SABI Magazine February March 2016 | Page 33

HowWater to... Nominal Pipe Size Pressure classes of AC pipe mm Outside Diameter of AC pipe Equivalent OD of PVC/HDPE pipe mm mm 50,63 50 F 69 75 D,E,F 96 75 100 C,D,E,F 122 110,125 150 C,D,E,F 177 160 200 B,C,D,E,F 232 200 250 B,C,D,E,F 286 250 300 B,C,D,E,F 345 315 350 B,C,D,E,F 426 355,400 450 B,C,D,E 507 450 500 B,C,D,E 587 500, 560 600 B,C,D 667 630 AC pipes are connected with Triplex push-fit rubber ring couplings, manufactured from fibre cement. The pipes were supplied with a machined spigot end to fit the coupling. Repair couplings, known as “short collars” also use rubber ring seals and are manufactured from ductile iron. Short-collars are currently still available, however they only fit the AC pipe diameters, hence the need for a range of variable sized couplings and adaptors to suit both the AC and the Standard ISO sizes of modern pipe materials, such as PVC and HDPE. Plastic pipes are flexible systems, as opposed to the “rigid” classification of AC pipes. This prevents the use of short-collars for adaption to flexible pipe systems, in combination with a PVC/ AC adaptor, due to the inadequate socket depth presented by the short-collar. It should also be noted that the nominal wall thickness of PVC pipe systems is far less than that of AC piping. This should not present any problems from a hydraulic point of view, however the specifications for trenching, bedding and backfilling of the two systems should be noted (rigid vs flexible) Coupling options AC pipe failures may be repaired through the use of shortcollars or stainless steel repair clamps, however the availability of replacement AC piping is a major problem to the Irrigation Engineer. Therefore the need exists to be able to quickly insert plastic pipes (PVC or HDPE) into an AC line, given the difference in the OD (outside diameter) of the two systems. be noted that these couplings are all designed to be used in buried or restrained pipe systems where the end thrust has been contained via thrust blocks or brackets. A range of restrained couplings is also available. The coupling incorporates a serrated grip ring that will accommodate the end thrust without the need for additional thrust restraint mechanisms. For details refer to the relevant product manual available on-line. Size Selection Table of Ranger Couplings Nominal Bore Pipe OD Range Nominal Bore Pipe OD Range Nominal Bore mm mm 50 59-72 65 80 100 125 mm mm mm mm 225 242-262 450 454-460 72-85 250 250-267 450 476-493 88-103 250 272-289 450 480-500 109-128 300 315-332 500 500-508 138-153 300 322-340 500 526-546 150 150-170 300 340-360 600 600-630 150 159-182 350 351-378 600 628-650 175 192-210 350 367-391 600 630-650 200 218-235 400 390-410 225 230-247 400 417-437 The size selection process is as follows. The example for size selection is based on the connection of a 100 NB AC pipe to a 110mm PVC pipe, using both of the above tables. ff The actual OD (outside diameter) of the 100mm AC pipe is 122mm ff The OD of the PVC pipe is 110mm ff The choice of coupling for this connection will be the 109-128mm ff The same coupling may be used for AC-AC or PVC-PVC connections The stainless steel repair clamp is used for the connection of similar pipe diameters such as AC-AC, PVC-PVC etc. the following table is based on the VARIplus-RC clamp sizes. Note that the clamps are pressure rated at PN 16 bar up to DN 234 [H[