A Basic Introduction To A Rotary Union

A rotating union, also known as a rotary union or rotary joint, is a type of union that allows the flow of different media from the supply passage (tubing or pipe) out of or into rotating equipment (spindle, cylinder or drum). This facilitates the rotation of united parts in machines. Hydraulic media and heat transfer are often used with rotating joints and include coolant, air, hydraulic oil, thermal oil, water, and steam.

The important application information includes:

- Rotational speed
- Fluid type (air, water, steam)
- Flow rate
- Pressure
- Equipment and piping connection sizes
- Temperature

Types of rotating unions

Many rotary joints are designed with multiple ports to handle different kinds of materials simultaneously. A unit with a straight port, for example, can transfer the medium directly through a rotary joint, while other designs like multiple ports and elbow port can cause the materials to come out at an angle.

A unit with multiple ports looks quite similar to a perforated cylinder with a threaded screw at the cylinder’s end. The medium being carried will flow into the cylinders and then out of the inputs. If a rotary joint has multiple inputs, a chamber separated by the seal will keep the medium from mixing inadvertently. This kind of rotary joint is typically applied in the manufacture of petroleum products such as plastics.

Composition of rotary unions

While rotating joints come in many configurations, sizes, and shapes, they always have the same 4 basic parts: a seal, a bearing, a shaft, and a housing unit.

- Seal

The seal is the heart of every rotary union. This part helps to prevent the medium from being leaked outside the joint during the operating process. Most models can have more than 1 seal, which would vary from o-ring, lip, non-pusher end-face, and pusher.

- Bearing

The second most important component of a rotary joint is the bearing. It plays an essential role in allowing in a part of the unit, either the housing or the shaft, to rotate. A rotary joint might have only 1 bearing, but 2 or more bearing are typically much more common, especially in these tasks that require to get pneumatic rotary union.

- Shaft

The shaft is a component which helps to carry the medium through the rotating union into the roll or drum. In many situations, it will turn with the roll or drum. Just like in large flanged rotary joints, the shaft might be stationary while a housing rotates. The seal and bearings are typically integrated around the shaft.

- Housing

It is easy to know that the housing accommodates all the other parts of the rotary joint. This component often comes with a threaded inlet port to which the pipe supplying the medium would be attached. If the rotary joint is used both to supply and remove fluid from a roll, it might be also designed with an outlet port. In large units, the housing is often bolted to the roll or drum with a flange. In these cases, it will rotate at the same speeds as the drum.