Document mB9BE4pZQmQoE1a02620OpjZO

522 CHAPTER 22 1953 Guide of 150 milinches per foot, or 600 milinches for 4 ft. If the first floor radi ators are located 3 ft above the mains, second floor radiators 12 ft above the mains, third floor 21 ft, and fourth floor 30 ft, the heads are 450, 1800, 3150, and 4500 milinches, respectively. In forced circulation systems flow is produced mechanically by means of a pump driven by electricity, steam, or other source of energy. As Hot Water Heating Systems 523 Table 1. Iron and Copper Elbow Equivalents* Fitting Iron Copper Pipe Tubing Fitting Iron Pipe Copper Tubing 1.0 Elbow, 45-deg............................ Elbow', 90-deg long turn------ Elbow, welded, 90-deg........... Reduced coupling.................... 1 Open return bend.................... 0.7 0.5 0.5 0.4 1.0 0.5 12.0 i:o 0.7 0.5 0.5 0.4 1.0 0.7 17.0 Angle radiator valve........... Radiator or convector.... Boiler or heater..................... 2.0 3.0 3.0 Tee, per cent flowing through branch: 100........................................ 50........................................ 25............................... 1.8 4.0 16.0 3.0 4.0 4.0 1.2 4.0 20.0 a The friction in one 90 deg standard elbow is approximately equal to the friction of alength of straight pipe of the same nominal size and 25 diam long. Hence, one elbow equivalent in feet of pipe equals 25 diam (in inches) divided by 12. - . Fig.1. Heads Resulting from Temperature Difference (Gravity Systems) forced circulation velocities are higher than those in gravity systems, and as the friction in a heating system varies almost as the square of the velocity, a given error in the calculation or assumption of the velocity is less im portant in a forced circulation system than in a gravity circulation system, and, consequently, it is easier to design a satisfactory forced circulation system than a satisfactory gravity circulation system. FRICTION LOSS Values' of friction loss due to flow of water in the various parts of a heat ing system must be known in order to design either gravity or forced circu lation systems. The friction loss of fittings is customarily expressed in equiv-