Document 6RX0EYM2nxybGpr1VrvBz0z8m

of and 1936American Society Heating Ventilating Engineers Guide, Expansion may be taken care of by any, or all, of three different methods, namely, (1) the spring in the pipe including offsets and expan- sion bends, (2) the turning of the pipe on its threads and s\ving joints, and (3) the use of expansion joints. '. By the first scheme, which is the most popular method where space permits, the pipe is offset, or broken, around rooms or corners, and is hung so that the spring in the pipe at right angles to the expansion movement is sufficient to absorb the expansion. If conditions do not lend themselves to `this treatment, regular expansion bends of the U or offset type may be used. In tight places such as pipe tunnels the expansion, joint is pre ferable. See additional material on pipe expansion bends in Chapter 34. On riser runouts and radiator runouts the swing joint is used almost without exception. On high vertical risers the pipes may be reversed every five to ten stories; that is, the supply is Carried over to the adjacent return riser location and the return riser; is run over to the former supply riser location, thus making horizontal offsets in each line. Corrugated copper expansion joints also are used on risers but must be made, acces sible in case future replacement becomes necessary. PIPING CONNECTIONS AND DETAILS Piping connections may be classified into two groups: first, those suitable for any system of steam heating; second, those devised for certain systems which cannot be satisfactorily applied to any other type. There are also various details that apply to piping on the steam side which cannot be used on the returns. An installation that is designed and sized correctly and installed with care may be rendered defective by the use of improper connections, such as runouts that do not allow for expansion, thermostatic traps unprotected from scale, pressure-reducing valves without strainers, and lack-of drips at required points. BOILER CONNECTIONS Supply Boiler headers and connections have the largest sizes of pipe used in a system. Cast-iron, horizontal-type, low pressure heating boilers usually have several tapped outlets in the top, the manufacturers recommending their use in order to reduce the velocity of the steam in the vertical up takes from the boiler and to permit entrained Water to return to the boiler instead of being carried over- into the steam main where it must be cared for by dripping. Steel heating boilers usually are equipped with only one steam outlet but many engineers believe that better results are obtained by specifying that such boilers1 have two. The second outlet, usually located 3 or 4 ft back of the regular , one, reduces the velocity 50 per cent in the steam uptake. Fig. 3 shows a type of boiler connection that was used for many years and one with which some boilers are now piped. The uptakes are carried as high as possible,. turned horizontally and run out to the side of the boiler and then are connected together into the main boiler runout which drops into the top of the boiler header through: a boiler stop valve. No drips are provided on. this type of runout except a very small one which is sometimes installed on the boiler side of the stop valve. Fig. 4 shows a 572 32--Chapter -Piping for Steam Heating Systems' type of boiler connection which is regarded as superior to that shown in Fig. 3 and which is the type illustrated in the system diagrams in Chapter 31. This type is similar to that shown in Fig. 3 except that the horizontal branches from the uptakes are connected into the main boiler runout, and the steam is carried toward the rear of the boiler. The branch to the building or boiler header is taken off behind the last horizontal boiler con nection. At the rear end of this main runout, a large size drip, or. balance pipe, is dropped down into the boiler return, or into the top of the Hart ford Loop, which is described in a following paragraph. As a result, any water carried over from the boiler follows the direction of steam flow Fig. 3. Old Style Standard Boiler Connections Fig. 4. Approved Method of Boiler Connections toward the rear and is discharged into the rear drip, or balance pipe, without being carried over into the system. Return Cast-iron boilers are generally provided with return tappings on both sides; but steel boilers often are equipped with only one return tapping. A boiler with side return tappings will usually have a more effective cir culation if both tappings are used. Check valves generally should not be used on the return connection to steam heating boilers from one and two pipe gravity systems because .they are not always dependable inasmuch as a small piece of scale or dirt lodged on the seat will hold the tongue open and make the check useless. These valves also offer a certain amount of: resistance to the returns coming back to the boiler, and in gravity systems will raise the water line in the far end of the wet return several inches3; However, if check valves are omitted and the steam pressure is raised with the boiler steam valve closed, the water in the boiler will be blown out into, the return system with the accompanying danger of boiler damage. These objections are ; largely overcome with the Hartford return connection. - See.method of calculating height above water line for gravity one-pipe systems in Chapter 31.' 573