US2315379A

US2315379A - Preserving perishables

Info

Publication number: US2315379A
Application number: US411240A
Authority: US
Inventors: Robson Hector Harris
Original assignee: United Fruit Co
Current assignee: United Fruit Co
Priority date: 1941-09-17
Filing date: 1941-09-17
Publication date: 1943-03-30
Anticipated expiration: 1960-03-30

Description

March 30, 1943. H. H. ROBSON PRESERVING' PERISHABLES Filed Sept. 17, 1941 5 Sheets-Sheet 1 March 30, 1943.

H. H. ROBSON 2,315,379

PRESERVING PERISHABLES Filed Sept. 17} 1941 5 Sheets-Sheet 2 ATTORNEY March 30, 1943. H, ROBSON 2,315,379

PRESERVING PERI SHABLES Filed Sept. 17, 1941 s SheetS-Sheet s v 35oL ATTORNEY H. H; ROBSO'N PRESERVING PERISHABLES Filed Sept. 17, 1941 March so, 1943.

5 Sheets-Sheet 4 Imxen'l'or Patented Mar. 30, 1943 PRESERVING PERI SHABLES Hector Harris Robson, Scarsdale, N. Y., assignor to United Fruit Company, Boston, Mass, a corporation of New Jersey Application September 17, 1941, Serial No. 411,240

22 Claims.

This invention relates to refrigerating systems for preserving perishables such as vegetables and fruit, and particularly bananas, during shipment, and its object is to provide an improved refrigerating system of the type in which air is withdrawn from the cargo compartment, cooled by being passed in contact with air cooling apparatus, and then returned to the cargo compartment and preferably passed generally vertically through the cargo. By my invention I have improved on such systems by minimizing the tendency of the air to dry the perishable cargo during refrigeration and by effectively controlling the amount of ripening of the fruit during the voyage.

This application is a continuation in part of my prior application Serial No. 296,080, filed September 22, 1939.

In the drawings:

Fig. 1 is a diagrammatic view, partly in. perspective, showing a portion of a cargo carrying ship equipped with a refrigerating system embodying my invention;

Fig. 2 is a diagram of electrically operated app-artus provided in each cargo compartment for controlling the rate of refrigerant flow and the fan speeds;

Fig. 3 is a diagram of an electric circuit showing apparatus for controlling the capacity of the central refrigerating plant in response to predetermined temperatures of the refrigerant in the system; I

Fig. 4 is a detail of a portion of the circuit of Fig. 3; v

Fig. 5 is a diagrammatic elevation view of a modification, and

Fig. 6 is a diagram of an electric circuit showing in detail the pressure responsive element 630 shown in Fig. 5.

In Fig. l I have indicated generally at A a sec- -tion of a ship having any desired number of cargo compartments, in this instance four, designated W, X, Y and Z. Each of these compartments, as illustrated by compartment W, is bounded by end partitions 2 and 4, side partitions 6 and 8, and by upper andlower decks I0 and I2.

Each ofthe cargo compartments is provided with a suitable system for circulating air, preferably, althoughnot necessarily, of the type noted in my prior. Patents Nos. 1,835,085 and 2,111,938. .As described in those patents in detail, such a system preferably embodies a perforate floor grat ing i4 resting on risers IE or the like, to form an air receivingspace I 1 between the grating and the under deck 12,. The cargo rests on the floor grating. Air is withdrawn from the interior of the compartment through suitable openings l8 in the end partition 2 by means of

fans

20 and 2| which force the air to port and starboard through ducts 22 and 24 containing

cooling coils

26 and 28 for lowering its temperature. The cooled air is forced lengthwise of the compart ment through side ducts 3B and 32, each of which contains a plurality of air directors 35. The directors 34 curve downwardly to direct air forced through the side ducts to variouspredetermined portions of the bottom of the compartment from whence it passes athwartship through the space I! beneath the floor grating. From space I! the air passes upwardly through the grating and through the cargo resting thereon and is withdrawn to complete the cycle'of air circulation.

Suitable provision may, of course, be made for removing stale air and admitting fresh air in a conventional manner. For further details of this system, reference should be made to my prior patents above noted. It is to be understood that each of the compartments W, X, Y and Z is equipped with a system of air circulation and distribution of whatever type employed.

A system embodying my' invention preferably includes apparatus for continually withdrawing the refrigerant from the

coils

26 and 28 of each compartment, cooling it and returning it to the coils. The refrigerant flowing through the coils may be of the so-called non-volatile type, of which brine is typical, or it may be of the volatile type suchas ammonia, Freon carbon dioxide, etc. and in the latter event the cooling system would be the direct expansion type. Any suitable system is within the scope of my invention, as will be described, and I shall first describe a system employing a non-volatile cooling medium which for brevity I shall refer to as brine, it being understood that any of the well known equivalents for brine may be used as well. I

The-coil 28 in each compartment .has an outlet 40 and the coil 26 in each compartment has an outlet 42 which lead to a common outlet header 44 connected by pipe 46 to pumps 50 for circulating the brine through the system. The pipe 46 communicates by stand pipe 52 with a reservoir 64 adapted to compensate for expansion and contraction of thebrine incident to changes in its temperature.

- From the pumps 50 thebrine flows through a further header having a branch 56 and a branch -58 from the latter of which the brine is conducted by pipes 60 and-62 through the coils 64 and-66 of cooling apparatus tobe described, for reducing its temperature. The cooled brine is conducted by pipes 68 and 16 to a delivery header 8!] from which it is conducted through pipes BI and 82 to the coil 28 in each compartment and by pipes 86 and 83 to the coil 26 in each compartment. 1

As will be described, a feature of my invention resides in its ability accurately to control the temperature of the surface of the brine coils. This control, furthermore, is automatic upon a variation in certain conditions within the system to be described. For that purpose the system which I have herein disclosed embodies cooling apparatus preferably having a plurality of automatically controlled brine cooling units, each I consisting of a compressor, a condenser and an evaporator, of which I have shown two for purposes of illustration, but it will be understood that a larger or smaller number may be employed in practice. The evaporators indicated at 99 and 92 enclose the aforesaid coils B4 and 6% respectively. These evaporators contain any suitable volatile refrigerant, such as ammonia, Freon carbon dioxide or the like. They are exhausted through pipes 94 and 95 by means of the compressors Iiiil and I82. The compressed refrigerant passes through the coils Hi4 and I96 of condensers Hi8 and H9 and thence through pipes III and Ill back to the evaporators 99 and 92 being expanded through suitable valves H4 and H6. The coils I84 and H36 within the condensers may be cooled by sea water introduced through pipes I29 and E22 from header I24 being pumped from the ocean through pipes I26 by means of pumps I28 and I30. From the condensers the sea water exhausts overboard through header I32.

To control automatically the operation of the system under the varying conditions prevailing in practice I provide cooperating controls automatically actuated in response to the temperatures of the air delivered to the cargo, of the air withdrawn from the cargo and of the brine delivered to the cooling coils. Thus, located within each of the

air delivery ducts

30 and 32 of each compartment is a thermostat Hi and I44 respectively and the brine return pipes 48 and 42 returning from the coils 28 and respectively in each compartment contain valves MI] and I42 which are automatically operated in response to temperatures registered by said thermostats I44 and I 38. Disposed in the path of the air withdrawn from the compartment through the apertures It is a thermostat I50 connected in the circuit that drives electric motors I52 "and I54 which operate

fans

28 and 2! respectively. In the brine deliveryheader 80 is a thermostat I60 which regulates the capacity of the cooling plant compressors. This control system will now be described in detail.

In Fig. 2 I have illustrated an electric circuit which automatically operates the valves I and I42 and controls the speed of fans 29 and 2! in each compartment. The electric circuit illustrated in Fig. 2 is duplicated for each of the compartments W, X, Y and Z. The valve I40 in each compartment is opened and closed mechanically by a reversible electric motor I14 connected to the valve by a suitable drive indicated at I16. The motor is connected across the power lines I13 and I12 by leads I16 and I80. Motor'IM is a reversing shunt wound motor and its field windings I82 and I83 are connected in parallel by line H3 to line I18 as indicated. W'inding I82 is normally energized to rotate motor I14 in a direction to open the valve by a circuit which includes armature :88 pivoted at I86 and spring pressed downwardly at I81 to close contact at Itfl, thus completing the circuit through lead I82 to line I89 and thence to power source I12. Thermostat I which, as above stated, is located in the air delivery duct 32, has a temperature indicating lever 29% electrically connected at 292 to line I12 and it has a terminal 266 against which lever 2G5) moves when a predetermined low temperature is reached. This circuit is then closed through solenoid 208 connected by lead 2H1 to line I'IQ, energizing the solenoid and attracting armature I88 to break the circuit through winding W2 and to complete the circuit through contact 2H and winding I83. When winding IE3 is energized motor I14 rotates in a direction to close valv I48. The valve Mil moves very slowly in either direction and is provided with the usual circuit interrupters (not shown) for automatically breaking the circuit when the extreme open or closed positions of the valve are reached. Preferably the valve takes about /2 minute to close from full open position and vice versa.

Similarly, valve I42is operated by a reversible shunt wound motor I'M and is automatically opened and closed in response to the temperature at thermostat Hit. The circuit operating motor I14 from thermostat I is identical to that above described for operating motor I14 from thermostat I 34 and accordingly need not be further described. The corresponding parts are indicated by the primes of the numerals above recited.

The aforesaid motors I52 and I54 for operating fans 29 and 2i respectively are connected across mains I10 and I12 by lines 2, 2I2, 2M and 2I6. Thermostat I58 disposed in the path of the return air automatically regulates the speed of both fans to vary the number of air changes per hour with reference to predeter mined temperatures of the return air. Motors I52 and I54 have shunt field windings 229 and r 222 respectively, connected in parallel by line 224. Resistance 226 connects line 224 with power source I12. Thermostat I59 has an indicating lever 230 connected by line 232 to line I12. A terminal 244, with which lever 23E closes contact when the temperature is high, is connected to solenoid 223 which is connected at 229 with line I19. Solenoid 228 rotates an armature 23I in circuit with line I12 through line 233. The armature is spring retracted at 235 against the attraction of solenoid 228 to close circuit through line 231 connected at 239 with resistance 226. On thermostat I5!) is also a terminal 234 connected by line 236 to line 224.

The speeds of fan driving motors I52 and l54 are automatically simultaneously regulated by introducing in series with their field windings 220 and 222 different amounts of resistance depending upon the temperature registered at I50, it being understood that the greater the resistance in series with the shunt field, the higher the fan speed. When the return air is at its highest temperature, lever 230 of thermostat I is against step 244 so that solenoid 228 is energized and the full value of resistance 22% is in series with the windings 2'20 and 222 so that the fans run at full speed. When the return 'air drops to a predetermined temperature needle 230 moves from contact 244 so that circuit is made through 'armature23l and line 231 thereby cutting out a portion of resistance 226 and slowing down the fans. As the temperature of the return air continues to drop needle 230 contacts terminal 234 to decrease further the resistance and again to slow the fans.

The cooling capacity of the brine cooling apparatus is automatically varied in response to different brine temperatures registered by the thermostat I (Fig. 1) in the brine delivery line. The circuit is indicated in Fig. 3 in which L+ and L indicate two leads from a suitable power source, not shown. Connected across these leads by lines 308 and 3I0 is a motor 3I3 adapted to drive the sea water pump I28 (Fig. 1). The line 308 contains a starting switch 3I2 and line 3I0 includes points 3M and p of the thermostat I60 as will be described. It will be apparent that seat pump I28 (Fig. 1) will be started when switch 3 I2 is closed provided contact is thenmade across points 3I4 and p of the thermostat I50. Within pipe I20 leading from pump I28 to condenser IIII is a valve 304 which is automatically opened when the pump is operated and closed when the pump stops. For that purpose the valve is electrically actuated by reversible shunt wound motor 306 connected to the power source by

Wires

322 and 320 when switch 3| 2 is closed.

The reversing field windings 324 and 32B of the motor are connected in parallel to line 322 by line 340. Selective energizing of the windings is efiected by armature 342 pivoted at 343 and connected by line 338 to line 320 and through switch 352 to L+. Armature 342 is spring drawn upwardly at 345 to close contact with wire 348 to energize winding 325. Solenoid 350, connected across lines 338 and 3I0 may be energized to attract the armature and break circuit through line 348 and make circuit through line 352 and winding 324. Valve 304 is opened when winding 324 is energized and is closed when current flows through winding 326. Thus, when switch 3I2 is closed and sea pump motor 3I3 is operated, solenoid 350 is energized and current flows from line 330 through the armature in a direction to open the valve. When the sea pump motor 3I3 is stopped, through breaking circuit across thermostat points (H4 and p--, valve 304 is automatically rotated to closed position.

The motor 318 driving compressor I02 is automatically started when sea water flows through pipe I20 as a result of sea pump I28 being started and valve 304 being opened. For that purpose I attach to pipe I20 (Fig. 1) leading from the sea pumps to condenser III) a switch designated 3I1 closed as the result of passage of sea water through pipe I20. Diagrammatically, I have illustrated a suitable arrangement in Fig. 3 wherein is shown the pipe I20 containing a pivoted diaphragm 350 linked by rod 352 to switch 3I1 spring pressed at 354 to open position and closed by movement of diaphragm 350 upwardly upon passage of sea water through pipe I20. In this fashion, upon starting of pump I28 and opening of valve 304, circuit is automatically completed across lines 360 and 382 to energize solenoid 364 connected by line 368 to power main L.

Core 381 or" the solenoid is thereby attracted clos- I ing circuit across

lines

310 and 312 to start motor 318 connected by line 380 to line 3I0 and thence through thermostat terminals 3I4 and p to the power source L. For ease in starting I preferably employ starting resistance of conventional character not shown, which is gradually cut out as full speed is assumed.

To slow down compressor driving motor 318 under certain conditions'which will ap pear, I

delivered to the cooling coils 28 and 2: 3.

provide in series with its shunt field winding 480, resistance 402 connected by line 404 to line 812. Electrically conducting lever 408 pivoted at M0 to which pivot the winding 400 is also connected and contacting the resistance efiects a change in the amount of resistance in series with the winding 400. When lever 408 is in its clockwise position indicated full resistance is in series with winding 400 and motor 318 rotates at maximum speed. Lever 408 is rotated counterclockwise to cut out resistance and hence to retard motor 318 by reversible shunt wound motor 4| 2 suitably connected by drive 4I4 to the shaft on which lever 408 is mounted. Motor M2 is connected by lead 4| 6 to power source L+ and by lead 8 to power main L. Its

shunt field windings

420 and 422 are connected in parallel at 434 and by line 425 to line 4I6. Selective energizing of

windings

420 and 422 is effected by pivoted armature 428 connected by line 430 to source L. Spring 432 rotates armature 428 in a direction to close circuit through winding 420, under which condition motor 4I2 moves switch lever 408 to its extreme counterclockwise position. To cut in resistance 402, armature 428 is attracted by solenoid 440 to close circuit through winding 422. Solenoid 440 is connected by line 442 to line LI- and by line 444 to two terminals 446 and p, also forming a part of thermostat I60, as will be described.

By this construction compressor driving motor 318 is automatically started When sea Water flows through pipe I28 and runs at full speed as long as contact is made across terminals 446 and p which cuts in all of resistance 402. When circuit is broken across terminals 448 and presistance 432 is cut out, thereby automatically reducing the compressor speed. The compressor automatically stops when circuit is broken across terminals 3I4 and p. Motor 4 I2 is, of course, provided with the usual circuit interrupters (not shown) to prevent rotation of the motor beyond the extreme positions of lever 408.

Sea pump I30 (Fig. l) is driven by motor 460 operated by a circuit which is precisely like that above described and in which the corresponding elements have been marked by the primes of the numbers above described. Similarly, valve 305 is automatically opened and closed by motor 306. Compressor I00 is likewise driven by a motor 318 started when switch 3I1' is closed as a result of sea water flowing through pipe I22, slowed when circuit is broken through thermostat 446 and 22-, and stopped when circuit is broken through thermostat points 3 I 4 and p-.

In Fig. 4 l. have illustrated the details of the thermostat I30 in brine line (Fig. 1). It includes suitable temperature indicating means, such as a thermometer 580 exposed to the brine Lead L is electrically connected to the mercury in the bulb of the thermometer at 12-. At four predetermined, comparatively low temperatures designated a, b, c and d, are leads 502, 584, 506 and 508 which make electrical contact with the mercury when it has risen above the respective temperatures, a, b, c and (Z, and these leads terminate at switch points 5I0, 5I2, SM and SIB respectively. A four pole switch designated generally at 5H3 has four switch arms pivoted at terminals 446, 3M, 443' and M4 and has an insulated switch bar handle 520 by which the four switch arms may be rotated as a'unitfrom their positions shown, contacting the points M0 to 5I8 inclusive, to a second position, as indicated in dotted lines. Disposed at higher temperatures h, f and g are three further

contacts having leads

522, 524 and 526 respectively connected to the three terminals 538, 532 and 53'. When the switch is in full line position circuit is completed from p to terminals 46-3, 356, 4% and 3M in the event that the mercury covers con tacts a, b, c and d. When the switch is moved to its dotted line position circuit is completed from p to terminals 3H1, i 'a' and 35 (but not to ME) provided the mercury has risen above temperatures h. f and As will be apparent, the individual circuits above described are cut out as the mercury falls below the individual temperatures indicated. The circuits that are thereby interrupted are indicated in Fig. 3 where the terminal points 34%, 3H5, M6 and Si t are shown.

To effect automatic movement of switch arm 52!! from its full line to its dotted line position at a predetermined temperature I pivot the arm to a lever 5i i which is pivoted at 5l3 and is adapted to be rotated clockwise about its pivot to move the switch to its dotted line position by spring 5(5. The switch is moved manually to its full line position by depressing end 51? of lever Eli and to hold the lever down against the action of spring MS I provide a solenoid Eit connected by lead 526 to power source L+ and byline 523 through contact points 525 and 52? to lead 536i which makes contact with the mercury at temperature e. Thus, if the temperature is higher than c and end 5 i! is depressed, circuit will be closed through solenoid 5l9 since end 5i"! of lever 5i! bridges contacts 525 and 52'? and the switch will be lieid in its full line position against the action of spring However, as soon as the mercury falls below temperature 6 circuit interrupted and switch EH8 is moved by spring 555 to its dotted line position. Even though the temperature again rises above 6, switch Sifi will remain in dotted line position until it is manually moved to full line position.

For simplicity I have shown in Fig. i an electric circuit in which current going through the mercury in thermometer 5% is employed directly to operate the apparatus in the circuits of "Fig. 3, although in an obvious manner relay circuits can be employed if it is desired to use a weaker current through the thermometer 5&3 than would be required to operate that apparatus.

When the cooling apparatus of 3 and i is started in operation to cool warm brine, switch 5|8 (Fig. 4) is set to its full line position and magnetically held as above described. Since the temperature of the brine at thermostat (6% is now well above a, contact is made from point pto points M6, 3M, 4 and 3!:3. Accordingly, the circuits across these points in Fig. 3 are now closed.

Switch Si? is then closed, completing the circuit to sea pump driving motor M3 and to motor 306 opening valve 3915. Consequently, sea water will flow through pipe i'zil (Fig. l) to condenser H0 and as it deflects diaphragm 350 within pipe I (Fig. 3) switch 3l'l will close to complete the relay circuit through lines 37%, 31.2 and 33a to start the compressor driving motor 3'53. The compressor will rotate at maximum speed since all of resistance 432 is in series with field Winding 400 of motor 3 48 as the result of motor 552 being energized in its field winding 422. 7

Similarly, when switch 3i2 is closed sea pump motor 450 rotates, valve 385 opens and compressor motor 318 operates at full speed.

pressor v releasing of armature #28 to energize field Wind- As the mercury drops in thermometer 500 as the result of brine cooling, the first thermostatic contact to be broken is from pto point M6 which automatically retards the speed of com H32. This is effected by the resultant ing 420 of motor M2 rotating the latter in a direction to cut out resistance 482 in series with field winding 450 of compressordriving motor 3'18.

Should the mercury again momentarily rise over point a full speed of compressor E02 will be resumed momentarily in an obvious manner.

As the mercury recedes below point I) interrupting circuit between 10- and 3M, sea pump driving motor -3l3 will stop, as will compressor driving motor 378. Valve 364 will now close automatically since circuit is still made to motor 306 and its field winding 32% will now be energized as the result of contact of armature 342 with line 348.

Should this result in the mercury rising to close again contact from 3 M to p, compressor driving motor 318 will not immediately start again since switch 3 has automatically been opened by spring 354 when sea water ceased to flow through pipe lZll as the result of the stopping of sea pump motor 3GB and the closing of valve 304. However, the compressor will be started automatically as soon as switch 3i! is again closed as the result of passage of sea water through pipe I20.

"In similar fashion, recession of mercury below point 0, breaking circuit across points 20- and retards compressor driving motor 313 and further recession below point d stops that compressor and sea pump driving motor 4% and closes valve 365. The temporary rising of the mercury above those points causes the reverse effect as indicated above for the points 12 and a.

'When the mercury drops below the temperature e, the holding circuit to switch M8 is interrupted releasing it for movement by spring '5i5 to dotted line position. Although I have shown temperature 6 as being lower than (1, in practice it will not, of course, be lower than the mercury will go when the last cooling unit has automatically been shut down. As soon as switch MS has thus been released, the mercury will gradually rise until temperature 9 is reached, at approximately which temperature 'I wish to hold the brine during the remainder of the voyage, for a purpose which will appear. At temperature g contact is made from pto 354, starting sea pump motor- 16B, opening valve 385 and driving compressor operating motor 313 at slow speed. Should the mercury continue to rise until temperaturef is reached, full speed or" compressor driving motor 3 18' will be attained bythe closing of circuit from p to 465'. This will usually be effective to cause the brine temperature again I to drop to ,g, but should it rise to the point It circuit will'be completed from p to M4 which will start sea pump 3l3, open valve 364 and start cmpressor driving motor 318 rotating slowly.

The operation of a refrigerating system embodying my invention to refrigerate perishable cargo "automatically in such a Way as to minimizeca'rg'o spoilage and drying and effectively to retard ripening will :now be described.

Aiter each cargo compartment has been loaded the apparatus specifically described with reference to Fig. 2, and duplicated in each compartment, is started in operation by closing a switch 605} for each compartment. Fan driving motors I52 and 154 in each compartment will thereby be rotated at maximum speed since the temperature of the air withdrawn from the compartment and passing thermostat I50 is now high and .pointer 230 will accordingly contact terminal 244 establishing all of the resistance 226 in series with field windings 220 and 222 of the motors. Valves I40 and I 42 in the brine return line from

coils

28 and 26 will now open automatically since circuit is completed to the valve opening motors I14 and I'M and also through their field windings I82 and I82. 7

Brine pumps 53 (Fig. 1) are started and to cool the brine the cooling apparatus of Fig. 3 is started in operation by closing switches 3I2 and 3I2' as above described. The thermostat I 60 in the brine delivery line will now have its switch 5I8 magnetically held in full line position.

Perishable cargo has a certain definite temperature at which it should be carried for best preservation. This temperature differs not only with difierent sorts of fruit and vegetables, but also with other factors such as the degree of ripening desired at the destination, and the proper temperature required for carrying specific cargo under prescribed conditions is a matter of common knowledge to shippers. By my invention I am able to reduce the temperature of the cargo to its prescribed carrying temperature quickly, thereby minimizing spoilage, and yet without undue absorption of moisture from the cargo. After the carrying temperature has been reached, I am able to maintain it constant within very narrow limits, and I thereby not only eliminate chilling and spoiling, but I effect a more accurate control of the desired amount of ripening during the voyage.

The setting of the thermostat I55 controlling the fan speeds and hence the number of air changes in the cargo compartment per unit of time, is such that the maximum rate of air change is automatically maintained until the cargo has nearly reached its carrying temperature. Thereby I effectively guard against moisture'absorption from the cargo bythe air While effecting a rapid reduction in cargo temperature. That is, the high rate of air flow past the cooling coils and through the cargo insures a small temperature difference between the air and the cargo so that the air, in cooling the first portion of cargo which it contacts, does not undergo such an abrupt rise in temperature as to enhance materially its ability to absorb moisture from portions of the cargo subsequently contacted by the air before it leaves the compartment. Furthermore, the temperature difference between the air withdrawn from the compartment and the cooling coils is also small so that there is little tendency to precipitate moisture on the coils and thereby unduly to dry the air before it is returned to the cargo.

As'the extraction of heat from the cargo continues the temperatures gradually drop at the air'delivery thermostats I44 and I that the air return thermostat I58 and in the brine flowing throughcoils 25 and 28. The thermostats M4 and I 45 are so adjusted as to temperature that when the delivered air contacting them reaches a temperature of no more'than a degree F. or so below the desired cargo carrying temperature, contact is made at terminals 2% and 2M respectively to close down slightly the valves 30 and I 42 by energizing the field coils I83 and I83 of the valve operating motors lid and H t. This climinishesthe how of brine through the coils and insures against harmful cargo chilling. 'In

the event of over adjustment indicated by a rise in air temperature above that at which the ther-- mostats make the contacts above described, the valves will again automatically move slowly toward open position until the over adjustment is corrected.

During this process of diminishing brine flow through the cooling coils of each compartment, the temperature of the brine will drop rapidly since the rate of flow of brine through the

evaporators

90 and 92 is also now decreased. When any of brine temperatures a, b, c or d isreached, the capacity of the cooling apparatus Will be reduced automatically in the manner above described.

The cooling continues with the delivery air maintained at or very slightly below the desired cargo carrying temperature and as the cargo also nears that temperature, the temperature of the air Withdrawn, registered by the thermostat I in each compartment, gradually approaches the temperature of the air delivered. When the cargo has reached its carrying temperature the temperature of the air withdrawn will be only a fraction of a degree F. or so above the desired carrying temperature of the cargo, particularly if, as is preferred, the fruit is cooled by streams of air distributed uniformly through the compartment (as by the side air directors s t-and air space I! beneath grating I 6) and directed generally vertically through the entire volume of cargo. Having predetermined this diiference, I utilize the temperature of the Withdrawn air to indicate when the carrying temperature of the cargo has been reached. Thermostat I50 is set so that as that predetermined temperature of the withdrawn air is approached the rate of air change is gradually reduced. This reduction is effected by lever 239 first breaking contact at 244 to cut out a portionrof resistance 22!; in series with field windings 220 and 222 of the. fan driving motors I52 and I54 and subsequently making contact at 234 further to reduce that resistance and again decrease the fan speeds to effect the low rate of air change at which the cargo is to be carried for the remainder of the voyage. Al-

though drying of the cargo is minimized, as

above described, by employing a high rate of air change during initial cooling of the cargo, drying is also reduced by using a low rate of air change to hold the cargo at its carrying temperature after it .has been reached.

. As a further safeguard against drying the cargo, my invention effects maintenance of the delivered air at the temperature necessary to hold the cargo at its carrying temperature by the use of a comparatively high rate of brine flow at moderate temperature, through the brine coils 26 and 23, rather than a lower rate of fiow of colder brine. Thereby I insure that the surface temperature of the coils is more nearly uniform throughout their entire exposed area with no portions so low in temperature as 'to causeexcessive moisture precipitation and hence drying of the air delivered to the cargo. Furthermore, I' thereby enhance the efiiciency of the compressors.

To that end when the brine temperature falls below 6 (Fig. 4) switch 5| 8 will be released'to' move to its dotted line position, with the result that the temperature of the brine will rise, without starting the compressors, until it reaches temperature 9. As described above, the brine temperature approximating tained thereafter.

As soon as the brine temperature rises the temperature of the delivered air also begins to g is automatically mainrise. Any slight rise in air temperature is felt at thermostats Hi4 and I46, causing contact to be broken at terminals 254 and 294 (Fig. 2) which effects energizating of field coils I82 and I82 of Valve operating motors I'M and HA. Conse quently the valves l4!) and M2 new open fully admitting more brine and thereby checking further rise in delivered air temperature. The brine temperature 9 is such with relation to the capacity of the cooling system and the load impressed on it by the cargo that for the remainder of the voyage the cargo will be kept at its desired carrying temperature with the brine valves I40 and. I42 fully open, or nearly so, and the fan speeds throttled to a minimum. Of course, this relationship may be disturbed, but it is automatically restored by the apparatus provided by my invention.

By insuring uniformity in the temperature at which the cargo is carried, my invention eliminates the spoilage incident to temperature fluctuations of the order commonly occurring in the conventional refrigerating system. Drying of the cargo is minimized by utilizing the temperature of the air withdrawn from the compartment as the factor controlling the rat of air change and this temperature as above described influences and cooperates with the entire system of controls since it influences the rate of brine flow through its efiect on the temperature of the air delivered and since it thereby also afiects the load on the cooling apparatus.

As stated above, other refrigerants than brine may be used and they may be either of the nonvolatile type, like brine, or the volatile type in which event the system would be of the direct expansion variety. In such a system the compressors or equivalent pressure applying means well known in the art would be retained, as I have shown at lilfla and W211 in Fig. 5, as would the condensers 68a and lllla. Preferably the cooling coils 26a and 28a function as evaporators. The volatile refrigerant that has been compressed and condensed flows from the condensers, as by pipes 609 and 652, to a receiver 604 from which it passes through line 605 to header Bila and thence through pipes Ma and 32a to the coil 28a in each compartment and by pipes 86a and 88a to the coils-25a in each compartment. At the entrance'end of each coil is an expansion valve 608 automatically actuated in response to the temperature at a thermostat EH3 at the outlet of the coil to efiect admission of the proper quantity of refrigerant for efficient operation of the evaporator as is well known.

Thermostat lMa in one air delivery duct and thermostat MBa in the other are connected to solenoid operated valves 62!! on the inlet side and 622 on the outlet side of the coils 28a and 26a respectively.

The refrigerant returns from the coils 25a and 28a through pipes 42a and M a. which join at a headerMa returning directly to the compressors. In the header Ma is an automatic pressure switch 630 responsive to the pressure in the header 44a and connected to the motors which drive the com pressors.

With such a system when the delivered air passing thermostat 144a or reaches a predetermined low temperature, the valves 62!] and 622 on opposite ends of the coil controlled by that thermostat automatically close simultaneously to stop further flow of refrigerant through the coil until a rise in temperature of the air acting on the thermostat Vida or [46a causes the valves again .to open. By providing for simultaneous closing of valves on opposite ends of each coil I insure that the coils retain the proper amount of refrigerant and are ready to start functioning immediately when their corresponding air delivery thermostats indicate the need for further air cooling.

The pressure responsive element 630 is preferably constructed to operate in precisely the same way as the temperature responsive element I illustrated in detail in Fig 4 except that the former operates in response to pressure rather than temperature That is. the mechanism of Fig. 3 is duplicated and automatically operated by a device such as is illustrated in Fig. 4 suitably modified to act in response to varying pressures in the line 44a. Essentially the modification may employ pressurestats of usua sort instead of the thermometer used in the embodiment of Fig. 4. Thus the pressure responsive element indicated generally at 63!] in Fig. 5 could, as shown in Fig. 6, include a series of pressurestats ml, 103, H35, Nil, 109, TH, H3, and H5. Each of these pressurestats may be of conventional construction and, as indicated by pressurestat 109, may have a lever Hi0 pivoted at 102 to the enclosing box-704 and connected to a bellows 10E communicating by a tube 168 with pipe Ma (see also Fig. 5) so that pressure in the line 44a causes expansion of bellows Hi6 and counterclockwise movement of the lever 1013 around its pivot I02. Lever 106 is electrically conducting and makes contact with terminal H9 electrically connected by line H2 with common terminal pto which is connected lead L from a suitable power source, not shown. Lever is also electrically connected by line 502 with switch MB.

In like manner the other pressurestats 10 I 153, H15, H31, Ill, H3, and H5 are connected by tubing I26, I22, 124, 126, 128, 730, and 132, respectively, with the pipe 440, and each pressurestat hasa pivoted lever which, like lever 10E! of pressurestat 109, is operated in response to pressure in the pipe 44a to close circuit between line 1 and switch 518 through lines 53!, 598', 5%, 584, 526', 524 and 522', respectively.

Each of the pressurestats has an adjustment of the conventional sort shown at M0 for pressurestat Hi9, for changing the tension in spring 142 which pulls downwardly on lever H19 so that the amount of pressure in bellows 796 from pipe Ma required to make contact at Hi! can be regulated. Just as the Fig. 4 embodiment operates in response to varying temperatures a, b, c, d, e, f, g and It, so the individual pressurestats are regulated by their adjustments 143 to complete electric circuit from pto switch 513 at corresponding varying pressures which I have indicated at a, b, c, d, e, f g and h.

The switch 558' to which each pressurestat is connected may be and preferably is in all respects identical in construction and mode of operation with switch 5|8 of Fig. 4 and the corresponding parts in Fig. 6 have been indicated by the primes of the reference characters employed in Fig. 4. Thereby the circuits of Fig. 3 would be selectively established and broken in response to changes in pressure in pipe 440. rather than in response to changes in temperature at thermometer 160. Like switch 5i8, switch M8 has a holding circuit employing lever 5| I and associated parts including a pressurestat operating at a minimiun pressure 6. The pressure at e, of course will not in practice be lower than the pressure in the pipe 44a when the last cooling unit has automatically been shut down.

The direct expansion system above described, like the non-volatile system first described, controls the rate of working of the compressors in response to the temperature of the refrigerant in the cooling coils, although in the direct expansion system the apparatus works indirectly through the pressure in the coil outlet corresponding to the temperature within the coil. Furthermore, the cooling effect of the refrigerant on the air is regulated in both systems by varying the rate of flow of the refrigerant through the coil, although in the direct expansion system the reduction in rate of flow is not gradual as in the non-volatile system, but amounts to complete cessation or to alternate, intermittent flowing and stopping.

It is to be understood that the embodiments of ply means for controlling said supply means to my apparatus above described may be varied considerably without departing from the spirit of my invention which is to be limited only as indicated in the appended claims. Thus, I have specifically described in detail the use of direct current apparatus because that source of power is more commonly available on board ship. However, A. C. equipment may, of course, be used or the motivating power may be steam, hydraulic, pneumatic or otherwise. The capacity of the cooling apparatus, of which there may be any desired number of units, may be varied otherwise than by varying the speeds of the compressors, as other throttling instrumentalities well known in the art may be employed. Similarly, the rate of air change may be varied otherwise than by varying the speed of the fans, such as by employing dampers automatically controlled by the thermostats i''ii. The variation in cooling effect of the refrigerant on the air can be varied without changing the rate of flow of the refrigerant such as by by-passing a portion of the air around the coils, or otherwise. Although I have shown the use of coils for cooling the air, such cooling may i be effected by spraying the air, employing cooling apparatus of the well known air washer type but regulated automatically in accordance with the principle of my invention Allv such modifications are to be included within the scope of my inventionin so far as the claims permit.

I claim:

1. Apparatus for preservingperishables in a cargo compartment comprising the combination of means for changing the air in the compartment by withdrawing it therefrom and returning it thereto through the cargo, cooling apparatus for lowering the temperature of the air delivered to the cargo, a refrigerant flowing through said apparatus, means for cooling said refrigerant, means responsive to the temperature of air delivered to the cargo for regulating the rate of flow of the refrigerant through said apparatus, means responsive to the temperature of air withdrawn from the compartment for regulating the rate of air change in the compartment, and means responsive to the temperature of the refrigerant for regulating the capacity of said refrigerant cooling means.

2. In a refrigerating system for preserving perishables in a cargo compartment, apparatus for establishing and maintaining a predetermined carrying temperature in said compartment including a cooling unit, means for recirculating air over said cooling unit and through said compartment, means for supplying refrigerant to said cooling unit, and means responsive to the temperature of the refrigerant delivered by said supsupply refrigerant to said cooling unit at a temperature which automatically decreases to a predetermined low for establishin said carrying temperature in the compartment and which thereafter automatically increases to and substantially stabilizes at a point between said low temperature and the carrying temperature of the compartment for maintaining said carrying temperature in the compartment.

3. In a refrigerating system for preserving per ishables in a cargo compartment, apparatus for establishing and maintaining a predetermined carrying temperature in said compartmentincluding a cooling unit, means for recirculating air over said cooling unit and through said compartment, means for supplying refrigerant to said cooling unit, and means controlling said supply means to supply refrigerant to said cooling unit at a temperature which automatically decreases to a predetermined low for establishing said carrying temperature in the compartment and which thereafter automatically increases to and substantially stabilizes at a point between said low temperature and the carrying temperature of the compartment for maintaining said carrying temperature in the compartment, said last named means including means responsive to the temperature of the air delivered to said compartment from said unit for decreasing the rate of flow of refrigerant through said unit when the temperature of the delivered air reaches a predetermined low and for again increasing the rate of flow of refrigerant through said unit when the temperature reaches a predetermined high.

4. In a refrigeratin system for preserving perishables in a cargo compartment, apparatus for establishing and maintaining a predetermined carrying temperature in said compartment including a cooling unit, means for recirculating air over said cooling unit and through said compartment, means for supplying refrigerant tosaid cooling unit, means responsive to the temperature of the air delivered to said ccmpartment from said unit for automatically retarding the rate of flow of refrigerant through said unit while th temperature of said delivered air is at or below a predetermined low temperature below said carrying temperature, and means responsive to the temperature of the refrigerant delivered by said supply means for controlling said supply means to supply refrigerant to said cooling unit at a temperature which automatically decreases to. a predetermined low for establishing said carrying temperature in the compartment and which thereafter automatically increases to and substantially stabilizes at a point between said low temperature and the carrying temperature of the compartment for maintaining said carrying tem-' perature in the compartment.

5. In a refrigerating system for preserving perishables in a cargo compartment, apparatus for establishing and maintaining a predetermined carrying temperature in said compartment including a cooling unit, means for recirculating air over said cooling unit and through said compartment, means for supplying refrigerant to said cooling unit, temperature responsive means controlling said supply means to supply refrigerant to said cooling unit at a temperature which automatically decreases to a predetermined low for establishing said carrying temperature in the compartment and which thereafter automatically increases to and substantially stabilizes at a point-between said low temperature and the carrying temperature of the compartment for maintaining said carrying temperature in the compartment, and temperature responsive means controlling said air recirculating means to recirculate the air automatically at a high rate for establishing said carrying temperature in the compartment and at a lower rate while the temperature of the compartment is substantially at the carrying temperature.

6. In a refrigerating system for preserving perishables in a cargo compartment, apparatus for establishing and maintaining a predetermined carrying temperature in said compartment in cluding a cooling unit, means for recirculating air over said cooling unit and. through said compartment, means for supplying refrigerant to said COOlll'lg unit, temperature responsive means controlling said supply means to supply refrigerant to said cooling unit at a temperature which automatically decreases to a predetermined low for establishing said carrying temperature in the compartment and which thereafter automatically increases to and substantially stabilizes at a point between said low temperature and the carrying temperature of the compartment for maintaining said carrying temperature in th compartment, and means responsive to the temperature of the air withdrawn from said compartment for controlling said air recirculating means automatically to recirculate the air at a high rate while the temperature of said withdrawn air is substantially above said carrying temperature and at a lower rate while the temperature of said withdrawn air is substantially at said carrying temperature.

'7. Apparatus for preserving perishables in a cargo compartment including an air cooler through which flows a refrigerant, means for withdrawing air from the compartment, passing it adjacent said cooler to lower its temperature and delivering it to the cargo, an element responsive to the temperature of the delivered air passing from cooler to cargo, refrigerating means operable to extract heat from the refrigerant at a rate to lower the temperature of the delivered air gradually to reduce the temperature of the cargo from a comparatively warm temperature to a lower carrying temperature, means actuated by the element to decrease the flow of refrigerant through the cooler. when the temperature of the delivered air falls below a delivered air carrying temperature necessary to maintain said cargo carrying temperature, and means responsive to the temperature of the refrigerant to stop the extraction of heat from the refrigerant after is how has so been decreased and to allow its temperature to rise and become substantially stabilized at a temperature effective to establish and to maintain said delivered air carrying temperature when the flow of refrigerant through the cooler is again increased.

8. Apparatus for preserving perishables in a cargo compartment including an air cooler through which flows a volatile refrigerant, means for withdrawing air from the compartment passing it adjacent said cooler to lower its temperature and delivering it to the cargo, an element responsive to the temperature of the delivered air passing from cooler to cargo, refrigerating means operable to extract heat from the volatile refrigerant at a rate to lower the temperature of the delivered air gradually to reduce the temperature of the cargo from a comparatively warm temperature to a lower carrying temperature, means actuated by the element to stop the flow of refrigerant through the cooler when the temperature of the delivered air falls below a delivered air carrying temperature necessary to maintain said cargo carrying temperature, and means responsive to the pressure of the refrigerant to stop the extraction of heat from the refrigerant after its flow has so been stopped and to allow its pressure to rise and become substantially stabilized at a pressure and temperature effective to establish and to maintain said delivered air carrying temperature when the flow of refrigerant through the cooler is again commenced.

9. The method of preserving perishable cargo by quickly reducing its temperature to a predetermined carrying temperature without excessively drying it, which consists in passing ai in proximity to cooling apparatus through which flows a cooling refrigerant, gradually lowering the temperature of the air by extracting heat from the refrigerant in an amount to maintain the temperature of the refrigerant only slightly below that of the air so that extraction of moisture from the air while it is so cooled is minimized, and delivering to and through the cargo streams of air so cooled to reduce the temperature of the cargo by air at a temperature maintained only slightly below that of the cargo and continually decreased as the temperature of the cargo is decreased to effect said lowering in temperature of the cargo without unduly absorbing moisture from it.

10. The method of preserving perishable cargo by lowering the temperature of warm cargo to a predetermined carrying temperature, which consists in passing air in proximity to cooling apparatus through which flows a cooling refrigerant, gradually lowering the temperature of the air by extracting heat from the refrigerant in an amount to maintain the temperature of the refrigerant only slightly below that of the air while maintaining the rate of flow of the refrigerant through aid apparatus at a predetermined maximum so that extraction of moisture from the air while it is so cooled is minimized, and delivering to and through the cargo streams of air so cooled to reduce the temperature of the cargo by air at a temperature maintained only slightly below that of the cargo and continually decreased as the temperature of the cargo decreases to eliect said lowering in temperature of the cargo without unduly absorbing moisture from it and restraining reduction in temperature of the cargo below said predetermined carrying temperature by reducing the rate of flow of said refrigerant through said apparatus as the temperature of the delivered air approaches that required to maintain said carrying temperature.

11. The method of preserving perishable cargo by lowering the temperature of warm cargo to a predetermined carrying temperature and thereafter maintaining said carrying temperature, which consists in passing air in proximity to cooling apparatus through which flows a cooling refrigerant, gradually lowering the temperature of the air by extracting heat from the refrigerant in an amount to cool the refrigerant gradually and maintain the temperature of the refrigerant only slightly below that of the air while maintaining the rate of flow of the refrigerant through said apparatus at a predetermined max imum so that extraction of moisture from the air while it is so cooled is minimized, and delivering to and through the cargo streams of air so cooled to reduce the temperature of the cargo by air at a temperature maintained only slightly below that of the cargo and continually decreased as the temperature of the cargo decreases to effect said lowering in temperature of the cargo without unduly absorbing moisture from it, restraining reduction in temperature of the cargo below said predetermined carrying temperature by reducing the rate of flow of said refrigerant through said apparatus as the temperature of the delivered air approaches that required to maintain said carrying temperature and thereafter maintaining the delivered air at said required temperature by again increasing the rate of flow of the refrigerant and allowing thetemperature of the refrigerant to rise to a temperature sufficient to hold said required delivered air temperature at said increased rate of flow of, the refrigerant.

I 12. lhe method of preserving perishable cargo by lowering the temperature of warm cargo to a predetermined carrying temperature and thereafter maintaining said carrying temperature, which consists in passing air in proximity to cooling apparatus through which flows a cooling refrigerant, gradually lowering the temperature of the air by extracting heat from the refrigerant in an amount to cool the refrigerant gradually and maintain the temperature of th refrigerant only slightly below that of the air while maintaining the rate of flow of the refrigerant through said apparatus at a predetermined maximum so that extraction of moisture from the air while it is so cooled isminimized, and delivering at a predetermined maximum velocity to and through the cargo streams of air so cooled to reduce the temperature of the cargo by air at a temperature maintained only slightly below that of the cargo and continually decreased as the temperature of the cargo decreases to effect said lowering in temperature of the cargo without uriduly absorbing moisture from it,irestrainingreduction in temperature of the cargo'below said predetermined carrying temperature by reducing the rate of flow of said refrigerant through'said apparatus as the temperature of the delivered air approaches that required to maintain said carrying temperature, and thereafter maintaining the cargo at its said carrying temperature by again increasing the rate of flow of the'refrigerant, allowing the temperature of the refrigerant to rise to a temperature sufficient to hold said required delivered air temperature at said increased 'rate of flow of the refrigerant and finally reducing to substantially below said maximum the velocity of air delivered to the cargo.-

13. In a, system for preserving perishables in a cargo compartment the combination with cooling apparatus, refrigerating means supplying refrigerant to the cooling apparatus, means for changing the air in th compartment by withdrawing it therefrom, cooling it by passing it adjacent said cooling apparatus and delivering it through the perishables in the compartment, of means maintaining a maximum rate of work of the refrigerating means and means maintaining a maximum of flow of the refrigerant through the cooling apparatus while the temperature of the refrigerant in the cooling apparatus and the temperature of the air delivered through the perishables are falling, means reducing the rate of flow of the refrigerant when the temperature of the delivered air reaches a predetermined low and for again increasing the rate of flow of the refrigerant when the temperature of the delivered air rises a predetermined amount, means reducing the rate of work of the refrigerating means when the temperature of the refrigerant in the cooling apparatus reaches a predetermined low and for holding it reduced until the temperature of the refrigerant rises a predetermined amount from said low whereby to effect said rise in temperature of the delivered air said predetermined amount to effect said increase in rate of flow of the refrigerant.

14. The method of refrigerating perishable cargo which consists in initially extracting the heat from thewarm cargo by passing air through the cargo at a predetermined high rate of flow while lowering the temperature of the air .by passing it over cooling apparatus containing a circulating refrigerant, reducing both the rate of flow and the temperature of the refrigerant while maintaining the said high rate of air flow until the temperature of the cargo reaches the desired carrying temperature, and holding the cargo at said carrying temperature by restoring, at least in part, the initial rate of flow of the refrigerant, increasing the temperatur of the refrigerant and reducing the rate of air flow.

15. In a system for preserving perishables in a cargo compartment, including cooling apparatus, refrigerating means supplying a refrigerant to the apparatus, means for changing the air in th compartment by withdrawing it therefrom, cooling it by passing it adjacent said cooling apparatus and delivering it to and through the perishables in the compartment, the combination therewith of valve means for controlling the flow of refrigerant'through the cooling apparatus, an element responsive to the temperature of the delivered air operatively connected to said valve means for maintaining a high rat of refrigerant flow while the temperature of the delivered air is falling, reducing the rate of refrigerant flow when the temperature of the delivered air reaches a-predetermined low and again increasing the rate of refrigerant flow when the temperature of the delivered air rises a small amount above said predetermined low, and means includ ing an element responsive to the temperature of the refrigerant for controlling the rate of work of the refrigerating means by reducing it when the temperature of the refrigerant reaches a predetermined low, holding it reduced until the temperature of the refrigerant rises sufficiently to allow said rise in temperature of the delivered air which effects said increase in rate of refrigerant flow and thereafter increasing it in the amount necessary to inhibit further rise in delivered air temperature substantially above said small amount.

16. In a system for preserving perishables in a cargo compartment including cooling apparatus, refrigerating means supplying a volatile refrigerant to the apparatus, means for changing the air in the compartment by withdrawing it therefrom, cooling it by passing it adjacent said cooling apparatus and delivering it to and through the perishables in the compartment, the combination therewith of valve means for controlling the flow of refrigerant through the cooling apparatus, an element responsive to the temperature of the delivered air operatively connected to said valve means for admitting refrigerant through the cooling apparatus while the temperatureand pressure of the refrigerant are falling, stopping the refrigerant flow when the temperature of the delivered air reaches a predetermined low and again 1 starting the refrigerant flow when the temperature of the delivered air rises a small amount above said predetermined low, and means infurther rise in delivered air temperature substantially above said smallamount.

"17. The system as defined in claim in which said means for controlling the rate of work'of said refrigerating means includes apparatus for supplying refrigerant to said'cooling apparatus atria temperature which decreases to a predetermined low for establishing a carrying temperature in the compartment and which thereafter automatically increases to and substantially stabilizes at .a pointbetween said low temperature and the corresponding temperature of the compartment for maintaining saidcarrying temperature.

18. The system asdefined in claim 16 in which said means for controlling the rate of work of said refrigeratingmeans includesmeans for supplying refrigerant to said cooling apparatus at a pressure whichdecreases to a predetermined low for establishing a carrying temperature in the compartment and which thereafter increases to and substantially stabilizes at a higher pressure for maintaining said carrying'temperature.

19. In a system for preserving perishables in a cargo compartment, including air cooling ap paratus and refrigerating means supplying refrigerant to the apparatus'the combination therewith of mechanism responsive to a low refrigerant temperature operative to reduce the rate-of work or the refrigerating meanswhen said low temperature is reached, mechanism responsive to-a higher refrigerant temperature operative vto control the rate of work of the refrigerating means substantially to-stabilize the temperature of the refrigerant at such higher temperature,

a control member adapted selectively to render either of said mechanisms operative and the other inoperative, and an element responsive to a predetermined temperature of the refrigerant and connected to said control member to operate it so that said first mechanism is rendered inoperative and said second mechanism is rendered operative automatically when said predetermined temperature is reached.

20. In a system for preserving perishables in a cargo compartment, including air cooling apparatus and refrigerating means supplying refrigerant to the apparatus, the combination therewithof mechanism responsive to a low refrigerant pressure operative to reduce the rate of work of the refrigerating means when said lowpressure is reached, mechanism responsive to a1higher of work of the refrigerating means substantially to stabilize the pressure of the refrigerant at such higher pressure, avcontrol member adapted selec tively to render eitherof said mechanisms operative and the other inoperative, and an element responsive to a predetermined pressure of the refrigerant and connected to said control member to operate it-so that said first mechanism is rendered inoperative and said second mechanism is rendered operative automatically when said predetermined pressure is reached.

21. In a system for preserving perishables in acargo'compartment, including air cooling apparatus and refrigerating means supplying refrigerant to the apparatus, the combination therewith of mechanism responsive to a plurality of successive low temperatures of the refrigerant operative to reduce the rate of work of the refrigerating means in stages as those successive temperatures of the refrigerant are reached, mechanism responsive to a plurality of succes sive higher refrigerant temperatures operative to control the rate of work 'of the refrigerating means substantiallyto stabilize the temperature of the refrigerant in the region of said higher temperatures, a control member adapted selectively to render either of said mechanisms operative and the other inoperative and an element responsive to a predetermined low'temperature of the refrigerant and connected to said control member to operate itsothat said first mechanism is rendered inoperative and said second mechanism is rendered operative automatically when said predetermined low temperature is reached.

22. In-a system for preserving perishables in a :cargo compartment, including air cooling apparatus and refrigerating means supplying refrigerant to the apparatus, the combination therewith of mechanism responsive to a plurality of successive low pressures of the refrigerant operative to reduce the rate of work of the refrigerating means in stages as those successive pressures of the refrigerant are reached, mechanism responsive to a plurality of successive higher refrigerant pressures operative to control the rate of work of the refrigerating means substantially to stabilize the pressure of the refrigerant in the region of said higher pressures, a control member adapted selectively to render either of said mechanisms operative and the other inoperative and an element responsive to a predetermined low-pressure of the refrigerant connected to said control member to operate it so that said first mechanism is rendered inoperative and said second mechanism is rendered operative automatically when "said predetermined low pressure is reached.

HECTOR H. ROBSON.