Rotary Joint Basics
A rotary joint, also referred to as a rotary union or swivel, permits the flow of fluid from a supply pipe in to and out of rotating equipment. The primary components of a rotary joint including the housing, shaft, guide, and seal.
The body of the rotary joints contains the fluid, holds pressure, and in some cases allows for hose connections. Also, it acts as torque restraint.
The nipple is the primary connection to the machine. Nipple connection options include tapered thread, straight thread, or flanged.
Bearing bushings or guides transmit rotational force to keep the rotary joint aligned.
The seal is the main wearing part of a rotary joint. During operation, the seal experiences internal loading forces from fluid pressure, as well as friction from contact with the rotating nipple and the stationary housing. Factors related to the application, such as machine speed, temperature, and fluid effect seal life.
The assembly plate fits between the rotary joint head and body to secure internal parts when the head is removed. As assembly plate is typically optional.
What is the difference between a rotary swivel, rotary joint, and a multi-passage union?
Rotary joints, unions, and rotary swivels are used in applications with only one media. When more than one media is used simultaneously, a multi-passage rotary union is used. Multi-passage rotary unions have off-center passages and can be used in higher pressure applications. Rotary swivels are used when bidirectional rotation is required. Rotary joints typically have pressure-type seals, while rotary unions use flat-face seals and ball bearings for support.
Proper equipment, installation, and maintenance are key for optimal performance of any type of union whether it be a rotary swivel, rotary joint, or multi-passage union. Equipment that fails, typically fail for one of the following reasons:
- Piping strains
- Lack of attention
- Improperly repaired
- Improperly applied
- Inadequate torque restraints
- Non-OEM parts
As manufacturers design new machines to operate at higher speeds, higher temperatures, increased efficiency, and more demanding applications, consideration must be given to the equipment to ensure it is capable of performing at these operating conditions.