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Compressor : Hitachi


What is a compressor?

Compressors are used in a wide range of industrial fields and have a wide range of applications.
These applications can be broadly split into the following 3 categories.

1. Applications that directly take and use compressed air

  • Painting or chemical spraying
  • Sand blasting
  • Air dusting,


Image: What is a compressor? Illustration 1

2. Applications in which something is rotated or vibrated by the force of compressed air

  • Air turbines
  • Air grinders
  • Air hammers


Image: What is a compressor? Illustration 2

3. Applications that carry out measurements or control using the flow of pressurized air

  • Various types of measuring instruments and control circuits


Image: What is a compressor? Illustration 3

Types of compressors

The types and characteristics of compressors can be broadly classified into 2 types: the capacity type and the centrifugal or turbo type.

Capacity type

  1. Screw type: Compression method is to rotate a male and female screw rotor within a casing
  2. Reciprocating type: Compression method is the reciprocating action of a piston

Centrifugal type

Turbo type: Compression method is the centrifugal force created the rotation of an impeller

Image: Comparison diagram of compressor types

Differences between the oil-free screw type and the oil-supply screw type

There are 2 types of screw compressors: the oil-free type and the oil-supply type.
The rotor shape is the same, but at the position where they mesh, the oil-free type rotates without contact, and the oil-supply type rotates with contact.
One feature of the oil-free screw compressor is that it generates clean compressed air that does not contain oil. This type is widely used in industries such as food processing, pharmaceuticals, chemicals, etc., where oil cannot be mixed in with the air, and as an air source for instrumentation in general industries.
Also, in the oil-free screw compressor, the rotors rotate without contact, so they have excellent durability with long intervals between maintenance timing, and do not require much labor.

Image: Differences between oil-free screw compressor and oil-supply screw compressor

Structure of a screw compressor

  1. Air is drawn in from the rotor inlet opening, the rotor rotates, teeth meshing is released, and air is sucked into the entire space between the teeth. After rotating further, the wall of the casing obstructs the air, the suction is complete.
  2. The air enclosed between the teeth and the casing is compressed by the rotors engaging.
  3. The air is moved in the axial direction by the rotation of the rotors, and is compressed further between the teeth and the casing, and at the outlet it arrives at the required pressure.
  4. The compressed air is expelled from an opened nozzle in the casing on the outlet side.

Image: Screw compressor drive