The tie rods in an expansion joint (also known as limit rods, guide rods, or support rods) play different roles in different expansion joint types, but their main functions typically involve the following:
Shipping Protection： The tie rod prevents the bellows, the core component of the expansion joint, from being crushed, deformed, or damaged during transportation and installation. They maintain the bellows in a preset, uncompromised shape until the expansion joints are properly installed in the ductwork.
displacement limit： The tie rod can limit the amount of displacement of the expansion joint and prevent it from exceeding its compensation capacity within the design range. This is especially important for those expansion joints that need to withstand large displacements during operation, such as large tie rod transverse corrugated expansion joints, whose tie rods not only limit position but also help offset pressure thrust in the pipeline.
Prevent blind board force： In some expansion joints, particularly transverse corrugated expansion joints, the tie rod can help counteract blind plate forces due to internal pressure in the pipe, which can cause damage to the expansion joint or system imbalance.
Guidance and support： Tie rods are also sometimes used to provide guidance and support, ensuring that the expansion joint moves in a predetermined direction when displaced, avoiding the creation of additional lateral forces or torque.
Pre-stretch： For some types of expansion joints, a tie rod can be used to pre-stretch the expansion joint prior to installation to reach a preset initial position or stress state in the piping system. Once installed and tested, these tie rods can be loosened or removed.
Proper handling of the tie rod is very important when installing and using the expansion joint. Depending on the specific type of expansion joint and the manufacturer's guidance, the tie rod may need to be removed immediately after installation, or it may need to be loosened or removed after the expansion joint has reached a specific displacement. Wrong operation can cause the expansion joint to not work properly or even damage the expansion joint and the entire piping system. Therefore, the installation guidelines and instructions provided by the manufacturer should be carefully read and followed before installing the expansion joint.