Document pdO9KbDX5kJ0dwLE0YdmmdJk

American Society of Heating and Ventilating Engineers Guide, 1932 Pressure 1 lb per square inch 1 oz per square inch 1 atmosphere 1 in. water'at 62 F 1 ft water at 62 F 1 in. mercury at 62 F Metric Units 1 cm 1 in. 1m 1 ft 1 sq cm 1 sq in. 1 sq m 1 sq ft 1 cu cm 1 cu in. 1 cu m 1 cu ft 1 liter 1 kg 1 lb 1 metric ton 1 gram 1 kilometer per hour 1 gram per square centimeter . 1 kg per square centimeter (metric atmosphere) 1 gram per cubic centimeter 1 dyne 1 joule 1 metric horsepower (force de cheval) 1 kilogram-calorie (large calorie) 1 kilogram-calorie per kilogram 532 144 lb per square foot 12.0416 in. mercury at 64 F 2.309 ft water at 62 F 27.71 in. water at 62 F j 0.1276 in. mercury at 62 F ( 1.732 in. water at 62 F 14.7 lb per square inch 2116.3 lb per square foot 33.974 ft water at 62 F 30 in. mercury at 62 F 29.921 in. mercury at 32 F 0.03609 lb per square inch 0.5774 oz per square inch 5.196 lb per square foot / 0.433 lb per square inch \ 62.355 lb per square foot 0.491 lb per square inch 17.86 oz per square inch 1.131 ft water at 62 F 13.57 in. water at 62 F = 0.3937 in. = 2.54 cm = 3.281 ft = 0.3048 m = 0.155 sq in. = 6.45 sq Cm = 10.765 sq ft - 0.0929 sq m = 0.061 cu in. = 16.39 cu cm = 35.32 cu ft = 0.0283 cu m = 1000 cu cm = 0.264 gal = 2.2046 lb = 0.4536 kg = 2205 lb (avdp) = 980.59 dynes = 0.002205 lb = 0.6214 mph _ / 0.2896 in. mercury, at 0 deg C \ 0.394 in. water, at 15 C = 14.22 lb per square inch f 0.03614 lb per cubic inch \ 62.43 lb per cubic foot = 0.00007233 poundals _ / 10,000,000 ergs ~ \ 0.73767 ft-lb _ / 75 kg-m per second " \ 0.986 hp (U. S.) { 1000 gram-calories calorie) (small 3.97 Btu = 1.8 Btu per pound Chapter 39--Physical Data . 1 gram-calorie per square centimeter = 3.687 Btu per square foot 1 m"'rie P" SqUar centimeter per centi-= }l.451 Btu persquare foot perinch 1 gram-calorie per second per square centimeter (2903 Btu per hour per square foot for a temperature graduation of 1 deg C per = ! for a temperature graduation of centimeter ( 1 deg F per inch of thickness. INSTRUMENTS FOR AND METHODS OF MEASUREMENT Pressure The pressure of the atmosphere is usually measured by a mecurial barometer which, in its simplest form, consists of a glass tube about three feet long, closed at the upper end, filled with mercury and inverted in a shallow bath of mercury. The atmosphere, pressing on the exposed top of the mercury in the cistern, supports a column of mercury in the tube to a height of about 30 in. Readings are taken of the height of the column between the levels of mercury in the tube and in the cistern. The pres sure of the atmosphere is the same as the pressure exerted by this sup ported column of mercury, and in pounds per square inch, is equal to its height times 0.491 which is tjie weight in pounds of one cubic inch of mercury. At latitude 45 deg and sea level, and at a temperature of 32 F, the atmosphere will support a column of mercury 29.921 in. in height. This pressure of 14.7 lb per square inch, derived by multiplying 29.921 by 0.491, is called standard or normal barometric pressure. Pressure is usually measured by means of gages which indicate the difference between the pressure being measured and the pressure of. the atmosphere at the same time and place. A gage which indicates higher pressures than that exerted by the atmosphere is known as a pressure gage, and a gage which indicates pressures lower than atmospheric pres sure is known as a vacuum gage. The most common type of these gages contains a flexible hollow brass tube of oval cross: section, known as a Bourdon tube. When subjected to pressure, this tube tends to straighten out, and the amount of pressure is measured by a pointer motivated by this straightening and reading against a suitably graduated scale. A gage which indicates pressures slightly: above |or below that;of the atmosphere is known as a draft gage.. It is essentially a U-tiibe containing either water, kerosene, alcohol or mercury, with one leg exposed to-the air and the other connected to the point where a pressure is to be determined. When the pressure being read is equal to that of the atmosphere, the level of the liquid in the legs will be the same, indicating a zero gage pressure. When a pressure is applied to a leg, one side will fall an amount and the other will rise an equal amount. The difference in height between the two liquid levels indicates the pressure expressed in inches of the liquid used in the gage. Temperature In engineering work, mercurial thermometers are largely employed, to measure the intensity of heat. These depend on the uniform expansion of mercury to indicate changes in temperature. An amount of mercury held in a sealed tube with a bulb at one end, will rise to one definite level when immersed in melting ice, and to another definite level when immersed in boiling water. These two points are marked, and the space between them 533