Document v1z1DYVjOLY9k9rLNVd4ZGeRY

Heating Ventilating Air Conditioning Guide 1939 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 pjpe runs horizontally or vertically, (2) the pitch of the pipe if it runs hori zontally, (3) the quantity of condensate flowing against the steam, and (4) freedom of the piping from water pockets which under certain con ditions act as a restriction in pipe size. Three factors of uncertainty always exist in determining the capacity of any steam pipe. The first is variation in manufacture, which appar. ently 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 5). The second is the reaming of the ends of the pipe after cutting, which, experiments indicate, might reduce the capacity of a 1-in. pipe as much as 28.7 per cent (Table 6). The third is the uniformity in grading the pipe line. All of the capacity tables given in this chapter include a factor of safety. However, the pipe Table 4. Comparative Capacity of Steam Lines at Various Pitches for Steam and Condensate Flowing in Opposite Directions3 Pitch of Pipe in Inches per 10 Ft Pitch or Pipe K m. Pipe Site Inches Sq Ft Rad. Based on 240 Btu a H Sq Ft Rad. Based on 240 Btu y 3 S 1 IN. Sq Ft Rad. Based on 240 Btu e a IMm. Sq Ft Rad. Based on 240 Btu 3 3 S 2 IN. Sq Ft Rad. Based on 240 Btu . 3 IN. Sq Ft Rad. Based on 240 Btu 3* 4 IN. Sq Ft Rad. Based on 240 Btu a 5 m. Sq Ft Rad. Based on 240 Btu 3 S % 25.0 12 30.3 14 37.3 18 40.4 19 42.5 20 46.1 21 47.5 22 49.3- 23 l IH 1M 2 45.8 104.9 12 18 52.6 117.2 15 20 63.0 133.0 17 23 70.0 144.5 20 25 75.2 154.0 22 27 83.0 165.0 23 28 87.9 172.6 25 29 90.2 26. 178.2 31 142.6 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 American Society of Heating and Ventilating Engineers Research Laboratory. on which Table 5 is based showed no particular defects or constrictions 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. 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 7 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. 312 ' Chapter 16. Piping for Steam Heating Systems - pgjj cent Difference in Capacity for Carrying Steam and Condensate Tables- pUE TO Variation of Pipe Size and Smoothness3 Maximum Condensation, Lb per Hour Size of PipeMinimum-- Maximum------------- Per cent variation.. Kin.- 14.00 15.20 8.6 1 In. 24.89 30.08 20.8 IK In. 45.42 52.08 14.7 IHln. 70.50 82.00 16.3 from American Society of Heating and Ventilating Engineers Research Laboratory. Table 6. Effect of Reaming Entrance to One-Inch One-Pipe Risers3 Maximum Capacity op Rlbeb Reamed entrances...... --................................... --Rounded entrances.--............................ -------------- Squared entrances........................................... .......... Three wheel cutter..................................................... Single wheel cutter-- ............................. --........... 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 Peb Cent Decrease 0.0 3.2 10.1 22.2 28.7 Data from American Society of Heating and Ventilating Engineers Research Laboratory. Table 7.' Length in Feet op Pipe to be Added to Actual Length op Run-- Owing to Fittings--to Obtain Equivalent Length Sue op Pipe Inches St'd. Elbow Side Outlet Tee Gate Valve Globe Valve Angle Valve Length in Feet to be Added to Run 2 2H 3 m 4 5 6 7 8 9 10 12 14 5 16 7 20 10 26 12 31 14 35 18 44 22 50 26 55 31 63 35 69 39 76 47 90 53 105 2 18 3 25 3 33 4 39 5 45 7 57 9 70 10 82 12 94 13 105 15 118 18 140 20 160 9 12 16 19 22 28 32 37 42 47 52 63 72 Example of length in feet of pipe to be added to actual length of run. i*..... MEASURED LENGTH. - BZ.-O 4"GATE YALtE. - 5.-0* * 4ELBOWS. - 56-0 : EQUIVALENT LEN6TH 193'-O' 313