Rotating unions are used to transfer media from a stationary input to a rotating outlet. They are usually made of brass, bronze, plastic, steel, or stainless steel and include one or more ports which range in size from 1/8 in. to 6 in. Straight ports direct media flow straight through the union. Elbow ports cause the media to exit at an angle from the inlet direction. Seals are made from a variety of materials and feature o-ring and bellows-type designs.
Rotating unions connect via flanges or threads and may use dual radial ball bearings to prevent side loading to seals. Flanges are rated by organizations such as the American National Standards Institute (ANSI) and the Society of Automotive Engineers (SAE). Common thread types for rotating unions include national pipe thread (NPT), British standard pipe (BSP), and unified coarse thread (UNC).
Specifications for rotating unions include pressure range, speed range, operating temperature, number of ports, seal type, dimensions, and special features. Pressure is usually measured in pounds per square inch (psi). Speed is usually measured in revolutions per minute (rpm). Operating temperature is a full-required range. Rotating unions with between 1 and 8 ports are commonly available. Rotating union seals are made from nitrile, fluoropolymer elastomers, ethylene propylene (EPDM), polyurethane, or silicone. Length and diameter are important physical dimensions to consider when selecting rotating unions.
In terms of features, some rotary union devices include an integral slip ring for electrical power or data transfer. Others include a thru-bore for mounting and wiring. Rotating unions with a slowing motion are used to regulate media speed. Devices with dry running protection can operate without lubrication; Rotating unions are used in the production of textiles, clutches and brakes, automobiles, chemicals, paper, rubber and plastics, and food and pharmaceuticals. They move media such as compressed or vacuum air, hydraulic fluid, steam, pressurized water, chemicals, gases, and slurries or solid materials. Rotating unions are also used to move petroleum products, gasoline, diesel, natural gas, and aviation fuel. Devices that move hot oil, steam, pressurized water, and heated air are often made of stainless steel to provide increased corrosion resistance. Fluorocarbon o-rings and bearing seals allow rotating unions to operate at higher temperatures and pressures. In applications where equipment misalignment is common, bellows-type seals provide added flexibility.