Document dkJQ0wQO3rKv5zdO3qyRngQq

American Society of Heating and Ventilating Engineers Guide, 1935 sufficiently before it reaches the trap so the trap will not be held shut bv too high a temperature. On down-feed systems of atmospheric, vapor and vacuum types, the bottom of the steam risers are dripped in the manner shown in Fig. 37. PROBLEMS EV PRACTICE -l.#.What is.the equivalent.length.of.run.in.a.steam-system?. .. .. _____ It is the length of straight pipe which will have the same friction and pressure drop as a shorter length of pipe of the same size with accompanying valves, tees, elbows, and other fittings will have, when both pipes are carrying the same amount of steam at the same pressure. 2 When the size of pipe is still undetermined, what arbitrary percentage is usually added to the actual length to.obtain the equivalent length? Usually 100 per cent; in other words, the actual length is doubled to allow for the added drop produced by the valves, tees, elbows, and other fittings. 3 What are the major factors to be considered in determining the flow of steam in pipes? a. The initial steam pressure available and the total pressure drop allowable between the source of steam supply and the end of the return system. The pressure drop should never exceed one half of the initial pressure. b. The maximum steam velocity allowable. When condensate is flowing against the steam, the velocity must not be so great as to produce water hammer, or hold up water in parts of the system until the steam flow is reduced sufficiently to permit the water to pass. The velocity at which disturbances take place depends upon: 1. Size of pipe. 2. Whether pipe is vertical or horizontal. 3. Pitch or grade of pipe. 4. Quantity of water flowing against steam. c. The equivalent length of run from the source of steartrsuppl.y to the farthest heating unit, with allowance for friction in pipe fittings and valves. 4 Name three fundamental considerations in designing the piping system for steam heating. a. Provision for the distribution of suitable quantities of steam to the various heating units. b. Provision for the return of condensate from the radiators and piping to the boiler. c. Provision of means for expelling air from the radiators and piping. 5 Why is the proper reaming of the ends of pipe necessary? The capacities of pipes depend upon the free area available for flow. In cutting the pipe this area may be restricted by a burr, which may decrease the capacity of a pipe more than 25 per cent in the smaller pipe sizes. 6 a. What are the major factors to be considered when selecting .a pressure reducing valve? b. How should such valve be installed? o. The initial pressure of the steam must be considered along with the desired reduced pressure. The connected load to be supplied must be known in square feet of equiva- 556 Chapter 32--Piping for Steam Heating Systems lent direct radiation or in pounds of steam per hour. For operation with a continuous load a semi-balanced or double seated valve operated by a diaphragm gives good results. Where the load is intermittent,"as in process work or with thermostatically controlled blast heaters, a so-called dead end or single seated valve should be used. , -j-jjg pressure reducing valve should be installed in a horizontal line with a gate valve 0 on each side, and with a by-pass operated by a valve. The pressure balancing pipe from the diaphragm chamber should be connected into the top or side of the low pressure main not less than 15 ft from the reducing valve. 7 What is the usual expansion allowance and how it is compensated for in heating system supply risers? The expansion of low pressure steam piping is normally taken as IK to IK.in. per 100 ft of pipe. With a five story building a double swing connection between the riser and the nrain will suffice. In buildings between 5 and 10 stories high the riser should be anchored near its center and have double swing connections to the main. For taller buildings expansion loops or riser offsets are used which are capable of handling a length of riser reaching 5 stories in either direction from the joint. The risers are anchored at each alternate 5 stories. All radiators must have double swing connections, and those con nected above where the riser is anchored must be given greater pitch to insure their having proper grade when the riser is heated. 8 Why should all boiler steam supply tappings be used full size? In order to operate at low steam velocities so the water in suspension can separate from the steam and remain in the boiler. 9 What is the Underwriters Loop or the Hartford Connection? An arrangement of piping on the returns to low pressure boilers wherein the return line is raised up nearly to the water line of the boiler and is then dropped back and con nected to the boiler return inlet; the high point is connected by a balance pipe to the steam runout from the boiler on the boiler side of all stop valves. With this loop no check valve is required, and water cannot be backed out of the boiler and into the return at a point lower than the invert of the pipe at the top of the loop. 10 What are the important factors in making radiator connections? Connections to radiators should be made as direct as possible, of proper size, with ample pitch of piping and allowance for expansion. 11 Why should careful attention be given to proper dripping and drainage of steam piping? The steam mains and risers must be quickly drained of condensate and where necessary vented of air in order to obtain a sufficient supply of steam to the radiators. Proper drainage is also necessary to insure a noiseless heating system. 12 What is the limit of pressure drop usually recommended in a vacuum system? Not over K lb (2 oz) per 100 It ol equivalent run, and not over 1 lb total drop. 13 When steam and condensation are flowing in the same direction, what is the maximum total pressure drop which should be used? The maximum total pressure drop should not exceed one half of the initial steam pressure. 14 What does a proper installation of a pressure reducing valve include? A strainer in front of the pressure reducing valve; a gate valve in front of the strainer; a gate valve after the reducing valve; a by-pass around the two gate valves, strainer, and pressure reducing valve; and a globe valve in the by-pass. Sometimes a safety valve on 557