristics:

Higher rotation speeds than other types
Designed for high capacity with continuous flow
Oil-free by design (oil lubricated running gear separated by seals)
Capacity controlled by adjusting inlet guide vanes

Typical Range: 100+ HP and above