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806 CHAPTER 36 1951 Guide ant ahead of the expansion valve. If the evaporator is to be located at a higher elevation than the condenser or receiver, account should be taken of the pressure drop for each foot of static liquid lift. Approximate values are 0.26 psi per foot for ammonia, 0.57 psi per foot for Freon-12, 0.51 psi per foot for Freon-22, and 0.64 psi per foot for Freon-11. Where there is a possibility of vaporization of some of the liquid before reaching the ex pansion valves, means for subcooling should be provided. Table 6. Maximum Tons of Compressor Capacity fob Fbeon-12 Lines (Only for temperatures indicated) Line She. Inches i OD I IPS 1 OD i IPS i OD i IPS If OD 1 IPS 11 OD li IPS If OD if IPS 2f OD 2 IPS 2f OD 2f IPS 3f OD 3 IPS 3f OD 3J IPS 4f OD 4 IPS 5 IPS 6 IPS 8 IPS 10 IPS 12 IPS . Suction Lines Based on 105 F Condensing Temperature Dischabos Lanes Pd Pressure Drop per 100 Ft Equivalent Length at 40 F Saturation Condensing Temperature i 0.14 0.17 0.25 0.35 1 0.20 0.24 0.35 0.45 2 0.28 0.34 0.51 0.65 3 0.35 0.42 0.62 0.79 4 0.41 0.49 0.73 0.93 6 0.45 0.54 0.81 1.03 115 F 1.43 1.87 90 F 1.15 1.50 0.55 0.68 1.26 1.43 0.76 0.94 1.80 2.01 1.10 1.35 2.57 2.89 1.34 1.65 3.17 3.54 1.58 1.92 3.76 4.17 1.75 2.12 4.15 4.60 2.97 3.26 5.05 5.29 2.38 2.62 4.05 4.25 2.21 2.70 3.40 4.05 3.12 3.82 4.78 5.75 4.45 5.37 6.79 8.10 5.50 6.72 8.42 10.12 6.38 7.68 9.77 11.6 7.05 8.48 10.8 12.8 7.72 9.16 10.92 12.5 6.19 7.35 8.75 10.0 6.12 7.66 12.0 12.0 8.60 10.9 17.1 17.1 12.1 15.3 24.0 24.0 15. i 19.2 30.1 30.1 17.4 32.2 34.6 34.6 19.2 24.5 38.2 38.2 19.2 20.6 32.2 32.2 15.3 16.5 25.9 25.9 19.1 20.9 27.8 30.2 27.2 29.4 39.7 43.2 38.2 42.3 55.7 61.0 47.8 51.8 69.8 76.1 55.0 60.0 80.3 87.0 60.7 66.2 88.7 96.0 51.5 54.5 72.0 78.8 39.8 43.8 57.6 63.3 38.6 40.7 71.3 126 55.2 . 58.6 100 183 78.0 83.0 141 257 97.3 103 176 322 111 118 203 366 123 130 224 . 403 . 95.8 101.6 171.5 266 77.1 81.6 137.8 214 211 297 422 - 523 602 664 461 370 352 503 712 887 1024 1130 725 582 550 780 1106 1373 1582 1748 1041 836 Since a reduction of suction pressure at the compressor results in an appreciable reduction in capacity and more power input per ton of refrigera tion, great care should be given to the proper sizing of suction lines between the evaporator and the compressor. Although comparatively high veloci ties, 500 to 5000 fpm, may be used, the optimum value will depend upon the refrigerant and the operating pressure range. Since return of the oil to the compressor must be considered in the case of Freon and methyl chloride, for these refrigerants the minimum velocity should be 500 fpm for horizontal runs and 1000 fpm for vertical runs. For the Freons, the Refrigeration 807 usual design velocities range between 1000 and 2000 fpm. Too high velocities create noise problems and excessive pressure drops. The total pressure drop in the suction line should be between one and two psi, if the velocity can be kept to within the specified limits. Compressor discharge or hot gas lines may be designed with velocities from 1000 to 5000 fpm, except for dense gases such as carbon dioxide, where noise considerations will reduce the upper limit. A pressure drop of 2 to 4 psi is recommended for the discharge lines. Extensive tables are available in the literature for the determination of pressure drops through refrigerant lines with various refrigerants. The capacities listed in Tables 5, 6 and 7 are published in ACRMA Equipment Standards-1946, of the Air Con ditioning and Refrigerating Machinery Association, and are used by permis sion. Table 5 shows the tonnage capacity normally allowed for Freon-12 liquid lines per foot equivalent length of pipe, and Table 6 the maximum tonnage for suction and discharge Freon-12 lines. Table 7 presents suc tion-line capacity factors for equal pressure drop. Table 7. Approximate 'Suction-line Capacity Factors for Equal Pressure Drop of Freon-12 Saturated Suction Temperature, F. 50 40 50 20 10 0 -10 -20 Factor......................... 1.09 1.00 0.92 0.86 0.80 0.74 0.66 0.56 ACCESSORIES Dehydrators, oil separators, strainers, vibration eliminators, sight glasses, and various types of valves are accessories frequently needed for the proper installation and operation of refrigeration systems. Refrigerant-line de hydrators or dryers usually consist of copper containers fitted with tubing connections at either end, and contain a desiccant such as silica gel, acti vated alumina, or calcium chloride. The liquid refrigerant is circulated through the dryer during operation of the system, and the moisture content of the refrigerant charge is thuskept to a minimum. Oil separators are installed between the compressor and condenser to prevent excessive oil removal from the compressor crankcase and its passage into the condenser and evaporator. The oil is separated from the gaseous refrigerant by gravity during its passage through a chamber of sufficient size to reduce the velocity. A float-operated valve maintains a maximum oil level in the separator, and additional oil is forced by pressure difference through a line back to the crankcase. Screen strainers are frequently installed in the liquid line piping before solenoid valves and expansion valves, as well as before regulating valves in water lines leading to water cooled condensers. Sight glasses which permit visual inspection of the condition of the refrigerant are sometimes installed on factory assembled commercial unit systems. It is particularly advisable to place such a fitting before the expansion valve, if the evaporator is located above the condenser. Flexible vibration eliminators, usually consisting of a bellows design covered with woven copper wire, are sometimes installed in copper lines where units such as compressors are installed on flexible mountings, or