Swivel joints are used in fluid and pneumatic systems that require torsional rotation between flow lines. They provide 360-degree rotation in 1, 2 or 3 planes and are usually made of forged materials. Some swivel joints use ball bearing raceways for better load distribution and spring-loaded seals to reduce torque drag. There are three basic types of swivel joints: straight-through, right-angle, and offset. Straight-through swivel joints are designed for applications in which the flow paths are coaxial. Right-angle swivel joints are used when the outlet ports are perpendicular to the inlet ports. Offset swivel joints combine a straight-through design with a 90-degree elbow integral to each end. In general, available space and fluid line routing determine the type of swivel joint that should be used.
Specifications for swivel joints include size, operating temperature, cold working pressure, torque drag, and end connection. Common inch-based sizes include: 3/4, 1, 1 1/4, 1 1/2, 2, 3, 4, 6, 8, 10, and 12 inches. Products with a longer radius provide less vibration and reduced abrasion in corrosive, high-rate pumping applications. Operating temperature is usually specified as a range. Cold working pressure is measured in pounds per square inch (psi). Torque drag is a measure of the swivel joint’s resistance to rotation. There are many different end connections for swivel joints. Some products are designed as threaded, beveled, or flanged. Other feature union fittings and male or female pipe threads. Split flange fittings and products such as a gas swivel joint may carry additional specifications.
Number of Planes and Materials of Construction
Number of planes and materials of construction are additional parameters to consider when specifying swivel joints. Single-plane swivel joints allow hoses to pivot in order to reduce mechanical stress from bending, stretching, and twisting. Products that transmit fluid through rotating manifolds are also available. With these swivel joints, a rotary seal between the stationary and rotating parts of the manifold contains the pressurized fluid, but allows relative rotation between the two halves. Seal materials include nitrile, food-grade nitrile, fluoroelastomer, polytetrafluoroethylene (PTFE), Kalrez? (DuPont), and Chemraz? (Green and Tweed). Choices for body material include: aluminum, bronze, ductile iron, fabricated steel, fabricated stainless steel, and cast stainless steel. Swivel joints that are made of proprietary materials such as Hastelloy (Haynes Intl.) and Monel (Special Metals Corp.) are also available.