What are Rotary Joints and Rotary Unions?

When attempting to transfer steam, water, coolant, hydraulic air, or other media types through piping and rotating systems, devices known as rotary joints or rotary unions are used. A rotary union is a type of rotary sealing device, capable of bridging the gap between a fixed pipe and a rotating equipment piece. While rotary unions are often relied on for the transfer of various media, they also serve to seal the passage between the stationary piping or tubing and the rotating element. In this blog, we will discuss the design and functionalities of rotary joints and unions, allowing you to better understand how they serve fluid applications.

With the use of an input valve, the rotary union is locked onto the assembly while being capable of revolving to maintain attachment to a rotating outlet. During standard operations, the liquid or gas will flow from the stationary piping into the union, kept within the assembly while the device moves. As the valve openings meet during the rotation of the union, the liquid or gas will continue down its path. Rotary unions are typically designed to follow a set axis, and they are well capable of operating under pressure and perpetual movement. To adjust the operations of the component, the pressure or rotating speed may be changed, or one may utilize more valves.

Despite rotary unions and rotary joints coming in a variety of shapes, sizes, and designs, all share the same basic components which are the housing unit, shaft, bearing, and mechanical seal. The housing serves as the main structural connection point for all elements of the rotary union, featuring a threaded inlet port for the connection of a tube or pipe. If the device is also meant for removing fluids from the assembly, then an outlet port may be present as well. While smaller rotary unions may feature a housing that is fixed, larger unions will regularly have their housing bolted to a drum or roll with a flange.

The shafts of rotary unions and rotary joints are important for facilitating the transfer of media, typically having such materials move through the device and into a drum or roll. Many times, the shaft will rotate alongside the drum or roll, or the shaft may be fixed while the housing rotates. Around the shaft, bearings and a sealing device are often present. With either a single bearing or multiple, the rotating movement of the assembly is made possible. In general, common bearings types that are used include ball bearings, tapered roller bearings, graphite bearings, and bronze bushings. The sealing device is also paramount for standard operations, preventing any escape of the transporting fluids. The types of seals that are commonly used include those that are pusher types and non-pusher types, as well as o-ring seals. Typically, a majority of rotary unions will utilize more than one sealing device for their functionality.

Depending on one’s application or needs, there are a variety of rotary unions that vary in their ports, size, shape, and more. As such components serve many applications ranging from machine tools to automotive design, it can be useful to take advantage of rotary joints and unions. ASAP NSN Distribution is an online distributor of aircraft parts and other diverse components, and we are your sourcing solution for top quality rotary joints and rotary unions that have been sourced from leading manufacturers that we trust. Whether you need items that are new, used, obsolete, or hard-to-find, we have you covered with rapid lead-times and competitive pricing on over 2 billion items that we carry. Take the time to peruse our massive catalogs, and our team of industry experts are readily on standby 24/7x365 to assist you through the purchasing process as necessary. Get started today with a personalized quote for your comparisons when you fill out and submit an Instant RFQ as provided on our website.


December 1, 2022

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