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HEATINC VENTILATING AIR CONDITIONING GUIDE 1940 16 measured on the diameter of the pipe so as to secure a tight joint. Threads of fittings are tapped to the same taper. The number of threads per inch varies with the different pipe sizes. All threaded pipe should be made up with a thread paste suitable for the service under which the pipe is to be used. 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. 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 3Yi 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 nj^lleable 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. As in the case of pipe, there are several weights of fittings 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. Malleable iron screwed fittings for 150 lb maximum saturated steam pressure. Cast-iron screwed fittings for 125 and 250 lb maximum saturated steam pressure. Steel flanged fittings for 150 and 300 lb maximum steam service pressure. 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. Screwed fittings include: nipples or short pieces of pipe of varying lengths: couplings, usually of wrought iron only; elbows for turning angles of either 45 deg or 90 deg; return bends, which may be of either the close 336 CHAPTER 18. PIPE, FITTINGS, WELDING 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. Fittings for copper tubing are available in the soldered, flared, or com pression types. Illustrations of each of these types is shown in Fig. 2. Fittings for copper pipe of IPS dimensions are available in screwed or soldered types of connection. The compression type fitting is generally limited to smaller size tubing while the flared and soldered types are used in both large and small sizes. souxK-iYre fitting m, ROVIGIRATOB TYPC FURED-TU8MG FITTINGS FLARCO-TUGING FITTINGS Fig. 2. Copper or Brass Tubing Fittings ? ' An American Standard, ASA A40.2-1936 has been prepared to stand ardize dimensions for brass fittings for flared'copper water tubes. : Flared tube fittings are widely used in refrigerating work where SAE dimensions and a 45-deg flare render most fittings interchangeable, although for refrigeration use, thread fits and tolerances on thread gages , must be maintained within close limits. Brass fittings with S.4.E dimensions are not interchangeable with the American Standard fittings for water tubes. Ammonia pipe fittings made of cast-iron were formerly used extensively in handling refrigerants in larger installations. Replacement of ammonia by other refrigerants operating at lower pressures has seriously curtailed the market for these fittings, and the use of copper tubing with special fittings and welded steel piping has further rendered ammonia fittings obsolete. For these reasons formulation of an American Standard for these fittings was abandoned by the ASA in 1936. 337