Document 8Vq2Q3BmQ8kd4jbD20QbMwMZe

American Society of Heating and Ventilating Engineers Guide, 1935 the 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. s 15 f Will a pressure reducing valve which is reducing the steam pressure from 100 lb gage to 50 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 Ttco-Pipe Systems, Selecting Pipe Sizes, Forced Circu lation, Effect of Variations in Pipe Sizes, Gravity Circulation, Mechanical Circulation, Expansion Tanks, 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. The fundamental rule in the design of a hot water system is that the total friction and resistance head in any circuit must equal the pressure head causing the water to flow in the same circuit. In designing a hot water heating system, it is necessary 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. Suitable pipe sizes. 6. The type and size of circulating pump (if forced circulation). 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 empirical expression and to substitute a logical unit based on the Btu. The Mb, the equivalent of 1000 Btu, and the Mbh, the equivalent of 1000 Btu per hour, which have been approved by the A.S.H.V.E., are used in this chapter on hot water systems to replace the square foot of radiation formerly used. ONE- AND TWO-PIPE SYSTEMS Pipe systems may be divided into two general types, namely, two-pipe and one-pipe systems. In a two-pipe system the piping is arranged so that the water flows through only one radiator during a circuit through the system, so that all radiators are supplied With water at practically the same temperature as that in the boiler. In a one-pipe system, the water flows through more than one radiator during its circuit. In that case, the 559