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How to Choose the Right Rotary union for your CNC spindle?

What is a Rotary Union? 

When theres a need to transmit gases, liquids or air between stationary and rotating parts, we need a mechanical device to maintain a continuous fluid or pneumatic connection while allowing the connected object or system to continue rotating, such a device is called a rotary union. Rotary union mainly rotate the air, gas, water, oil and steam.

Rotary unions have a multitude of names, such as Rotary Unions, Rotary joints, Rotating Coupling, Rotating Connector, Swivel unions, Swivel Fitting, Fluid Rotary Joint, air rotary unions, steam rotary unions, etc. These alternative names are used in different industries and contexts, but they all refer to the same essential component.

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What are the parts of a rotary union?

Rotary adapters have the property of flexible rotation and can transfer forces and rotation between different parts of mechanical equipment. 

The working principle of rotary joints mainly involves their construction and materials.


Rotary joints generally consist of components such as shafts, housing, bearings, and seals.

* The Shaft mainly transfers media (water, oil, gas) through the device to the rotating parts.

* The housing is the external protective layer of the rotary joint, with the role of withstanding external forces and environmental impacts.

* The seals play the role of sealing to prevent external impurities from entering into the rotary joint.

* The bearing supports and guides the movement of the rotary joint.

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How do rotary unions work?

The working principle of a Joint Union is based on the free rotation of an internal ball. When the rotary union is affected by an external force, the force is transferred to the internal ball, which causes it to rotate. The rotation of the internal ball can drive mechanical components attached to it to rotate together. At the same time, the rotation of the internal ball can also keep the rotary joint's outer casing relatively stationary, enabling the rotation of mechanical equipment without the need for overall movement.

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How to classify types of rotary unions:

•  Types of rotary joints according to channel/passage:

Rotary joints are categorized into single-channel rotary joints and multi-channel rotary joints.

In a single-channel rotary joint, the heat transfer medium flows in one direction. The medium enters at one end of the combiner and exits at the other end, so the rotary union has only one passage.

Multi-channel rotary joints have multiple channels in the same or different directions. Multi-channel rotary joints are used where multiple media are used simultaneously.

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•  Types of rotary joints according to the rotary union material

Stainless Steel: These rotary joints are made of stainless steel and are suitable for corrosive environments and sanitary applications.

Brass: Brass rotary joints are suitable for applications requiring high corrosion resistance and electrical conductivity.

Aluminum: Aluminum rotary joints are lightweight and suitable for applications with high weight requirements.

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•  Types of rotary joints according to application

CNC Machine Tool Industry

Rotary unions are integral to manufacturing processes, enabling the transfer of various fluids and gases within rotating equipment like machine tools, rollers, and industrial mixers, especially for CNC spindles, robotics, etc.


Hydraulic machinery

Rotary joints, including loaders, excavators and various construction equipment are commonly used to rotary hydraulic hoses and maintain fluid transfer and are often referred to as hydraulic rotary joints.


Also application in the below area:

Oil and Gas Industry, Agriculture, Food and Beverage Processing, Aerospace and Aviation, Marine and Shipping, Automotive Industry, Chemical and Petrochemical Processing, Water Treatment and Distribution, Entertainment and Theme Parks, Mining Industry, Firefighting and Emergency Services, Energy and Power Generation, Renewable Energy, etc.

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Famous Rotary Union Suppliers and Rotary Union Manufacturers in the world

Several well-known brands and manufacturers produce rotary unions for various industries.  

RicoCNC highly recommend the following five top brands of CNC machine tool spindle rotary unions, both in terms of brand reputation, quality and after-sales service::

•  RIX Rocky Joint- Rotary Union manufacturer from Japan

RIX Rocky Joint.jpg

•  DEUBLIN- Rotary Union Supplier from US

•  ROTOFLUX- Rotary Union Manufacturer from Italy

ROTOFLUX- Rotary Union Manufacturer from Italy.jpg

•  OTT-JAKOB- Rotary Union Manufacturer from Germany

•  SMARTC-Rotary Union Manufacturer from TAIWAN

SMARTC- Rotary Union Manufacturer from TAIWAN.jpg

How to Choose the right Rotary union for your CNC spindle?

Here are the aspects we would consider when purchasing and replacing a new rotary union:

•  Compatibility and fit: Ensure that the rotary union is compatible with the particular CNC machine model and its requirements.

•  Performance: Evaluate the rotary union's performance specifications, such as speed, torque and load capacity. Matching these specifications to the CNC machine's requirements to ensure efficient operation. It is important to consider the precision and accuracy of the rotary union, especially if the CNC machine is used for high-precision machining.

•  Brand reputation: Reliable brands are likely to offer better performance and durability. Use the brands we recommend above.

•  Durability and reliability: Evaluate the quality of manufacturing and materials used in the rotary union. It should be durable enough to withstand the demands of a CNC machining environment.

•  Cost: Consider the service life and performance of rotary union along with the overall price/performance ratio.

•  Technical support and service: Check the availability and quality of technical support provided by the manufacturer. How easy it is to obtain replacement parts when needed.

•  Adaptability to future upgrades: Consider whether the rotary union will be able to accommodate future upgrades or changes to the CNC machine setup. As technology continues to evolve, this flexibility is invaluable.

•  Ease of installation: Consider how easy it is to install and integrate rotary unions into a CNC machine. A straightforward installation process saves time and reduces the likelihood of errors.

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With all these factors in mind, our goal was to ensure that the rotary unions we chose would not only meet the immediate needs of CNC machine tools but also provide a reliable, efficient and long-term solution.

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RicoCNC is a specialized supplier of machine tool parts, we are not only to provide high-quality parts, but also have expertise in machine tool parts and maintenance, we hope that we can learn together to achieve the sustainable use of machine tools.

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