Document x1RrQRdqJmOX7EVbwk3B7edZQ

594 CHAPTER 28 . 1950 Guide duits (H) and (I) are prefabricated. Both-of these conduits are enclosed in metal jackets. ' : At (C) and(E) are shown two tile conduits using sectional insulation. In these particular designs the space surrounding the pipe is filled partially or wholly with a loose insulating material. The addition of this loose in sulating material to the sectional insulation is, of course, optional and is justified only where high pressure steam is used. (E) and (F) are conduits used by two district heating companies, and have the advantage of being constructed of common materials. Conduit (G) is of cast-iron construction, assembled with lead joints and Fig. 2. Connections fob Reducing Valve Without Bypass is water-tight, if properly laid. It is obviously expensive and is justified only in exceptional cases. \ Since it is difficult to make a concrete or masonry conduit absolutely water-tight, provision should be made for some seepage. The pipe should be protected by a waterproof jacket over the insulation, and the seepage drained from the inside of the conduit. Underdrainage of the conduit is generally provided for by a tile drain laid in crushed stone or gravel under neath the conduit. The tile underdrain should be carried to the sewer or some other drainage point. Manholes are required at intervals for access to valves, traps, and some types of expansion joints. .. Where steam and return piping are installed in the same conduit, the return piping'usually follows the same grade as the steam piping. In general, the condensation is pumped back under pressure. ` J Wliei^s. it impossible .to use basement or sub-sidewalk space for the distribu tion piping the cost of installation and maintenance is greatly reduced/ ' . District Heating ,595 . PIPE TUNNELS ' Where steam heating lines are installed in tunnels large enough to pro vide walking space, the pipes are supported by. means of hangers or roller frames on brackets or frame' racks at the side or sides of the tunnel. The pipes are insulated with sectional pipe insulation over which is placed a sewed-on, painted canvas jacket or a jacket of asphalt-saturated asbestos water-proofing felt. The tunnel itself is usually built of concrete or brick, and water-proofed on the outside with membrane water-proofing. . Because of their relatively high first cost as compared with smaller, con duits, walking tunnels are sometimes omitted along heating lines, unless they are required to accommodate miscellaneous other services or provide underground passage between buildings. OVERHEAD DISTRIBUTION. In some industrial and institutional applications, the distribution piping inay be installed, entirely or in part, above ground. This method of con- Pressure reducing valve At least 12 feet of pipe Customer's pressure reducing valve Customer's work starts here Note--All valves, fittings, and traps up to and Ineluding customer's control valve to be at least equal to AmeH- Ican Standard 160 lb. S. S. P. PIpe to be Sched ule 40. Continuous-flow type float trap Fio. 4. Steam Supply Connection when Using Two Reducing Valves struction has the advantage of requiring no excavation and being easily maintained. INSIDE PIPING Figs. 2 and 3 show typical service connections used for low pressure steam service. Fig. 2.shows.installation of a reducing, valve without a by-pass, which is usually omitted in the case of smaller size valves.. . Fig. 3 illustrates the use of a reducing valve, with a by-pass -which.is gen erally provided for larger installations. This latter construction permits the operation of the line in case of failure in the reducing valve. . In the smaller sizes, the reducing Valve can be removed, a filler, installed, and the house valve used to- throttle the flow, of steam until' repairs are made. Fig. 4 shows a typical installation used for high pressure steam service1. The first reducing valve effects, the initial pressure reduction. The second reducing valve reduces the steam pressure to that-required. In a heating system the pipes carrying condensate are more subject to corrosion than other parts of the system. Care must be taken to give proper, pitch to the pipes and provide proper venting of non-condensable gases. (See Chapter. 42, Corrosion). . . . .. : Most district heating companies enforce certain,regulations'regarding the consumer's installation, partly to safeguard their, own interests, but 'Code for Pressure Piping, B31-1, 1942, American Standards Association, Para graph 408, p. 115.