While rotating joints come in many shapes, sizes, and configurations, they always have the same four basic components: housing, a shaft, a bearing (or bearings) and a seal.
The heart of the Rotary Union or rotary joint is the seal. The seal prevents the medium (water, oil, air, etc) from leaking outside the Rotary Union while the Rotary Union is in operation. Duff-Norton uses four basic types of mechanical seals in its Rotary Unions: 1) pusher-type end face mechanical seal, 2) non-pusher type end face mechanical seal, 3) lip seals and 4) o-ring seal. Rotary Unions may have more than one seal.
The second most important part of the Rotary Union is the bearing. A Rotary Union may have only one bearing or multiple bearings. Roller bearings, such as ball bearings and tapered roller bearings, or non-roller bearings, like graphite bearings and bronze bushings, 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 Rotary Union into the drum or roll. In many cases, the shaft will turn with the drum or roll. In some cases, like in larger flanged rotary Unions, 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 Rotary Union together. The housing has an inlet port, which is a threaded port to which the hose supplying the medium will be attached. The Rotary Union 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 Rotary Unions, the housing is stationary. In larger Rotary Unions, the housing maybe bolted to the drum or roll using a flange. In these cases, the housing rotates at the same speed as the drum.