Rotary unions and hybrid joints

What a rotary unions and hybrid joint is

A rotary union, also called a rotary joint or swivel, transfers fluids such as compressed air, vacuum, hydraulic oil, water or coolant from a fixed supply into a rotating shaft or table. A rotating shaft runs inside a stationary housing, and each fluid passage is isolated by seals between grooves, so several media can pass through one unit. Many designs combine with an electrical slip ring into one assembly, providing both fluid and electrical paths through continuous rotation.

When to choose a rotary unions and hybrid joint

Choose a rotary union when pneumatic grippers, vacuum cups, hydraulic clamps or cooling circuits sit on a rotating part. The alternative of hoses limits rotation to a few turns. The trade-offs are seal friction, leakage and wear: seal choice sets pressure, speed and media compatibility, and dry running damages some seals. Mixing vacuum and pressure in one unit needs suitable seals. Combining the union with a slip ring saves space but makes the assembly larger and more application-specific.

How to specify rotary unions and hybrid joints

• Number of passages and the medium in each
• Pressure and vacuum levels (bar)
• Flow rate or port size (l/min, mm or BSP)
• Fluid temperature (°C) and compatibility
• Speed (rpm)
• Permitted leakage and drain or vent provision
• Electrical circuits if combined with a slip ring

Common mistakes

• Running a union designed for lubricated media on dry air or without flow
• Not providing a leak drain between media and the electrical section of a combined unit
• Applying side load from rigid pipework instead of using flexible hoses and a torque arm
• Ignoring pressure spikes from valve switching when choosing seals

Series compared

Maximum figures across each series, summarised from manufacturers' published data on the date shown on each series page. Always confirm against the current datasheet.

Where rotary unions and hybrid joints are used

Rotary unions and hybrid joints: frequently asked questions

Can one rotary union pass air, vacuum and water at the same time?

Yes, multi-passage rotary unions isolate each medium in its own groove with seals between them. Each passage must be specified with its medium, pressure and flow, because seals that suit air may not suit water or vacuum. Leakage paths between passages and a drain for any seepage should be agreed with the supplier.

How is a rotary union combined with a slip ring?

A common layout puts the rotary union on the axis and the electrical slip ring around or beside it in a single assembly, so both fluids and electrical circuits pass through one rotating connection. The design must keep fluid away from the electrical rings, often with a drain chamber. Specify both parts together so the supplier can manage sealing, length and bearing loads.