The Hidden Cause of Premature Rotary Joint Wear
Have you ever encountered this situation while using a rotary joint? A newly purchased unit is installed and put into operation, only to develop leaks, abnormal noises, or a seized bearing within just a few days.
Although the seals and medium pressure were carefully inspected, the root cause could not be identified. Even after replacing the rotary joint with a new one, the problem persisted.
Based on Sun Hong's more than 30 years of experience in manufacturing rotary joints and our technical expertise, we can confirm that the root cause of this issue lies not in the rotary joint itself, but in the improper installation of the associated flexible tube.
Incorrect Installation Method Accelerated Rotary Joint Wear
Improper Length of Flexible Tube
If There are also specific requirements for flexible tube when installing rotary joints. If the flexible tube is too short, it will be subjected to forced stretching during installation. And if it is too long, it may sag or become tangled. Both scenarios exert tensile or compressive forces on the rotary joint.
This will damage the internal sealing structure of the rotary joint, causing the spring to lose its compensating capability, leading to leakage of the fluid flowing through the joint, and accelerating abnormal wear on the internal bearings and seal rings.
The Impact of Flexible Tube Bend Radius on Rotary Joint
This manifests as the flexible tube bending sharply at the base of the fitting, or the bending radius falling below the tube's minimum allowable value (typically 5–8 times the hose diameter for static applications and 10 times the diameter for dynamic applications).
If the bend is too sharp, excessive local stress will develop at the bend of the flexible tube, leading to fatigue of its body, resulting in fracture or perforation.
In addition, lateral forces resulting from bending are transmitted to the rotary joint housing, subjecting the internal bearings and seal rings to additional loads and causing abnormal wear.
Damage to Rotary Joints Caused by Flexible Hose Torsion
This phenomenon typically occurs because the flexible tube undergoes a "twisting" (or corkscrew like) deformation along its axis during installation, or because the tube twists due to misalignment between its axis and the direction of equipment operation.
Torsion not only damages the structure of the flexible tube, causing wear and seal failure of the braided sleeve and bellows, but also creates a deflection force on the rotary joint, resulting in uneven sealing rings and premature leakage.
Flexible Tube Improper Application of Force
If the flexible tube is installed in a state where it is under tension, compressed, or completely rigidly fixed, the vibrations, thermal expansion, and minor displacements generated during equipment operation cannot be absorbed by the hose. Instead, they are transmitted directly to the rotary joint.
In the long run, this can cause the slight displacement of the tube or thermal expansion and contraction during equipment operation to be directly transmitted to the housing of the rotary joint, resulting in housing deformation, damage to the seals, and obstruction of normal axial displacement compensation of the rotary joint.
Improper Flexible Tube Support and Restraint
If the flexible tube is not secured with a clamp or with an independent anti rotation support device, and instead "anti rotation" is achieved by tightening the tube, the torque and vibration generated during equipment operation will be directly transmitted to the rotary joint.
Under sustained loading, the fatigue deterioration of the flexible tube itself will be accelerated, and the rotary joint's normal displacement compensation is also restricted. This subjects the internal bearings and sealing rings to additional stress, thereby leading to abnormal wear and leakage.
Standard Installation Requirements for Flexible Tube
Proper Allowance for Length and Stress-Free Installation
When installing the flexible tube, a length allowance of approximately 5% to 10% should be reserved to prevent the tube from being in a state of tension or under stress.
After installation, the tube should remain in a naturally curved and slack state, allowing for a certain degree of movement when gently shaken by hand.
It is recommended that two people work together during installation to avoid forcibly dragging or twisting the tube and ensure it connects to the rotary joint without any additional stress.
Avoid Bending at the Root and Provide Adequate Support
The flexible tube should not be bent directly at the connection point with the rotary joint. If a change in direction is required, a rigid elbow should be used for the transition.
Additionally, appropriate pipe clamps and an independent anti rotation device should be used to secure the tube, preventing torque generated during equipment operation from being transmitted directly to the rotary joint.
Maintain a Flexible Connection
A flexible connection using a flexible tube should be established between the rotary joint and the equipment piping, with necessary allowance for expansion and contraction. This enables the tube to absorb vibrations, thermal expansion, and positional shifts occurring during equipment operation, thereby reducing the additional stress exerted on the rotary joint.
