Document oDNgXVYZ9ZkeYGNb541J71g58

950 CHAPTER 36 1958 Guide 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 Refrigeration 951: compressor, with increase in evaporator temperature. , Similarly, the ca pacities of the steam ejector and centrifugal compressors increase-more rapidly than those of the reciprocating compressor with increase in evapo rator temperature. Thus, both the steam jet and centrifugal machines tend to be more self-regulating than the reciprocating. It is also evident from Fig. 19 that the steam jet equipment is best suited for operation at high evaporator temperatures. The effect of condenser temperature upon the power and capacity of the different types of compressors is shown in Fig. 20. It may be noted that the power required by the reciprocating compressor increases rapidly with increase in condenser temperature, while the power curve for the Fig. 19. Pebformance Characteristics of Compression Refrigeration Machines at Constant Speed 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 where vibration is otherwise a problem. Packed or packless shut-off valves are necessary where it may be required to isolate portions of a system. EQUIPMENT CHARACTERISTICS AND SELECTION The various types of compression systems have quite different charac teristics of capacity and power with varying evaporator and condenser temperatures, as may be noted from curves in Figs. 19 and 20. From Fig. 19 it may be observed that power requirements for the centnlugal compressor increase much more rapidly than for the reciprocating 85 90 95 100 105 110 CONDENSER TEMPERATURE, DEG FAHR Fig. 20. Performance Characteristics of Compression Refrigeration Machines at Constant Speed centrifugal compressor is relatively flat. It is also evident that the ca pacity of the steam jet compressor is independent of condenser temperature until a certain point is reached, where it drops to zero. As previously stated, steam jet equipment requires more condensing water than other tyP f compression systems. Consequently, steam jet systems are well suited to those applications where condensing water is cheap, or where condensing water is rather high in temperature. . selection of proper refrigeration equipment for any air conditioning job is of utmost importance for satisfactory results. The most important actors in the selection of the equipment are: Loads (as determined by the conditions of the space to be cooled). ' Economics (both initial and operating costs), to bemused) ^0Ca* sa^ety codes must be adhered to and influence the type of system A broad division of equipment to be used for a particular installation or