Hot Oil Rotary Union for Thermal Oil Systems

Description

A hot oil rotary union transfers heated thermal oil or heat transfer fluid from stationary piping into rotating drums, rollers, cylinders, and other rotating equipment.

Unlike a standard hydraulic rotary union, a thermal oil rotary union must operate continuously under elevated temperatures while controlling leakage, thermal expansion, seal wear, and bearing load.

Dann Hydraulic manufactures hot oil rotary unions for industrial heating and temperature-control systems. Our rotary unions are suitable for equipment used in rubber, plastics, textile, paper, laminating, printing, chemical processing, and other applications where thermal oil must circulate through rotating machinery.

Hot Oil Rotary Union Specifications

Parameter	Specification
Product Type	Hot Oil Rotary Union / Thermal Oil Rotary Joint
Maximum Temperature	250°C
Maximum Pressure	2.0 MPa
Maximum Speed	200 RPM
Media	Thermal Oil, Hot Oil, Compatible Steam Applications
Main Materials	Stainless Steel, Carbon Graphite, Carbon Fiber
Rotation	Continuous 360° Rotation
Configuration	Single-Passage or Application-Specific Design
Connection	BSP, NPT, Metric or Customized
Customization	OEM and Custom Dimensions Available

Important: Maximum operating temperature, pressure and rotational speed should not be considered independently. Final operating limits depend on the media, connection size, seal configuration, rotational speed, installation method and working cycle.

Contact our engineering team with your actual operating conditions before selecting a model.

Why Hot Oil Applications Require a Specialized Rotary Union

Thermal oil systems expose rotary joints to conditions that are very different from ordinary water or low-temperature hydraulic applications.

During operation, the rotary union may experience:

• Continuous high operating temperatures
• Repeated heating and cooling cycles
• Thermal expansion of the shaft and housing
• Changes in thermal oil viscosity
• Pressure fluctuations
• Continuous rotation
• Seal face wear
• Bearing load
• Pipe stress and misalignment

A rotary joint that works normally with water or hydraulic oil at room temperature may not provide acceptable service life when exposed to hot thermal oil.

For this reason, the sealing materials, internal clearance, bearing arrangement and connection method should be selected specifically for the actual temperature and operating conditions.

Designed for Thermal Oil and Heat Transfer Fluid

Our hot oil rotary union is designed for industrial systems where thermal oil circulates between stationary piping and rotating equipment.

Typical media include:

• Thermal oil
• Heat transfer oil
• Heat transfer fluid
• Compatible synthetic thermal fluids
• Industrial heating oils

The correct sealing configuration is selected based on the operating temperature, pressure, rotational speed, and chemical characteristics of the heat transfer fluid.

If you are replacing an existing rotary joint, please provide the original model number, installation drawing or physical dimensions so our engineers can evaluate compatibility.

Typical Applications

Rubber and Tire Manufacturing

Hot oil rotary unions are commonly installed on:

• Rubber mixing equipment
• Calender rollers
• Rubber processing rolls
• Vulcanizing equipment
• Heating drums
• Tire manufacturing machinery

Thermal oil circulating through the rotating roller helps maintain stable process temperatures during rubber forming and processing.

Plastic Processing Machinery

Typical applications include:

• Extrusion equipment
• Plastic film machines
• Laminating rollers
• Heating cylinders
• Plastic sheet production lines
• Calendering machines

Reliable thermal oil circulation helps maintain consistent roller temperatures and improves process stability.

Textile Machinery

Hot oil rotary joints can be used in:

• Textile drying cylinders
• Finishing equipment
• Heating rollers
• Coating machinery
• Laminating machines

The rotary union transfers heat transfer oil into the rotating cylinder while allowing continuous rotation.

Paper and Converting Equipment

Thermal oil rotary unions may also be used on:

• Paper drying equipment
• Heated rollers
• Coating lines
• Laminating machines
• Converting machinery

Chemical and Industrial Processing

Other applications include:

• Industrial mixers
• Heated reactors with rotating components
• Process drums
• Dryers
• Thermal processing machinery
• Heat transfer equipment

Common Problems in Hot Oil Rotary Unions

1. Thermal Oil Leakage

One of the most common problems is leakage around the rotating seal.

Possible causes include:

• Worn sealing surfaces
• Incorrect seal material
• Excessive operating temperature
• Shaft misalignment
• Pipe load transferred to the rotary union
• Contaminated thermal oil
• Excessive pressure
• Improper installation

Inspect a leaking rotary union promptly because hot thermal oil can create both maintenance and safety problems.

2. Premature Seal Wear

Thermal cycling continuously expands and contracts components inside the rotary joint.

If the seal material or mechanical design is not suitable for high-temperature service, the sealing surfaces may wear rapidly.

We select sealing materials according to temperature, pressure, media and rotational speed instead of using one seal configuration for every application.

3. Bearing Damage

Bearing problems may result from:

• Excessive radial load
• Incorrect pipe installation
• Misalignment
• Operation beyond rated speed
• High operating temperature
• Contaminated lubricant
• Vibration from connected machinery

Correct hose and piping installation helps prevent external loads from being transferred directly to the rotary union.

4. Carbon Deposits and Thermal Oil Degradation

Thermal oil can deteriorate after prolonged exposure to excessive temperature.

Degraded oil may form deposits around internal passages and sealing surfaces, affecting flow and seal performance.

Regular inspection of the heat transfer fluid can help extend the service life of both the rotary union and the complete thermal oil system.

5. Leakage After Temperature Cycling

Some rotary unions operate correctly when cold but begin leaking after the system reaches operating temperature.

This may indicate:

• Incorrect internal clearance
• Thermal expansion problems
• Seal deformation
• Shaft misalignment
• Improper seal material selection

When selecting a hot oil rotary union, always provide the actual working temperature rather than only the room-temperature operating conditions.

How We Improve Reliability in Hot Oil Applications

High-Temperature Seal Selection

Seal materials are selected according to:

• Thermal oil type
• Maximum temperature
• Working pressure
• Rotational speed
• Duty cycle
• Equipment environment

Carbon graphite and other high-temperature sealing materials can be used according to the application.

Precision Machining

Stable rotary sealing depends heavily on machining accuracy.

Critical components are controlled for:

• Shaft concentricity
• Sealing surface accuracy
• Bearing seats
• Thread dimensions
• Internal flow passages
• Surface finish

Accurate machining helps maintain proper seal alignment during continuous rotation.

Application-Based Engineering

We do not recommend a rotary union based only on thread size.

Before model selection, our engineers evaluate:

• Operating temperature
• Working pressure
• Thermal oil type
• Rotational speed
• Connection size
• Installation dimensions
• Rotation direction
• Operating hours
• Existing rotary union model
• Machine type

This reduces the risk of selecting a rotary union that physically fits the machine but is unsuitable for the actual operating conditions.

Hot Oil Rotary Union Manufacturer in China

Dann Hydraulic specializes in rotary unions, rotary joints and industrial fluid transfer solutions.

Our manufacturing capabilities include precision CNC machining, component inspection, assembly and pressure testing.

Our factory supports:

• Standard hot oil rotary unions
• OEM rotary union manufacturing
• Custom shaft dimensions
• Custom housing dimensions
• BSP, NPT and Metric connections
• Customized sealing materials
• Single-passage designs
• Application-specific rotary union development
• Replacement rotary union evaluation
• Small-batch and production orders

We manufacture rotary unions for OEM equipment manufacturers, industrial distributors, maintenance companies and machinery users worldwide.

Quality Control

Rotary unions operate at the interface between stationary piping and rotating machinery, so manufacturing accuracy directly influences sealing performance and service life.

Dann Hydraulic applies controlled inspection procedures during manufacturing and final assembly.

Quality control can include:

• Raw material inspection
• CNC machining inspection
• Dimensional inspection
• Seal surface inspection
• Thread inspection
• Assembly inspection
• Pressure testing
• Leakage testing
• Final visual inspection

The final rotary union configuration is confirmed according to the customer’s operating requirements.

OEM and Custom Hot Oil Rotary Unions

Standard rotary unions cannot fit every machine.

We can manufacture customized thermal oil rotary unions according to customer drawings, samples or installation dimensions.

Customization options include:

• Different shaft diameters
• Different connection threads
• Custom overall length
• Housing modifications
• Stainless steel construction
• Different sealing materials
• Special mounting dimensions
• Application-specific flow passages

If you currently use an imported rotary union, send us:

1. Original model number
2. Product drawing
3. Photos
4. Thread dimensions
5. Operating temperature
6. Working pressure
7. Rotational speed
8. Thermal oil type

Our engineers can evaluate the application and recommend a suitable configuration.

How to Select a Hot Oil Rotary Union

Correct selection is more important than simply choosing the same thread size.

Working Temperature

Provide both the normal operating temperature and maximum possible temperature.

For this product series, the maximum reference temperature is 250°C.

Working Pressure

Provide the normal operating pressure and maximum pressure during system startup or pressure fluctuations.

Maximum reference pressure for this product is 2.0 MPa.

Rotational Speed

The maximum reference speed is 200 RPM.

Actual allowable speed may vary according to temperature, pressure, size and configuration.

Thermal Oil Type

Different heat transfer fluids have different viscosity, additives and temperature characteristics.

Providing the oil brand or technical data sheet helps us select suitable sealing materials.

Connection Size and Thread

Please provide:

• Thread type
• Thread diameter
• Installation length
• Shaft dimensions
• Existing drawing if available

Operating Cycle

Tell us whether the machine operates:

• Intermittently
• Several hours per day
• Continuously
• 24 hours per day

Duty cycle can influence bearing and seal selection.

Hot Oil Rotary Union Replacement

If your existing thermal oil rotary joint has started leaking, overheating or requiring frequent maintenance, replacing it with exactly the same dimensions is not always enough.

Before manufacturing a replacement, we recommend checking:

• Actual operating temperature
• Actual system pressure
• Rotational speed
• Shaft alignment
• Hose installation
• Thermal oil condition
• Existing seal material
• Previous failure position

Understanding why the previous rotary union failed can help improve the service life of the replacement.

Dann Hydraulic can evaluate existing rotary unions based on model numbers, drawings, dimensions or physical samples.

Frequently Asked Questions

What is a hot oil rotary union?

A hot oil rotary union is a mechanical component that transfers thermal oil or heat transfer fluid from stationary piping into rotating machinery while allowing continuous rotation.

It is commonly installed on heated rollers, drums, cylinders and other rotating equipment.

What is the maximum temperature of this hot oil rotary union?

The reference maximum temperature for this product is 250°C.

The final allowable temperature depends on operating pressure, rotational speed, thermal oil type, seal material and duty cycle.

What is the maximum pressure?

The reference maximum pressure is 2.0 MPa.

Please provide your normal and peak operating pressure when requesting a quotation.

What is the maximum rotational speed?

The reference maximum rotational speed is 200 RPM.

Temperature, pressure and speed interact with each other, so the maximum values should not automatically be combined in the same operating condition.

Can it be used with thermal oil?

Yes. This rotary union is designed for compatible thermal oil and heat transfer fluid applications.

Please provide the thermal oil specification and operating temperature so we can confirm seal compatibility.

Can it be used for hydraulic oil?

Some configurations may be compatible with hydraulic oil, but hydraulic systems and thermal oil systems have different operating requirements.

For conventional hydraulic applications, we recommend selecting a dedicated hydraulic oil rotary union according to system pressure and speed.

Why does a hot oil rotary union start leaking?

Common causes include:

• Worn sealing surfaces
• Excessive temperature
• Incorrect sealing material
• Pipe stress
• Shaft misalignment
• Bearing wear
• Contaminated thermal oil
• Operating conditions beyond the design specification

The entire system should be checked before replacing the rotary union.

Can you manufacture according to our drawing?

Yes.

We support OEM and customized rotary union manufacturing based on 2D drawings, dimensions, existing model information or physical samples.

Can you replace an imported hot oil rotary union?

We can evaluate replacement requirements based on the original model, drawing and operating conditions.

Dimensional compatibility alone is not sufficient. Temperature, pressure, speed, media and sealing requirements must also be confirmed before production.

What information do you need for a quotation?

Please send:

• Thermal oil type
• Maximum temperature
• Working pressure
• Rotational speed
• Connection size
• Thread standard
• Installation dimensions
• Machine application
• Existing rotary union model or drawing

Providing complete operating information allows us to recommend a more appropriate rotary union.

Request a Hot Oil Rotary Union Quote

A reliable hot oil rotary union must do more than fit the machine. It must match the actual thermal oil, temperature, pressure, speed and operating cycle of the equipment.

Dann Hydraulic provides standard, OEM and customized thermal oil rotary unions for industrial machinery worldwide.

Send us your operating parameters, drawing or existing rotary union model, and our engineering team can evaluate the application and recommend a suitable solution.