Document wDz1VqqqxeNVbEEN4pnKQnaJd

American Society of Heating and Ventilating Engineers Guide, 1930 It should be emphasized that in any part of a system in which water from the heating units returns counter to the steam the velocity of the steam must be kept below the point where it will seriously interfere with the returning water. The maximum allowable velocity of steam for satis factory operation has been determined by the American Society of. Heating and Ventilating Engineers Research Laboratory. Table 5 gives the maximum allowable capacity and velocities of flow for up-feed one-pipe risers while Table 6 gives the maximum capacity and velocity for horizontal pipes with various pitch. Since the maximum velocity must not be exceeded in any part of the system, if silent and satisfactory operation are desired, care should be exercised to eliminate obstructions due to poor pipe, lack of or faulty reaming and improper use of pipe dope. Tables 7 and 8 give the variation in capacity of pipe due to reaming and variation in size and smoothness of pipe as determined by experiments at the American Society of Heating and Ventilating Engineers Research Laboratory. There are certain variations in manufacture which Table 6. Comparative Capacity of Steam Lines at Various Pitches3 Pitch of Pipe in Inches per 10 Ft. Pitch of Pipe--in. H ra. 1 IN. 1H IK. 2 IN. 3 IN. 4 IN. 5 IN. Pipe Sise Inches Sq. Ft. Rad. 3 iBased a aon 240 1B.tu. t Sq. Ft Rad. Based on 240 B.tu. X Sq.Ft Rad. Based on 240 B.tu. X Sq. Ft Rad. Based on 240 B.tu. s X Sq. Ft Rad. on 240 B.tu. Max.VeL Sq.Ft Sq.Ft Sq. Ft Rad. i 3Based aon 240 B.tu. X Rad. Based on 240 B.tu. 3 X Rad. on 240 B.tu. 3 > a s F 25.0 12 30.3 14 37.3 18 40.4 19 42.5 29 46.1 21 47.S 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 IM 104.9 18 117.2 20 133.0 23 144.5 25 154.0 27 165.0 28 172.6 29 178.2 31 IM 142.6 18 1S9.0 21 181.0 23 196.5 25 209.3 27 224.0 28 234.8 30 242.6 31 2 236.0 19 263.5 20 299.5 23 325.5 25 346.5 27 371.5 28 388.4 29 401.1 30 Table 7. Effect of Reaming Entrance to One-Pipe Risers3 Maximum Capacitt of Riser 24.7 lb. per hour 23.9 lb. per hour 22.2 lb. per hour 19.2 lb. per hour 17.6 lb. per hour Pea Cent Decrease 0.0 3.2 10.1 22.2 28.7 Table 8. Per Cent Difference in Capacity Due to Variation of Pipe Size and Smoothness3 Size of Pipe............................................. Maximum.. .............. ................ ............. Per Cent Variation. Maximum Condensation, Lb. per Hr. X" 14.00 15.20 8.6 . 1* 24T89 30.08 20 .'8 IX' 45.42 52.08 14.7 IX' 70.50 82.00 16.3 aData from American Society of Heating and Ventilating Engineers Research Laboratory. 342 Chapter 20--Piping for Steam Heating Systems . apparently cannot be avoided, which actually caused a 20 per cent variation in the capacity of a 1 in. pipe, as indicated by Table 8. A factor of safety has been allowed in all of the capacity tables in this chapter so that Table 8, while interesting, need not be used to discount the other .tables. Table 9 is to be used in designing one-pipe systems up to 200 ft. equivalent length of run.. For designing larger one-pipe systems where uniform distribution of steam tq all parts of the building is difficult to obtain, Table 10 shall be used. Gravity One-Pipe Down-feed System The one-pipe gravity down-feed system illustrated in Fig. 2 is a modification of the one-pipe up-feed system and the same tables apply Fig. 2. Typical Gravity One-Pipe Down-feed Steam System to it as for the up-feed system. The branches may leave the overhead main from the top, in which case the condensation drains at die end, or the branches may leave the overhead main from the bottom, in which case each branch drains the condensation, and in which case the instal lation of eccentric fittings in the overhead main may be avoided. The illustration indicates no drain at the base of the main supply .riser. When this riser is mere than very few feet from the boiler a connection from the bottom of the riser into the wet return should be made. Gravity Two-Pipe System- Two-pipe systems, Fig. 3, require-separate supply and return mains and a separate supply and return connection for each heating unit. Xike one-pipe systems, they require air valves on heating units and mains. The connection may be either at the top or the bottom of the unit, but the outlet is always__at the bottom so that all condensation will drain through this to the return mains instead of back through the inlet con- 343