Document REDd1Knzq7Jq4g8dJDNVOYBV

532, ' CHAPTER 29 1946 Guide tially or wholly with a loose insulating material. The addition of this loose insulating 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 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 Fig. 2. Connections for Reducing Valve Without Bypass Fig. 3. Connections for Reducing Valve with Bypass 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 underneath the conduit. The. tile under drain 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. PIPE TUNNELS Where steam heating lines are installed in tunnels large enough to provide walking space, the pipes are supported by means of hangers or District Heating 533 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 conduits, 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 may be installed, entirely or in part, above ground. This method Pressure reducing valve Fig. 4. Steam Supply Connection when Using Two Reducing Valves of construction 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 bypass, which is usually omitted in the case of smaller size valves. Fig. 3 illustrates the. use of a reducing valve,, with a bypass which is generally 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, arid the house valve used to throttle the flow of steairi until repairs are made. -- Fig. 4 shows a typical iristallation 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; 1 Most district heating companies enforce certain regulations regarding the consumer's installation, partly to safeguard their own interests but principally to insure satisfactory and economical service to the consumer. There are certain fundamental principles that should be followed in the design of a building heating system which is to be supplied from street mains. Although some of these apply to any building, they have been demonstrated to be especially important when steam is purchased.