Expansion and Compensation in Plastics Piping Systems
Even though thermal expansion is higher in plastics than metals and building materials, it does not cause problems in walled installations because, changes in direction (bends, tees etc.) are frequent in this kind of laying. Even in absence of direction changes, deformation due to expansion in PP-R are absorbed due to "low elastic modulus" of the pipe material. Where as in PVC expansion is comparatively low, therefore no real problems are envisaged due to expansion in concealed installations.
In case of external applications on ceiling or walls, where long lengths are installed, the effects of expansion/contractions shall be considered while assembly of plastic piping system. This is required to account the effect of thermal elongation of pipes caused by varying temperature of the medium that flows through the system. This problem can be solved either by using suitable expansion joints or by suitable clamps. It is necessary to fix the pipes with suitable clamps. This will prevent sagging and snaking of pipelines. The variation in length or expansion in pipelines can be calculated by the following formula.
Good value of thumb in design of PVC piping system is to allow 0.81 mm of length variation for every length of 3 m pipe for each 5 ºC change in temperature.
Compensation Methods Fixed points
Fixed bearing or fixed point (FP) is a fixing clamp closely located between two pipe couplings and close fitted to the pipe. Such type of bearing restricts axial movements of the conduit and is used for suitable segmentation of the conduit system into sections that independently expand as temperature changes (thermal elongation is not transferred beyond a fixed point) Such segmentation is essential in external pipelines to prevent uncontrolled movements of the pipelines.
Traveling bearing or sliding point is a fixing clamp used for anchoring the conduit system to structural elements of the building and protecting the pipes against excessive buckling . It keeps the system aligned and allow the axial sliding of the pipe. The sliding points are to be firmly mounted, in order to prevent vibrations and transmission of noise. Spacing of such bearings depends on the temperature of a conveyed medium and diameter of the conduit.