The primary purpose of a rotary union or hydraulic swivel is to transfer the fluid between the stationary and rotating part of the equipment by providing a reliable and effective seal under pressure. Rotary unions are often an overlooked component, although they are a critical piece of the puzzle that allows all the other components in the equipment to function.

Rotary union design and function often appear simple, but rotary union sealing can be challenging to ensure that the rotary union doesn’t leak. Many factors can impact the overall sealing performance and quality of the rotary union.

• Media Type – Compatibility of the seals with the media, such as oil, hydraulic fluid, air, gas, water, or coolant, plays a vital role in ensuring that the seals will prevent leaks.
• Temperature and Pressure – The operating temperature and pressure of the media used in rotary union need to be within the designed range for the seals used in the design.
• Rotational Speed and Duty Cycle – Operational life is dependent on rotational speed and duty cycle. The rotary union needs to be operated within the given RPM range. Going beyond this can damage the seals.
• Environmental conditions – Temperature at which the rotary union will be operated and its exposure to vibration and shock can impact its sealing capability.
• Media Filtration – The rotary union must be operated with contaminant-free media, as contaminants can damage the seals at high pressure.
• Flow Rate – Ports in the rotary union need to have a sufficient flow area. Less flow area can alter the pressure and temperature of the media flowing through the rotary union, affecting the life of the seals.
• Torque Drag– Torque drag is the resistance to rotation. This variable needs to be minimized as much as possible by using an appropriate bearing seal.
• Maintenance and Serviceability – Using proper measures and procedures to service the swivel and keeping track of maintenance intervals by replacing the seals on time ensures that the rotary union will operate at the highest level possible.

All the above parameters play an important role in determining the design and compatibility of the materials of the spool, housing, seals, bearings, mounting plates, and torque arms. Each and every factor of these is considered at UEA while designing the rotary union.

Sealing the fluid in a rotary union comes with distinct challenges that require years of experience and knowledge to design. UEA uses our engineering experience to build a well-functioning rotary union that meets customers’ expectations. Contact us to develop a custom rotary union for your equipment today.

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