What is a rotary union?

Rotating unions, also called rotary unions or rotary joints, transfer fluid from a stationary supply into rotating machinery, such as a spinning drum heated by oil or chilled by water. Different types are used to match each set of requirements.

Pressure Joints

Pressure joints are sealed by media pressure, with a strong spring to keep seals together at startup or very low pressures. This classical technology requires a relatively large amount of torque and is suitable only for relatively media low pressures (<250 psi or 17 bar)

Pressure Joint

Plastomeric Seals

Plastomeric rotary unions use custom or commercially available “soft seals” made from application-specific polymers or elastomers. They are most suitable for applications with intermittent rotation and pressure. Though compact, these seals exhibit significant torque, heat generation, and wear rates.

Plastomeric Seals

Hydrostatic Seals

Hydrostatic rotary unions deploy precise tolerances to provide no-contact sealing at high pressures, extending life and minimizing maintenance. The rotating element is suspended on a fluid film that circulates continuously at a very low flow rate. Fluid shearing limits the maximum speed of these unions to a few thousand RPM.

Hydrostatic Seals

Mechanical Seals

Mechanical seal rotary unions minimize seal wear, torque, and heat generation through intentional balancing of hydrodynamic forces. Flatness must be controlled within microns, and different seal materials are employed according to the desired RPM, pressure, and media. These unions perform reliably even at pressures >140 bar and speeds >40,000 RPM. Mechanical seal unions can be engineered to behave differently as the machine's operating condition changes.

Mechanical Seals

Used throughout the industrialized world

Rotary unions allow the feedthrough of water, air, hydraulic, metalworking fluids, hydraulic oil, steam, vacuum and a variety of other media. They can be installed at the end of or around a rotating shaft.