Expansion joints expand in length when under pressure. The force created by this pressure is designated as pressure thrust. Where the pipe supports are not designed to absorb this force, tie-rods must be incorporated across the joint from flange to flange so that the expansion joint is restrained in axial direction and can move lateral only. Based on the Pressure Equipment Directive PED 2014/68/EU the number and size of tie-rods must be calculated to take the full pressure thrust at the required hydraulic pressure test with extra safety margins. 

Most commonly tie-rods are directly integrated into the backing flanges which influences their construction thickness depending from the design pressure and dimensions. Recommended on most applications to prevent damage due to excessive pipe movements, each rod shall be borne in spherical washers to allow lateral movement secured by double-nuts on the in- and outside to restrict axial expansion and compression. 

Moderate axial installation tolerances can be accommodated by adjusting the nuts and washers according to the real installation length of the expansion joint. Nevertheless our spherical washers are always PTFE-coated frictional forces must be considered in addition to the spring rates.