Document 3JD8zk3XZqp6d5VnZkdJY5mXa

American Society of Heating and Ventilating Engineers Guide, 1937 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. - u 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 0 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 0 What .is the limit of pressure drop usually recommended in a vacuum system? Not over lb (2 oz) per 100 ft of equivalent run, and not over 1 lb total drop. 13 0 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 0 What does a proper installation of a pressure reducing valve include? A strainer in front of the pressure reducing valve; a gate valve in froift 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 die low pressure side and pressure gages on both sides are installed. The high pressure line should be dripped just before the high pressure steam enters the pressure reducing valve assembly. 15 0 Will a pressure reducing valve which is reducing the steam pressure from 100 lb gage to SO lb gage pass more or less steam than the same valve when reducing the steam pressure from 100 lb gage to 5 lb gage? The valve will pass practically the same volume of steam in each case as the velocity of steam flowing through an orifice shows no material increase after the reduced absolute pressure has fallen to 58 per cent of the initial absolute pressure. Because of its greater density, the weight of steam passed will be greater in the case of the reduction to 50 lb gage. Chapter 33 hot water heating systems and piping One- and Two-Pipe Systems, Mechanical Circulation, Circulators, Pipe Sizes, Forced Circulation, Effect of Variations in Pipe Sizes, Gravity Circulation, Expansion Tanks, Relief Valves, Installation Details AHOT water heating system is one in which water is the medium by which heat is carried through pipes from the boiler to the heating units. There are two general types, namely, forced circulation and gravity circulation systems. In the former the pressure head maintaining flow is produced mechanically, whereas in the latter the pressure head is pro duced by the differences in weight of the water in the flow and in the return risers. Both forced circulation and gravity circulation systems may be further divided into high or low temperature classifications. The use of high temperature water in conjunction with forced circulation permits a material reduction in the size of piping and radiation, thereby lowering installation cost. The less bulky radiation of this type of system also lends itself to the current practice of concealing or recessing the heating units. Low temperature water is considered as that which affords a heat emission per square foot of radiation of from 150 to 160 Btu, while high temperature water will deliver from 200 to 240 Btu. The fundamental rule in the design of a hot water system is that the total friction head in any circuit will equal the pressure head causing the water to flow in the circuit. This means that it is necessary to size the pipe in any circuit so that the friction loss produced by the movement of a sufficient volume of water to handle the heating load will not be greater than the available pressure head. In designing a hot water heating system, it is necessai^ to determine: 1. The heat losses of the rooms or spaces to be heated. (See Chapter 7.) 2. The size and type of boiler. (See Chapter 25.) 3. The location, type, and size of heating units. (See Chapter 30.) 4. The method of piping. 5. The type and size of circulating pump (if forced circulation). 6. Suitable pipe sizes. 7. The type and size of expansion tank. _ The unit, a square foot of equivalent direct radiation, EDR, has been used for many years for rating purposes in both steam and hot water systems, but its use, especially in hot water systems, has always resulted in complications and confusion. It is the plan of The Guide to eventually eliminate this 601