CHAPTER VI REFRIGERATING SYSTEMS. (Part 5)

unit has proven more successful comnierciall>- in Europe than in the United States. Valves. — The suction and discharge ^'alves should be de- signed for service, quietness, positive opening and closing ac- tion, and efficiency. The suction vahe is usualU' simi)ly a port or slot in the cylinder wall which is uncovered b- the piston during its relatively slow rate of travel at the end of the stroke. This type of valve has a relatively low efficiency but is free from service troubles, operates quietly, and is positive in action. The port valve has a loss in efficiency due to the necessity of producing a vacuum in the cylinder, as the top of the piston returns on the suction stroke. The gas rushes in the cylinder at the end of the stroke during the short interval of time that the port is unco'ered by the piston sometimes causing wire drawing, a further loss in efficiency. The port valve c;in be used to good advantage on com- pressors with lapped ])istons, as some difficulty has been expe- rienced in using piston rings which must pass over ports in the cylinder walls. A floating val-e of the poppet type is used in the pistons of some of the larger compressors. These valves have not proven so successful as the port type, as a small particle of scale, sand, carbon or dirt can be de])osited on the seat and will prevent the valve closing tightly. This frecpiently hap- pens on a new machine and is prevented to a certain extent by placing a fine mesh screen in the suction line of the com- pressor. Some designs use a slight rotating movement of the cyl- inder itself to uncover ports. Many varieties of discharge valves are used. These are simph' check valves permitting low-pressure gas to enter the cylinder on the suction stroke. The poppet type valve has proven successful with a light spring to assist in closing. Disc steel valves are also used. These are more difficult to manufacture than the poppet type, however the' make less noise. REFRIGERATING SYSTEMS 167 The steel spring flapper valve is used to a considerable extent. These valves require very close limits in manufacture. They give good service once they are assembled properly, and are not easily affected by corrosion or dirt. The discharge valve should be capable of opening more than the normal lift, in order to discharge liquid refrigerant or lubricant which is sometimes pumped by the compressor. An important feature to be considered in valve design, is to construct a valve which Avill give service for years without requiring adjustments or service of any kind. A service call is quite expensive and with most of the refrigerating gases in common use, such repairs can only be made by a trained serv- ice man. This is probably the fundamental reason for using port suction valves even at large loss in ef^ciency, by some of the most successful manufacturers. Shut-off valves are very important in order to facilitate re- pairs to a certain part of the refrigerating system. It is customary to use three of these valves, one on the suction or inlet line to the compressor, one on the discharge line between the compressor and condenser, and the third between the con- denser and expansion valve. The valves near the compressor usually have double seats so that they nia- be closed against a gauge or charging connection. It is important to have the valve stem opening limited by a stop to prevent backing out the stem and thus losing some of the refrigerant. When the refrigerating system is not used for a period of weeks, it is sometimes advisable to close the two valves on the compressor, suction, and discharge lines, to prevent loss of refrigerant through the packing gland. Alco Liquid Control Valve. — Fig. 19 is a cross-section of the automatic liquid control valve manufactured by the Alco Valve Company, at St. Louis, Mo. The liquid refrigerant enters at F. In operation the valve needle J opens from the valve seat G and the liquid refrigerant discharges through tube K. These discharge tubes are furnished in different sizes for different capacity machines. Expansion of the refrigerant is prevented in the valve body by using the small discharge tube K. It is claimed that this 168 HOUSEHOLD REFRIGERATION feature eliminates the following troubles experienced with the regular type expansion valve. 1. Frost forming on the valve. 2. Water freezing on the diaphragm. 3. Oil congealing in the valve. 4. Scoring of pin or seat. FIG. 19.— CROSS SECTION ALCO LIQUID CONTROL VALVE. American Automatic Expansion Valve. — Fig. 20 shows the automatic expansion valve made by the American Radiator Company of Buffalo, N. Y. These valves are designed for use with the following re- frigerants : Methyl chloride, sulphur dioxide, ethyl chloride, or any refrigerant not having a detrimental effect on brass. Fig. 21 is a sectional view of this valve. Adjustment is made by turning the adjusting screw, regulating the spring pressure against the bellows. The valve closes against pressure, thereby eliminating chattering and wire drawing, and making the valve seat self- cleaning. Pressure is on the outside of the bellows, a desirable con- struction feature. REFRIGERATING SYSTEMS 169 Valves are supplied with 3/8-inch pipe thread or flanged connections. FIG. 20.— AMERICAN AUTOMATIC EXPANSION VALVE. FIG. 21.— SECTIONAL VIEW OF AMERICAN AUTOMATIC EXPANSION VALVE. American Float Valve and Refrigerating Section. — Fig. 22 shows the float valve which may be used either as a low or high pressure float. 170 HOUSEHOLD REFRIGERATION The float is cylindrical, thereby making the vah'e more compact than is the case when the nsual bulb t} pe is used. FIG. 22.— AMERICAN FLOAT VALVE. A new style of domestic refrigerating section is now manu- factured as in Fig. 23. This section is made in two types, one as illustrated, containing the float chamber, and a similar type FIG. 23.— AMERICAN REFRIGERATING SECTION REFRIGERATING SYSTEMS 171 without the float chamber. These are made for fi'e or seven ice travs, each tray containino- eig'ht cubes, one cube wide and eight cubes dee]). FIG. 24.— A.[ERIC AX RKFK ICERATIXG SKCTIOX IXSTAT.LKD. Fig. 24. shows one of these refrigerating sections installed in a cabinet. This design gives more space in the refrigerator for the storage of food than cooling units of conventional design. Flow of Air Through Orifices. — Table LX gives the amount of free air in cubic feet which will flow through circu- lar orifices in a receiver into air at atmospheric pressure, cor- responding to various air gauge pressures in pounds per square inch in the receiver. The diameter of the orifices varies from 1/64 in. to 2 ins. 172 HOUSEHOLD REFRIGERATION V^t^oof^i^ ^ ,— c CM ■* lO t^ vO r^ M ^ VOU^ O _ ,-1 (^i rr, -rf \D <-> ,_ IT) .-' VO LO . . ■ _• • ■ (NJ 00 rt K CO ^ 5 5^, .9 S ^ ,-. C^l ro t U-, 00 U-< 00 ro O O oU-'^ONt^OO • ^ t< O On <^ <^ t^ £° Si S ro CO ^ ^ t^ . • • • ^■ Tt CNl O ^ OO'^MSLO 2orO'^"°° _:^H oor~» uo ^ Tj- On 00 ■^ . . • ■ ^" t-»; »-«' vri CM N vO ro (M 00 O 00 , cv] lo r^ o Ht^ " 00 .... (M O <~^ ^ ^ ^ ^ CM Tt VO On \0 l^ t^ o PO Tj- 00 VO .... (M On •— ' r^ ^ S; (VI r<ovr) 00 ro ro f^J _ ro ro fO CM . . . . ^^ ' —Iio^uS'-'OCMioO ^^F^SoN^fovps I ro u^ t^ ^ On On ^ '^ ^ U^ ?0 Tt NO On n£) "^ O CM O CM CC vj, i^ ^ 00 o 3^ J>J ^ ^ U-) VO c^i o r^ .-H (M -^ VO 00 ^^00 fo ON NO to ;^ 00 "^ " _.. ,-% CM On NO "-O CM . \— I CV) ro lO l^ On CM 00 rO -* 00 . . . ■ ■ • •^r'^cOr^vnvDCMOOO S CM ^ ro 22 ."S ^ ,-1 CM rO '^ ^ 00 ,,-irO"^vOt^ •^^•;^^^^^ §?- QO REFRIGERATING SYSTEMS 173 Temperature Control. — The automatic temperature control is an important part of the refrigerating system. The food compartments should be maintained at a tempera- ture never warmer than 50° F. and never colder than 40° F. These temperature limits have been definitely established by experience. Perishable foods keep well at a temperature below 50° F. Food compartment temperatures below 40° F. will cause unnesessary heat losses even with a well-insulated cab- inet, and the outside surface of the cabinet will frequently be damaged by sweating. The automatic control should be arranged to freeze water or desserts in a reasonable length of time, and to constantly maintain the food compartment temperatures between 40° and 50° F. It is desirable to freeze water or desserts in less than the shortest time interval between meals which is about six hours. An average brine temperature of 20° F. will freeze water in the ordinary cube form in from four to six hours. The tem- perature should not vary more than four degress from thi^i value. It is more difficult to freeze desserts than water, espe- cially if the ice tray grids are removed. Some of the first mechanical refrigerators sold had the Hquid tube of the thermostat line suspended in the cold air flue. This liquid tube was connected by tubing to a diaphragm or metal bellows which operated the motor switch. A 1/4-hp. motor was generally used and this required a quick make and break type of switch. This was called the food compartment temperature control system. Some of the volatile liquids used in these thermostat sys- tems were : Sulphur dioxide, methyl chloride, ethyl chloride, and ether. The usual method of operating the switch is by means of a violatile liquid. This liquid is trapped in a closed gas system, so that the liquid tube itself is always immersed in the brine or in close contact with the place where the tempera- ture is to be regulated. The diaphragm or metal bellows can be placed above or below this liquid trap. The gas pressure in the closed system is always definitely determined by the temperature of the volatile liquid. The switch can be adjusted 174 HOUSEHOLD REFRIGERATION to operate at any desired temperature, within the working range of the liquid used. An improvement in the l:)rine temperature regulating sys- tem is to use an automatic damper in the cold air flue. This FIG. 25.— PEXX ELECTRICAL CONTI^OL. damper opens and increases the air circulation when the food compartment temperature increases. Another method of improving this temperature control, is to have the liquid tube located close to the last turns of the evaporating coil. Then if the evaporating coil frosts through, the liquid controlling the temperature in the thermostat will be rapidly cooled, thus stopping the compressor. REFRIGERATING SYSTEMS 175 Other manufacturers use a temperature control partly in- fluenced by the temperature of the brine and partly by the temperature of the circulating air. This kind of regulation has advantages of both of the systems previously described. Some machines are operated by a time clock. The clock operates a switch and can be set for a certain number of cycles per day. Usually this type of control is adjusted for a summer or winter condition. This system does not com- pensate for cold nights and gives rather unsatisfactory food compartment temperature regulation. Some switches are operated by using a bimetallic thermo- stat. The small temperature differential, usually from 4° to 10° F., makes the design of a bimetallic thermostat a difficult problem. Swatches of this type have not proven a success commercially. An improvement in the bimetallic sw'itch is being used now. It consists of mounting to a bimetallic member a glass tube, containing a small amount of mercury which flows from one end to the other. In this way a quick make and break contact is secured. These tubes have the air exhausted from them and contain an inert gas so that any arcing will not affect the mercury or terminal contact points. Fig. 25 show^s a switch made by the Penn Electric Machine Co., of Des Moines, la. This swutch is provided with a bellows type diaphragm, which can either be filled with a volatile fluid or attached to a bulb, which contains the volatile fluid and which causes the diaphragm to expand, closing the switch contacts when the temperature increases to the predetermined amount. The switch may be placed inside or outside the refrigera- tor. When placed outside, the bulb containing the volatile fluid is inside at the desired location for proper temperature control. This installation simplifies the wiring connections. The contacts are of the two-pole double break per line type. The swatch is approved by Underwriters for use on motors up to 5 hp., 3-phase, 550-volts. This type switch is compact, easily installed, and conven- ient for wiring. 176 HOUSEHOLD REFRIGERATION Thermostat Operation. — Figs. 26 and 27 show the opera- tion of a volatile liquid thermostat. The volatile Hquid is contained in a tube immersed in the brine. Sufficient liquid is placed in this tube so that at the highest operating temperature there will still be liquid in the thermostat bulb. In this way, the pressure in the thermostat line is always the corresponding pressure for the temperture of the liquid in the bulb. (3A5 AT HIGH PRESSURE. THERMOSTAT BULB M TEMP 24 F brihe: tank METAL BELLOWS RELEASED SWITCH CLOSED 5PRIHQ HIGH PRESSURE IN thermostat Lm.E CL05E5 SWITCH AGAINST SPRING FIG. 26.— OPERATION OF VOLATILE LIQUID THERMOSTAT. In Fig. 26 the brine temperature has increased to 24°, vaporizing some of the liquid in the thermostat bulb and in- creasing the gas pressure, until finally the metal bellows ex- pands against the spring, closing the motor switch. The motor then operates the compressor cooling the brine. The thermostat bulb is cooled decreasing the gas pressure in the thermostat system. The gas pressure is decreased as gas is condensed into liquid form in the thermostat bulb. REFRIGERATING SYSTEMS 177 Finally the pressure is lowered to a pressure so that the spring will compress the metal bellows and open the motor switch. By adjusting the compression of the spring, the motor may be started or stopped at any desired brine temperature. When too much liquid is charged into a thermostat sys- tem of this kind, the pressure will be a function of the thermo- GAS AT LOW PRESSURE THERMOSTAT BULB Mtehp ig°p BRINE TANK HETAL BELLOWS CONTRACTED SWITCH OPEN SPRING* LOW PRESSURE IN THERMOSTAT LIME PERMITS SPRiNQ TO OPEH SWITCH FIG. 27.— OPERATION OF VOLATILE LIQUID THERMOSTAT. Stat line temperature and the control will not operate satis- factorily. If the volatile liquid charge is too small, all the liquid will vaporize at the higher brine temperature and the control will not function properly. Air or foreign gases in the thermostat system will produce an abnormally high pressure at all times. Oil in the thermo- stat will cause a sluggish action. 178 HOUSEHOLD REFRIGERATION Water Controls. — When a water-cooled condenser is used with the compression ty])e household machine, it is desirable to have the following controls. 1. Open the water valve when the compressor starts to operate. 2. Close the water valve when the compressor shuts down. 3. Regulate the amount of water supplied to the condenser com- pensating for a warmer or colder tap water temperature. 4. Regulate the amount of water supplied to compensate fur different loads on the compressor. 5. Compensate for different water supply line pressures. 6. Prevent the compressor from operating when the water sup- ply fails. 7. Permit the compressor to function normally when the water supply is again available. A method of water control in common use is to open, close, and regulate the water valve l)y means of a diaphragm or metal l)ellows responsive to the condensing pressure. The valve is set to open at a certain pressure slightly higher than the pressure ever obtained in the condenser dur- ing the inoperative part of the c}cle. An increase in con- densing i^ressure will open the water valve still more. This increase in condensing pressure may be due to an increased load on the compressor or to a higher tap water temperature or to a decrease in the water supply line pressure. Another system of water control is to use a water valve opened and closed 1)' means of a solenoid coil. This coil is placed in the motor circuit and holds the A'alve open while the compressor is operating. This system does not compen- sate for dififerential water tem])eratures and changes in the refrigerating load. A water cooling system used to some extent consists of a val-e opened l)}' the centrifugal force of weights mounted on the compressor or motor shaft. This gives a control function- ing in a wav similar to the electric val\e but entirely mechan- ical in operation. This system does not regulate the amount of water supplied, in accordance with the requirements due to changes in temperature, pressure, and load. A dead w-ater tank has been used to some extent. The condenser is immersed in a rather large tank of water. Dur- ing the inoperative part of the cycle, this water is cooled to a temperature ap})roaching that of the room. As a household REFRIGERATING SYSTEMS 179 machine usually (jperates about 25 i)er cent of the time, there is a sufficient time interval between runs for the condensing water to cool to nearly the room temperature. Mercoid Control. — Fig. 28 and 29 shows a special control for domestic refrigerating machines made by the American Radiator Company of Buffalo and the Federal Gauge Com- ])an} of Chicago. v_J U I FIG. 28.— MERCOID CO.XTKOL, FLKXIIU.K TlliE TVl'E.