What is a rotary union used for?

Rotary unions, also known as rotary joints or swivel joints, are critical components in industrial machinery that enable the transfer of fluids (liquids, gases, or steam) between stationary and rotating parts. These devices are indispensable in applications requiring continuous rotation while maintaining leak-free media transmission under high pressure, temperature, or speed.

Understanding Rotary Unions: Definition and Core Functions

A rotary union is a precision-engineered mechanical seal designed to connect stationary supply lines to rotating equipment, ensuring seamless transfer of media without leakage. Its primary functions include:

1. Fluid/Gas Transfer

Transmit coolant, hydraulic oil, compressed air, or steam.

2. Pressure and Temperature Management

Operate in environments ranging from vacuum conditions to 6,500 psi (448 bar) and temperatures between -20°C to +230°C.

3. Multi-Channel Support

Advanced models like Deublin’s *Deu-Plex* series allow simultaneous transfer of multiple media (e.g., air and coolant) through independent channels.

How Does a Rotary Union Work?

Rotary unions rely on a combination of rotating and stationary seals to maintain a tight interface. Key components include:
Housing: Typically made of stainless steel or brass for corrosion resistance.
Bearings: Reduce friction and support the rotational movement.
Seal Assembly: Carbon-graphite, ceramic, or tungsten carbide seals prevent leakage even at high RPMs.
For example, in CNC machines, coolant flows through the union’s rotating spindle to cool cutting tools, while hydraulic systems in wind turbines use rotary joints to adjust blade pitch under extreme weather.

Key industrial Rotary union applications

Rotary unions are ubiquitous in sectors demanding reliable fluid transfer:

1. Hydraulic rotary unions in Machine Tools and Manufacturing

Coolant and Lubricant Delivery: In machine tools like lathes, milling machines, and drilling machines, hydraulic rotary unions are used to deliver coolant and lubricants to the cutting tools, ensuring they remain cool and well-lubricated during operation.
Spindles and Rotating Components: The hydraulic rotary unions are used in spindles and other rotating components to provide a reliable fluid connection.
CNC Machining: Deliver high-pressure coolant (up to 140 bar) to spindles for precision cutting.
Packaging Machinery: Transfer air for pneumatic controls and vacuum for product handling.

2. Paper and Pulp Industry

In the papermaking industry, the rotary joint connects the drying cylinder of the paper machine and the fixed pipeline to ensure that steam can be continuously supplied to the drying cylinder to achieve paper drying.
Steam and Water Transfer: Hydraulic rotary unions are used to transfer steam and water to and from paper-making machines, such as calendar rolls, where they help in the drying and finishing processes.
Coating and Laminating: In coating and laminating machines, Hydraulic rotary unions supply adhesives, coatings, and other fluids to the rotating parts.

3. Plastic and Rubber Processing

Mold Cooling and Heating: In injection molding, blow molding, and extrusion processes, Hydraulic rotary unions are used to circulate cooling water or heating fluids through molds to control their temperature.
Rotary Molds and Dies: Hydraulic rotary unions ensure consistent temperature control in rotating molds and dies, which is crucial for the quality of the final product.

4. Textile Industry

In the textile industry, the rotary joint connects the dyeing cylinder and the fixed pipeline to ensure that the dye can be continuously supplied to the dyeing cylinder to achieve textile dyeing.
Dyeing and Finishing: Hydraulic rotary unions are used in dyeing and finishing machines to supply dyes, chemicals, and hot water to the rotating drums or cylinders.
Winding and Unwinding: In winding and unwinding operations, Hydraulic rotary unions provide a fluid connection for tension control and lubrication.

5. Food and Beverage Industry

Cleaning and Sterilization: Hydraulic rotary unions are used in cleaning and sterilization systems to supply hot water, steam, and cleaning agents to rotating equipment, ensuring hygiene and food safety.
Beverage Filling and Packaging: Hydraulic rotary unions provide a fluid connection for the transfer of liquids and gases.

6. Hydraulic rotary unions in Aerospace and Defense

The role of rotary joints in the aerospace field: In aerospace vehicles, the rotary joint connects the rotating parts and the fixed pipeline to ensure that the hydraulic oil, fuel, and other fluids can continuously supply to ensure the normal operation of the aircraft.
Hydraulic and Pneumatic Systems: In aircraft and military vehicles, Hydraulic rotary unions used in hydraulic and pneumatic systems to transfer fluids and gases to rotating parts, such as landing gear, weapons & radar antennas.
Satellite and Spacecraft: Hydraulic rotary unions used in satellite and spacecraft systems for the transfer of fuel, coolant, and other critical fluids.

7. Chemical and Petrochemical Industry

Reactors and Vessels: Hydraulic rotary unions used to supply and remove process fluids, such as reactants, solvents, and coolants.
Mixing and Blending: Hydraulic rotary unions are used in mixing and blending equipment to provide a fluid connection for the addition of ingredients and the removal of products.

8. Automotive Industry

Engine Testing and Development: Hydraulic rotary unions used to supply and remove fluids for testing and development purposes.
Rotary Components: Hydraulic rotary unions used in various automotive manufacturing processes, such as the assembly of engines and transmissions. Providing a fluid connection to rotating components.

9. Renewable Energy

Wind Turbines: Hydraulic rotary unions are used to transfer hydraulic fluid and other media to and from the nacelle. Enabling pitch control and yaw systems.
Solar Thermal Systems: Hydraulic rotary unions used in solar thermal systems to transfer heat transfer fluids to and from rotating mirrors or receivers.

10. Hydraulic rotary unions in the agricultural field

Application of rotary joints in grain harvesting equipment (such as combine harvesters, tractors, etc.): Combine harvesters need rotating drums to separate grains and straw during harvesting. The rotary joint connects the drum and fixed pipeline to ensure that fluids such as hydraulic oil can be continuously supplied to the drum to achieve normal rotation.
Use of rotary joints in crop processing equipment (such as cooling conveyor belts, rice mills, etc.): In rice mills, the rotary joint connects the rice milling roller and fixed pipeline to ensure that cooling water can continuously supply to the rice milling roller to prevent it from overheating.

11. Automobile manufacturing industry

The key role of rotary joints in the manufacturing and assembly of automobile parts: In the manufacturing and assembly of automobile engines, gearboxes and other parts, rotary joints connect rotating parts and test equipment to ensure that fluids such as coolant and lubricating oil.
In the test of automobile wheel hub bearings, the rotary joint connects the test equipment and the wheel hub bearing to ensure that the test fluid can continuously supply to the bearing to simulate the lubrication conditions during actual driving.

12. Oil and gas drilling industry

During oil and gas drilling, rotary joints connect the drill bit and fixed pipelines to ensure that drilling fluid can continuously supply to the drill bit so that drilling can proceed smoothly.

13. Marine engineering industry

On deep-sea drilling platforms, rotary joints connect drill pipes and fixed pipelines to ensure that drilling fluid and mud can continuously supply to the drill pipe so that deep-sea drilling can proceed smoothly. With its high-pressure and corrosion-resistant properties, rotary joints play an important role on deep-sea drilling platforms.

Types of Rotary Unions

Classification by structure: can divide into single-channel, dual-channel, multi-channel, and other types.
Single-Passage rotary union: Transfers one medium (e.g., coolant). Ideal for simple systems.
Multi-port rotary union: Supports 2–12 channels. Used in complex machinery.
Classification by fluid type: can divide into water, steam, hydraulic oil, gas, and other types.
By rotation direction: can divide into unidirectional rotation, bidirectional rotation, and other types.
High-pressure swivel joint: Withstands over 6,500 psi for hydraulic systems.
High-temperature heat-resistant rotary union: Handles steam or thermal oil up to 230°

Selecting the Right Rotary Union: A Buyer’s Guide

Choosing the optimal rotary union requires evaluating:

1. Operational Parameters

Pressure and Temperature: Match specifications to your system’s extremes.
Media Compatibility: Ensure seals resist corrosion from chemicals or abrasives.

2. Mechanical Requirements

Speed: Standard unions handle up to 500 RPM, while high-speed models exceed 20,000 RPM.
Connection Type: Threaded (G1/4” to G2”) or flanged interfaces.

3. Customization Options

Non-Standard Sizes: Tailored solutions for unique machinery layouts.
Smart Features: Leak detection sensors (e.g., Deublin’s HPS Steam series) for predictive maintenance.

Maintenance Best Practices

Prolonging rotary union lifespan involves:

1. Regular Inspection: Check seals for wear and lubricate bearings annually.

Replace the seals and wear parts of the rotary joint regularly;
Regularly clean and lubricate the rotary joint.
Be careful to avoid excessive impact and vibration of the rotary joint.

2. Leak Management: Address minor leaks immediately to prevent system contamination.

3. Component Replacement: Swap worn seals every 12–24 months, depending on usage.

Regular inspection and maintenance of the rotary joint can detect and solve problems in time and extend its service life.

Conclusion

Rotary unions are the unsung heroes of industrial automation, enabling efficient fluid transfer in demanding environments. By understanding their applications, selecting the right type, and adhering to maintenance protocols, businesses can minimize downtime and maximize productivity. For engineers and procurement specialists, partnering with trusted suppliers ensures access to cutting-edge solutions tailored to specific operational needs. If u have any queries, kindly contact us.