Compensator screw rods, also known as limit rods or transport rods, play several key roles in the application of corrugated compensators (expansion joints):
Shipping Protection：
During transportation, the screw rod can prevent the bellows from being impacted and shocked, avoiding bellows deformation or weld cracking. This is because in the natural state, the bellows may be deformed due to external forces, and the screw rod provides structural stability.
Installation and positioning：
When installed, the screw rod helps keep the compensator in the correct position until the plumbing system is fully assembled and ready. They can limit excessive movement of the compensator during installation.
limiting action：
When the compensator is put into service, the screw rod prevents the bellows from over-stretching or compressing due to external pressure or temperature changes, which helps protect the compensator from exceeding its designed displacement range and avoiding damage.
Prevent blind plate force：
In some designs, particularly large and small tie rod type corrugated compensators, the screw rod also assumes the role of preventing additional blind plate forces. Blind plate force is the force exerted on the compensator when there is pressure in the piping system, but there is not enough displacement to absorb the pressure change. The screw rod balances this force by limiting the displacement of the bellows, avoiding overloading the compensator.
Pre-stretch/pre-compress：
In some cases, the screw rod may be used to pre-stretch or pre-compress the compensator so that the compensator can more effectively absorb displacement as the system thermally expands and contracts.
Safety measures：
If the main fixation bracket is damaged, the screw rod can be used as a temporary safety measure to prevent excessive displacement of the compensator until the bracket is repaired or replaced.
During the installation and commissioning phase, the condition of the screw rod needs to be adjusted on a case-by-case basis. Some screw rods should be loosened after installation, but cannot be completely removed to allow the compensator to expand and contract freely under operating conditions. While for some types of compensators, such as large and small tie rod types, the screw rods should not be removed during operation because they continuously act as limiting and preventing blind plate forces.
Manufacturers will typically paint the screw rods with a specific colored mark (such as yellow) indicating which screw rods can be removed and which should be retained. It is essential to follow the manufacturer's guidance and recommendations during operation and maintenance.