Duff-Norton Rotary Unions and Swivel Joints

A rotary union (or rotary joint or swivel union) is a device that provides a rotating seal between two parts. It rotates 360 degrees on an axis or swivels part-way if full rotation is not required.

Rotary unions transfer media (water, steam, air, oil, hydraulic fluid, etc) from a stationary source to rotating machinery, such as a drum or an indexing table. They are used in process industries such as; paper, printing, rubber and plastics, textile and chemical.

Rotary Unions are also used on cranes, machine tools and many other applications. Duff-Norton Rotary Unions are used to provide heating or cooling media like steam, hot oil, water or coolant to control the surface temperature of a drum or roll, to transfer air or hydraulic fluid to moving components or to add fluids to mixers while in motion.

Rotary unions, rotary joints and rotating joints ranging up to 750 psi and up to 5,000 RPM are available.


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Rotary Union Engineering Guide - Design

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.


Mechanical 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 (See the next page for recommended hose installation). 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.