BS 8490-2007 pdf free download

BS 8490-2007 pdf free download.Guide to siphonic roof drainage systems.
recommendations given in Clause 6 for minimum pressure, minimum velocity, degree of balancing between outlets, and speed of priming are met.
8.4.2 Values of pressure and velocity in the ipes should be calculated at all changes of direction or diameter in a system in order to ensure that the lowest values of these parameters are i(lentified and are within the allowable limits. Particular attention should be given to the pipework at or near the top of the downpipe because the lowest pressures normally occur near this point.
8.4.3 The head losses in straight lengths of pipe should be calculated using an established hydraulic equation or a corresponding set of flow tables or charts. In case of dispute, the Colebrook—White equation 12] should be used (see Annex A and cf. BS EN 12056-3:2000, 6.3.1).
8.4.4 When calculating the flow capacity of a system, the value of pipe roiighnes.s used should take account of the effects of )ipc joints, ageing and possible deposition of line sediment washed through the outlets. For the Colebrook—White equation 121, the minimum value of pipe roughness used for design should be k = 0. 1 5 mm.
8.4.5 Head loss coefficients for the types of pipe fitting used In the system (e.g. bends, reducers. increasers, junctions, etc.) should be determined from tests or obtained from appropriate published data 13, 4]. Loss coefficients for a given geometry of pipe junction caim vary according to the relative flow rates in the branches. The loss coefficient for the siphonic outlets should be determined by test using the procedure given in Annex B.
8.4.6 Pressures In a siphonic system should be calculated starling at its downstream end and working upstream (see Annex A). Unless a suitably designed siphon break is installed (see 8.10.4 to 8.10.6). account should be takemi of possible surcharging in the downstream site drainage system when determining the flow capacity of the siphonic drainage system. If the first downstream manhole or chamber has a suitable vented cover (see 8. 10.1), it may be assumed that the positive pressure head acting at the point of discharge from the siptionic system will not be greater than the height of the vented cover above the end of the last pipe. If a siphon break is used above ground level, atmospheric pressure may be asswned to apply at the siphon break provided that it is fully ventilated and that no surcharging to that level can occur from the downstream site drainage system.BS 8490-2007 pdf free download.