How does an Air rotary union work?

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Air rotary union work

In mechanical systems, there are various components that play a critical role in the application. One example of such components is rotary unions.

A rotary union or swivel joint is a mechanism used to transfer fluid (under pressure or vacuum) from a stationary inlet to a rotating outlet. Thus, it preserves and isolates the fluid connection.

Rotary unions are also called rotary joints or rotary couplings. They are called fluid swivels or swivel joints as well.

Rotary unions are engineered to endure a large range of temperatures, pressures, and speeds for a wide range of conditions and environments.

Rotary unions typically function by connecting to input and securing onto another mechanism while it allows a moving connection to be preserved.

Rotary unions are used in many applications; from miniature rotary unions to the semiconductor industry, from large and rugged-duty rotary unions for industrial applications.

There are three types of rotating unions

Air rotary unions

These unions build reliable rotating unions for high-performance applications where applications need high pressures and high speeds. These unions are categorized by four categories:

  • one-channel air unions
  • low-speed one-channel unions
  • low-speed multi-channel unions
  • dual passage air unions


Coolant rotary unions offer many capabilities to bring down overall maintenance cost.  Coolant rotary union is bearing less.

It has a compact design with a high RPM because there is no presence of bearings. It reduces the overall cost. The off-the-shelf rotating unions offer many configurations that can fit any machining application.

Hydraulic unions

Reliable hydraulic rotary unions are known for their utility in high speed, high-pressure applications. They are available in a variety of mounting configurations. Hydraulic unions are available in many sizes to fit small spaces. These unions are constructed for harsh environments.

How does a rotary union function?

A rotary union locks onto an input valve when it rotates so that it can meet an outlet. During this time, the liquid and/or gas flows into the rotary union from its source and it is held within the device during its movement.

The liquid and/or gas leaves the union when the valve openings meet during rotation, and it results in the flow of more liquid and/or gas into the union again for the next rotation.

A rotary union is designed to rotate around an axis. It often functions under high pressure and constant movement. The design of a rotary union can be altered to change it or to increase the RPM or PSI it is supposed to withstand, and the number of valves required.

Also Read: Where are rotary joints used?

Rotary unions are available in several sizes, shapes, and configurations. However, the four fundamental components that always remain constant are: a housing unit, a shaft, a bearing (mechanical) (or bearings), and a seal.

Rotary unions are made from stainless steel in general because stainless steel resists rust and corrosion. However, they are made from other metals like aluminum. Some rotary unions have multiple ports, and they can handle different types of material simultaneously. These versatile components are widely used in several applications.

Also Read: Best Rotary Joints Manufacturers in India

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