Heating and ventilating buildings : a manual for heating engineers and architects . point, waterexpands parts in 100, or over 4 per cent. The forceof expansion is nearly irresistible, and the increase in volumedue to it must be provided for, so asnot to produce a dangerous press-ure. The method ordinarily adopted con-sists in the use of a vessel called anexpansion-tank, whose cubical contentsmust be somewhat greater than onetwentieth of the total cubical contentsof heater, pipes, and radiators. Itmust be connected to the heating sys-tem in such a way as to receive the in-crease in volume,
Heating and ventilating buildings : a manual for heating engineers and architects . point, waterexpands parts in 100, or over 4 per cent. The forceof expansion is nearly irresistible, and the increase in volumedue to it must be provided for, so asnot to produce a dangerous press-ure. The method ordinarily adopted con-sists in the use of a vessel called anexpansion-tank, whose cubical contentsmust be somewhat greater than onetwentieth of the total cubical contentsof heater, pipes, and radiators. Itmust be connected to the heating sys-tem in such a way as to receive the in-crease in volume, and should be placedon a level somewhat above that of thehighest radiating surface. If there is to be no sensible increasein pressure due to expansion the tankis connected with the outside air by avent-pipe, and in this case the pressureinside will be atmospheric ; the pressure on the heating system will depend on the distance from thewater-level in the tank, each foot corresponding to poundsper square inch ( feet being equivalent to one pound ofpressure at 212° F.).. Fig. 156. Expan-sion-tank. SETTINGS AND APPLIA NCES 189 In case a pressure in excess of the atmosphere is required,the vent pipe is closed and a safety-valve attached which willopen when the pressure reaches the desired point. By increas-ing the pressure on the system the boiling temperature of thewater will be much increased, and hence it will be possible tomaintain a higher temperature throughout the system. Asshowing the increase in temperature of the boiling point withexcess of pressure, the following table is inserted : Pressure. Temperature of Pounds Boiling Point per sq. in. Equivalent Head, (degrees F.), above in Feet. Atmosphere. O O 212 5 12 22S 10 24 240 15 37 250 20 49 259 25 61 267 30 74 274 35 87 28o 40 ICO 287 45 3 292 50 125 297 55 i37 302 60 I51 307 70 i77 316 80 205 324 90 237 332 100 6d 338 • 125 327 352 150 393 365 i/5 469 378 200 54o 388 Pressure systems of hot-water heating were
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