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<br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br /> <br />Permastran is relatively light-weight and easy to handle. It comes in 20-foot <br />lengths joined by a slip-on, gasketed, bell-and-spigot joint. Like PVC, <br />12-inch Permastran can be laid around a 300-foot radius curve without the use <br />of special fittings. The same wide variety of standard fittings that can be <br />used with ductile iron pipe can also be used with Permastran since it is <br />fabri cated with outsi de di ameters that match ductil e iron pi pe. 11.1 though <br />quite durable, Permastran requires more care in handling and installation than <br />does ductile iron or steel pipe. The compacted or special backfill zone <br />should, like PVC, extend to six inches above the pipe. <br /> <br />3.5.4 Ductile Iron Pipe <br /> <br />Ouctile iron is generally a strong competitor in pipelines of the size and <br />high pressure classes required for the Towaoc water supply liM. Ductile iron <br />pipe has good flow characteristics with inside diameters generally greater <br />than most other types of pi pe havi ng the same nomi nal di ameters. Although <br />q1li te heavy, ducti 1 e iron pi pe is consi dered to be an easy pi pe to handl e and <br />instal1. The pi pe comes in 18 or 20 foot 1 enqths, generally connected hy a <br />slip-on, gasketed, hell-and-spigot joint for pressure classes up to 250 psi. <br />Large radius curves can be made by utilizing the allowahle joint deflecti'ln <br />(up to 30 for 14-inch pipe and up to 50 for diameters less than 14 <br />inches). Sharper bends can be made usi ng standard fi tti ngs. A 1 arge vari ety <br />of standard fittings is available for use with ductile iron pipe. <br /> <br />The mi nimum pressure cl ass (Cl ass 50) for both 12-i nch and 14-i nch ductil e <br />iron pipe is rated for working pressures of 350 psi (plus an allowance for <br />hydraulic transient pressures of an additional 100 psi) with safety factors <br />slightly over 2.0. Class 50 12-inch and 14-inch pipe is also strong enough to <br />be buried up to at least nine feet deep. If covers greater than nine feet are <br />desired, the pipe class could be increased. Based on the expected internal <br />pressure and external load condi ti ons for the Towaoc water supply 1 i ne, it <br />appears that Cl ass 50 ductil e iron pi pe may be adequate for the enti re 1 ert'lt~ <br />of the Towaoc line. <br /> <br />3-21 <br /> <br />l060c <br />