Rotary Joint Selection and Inner Tube Connection Types
A rotary joint is a sealed transition device that transfers fluid media from a stationary system to a rotating system. Selecting the correct rotary joint ensures optimal performance, extends service life, and improves equipment efficiency. Its can be classified based on various criteria, including the type of fluid, the number of passages, the sealing configuration, temperature, and pressure.
Classification Criteria for Rotary Joints
By medium: thermal oil, steam, water, and compressed air rotary joints.
By sealing type: mechanical seal and hydraulic seal rotary joints.
By number of passages: single passage, double passage, and multi passage rotary joint.
By pressure: low-pressure, medium-pressure, and high-pressure rotary joints.
By temperature: ambient-temperature and high-temperature rotary joints.
By rotational speed: low-speed and high-speed rotary joints.
Rotary Joint Selection Steps
When selecting a rotary joint, the first step is to determine whether a single passage, double passage, or multi passage port structure is required based on the equipment’s structure and operating principle. If the input and output media are on opposite sides of the equipment, a single passage rotary joint is needed; if the input and output media are on the same side of the equipment, a double passage rotary joint is required; If the equipment needs to convey multiple media or deliver media to multiple locations, a multi passage rotary joint should be selected. Secondly, determine the nominal diameter based on the flow rates of the input and output media. Third, select a rotary joint suitable for the media’s pressure, temperature, and rotational speed. Finally, determine whether the rotary joint should use flange or threaded connections, as well as the connection type for the inner tube, based on the connection method between the roller and its rotating shaft.
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Connection Methods Between the Drive Shaft of a Rotary Joint and the Roller
The drive shaft of a rotary joint is typically connected to the roller via threaded or flanged connections. Threaded connections primarily include British standard threads and American NPT threads, while flanged connections include quick-release flanges and fixed flanges.
There are Two Main Types of Inner Tube Connections
including rotating inner tube and fixed inner tube.
Rotating inner tube: The inner tube is mounted at the tail end of the rotary joint and rotates in sync with the roller and drive shaft. O-rings or anti-friction sleeves are used to seal and separate the inlet and outlet media. The fit between the inner tube and the mounting hole must be within the appropriate tolerance; a fit that is too tight will affect the service life of the rotary joint, while a fit that is too loose will affect the heating and cooling efficiency of the roller.
Fixed inner tube type: The inner tube is mounted at the tail end of the rotary joint and connected to it via threads. While the roller and the rotary joint’s rotating shaft rotate in sync, the inner tube remains stationary. However, it is important to note that for rollers with threaded connections, the direction of rotation of the inner tube’s threads must match that of the roller's threads.
Determining the Length of the Inner Tube
In rotary joints where the inner tube rotates, an inner tube that is too long can cause runout and uneven wear, which compromises sealing performance and shortens the service life of the rotary joint (in severe cases, it can even lead to thread wear through). In such cases, the rotary joint’s inner tube can be divided into two sections, with additional supports added to each section. This minimizes the inner tube’s runout while limiting its axial movement, ensuring the rotary joint operates smoothly after installation.
When selecting a rotary joint, there is no All-round model; rather, the optimal choice is the solution that best fits your specific operating conditions. Regardless of whether the structure involves single passage, double passage, or multi passage configurations, the specific connection method must be carefully determined. If you still have any other questions about rotary joints (such as rotary joint maintenance and installation), please feel free to contact us. At Sun Hong, we provide not only technical support but also customized services, offering you cost-effective, stable, and reliable rotary joint solutions.
