Document jm8wZq2LkyYG2mozOxR4r2O79

494 CHAPTER 21 1953 Guide the counter-flowing water may produce objectionable 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 horizontally; (3) the quantity of condensate flowing against the steam; and (4) freedom of the piping from water pockets which under certain conditions act as a restriction in pipe size. Reaming Important 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. The second is the care used in reaming the ends of the pipe after cutting. The effect of both of these factors increases as the Table 3. Compabative Capacity op Steam Lines at Various Pitches fob Steam and Condensate Flowing in Opposite Directions* Pitch of Pipe in Inches per 10 Ft Velocity in Ft per Sec ' Pitch of Pipe M IN. Yi IN. 1 IN. IH IN. 2 IN. 3 IN. 4 IN. 5 IN. Pipe Si*e Inches >> >> > >> > > a O i S a O > s3 > O. O. i S ,a O > K s a O > 3 a o > i S > a O j S `3 a O > a S Capacity Expressed in Square Feet E D R 1 m m .2 25.0 45.8 104.9 142.6 236.0. 12 30.3 12 52.6 18 117.2 18 159.0 19 263.5 14 37.3 15 63.0 20 133-0 21 181.0 20 299.5 18 40.4 17 70.0 23 144.5 23 196.5 23 325.5 * 19 42.5 20 75.2 25 154.0 25 209.3 25 346.5 20 46.1 22 83.0 27 1165.0 27 j224.0 27 371.5 21 47.5 23 87.9 28 172.6 28 234.8 28 388.4 22 49.3 25 91.2 29 178.2 30 242.6 29 401.1 23 26 31 31 30 Capacity Expressed in Pounds per Hour H 6.3 12 7.6 14 9.3 18 10.1 19 10.6 20 11.5 21 11.9 22 12.3 23 1 11.5 12 13.2 15 15.8 17 17.5 20 18.8 22 20.8 23 22.0 25 22.6 26 1H 26.2 18 29.3 20 33.3 23 36.1 25 38.5 27 41.3 28 43.2 29 44.6 31 W 35.7 18 39.8 21 45.3 23 49.1 25 52.3 27 56.0 28 58.7 -30 60.7 31 2 59.0 19 65.9 20 74.9 23 81.4 25 86.6 27 92.4 28 97.1 29 100.3 30 * Data from American Society op Heating and Ventilating Engineers Research Laboratory. pipe size decreases. According to A.S.H.V.E. Research Laboratory tests, either of these factors may affect the capacity of a 1 -in. pipe as much as 20 percent. The third factor is the uniformity in grading the pipe line. All of the capacity tables given in this chapter include a factor of safety. However, 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 4 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 ft k r,, 2' Steam Heating Systems 495 length of run as distinguished from the actual length of pipe in feet. The length of mn is not usually known at the outset; hence, it may be 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. TABLES FOR PIPE SIZING FOR LOW PRESSURE SYSTEMS* Tables 5, 6, and 7 are based on the actual inside diameters of the pipe and the condensation of | lb (4 oz) of steam per square foot of equivalent direct radiation (abbreviated EDR) per hour. The drops indicated are Table 4. Length in Feet of Pipe to be Added to Actual Length of Run-- Owing to Fittings--to Obtain Equivalent Length Sub of Pipb Inches Lsngth in Fret to be Added to Run Standard Elbow Side Outlet Tee Gate Valve* Globe Valve* Angle Valve* M 1.3 3 0.3 14 7 H 1.8 4 0.4 18 10 l 2.2 5 0.5 23 12 m 3.0 6 0.6 29 15 3.5 7 0.8 34 18 2 4.3 8 1.0 46 22 5.0 . 11 1.1 54 27 3 6.5 13 . 1.4 66 34 m 8 15 1.6 80 40 4 9 18 1.9 92 45 5 11 22 2.2 112 56 6 13 27 2.8 136 67 8 17 35 3.7 180 92 10 21 45 4.6 230 112 12 27 53 5.5 270 132 14 30 63 6.4 310 152 Valve in fuQ open position. ~ rt Example of length in feet of pipe to be added to actual length of run. W*------- --: Measured Length 4 in. Gate Valve 4--4 in. ElbowB 132.0 ft D l.O.ft -- 38.0 ft ------------ -*------------- V i??."lv.^eDt..Ifneth " ,69 9ft 1 ^--. -....................-| drops in pressure per 100 ft of equivalent length of run. The pipe is assumed to be well reamed and without unusual or noticeable defects. Table 5 may be used for sizing piping for steam heating systems by pre-determining the allowable or desired pressure drop per 100 equivalent feet of run, and reading from the column for that particular pressure drop. This applies to all steam mains on both one-pipe and two-pipe systems, vapor systems, and vacuum systems. Columns B to G, inclusive, are used where the steam and condensate flow in the same direction, while Columns H and I are for cases where the steam and condensate flow in opposite directions, as in risers and runouts that are not dripped. Columns J, K, and L are for one-pipe systems and cover riser, radiator valve and vertical connection sizes, and radiator and runout sizes, all of which are based on the