Document xdaOjXr1rEk56g99BxJM9BJqE

American Society 0/ Heating and Ventilating Engineers Guide, 1936 Table 2' ^Maximum Allowable5 Capacities' of Up-Feed Risers for Two-Pipe Low'"Pressure Steam Based on A. S. H. V: E Research Laboratory Tests Pipe Sub-- Inches ___ Yblocitt----Feet per Second Pressure Drop - Ounces per 100 Ft- ......... A.'...___ ___ B ... ...... -....... C .... . x ,, 20........ ................ . ........i . .. ______ 23 ........ 1.78 . -- IK :. - .. . .27........ . .. .1.57 ...... i'A......... ...........30.:....'... . .1.48 2. . ........... 35. .... 1.33 . 2'A ... ... 38' .. 1.16 . 3. ._ 41 . . 0.95 3K7 42 0.81' 4 43 0.71 Sq Ft Radiation .D . 40 74 151 228 . 438 678 1129 ' 1548 2042 - Capacitt Btu per Hoar Lb Steam per Hour . E . F. 9550 . 10.0 17,900 . 18.45 36,500 37.65 55,200 57.0 106,100 . 109.5 164,100: . 169.4 273,500 282.2 375,500 : 495,000 387.0 510.5 vi ........................ INSTRUCTIONS FOR USING TABLE 2 r.-.:'1. The capacities given in this table should never be exceeded on-two-pipe risers. 2. Capacities are based on J^-lb. condensation per square foot equivalent radiation and actual diameter of standard pipe. - ' ,3::An pipe'should he.well reamed and-free from constrictions. Fittings should be up to size. (See Tables.4 and 5.) condensate is flowing, and the pressure* drop in the pipe. Where the quantity of condensate is limited and is flowing in the same direction as the steam, only the pressure drop need be considered. When the con densate must flow against the steam, even in limited quantity, the ve locity of the steam must not exceed limits above which the disturbance between the steam and the counter-flowing water may produce object ionable sounds, such as: water hammer, or may result in the retention of water in certain parts of the system until the steam flow is reduced sufficiently to permit the water to pass. The velocity at which such disturbances take place is a function of (1) the pipe size, whether the pipe runs horizontally or vertically, (2) the pitch of the pipe if it runs, hori zontally, and (3) the quantity of condensate flowing against the steam. Two factors of uncertainty always exist in determining the capacity of any steam pipe. The first is variation in manufacture, which apparently cannot be avoided and which caused an actual difference of 20 per cent in the capacity of a 1-in. pipe in experiments carried on at the A.S.H.V.E. Research Laboratory (Table 4). The second'is the reaming of the ends of the pipe after cutting,, which, experiments indicate, might reduce the capacity of a Inn. pipe as much , as 28.7 per cent. (Table '5) . All of the capacity tables given in this chapter include a factor of safety. However, the pipe on which Table 4 is based showed no particular defects or con strictions on the inside, and the factor Of Safety referred to does not cover abnormal defects Or constrictions nor does it cover pipe not properly reamed. Chapter 32--Piping for Steam Heating Systems Table 3. Comparative Capacity of Steam Lines at Various .Pitches* Pitch of Pipe in Inches per 10 Ft ................................. ; Pitch of Pipe X IN. Pipe Sise Inches Sq Ft Rad. Based on 240 Btu > 1 2 M IN. Sq Ft Rad. Based on 240. Btu --i i s 1 IN. 1H IN- Sq Ft Rad. Based on 240 Btu Sq Ft >1 Rad. Based 2 on 240 Btu Max.Vel. 2 m. 3 IN. 4 IN. - .5 IN..-. Sq Ft Rad. Based on 240 Btu 1 2 Sq Ft Rad. Based' on 240 Btu a 2 Sq Ft Rad. Based on 240 Btu MS 2 SqFt Rad. :S-. Based' on 240 Btu S3 2 25.0 12 30.3 14 37.3 18 40.4 19 42.5 20 46.1 21 47.5 22 49.3 23 45.8 12 52.6 15 63.0 17 70.0 20 75.2 22 83.0 . 23 87.9 25 90.2 26 114 104.9 18 117.2 20 133.0 23 144.5 25 154.0 27 165.0 28 172.6 29 178.2 31 lH 2 142.6 18 159.0 21 181.0 23 196.5 25 209.3 27 224.0 28 234.8 30 242.6 31 236.0 19 263.5 20 299.5 23 325.5 25 346.5 27 371.5 28 388.4 29 401.1 30 Data from A.S.H.V.E. Research Laboratory. Equivalent Length of Run All tables for the flow of steam in pipes, based on pressure drop, must allow for the friction offered by the pipe as well as for the additional resistance of the fittings and valves. These resistances generally are stated in terms of. straight pipe; in other words, a certain fitting will produce a drop in pressure equivalent to so many feet of straight run of the same size of pipe. Table 6 gives the number of feet of straight pipe usually allowed for the more common types of fittings and valves: In all pipe sizing tables in this chapter the length of. run refers to the equivalent length of run as distinguished from the actual length of pipe in feet. The length of run is not usually known at the outset; hence it is necessary to assume some pipe size at the start. Such an assumption frequently is considerably in error and a more common and practical method is to assume the length of run and to check this assumption after the pipes are sized. For this purpose the length of run usually is taken as double the actual length of pipe. Table 4. Per Cent Difference in Capacity for Carrying Steam and Condensate Due to Variation of Pipe Size and Smoothness3 Maximum Condensation, Lb per Hour Size of pipe Minimum. .. Maximum... Per cent variation Hln. 14.00 15.20 8.6 1 In. 24.89 30.08 20.8 - IX In. . . 45.42 52.08 14.7 IX In. 70.50 82.00 16.3 Data from American Society of Heating and Ventilating Engineers Research Laboratory. Table 5. Effect of Reaming Entrance to One-Inch One-Pipe Risers* Maximum Capacitt op Riser Per Cent Decrease Reamed entrances Rounded entrances Sauared entrances Three wheel cutter Sineie wheel cutter '- 24:7 lb per hour 23.9 lb per hour 19.2 lb per hour 17.6 lb per hour 0.0 32 10.1 22 2 28.7 Data from American Society of Heating and Ventilating Engineers Research Laboratory. 561