The Ultimate Glossary of Rotary Joint Terms

RX Rotary UnionRotary joints are sealing devices that allow a rotating device to be connected to fixed piping. They are found in numerous applications across many resource-intensive process industries and provide a critical function within the manufacturing process. Expand your knowledge of rotary joints with the following glossary of commonly used terms.

Anti-Rotation Rods – Stiff, smooth rods that extend from a special bracket or lug hole on the body or head of the rotary joint to a stationary external surface.

Assembly Plate – Fits between the rotary joint head and body to secure internal parts when the head is removed.

Balanced Seal Rotating Unions – Generally used with fluid service (e.g. water, coolant, etc.), but can be used with steam and other gases. The balanced seal technology relies on external spring pressure to create a positive seal within the rotating union.

Bearings – Transmit rotational force to keep the rotary joint aligned and provide radial and axial support.

Dryer Bars – Stainless steel axial bars, installed on the inside of rolls and used to induce turbulence inside the roll, to improve the roll surface temperature uniformity and rate of heat transfer.

Dual-Flow – When the media flows into and out of the rotary joint using a syphon or distribution pipe.

DuraSeal™ Seal Technology – Elastomeric (O-rings) or plastomeric (teflon-based seals) used in a dynamic rotary sealing application.

Externally Supported Rotary Joints – Rely on external stationary framing to support the body (housing) of the rotary joint; most commonly by two support lug rods or a bracket.

Flexible Metal Hose – A hose that is designed to hold the media pressure and provide flexibility in the position of the rotary joint.

Guide – Carbon graphite bushing installed around the nipple used to support a rotary joint.

Mechanical Face Seal – Uses a spring, or springs to provide most of the force required to load the seal faces. Typically, the media pressure is near-balanced such that an increase in the pressure of the media does not have a significant impact on seal loading.

Media – Fluids used with rotary joints and unions. The most common media used with rotary joints are steam, water, air, thermal oil, hydraulic fluid, and coolants.

Multi-Passage Unions – Required when more than one media is used simultaneously. These rotary unions provide multiple seals between stationary connections and rotating equipment, such as a drum, index table, clutch, or spindle.

Nipple – The primary connection to the machine. Can be threaded or flanged.

Over-the-Shaft Rotary Union (OTS) – A solution for machinery that requires cooling on the drive side of the driven rolls or for rolls that cannot accept an axially mounted union for other reasons.

Pressure Joint – A rotary joint in which an internal seal ring carries the entire force created by the internal fluid pressure tending to push the stationary body against the rotary joint’s nipple.

Q-Flange – A quick release flange that comes as a set and includes a flange, split ring or wedge, and a copper or aluminum gasket. A rotary joint or union will use a Q-Flange to connect the rotor or nipple to the rotating equipment.

Rotary Joint – A device that provides a seal between a stationary pipe and a rotating drum, cylinder, or other device, allowing a fluid to flow into and/or out of the rotating part. The term rotary joint is more commonly used when referring to steam applications and the term rotary union is more commonly used with media other than steam.

Rotary Swivels – A coupling between two parts enabling one to revolve without turning the other. Used when bidirectional rotation is required.

Rotor – The rotating part of a rotary joint or union that connects to the rotating equipment. Can be threaded or flanged.

Seal Rings – Main wearing part of the rotary joint or union. During operation, the seal or seals experience internal loading forces from fluid pressure, as well as friction from contact with the rotating nipple and the stationary housing.

Self-Supported Rotary Joints – Directly and rigidly attach to the end of the dryer journal via the rotary joint nipple. The rotary joint is supported using either roller bearings or carbon graphite support guides.

Sight Flow Indicators – Provides visual observation of liquid and gas flows in a pipeline.

Single-Flow – When the media flows in one direction through the rotary joint. Also known as through-flow.

Syphon – An arrangement of piping inside a rotating cylinder consisting of a horizontal pipe, elbow, and vertical pipe that allows a fluid to flow from inside the cylinder out through the rotary joint. Syphons can be stationary or rotating depending on the application.

Wear Plate – A removable metal seal plate bolted to the rotary joint body designed to be replaced after it has reached the end of its usable life.