Document Vzy2ojL8rYBd5K69JLO9m7qN

HEATING VENTILATINC AIR CONDITIONING GUIDE 1944 screwed or flanged elbows or with arcs of. circles having radii five to six times the pipe diameter. Use of welding elbows with radii of 134 times the pipe diameter will decrease the end thrusts somewhat but will raise the fiber stress correspondingly. All risers must be anchored and safeguarded so that the difference in length when hot from the length when cold shall not disarrange the normal and orderly provisions for drainage of the branches! Proper anchoring of piping is especially necessary with light-weight radiators, to allow for freedom of expansion in order that no pipe strain will distort the radiators. When expansion strains from the pipes are permitted to reach these light metal heaters they usually emit sounds, of distress which are exceedingly troublesome. HANGERS AND SUPPORTS Heating system piping requires careful and substantial support. Where changes in temperature of the line are not large, such simple methods of support may be utilized as hanging the line by means of rods or perforated . strip from the building structure, or supporting it by brackets or on piers. When fluids are conveyed at temperatures of 150 F or above, however, hangers or supporting equipment must be fabricated and assembled to permit free expansion or contraction of the piping. This can be accom plished by the use of long rod hangers, spring hangers, chains, hangers or supports fitted with rollers, machined blocks, elliptical or circular rings of larger diameter than the pipe giving contact only at the bottom, or trolley' hangers. In all cases, allowance should be made for rod clearance to permit swinging without setting up severe bending action in the rods. . For pipes of small size, perforated metal strip is often used. For horizontal mains, the rod or strip usually is attached to the joists or steel work of the floor above. For long runs of vertical pipe subject to con siderable thermal expansion, either the hangers should be designed to prevent excessive load on the bottom support-when expansion takes place, or the bottom support should be designed to withstand the entire load. THREADING PRACTICE In all threaded pipe for heating and ventilating installations the American Standard taper pipe thread, ^..5.^4. B2.1-1942 is used. This thread is cut with a taper of 1 in 16 measured on the diameter of the pipe so as to secure a tight joint. The number of threads per inch varies with the pipe size. Threads for fittings are the same, except that it is regular practice to furnish straight tapped couplings for Schedule 40 pipe 2 in. and smaller. For steam pressures in excess of 25 lb per square inch, it is recommended that taper tapped couplings be used to obtain a tight joint. These may be secured by ordering line pipe8 which is used for oil piping, the couplings of which are provided with taper-tapped threads and may be used with regular mill-threaded standard weight pipe. Thread lengths should be in accordance with A.S.A. B2.1. Right-hand threads are used unless otherwise ordered. To facilitate drainage, some elbows have the *See API Specification SLfor Line Pipe, American Petroleum Institute, 330 I CHAPTER 17. PIPE, FITTINCS, WELDINC thread tapped at an angle to provide a pitch of the connecting pipe of 34 in. to the foot. These elbows are known to the trade as pitch elbows and are commercially available. -All threaded pipe joints should be made up with a thread paste suitable for the service for which the pipe is to be used. TYPES OF FITTINGS Fittings for joining the separate lengths of' pipe together are made in a variety of forms, and are either screwed or flanged, the former being generally used for the smaller sizes of pipe up to and including 3J4 in., and the'latter for the larger sizes, 4 in. and above. Screwed fittings of large size as well as flanged fittings of small size are also made and are used for certain classes of work at the proper pressure. The material used for fittings is generally cast-iron, but in addition to this, malleable-iron, steel and steel alloys are also used, as well as various grades of brass or bronze. The material to be used depends on the character of the service and the pressure. Malleable iron fittings, like brass fittings, are cast with a round instead of a flat band or bead, or with no bead at all. Fittings are designated as male or female, depending on whether the threads are on the outside or inside, respectively. Screwed galvanized fittings are made according to the 150 lb American Standard. As in the case of pipe, several weights of fittings are manufactured. Recognized American Standards for the various weights are as follows: Cast-iron pipe flanges and flanged fittings for 25 lb (sizes 4 in. and larger), 125 lb, and 250 lb maximum saturated steam pressure, A.S.A. B16b2, B16a, and Bl6b respectively. Malleable iron screwed fittings for 150 lb maximum saturated steam pressure, A.S.A. B16c. Cast-iron screwed fittings for 125 and 250 lb maximum saturated steam pressure, A.S.A. B16d. Steel flanged fittings for] 150 and 300 lb maximum steam service pressure, A.S.A. B16e. The allowable cold water working pressures for these standards vary from 43 lb for the 25 lb standard to 500 lb for the 300 lb steel standard. War standard ratings in effect for the duration of the emergency now permit higher ratings for certain sizes of the 125 lb cast-iron flanged fitting standard, and for 300 lb steel flanges and flanged fittings than are shown in the regular American Standards mentioned previously. Screwed fittings include: nipples or short pieces of pipe of varying lengths; couplings of steel or wrought-iron; elbows for turning angles of either 45 deg or 90 deg; return bends, which may be of either the close or open pattern, and may be cast with either a back or side outlet; tees; crosses; laterals or Y branches; and a variety of plugs, bushings, caps," lock-nuts, flanges and reducing fittings. Reducing fittings as well as bushings, both of which are used in changing from one pipe size to another, may have the smaller connection tapped eccentrically to permit free drain age of the water of condensation in steam lines or free escape of air in water lines.