Multi-passage rotary unions offer a unique combination of utility and versatility. The design allows users to run a mixture of different fluids through the rotary union at the same time without contact.  One common combination is to use water for a cooling application and pressurized air for pneumatic valve control. Other times, instead of air for valve control, electrical signals are needed to be passed through the rotary union. In other instances, hydraulic fluid or steam is transferred through the rotary union to perform its purpose.

Multi-passage rotary unions are designed to perform on a wide range of pressures (including vacuum), speeds, and temperatures.  Providing the operating fluids and parameters is critical to determining the best seal combination. Several other criteria to consider to consider when looking for the most appropriate design include;

• Drive torque available
• Expected duty cycle
• Dwell time at pressure
• Fluid temperature
• Fluid heat carrying capacity
• Fluid flow rate

These criteria will all have an impact on heat generation at the seals. The reason this is important is that heat generation at the sealing interface is the driving force in seal wear. Seal wear will determine the expected operating life time of the union.

There are applications where a multi-passage rotary union can benefit from a combination of seal designs. For example, consider a rotary union spinning at a high speed that needs to pass both high-pressure water and low-pressure air. In this application example, the combination of plastomeric or elastomeric materials are used for the air service and mechanical face seals for the water service will provide satisfactory performance.  This performance is balanced with the inherent cost differences of the two seal types to give the best value.  Still, other applications would benefit from a controlled leakage design where the sealing is performed without contact.

Multi-passage rotary unions are highly configurable for mounting, connections, and reparability. These units can be table-mounted vertically, shaft-mounted horizontally, or at any angle needed. The connections can be different sizes, industry types, and orientations. Units can be configured with options that make it easy to refurbish with seal and bearing repair kits and provide a lower total cost of ownership. It is usually more cost effective if a standard design can be adapted to fit the application. However, there are plenty of options available for customization to make sure the best solution is provided for the application.