Rotary Joints, Rotary Unions, and Rotating Unions

 

A rotary joint, also referred to as a rotary union or rotating union, provides a mechanical seal between a stationary supply pipe and a rotating drum or cylinder to permit the flow of heat transfer media into and/or out of the rotating roll. Heat transfer media typically used with rotary joints and rotating unions include steam, water, thermal oil, hydraulic oil, and coolant.

 

G Rotary Unions   MP Rotary Joints   OTS Rotary Unions

 

 

With conventional rotary joints, a spring-loaded mechanical seal is used to keep the fluid or gas medium from being dispersed into the atmosphere. The spring is used in the rotary joint to maintain the initial internal seating, and the rotary joint is pressure-sealed once in operation. Low pressure or vacuum service relies on the spring force to create the seal. Conventional rotary joints are either self-supported with the use of an internal carbon bushing, or external-supported using rods or a mounting bracket.

 

Balanced seal rotating unions are generally used with fluid service (e.g. water, coolant, etc.), but can be used with steam and other gases. The balanced seal technology relies on external spring pressure to create a positive seal within the rotating union. The operating pressure of the media has little, if any, affect on the seal load. Balanced seals are typically flat face seals and the rotary unions are usually supported by ball bearings.

 

The seal ring is the main wearing part of the rotating union. During operation, seal rings can experience internal loading forces from fluid pressure, as well as friction from contact between the sealing faces. Factors related to the machine speed, temperature, and media used can also affect the life of the seal ring. To a large extent, a rotary union is only as good as its seal package. Poor quality seals naturally wear out more rapidly, leading to an increase in maintenance, downtime, and repair cost. When a seal fails, media escapes and the efficiency of the entire heating or cooling process suffers. All of this makes the actual replacement cost of the seal just a small portion of the total cost of a seal failure.

 

ELSN Rotary Joint   RX Rotary Union   SX Rotary Joints

 

Flow Configuration

 

In a mono-flow rotating union, the medium flows in only one direction through the union. A single-flow rotating union is used where the medium enters at one end of a drum or cylinder and exits the other end, making a single pass through the union.

 

In a duo-flow rotating union, the media enters and exits through the same union. It is most often utilized in applications where syphon or distribution pipes are used. A duo-flow rotating union seals between both media, as well as between one of the media and the surrounding atmosphere.

 

In multi-passage rotating unions, various types of media make multiple passes through the same rotating union. These directions of flow can be in the same direction or opposing directions with any combination thereof.

 

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