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Rotary Unions# Definition
Rotary Union' is Duff-Norton's registered trade name for a type of product known as a rotating joint, rotary joint, swivel joint or rotating union. A rotating joint is a precision mechanical device that allows for the transfer of medium from a stationary fluid supply to a revolving drum or roll.
It is often necessary to heat or cool drums or rolls in process industries like textile, rubber, plastic, paper, and many others. In the paper industry, for example, dryer cans must be kept at a certain temperature in order to dry the wet paper moving over the rolls. Steam is injected into the rolls to heat them up to make the paper dry. However, the dryer cans must keep turning, and the steam supply hose is stationary. A rotating joint is used to transfer the steam (the medium in this case) from the stationary hose that is supplying the steam to the dryer can, which is continually revolving.

Basic Design

While rotating joints come in many shapes, sizes, and configurations, they always have the same four basic components: a housing, a shaft, a bearing (or bearings) and a seal.
 
The heart of the rotating joint is the seal. The seal is the element that prevents the medium from leaking outside the joint while the joint is in operation. DuffNorton uses four basic types of mechanical seals in its Rotary Unions°: pusher-type end face mechanical seals, non-pusher type end face mechanical seals, lip seals, and o-ring seals. Joints may have more than one seal. The second most important part of the rotating joint is the bearing. A Rotary Union may have only one bearing or multiple bearings. Roller bearings (like ball bearings and tapered roller bearings) or nonroller bearings (like graphite bearings and bronze 4ushings) may be used in the Rotary Union. The "bearings are, always used to allow a part of the joint (either the shaft or the housing) to rotate. The shaft is the component that carries the medium through the joint into the drum or roll. In many cases, the shaft will turn with the drum or roll. In some cases, like in larger, flanged joints, the shaft may be stationary while the housing rotates. The bearings and seal are typically assembled around the shaft. The housing is the component that holds all of the other elements of the joint together. The housing has an inlet port, which is a threaded hole to which the hose supplying the medium will be attached. It may also have an outlet port, if the same joint is being used both to supply fluid to a roll and to remove fluid from the roll. In smaller joints, the housing is stationary. In larger joints, the housing maybe bolted (using a flange) to the drum or roll. In these cases, the housing rotates at the same speed as the drum.