US3361517A - Sterilizing apparatus and method - Google Patents

Description

Jan. 2, 1968 H. G. SKALLER 3,361,517

STERILIZING APPARATUS AND METHOD Filed Feb. 28, 1966 4 Sheets-Sheet 1 INVENTOR.

Hams fi eorgeSlcaller ATTORNEY Jan. 2, 1968 H. G. SKALLER STERILIZING APPARATUS AND METHOD Filed Feb. 28, 1966 4 SheetsSheet 2 INVENTOR. Hans flew/ya Skalier BY ATTORNEY Jan. 2, 1968 H. G. SKALLER 3,351,517

STERILIZING APPARATUS AND METHOD Filed Feb. 28, 1966 4 Sheets-Sheet 5 I NVEN TOR. Halls fieorg'ejkallar Y ATTORNEY /.I\.LA Am w 07a (I 3 wn' W1 8 2 m 9 1 Wu W L 4 I W m 9 mad, 4 n 3 W 1 9 b m1: L

' .U M M 0 U m w w r a O O O 3 M if? 0 o 9 n a 00 v 00 b f a 5 Z Q 6 M 8 Jan. 2, 1968 H. G. SKALLER 3,

I STERILIZING APPARATUS AND METHOD Filed Feb. 28, 1966 4 Sheets-Sheet 4 FIG. 8.

n a r F T 90 i 300 53 280 34 270 278 256 8! 264 250 I5 1- ZIZ O 20 150 I LBS/SQ. IN.

INVENTOR.

HANS GEORGE SKALLER BY 0 s 0 I5 20 25 MM 2-M TIIME MIN.

ATTORNEYS.

United States Patent Oiiice 3,361,517 Patented Jan. 2, 1968 ABSTRACT OF THE DISCLOSURE Means for sterilizing in which a unified closed pressure system is employed having three separate but interconnected regions, one a loading chamber, another a Water storage compartment, and a condensing compartment subject to cooling action by a fan, or the like, when desired temperatures are attained in the system. The closed system operates automatically to permit free flow of the sterilization medium without the use of valves.

This application is a continuation-in-part of co-pending application S.N. 192,512, filed May 4, 1962, now abandoned.

Background of the invention This invention relates to the art of sterilizing and is particularly directed to an improved sterilizing method and to self-contained steam-generating autoclaves adapted to sterilize such items as surgical, dental, bacteriological, medical and related goods.

Sterilization of goods of the above-mentioned type, is generally accomplished by enveloping the goods in saturated steam at control temperatures for a predetermined period of time. When such sterilization is in a closed chamber, it is desired that, after sterilization has been completed, the steam in the chamber be dissipated before the door of the apparatus is opened and the goods removed. There are various devices for accomplishing such objectives, but it is generally recognized that known devices of this class have certain inherent shortcomings. Thus, many widely used types employ an arrangement of manually or electrically operated valves for releasing the steam into the atmosphere upon the termination of the sterilization period. The repeated release of vapour into the room in which sterilizating apparatus is located frequntly causes damage to the wall and ceiling surfaces because of the dampening action of saturated steam; and moreover, the dissipation of such steam into the atmosphere makes it necessary frequently to refill the water reservoir constituting the steam source for the sterilizing chamber.

In order to overcome the aforesaid danger of damage to Wall surfaces, another type of autoclave device has been evolved that releases the steam to a reservoir filled with cold water, so as to condense the steam. It has been fond, however, that in the latter type of device the condensing Water absorbs the latent heat of the steam to an extent that the water rapidly reaches the boiling point consequently losing its condensing effectiveness, with the result that the remaining wet steam released from the sterilizing chamber is only partially condensed, the rest entering the atmosphere of the room. It has also been observed that in both of the conventional methods above described, the sudden release of steam, whether direztly into the room or into a water-filled condensing device, is accompanied by a hissing noise which is often found disturbing in a hospital or doctors surgery.

So called auto-condensation means have been employed by which the steam is permitted to condense gradually by heat exchange with the air surrounding the sterilizing chamber upon the discontinuation of the supply of heat; but the time required to accomplish such auto-condensation is excessive and thus prohibitive from a practical viewpoint, and moreover, extended exposure of the goods being sterilized to elevated temperatures has a deleterious effect on most goods, particularly rubber and fabrics. Furthermore, said auto-condensation methods result in Wet sterilized goods, undesirable for routine sterilization.

Summary It is with the above considerations in mind that the present improved sterilization process and apparatus have been evolved, a method and apparatus in Which the sterilizing and cooling cycle is completed in a minimum of time, practically no steam is lost, the operation is not accompanied by disturbing noises, the steam is maintained at all times in saturated condition, and no manually-set timing devices are employed. By using accelerated cooling, this sterilizing process maintains a temperature-pressure relationship that is always in equilibrium, there being a fixed pressure and temperature drop relation after the sterilization period, whereby there can be no boiling water over of a bacteriological liquid being processed.

It is accordingly among the objects of my invention to provide a sterilizing process and apparatus that has none of the aforesaid shortcomings, and which is adapted efliciently and effectively automatically to accomplish its intended sterilization function in a self-contained unit in which there is no release of the generated steam into the atmosphere.

The application of my process is effected in a preferred embodiment thereof, which may be generally described as comprising three separate but interdependent regions or compartments, one being a loading chamber in which the goods to be sterilized are positioned, another a water storage compartment adjacent a heating element, and the third a condensing compartment subjected to cooling action, such as by a fan or other means adapted to induce accelerated condensation that is set into action when the peak temperature is reached and the heat supply discontinued. This combination forms a unified closed pressure system through which air and steam currents flow without the interposition of any valves or other moving parts. The automatic operation is such that the time of the sterilizing cycle is interrelated to the volume of the entire pressure sysem and the energy input required to reach the preselected peak temperature at which time the heat input is interrupted and rapid condensation induced.

Brief description of drawings Other objects, features and advantages of the invention and the best mode for practising same will become apparent and described in clear, concise and exact terms in conjunction with the drawings in which:

FIG. 1 is a part side elevation, part vertical section of an embodiment of my invention shown in closed operative position, parts being broken away for clarity.

FIG. 2 is a section of FIG. 1 taken along line 22 of FIG. 1;

FIG. 3 is a front view of the device of FIG. 1, parts being broken away and shown partly in section for clarity the dot-dash lines showing the door in inoperatively open position;

FIG. 4 is a section of FIG. 1 taken along line 4-4 of FIG. 1;

FIG. 5 is a section of FIG. 1 taken along line 5-5 of FIG. 1;

FIG. 6 is a wiring diagram schematically showing the electrical circuit embodied in the form of the device illustrated in FIGS. 1-5;

FIG. 7 is a schematic longitudinal cross-sectional view through another embodiment of an autoclave embodying the principles of my invention;

- 3 FIG. 8 is a schematic transverse cross-sectional view through the FIG. 7 embodiment; and

FIG. 9 is a time-temperature diagram illustrating one preferred range of operation.

Description of the preferred embodiments In the embodiment of the invention shown in FIGS. 16, the casing 10 constitutes the closed pressure system of the apparatus, said casing being disposed within a housing 11 mounted on legs 12. Within the housing 11 is a bracket 13 which supports the motor 14 and attached fan 15 positioned behind said casing 10. In this illustrated form of my invention, said casing 10 comprises a cylindrical shell 16 with a front peripheral flange 17 defining the front opening 18, the rear partition wall 19, and the rear condenser pressure head 20 having an annular wall 21 mounted upon and attached to the rear of said shell 16 and the preferably concave end wall 22 spaced from partition wall 19.

' Extending through the apertures 23 and 24 in the front annular panel 25 of the said housing 11 as best seen in FIG. 2 are bolts 26 and 27, on which the respective washers 28 and 29 and nuts 30 and 31 are operatively mounted. Swingably mounted upon the said bolt 26 is the closure pressure bar 32, said bar having an aperture 33 through which the shank of bolt 26 extends, the opposite end of said bar having a hooked portion 34 with an open slot proportioned to fit over and retractably engage the shank of bolt 27. Bar 32 is maintained in spaced relation to the front of said casing by the two I sleeves 35 and 36 mounted over the respective bolts 26 and 27, the respective rear ends of said sleeves engaging said front wall 25 and the forward ends engaging the said bar.

Extending through in threaded engagement with bar 32 at the middle portion of said bar is the pressure screw 38, as seen in FIG. 1, the forward end of said screw 38 having affixed there-to the handwheel 40 and the rear portion thereof protruding through a bearing 41 which in turn is screwed into the hollow boss 42 integral with the central portion of the door 43. A retaining pin 42a maintains a fixed spacedrelationship between the door 43 and the pressure screw 38 while permitting free rotation of screw 38 within the bearing 41.

The peripheral portion 44 of door 43 carries the annular gasket 45 adapted :for pressing engagement with peripheral flange 17 of the casing. The rearmost terminal 46 of pressure screw 38 is engageable with the inner wall 47 of the cavity in the hollow boss 42, the arrangement being suc'h thatupon an operative turning of the hand- Wheel 40 in a clockwise direction, terminal 46 will bear against said inner wall 47, whereby the entire door 43 will be brought into pressing engagement with annular flange 17, gasket 45 serving as a gastight seal. To retract door 43 from its operatively closed sealing position, the handwheel is turned in a counter-clockwise direction and the door then swung around bolt 26 to the open position shown by dot-dash lines in FIG. 3.

The cylindrical shell 16 constitutes the sterilizing compartment of my apparatus, said shell supporting therein the laterally enclosed open-ended rack 48 having the shelves 49a and 49b supporting the respective conventional perforated trays 5G and 51 adapted to support therein the articles to be sterilized. The interior 48a of the rack functions as a sterilizing chamber. The open rear end of 52 of said rack is in abutment with rear partition wall 19, the front end 53 being spaced rearwardly from the front end of the shell 16 so as to permit the operative flow of currents of air and steam in the manner hereinbelow set forth.

The rear condenser pressure head 26- is made of relatively high heat conducting material, such as copper, said head together with partition wall 19 forming the accelerated condensing chamber 54 communicating through the bottom port 55 in partition wall 19 with the water reser- L voir 56 at the bottom of shell 16 below the rack 48, and through the upper ports 57 with the jacket 58 formed by the space between the top 59 and sides 60, 61 of said rack 48 and the adjacent arcuate wall 62 of the said shell 16.

The water reservoir is defined by the lower portion 63 of the shell 16, the corresponding lower portion of the condenser head 20 and the front barrier 64, the upper edge 65 of the latter being spaced below the bottom wall 66 of said rack to provide the passageway 67. The arrangement is hence such that all portions of the pressure vessel 10 are in intercornmunication. More specifically, the water reservoir 56, the condensing chamber or compartment 54 and the entire interior of the shell 16 including the jacket 58, the interior of the sterilizing compartment rack 48 and the passageway 67 are in intercommunication.

Disposed within the condensing chamber 54, as best seen in FIGS. 1 and 5, is an air escape tube 68, the lower portion of which is connected to the fitting 69 attached to the partition 19 and in communication through the port 70 with the interior of the sterilizing compartment 48. The upper portion of tube 68 is'connected to a conventional air release valve 71 the inner chamber 72 of which contains a ball member 73 normally resting upon the seat 74 at the top of said tube 68, there being an outlet passageway 75 communicating between valve chamber 72 and the atmosphere. The operation of valve member 7 1 is conventional. Thus ball 73 is raised above its seat by air passing upwardly through tube 68 to permit the air to enter the valve chamber 72 and pass out through passageway 75. When steam enters the tube 68 the ball is raised to the level of upper seat 76 closing the passageway 75.

Underlying the bottom wall portion 63 of the vessel is the conventional electric heating element 77 suitably embedded within the strip 78 in known manner, the clamping bands 79 enveloping the shell 16 and tying the strip 78 thereto so that the heating element is disposed below water reservoir 56. The terminals 80 and 81 are electrically connected to heating element 77 for connection to a suitable source of electrical energy.

The casing 10 is also provided with a steam safety valve 82 of conventional construction for releasing, in well-known manner, the steam from the casing into the atmosphere when a predetermined pressure is exceeded;

In the embodiment illustrated, the sensor element 83 is attached to the shell 16, said element being connected in known manner to a thermostat 84, the arrangement being such that when a predetermined temperature within casing 18 is reached, sensor element 83, heated by vapors entering the cavity 85, will activate the thermostat 84 to operate a switch in a manner to be hereinafter described The sensor 83 and thermostat 84 are of conventional constructions which need not be described for an understanding of this invention. Sufiice it to say that in the form iilustrated, the sensible heat of the sensor is transmitted to a heat-sensitive switch memben'such as a bimetal, so that when the predetermined temperature is reached the switch element within the thermostatwill move from one position to another. The embodiment shown contains the reset button 86 for returning the thermostat to its original position for a new operative cycle. The switch in the thermostat is schematically shown as member 87 in the wiring diagram of FIGURE 6, said switch being permanently electrically connected to terminal 88, and alternately electrically engageable'with th terminals 89 and 90.

At the bottom of the device is the conventional tern: perature overload switch 91 which is thermally connected ment therein, identified in FIGURE 6' by the reference" numeral 92, will open the circuit connected to the heat ing element 77. The switch element 92 of switch member 91 is electrically connected to the terminals 93 and 94 in series with the main current-supply lines 95 and 96. A reset button 97 connected to the actuating rod 98 is adapted to reset the switch member 91 in known manner.

The switch member 99 of the main on-ofi" switch 100 is operatively connected, in known manner, to the internal switch elements identified in FIGURE 6 by the reference numerals 101 and 102 for connecting the respective terminals 103 and 104 with the switch terminals 195 and 106.

As aforesaid, the said motor 14 and fan 15 are mounted at the rear of the casing 10, with the fan establishing a cooling air stream in heat exchange relation to the steam in the vessel 10 adjacent condenser head 20. The motor is electrically connected to the terminals 107 and 108 in series with the said main lines 95 and 96. The motor-fan assembly is positioned in front of the rear wall 109 of the outer housing 11, said Wall having ventilation perforations 110 therein. At the front of the apparatus, mounted on the door 43 and operatively communicating with the interior of the pressure chamber, is the thermometer 111 for indicating the temperature prevailing within said chamber.

The apparatus above described is a self-contained portable unit with the pressure vessel 10 in coactive relation with a cooling device illustrated as the motorized fan 15. The said pressure vessel is divided into a number of compartments, as hereinabove described, but since the compartments are in intercommunication with each other, the pressure vessel 10 is to be regarded, within the meaning of this invention, as a unitary member embodying components having the functions of the condensing chamber 54, water reservoir 56 and sterilizing chamber 48a. Although a thermal sensor 83 and thermostat 84 are operatively connected to the specific form of my invention illustrated, it is to be understood that other forms of switch means sensitive to conditions within the pressure chamber may be employed-such as a conventional pressure-sensitive switch or a combination of temperature and pressure-sensitive switches.

The wiring diagram shown in FIGURE 6 is exemplary of a circuit employable with my apparatus. In this particular circuit it will be noted that the heating element 77 and motor 19 are in parallel, and so arranged that when one is in operation the other is nonoperative. For example, in the full-line position of the switch components as shown in FIGURE 6, the switch element 87 of the thermostat 84 bridges the terminals 88 and 89 to close the circuit through the heating element 77, the circuit through the motor 14 being open since the two-position switch element 87 is not in contact with the terminal 90. When the thermostat 84 is operaively tripped by the prevailing temperature within the pressure chamber 10, the switch element 87 will move to the broken-line position indicated, bridging the terminals 88 and 90 and thereby closing the circuit through the motor 14 and opening the circuit through the heating element 77. When the reset button 36 is actuated, the said switch element 87 is returned to its position closing the circuit through the heating element 77 and opening the motor circuit.

In the operation of this device, the door 43 is opened, and the reservoir 56 is filled with water to a predetermined level. The items to be sterilized are placed upon the trays 50 and 51 within the rack 48, the rack then being operatively positioned within the shell 16 -as illustrated. The door is thereafter closed and the switch member 99 actuated to close the circuit through the main on-oif switch 100. The reset button 86 is pushed to close the circuit through the heating element 77, as aforesaid. The device is now in an operating condition.

As the water in reservoir 56 is heated by the element 77 and vapours are generated, circulation is started within the apparatus. It is to be noted that since steam is lighter than air, it tends to accumulate at the top of the sterilizing compartment. During the operative cycle, some steam passes through the port 55 into the condensing chamber 54, then through ports 57 into the jacket 58 and back into the sterilizing chamber 48a, some steam also passing outwardly through the front passageway 67 into said sterilizing chamber. These currents of steam force the air in the chamber out through the escape port 7 0 upwardly into the tube 68 and operatively out through the air valve 71. As the steam pressure builds up it reaches a point at which the ball member 73 engages the seat 76 to close the passageway 75, in the manner aforesaid, so that the device acts as a closed steam-generating chamber. At a predetermined tempenature-pressure point, the heat in the sensor 83 operatively aotuates the thermostat 84 to open the circuit through the heating element 77, thereby discontinuing the further generation of steam. When the circuit operating the heating element 77 is opened, the motor 19 is energized, thereby setting the fan 15 into motion. Inasmuch as the material out of which the condenser head 20 is composed is of high heat conductivity, the steam within chamber 54 will be rapidly condensed. And since the condensing chamber 54 communicates, in the manner above described, with the jacket 58 and the sterilizing chamber 48a, the cooling process caused by the action of fan 15 will rapidly cause a regional condensation of all the steam within the chamber, the condensate returning to the reservoir 56. When the temperature shown by the thermometer 111 indicates that the pressure Within the chamber has been reduced to that of atmospheric level, the switch member 99 is manipulated to the o position, thereby to discontinue the action of the fan 15. The door 43 is then opened and the rack 48 with the sterilized items removed from the shell 16.

The amount of heat input via the heating element 77 is of such a quantum with respect to the predetermined pressure and temperature conditions within the chamber for an adequate sterilizing cycle, that the heat cut-off and the accelerated cooling cycle are set to begin at a proper predetermined peak temperature. In other words, my invention enables automatic and timed sterilization to be effected by virtue of a known predetermined relationship between the volume of the entire pressure system, the energy input and the rate of condensation.

All that need be done then is to set the control device 84 to a preselected temperature or corresponding pressure, whereafter the heat supply is automatically discontinued and the accelerated condensation process automatically begun, it being understood of course, that trip switch 83 may be made either temperature or pressure sensitive.

In the above description, the invention has been disclosed merely by way of example and in preferred manner; but obviously many variations and modifications may be made therein.

For example, in lieu of the condensing chamber 54 being an integral part of sterilizer chamber 16 shown in the particular application described herein, it would be feasible to install the condenser as a separate device together with the cooling fan but interconnected with the sterilizer chamber 16 as described in this invention so that closed circuit system as fully described would be maintained.

Similarly, m lieu of thewater reservoir 56 being an integral part of the sterilizer 16 as shown in the description for the particular execution of the invention, it would be feasible to provide a water reservoir as a separate unitallowing the water to be filled through a supply valve to flow into the sterilizer chamber from where it would be transformed into steam and then return through the condenser into said reservoir in the sterilizer chamber, all functions taking place within a closed system operating at all times at the same pressure levels.

Such possible modifications in design that may appear obvious to one skilled in the art are shown by way of example in FIGS. 7 and 8, in which the numerals employed correspond to those used in describing the FIGS. 1-6 description with each numeral prefixed by the number 2. Thus the pressure vessel 210 is seen to have door 243 forming a pressure tight closure by means of door gasket 245. A sterilizing compartment 248 is arranged within the vessel 210 above water reservoir 256 which may be filled with water from supply 256a connected via valve 256!) and conduit 256a to reservoir 256. The heating element 278 is afiixed to the underside of the vessel 210. The condensing compartment 254 is shown as spaced from the sterilizing compartment 248 and condensing compartment 254 is fitted with high heat conductive fins 220a to accelerate the condensing process induced by the action of fan 215. The air escape conduit 268 and air release valve 271 are shown in identical manner as conduit 68 and valve 71 of FIGS. 1, 4 and 5. The condenser 254, sterilizing chamber 248 and reservoir 256 form an integrated closed pressure vessel.

The gist of the inventive concept may be readily comprehended from the graph (FIG. 9) in which time is plotted along the abscissa temperature on the left side ordinate and pressure on the right side ordinate. As the graph reveals for any given temperature, the same pressure is obtained, whether during the heating or cooling portion of the cycle. Thus for every drop in pressure, there is a corresponding substantially instantaneous drop in temperature. The graph shows that the temperature pressure relationship is undisturbed during the entire sterilizing process from beginning to end on all three basic regional compartments that constitute the closed pressure system i.e., the sterilizing chamber, the condensing chamber and the water reservoir from where the steam is generated and flows back as water upon completion of the condensation phase.

The shaded area in the graph, delineated -by the abscissa drawn at 250 F. shows the efiective sterilizing range to which the good in the sterilizing chamber are exposed. The sterilizing eflicacy of this shaded area is automatically maintained and determined by the heat input for generating the steam, the rate of accelerated condensation and the heat losses of the entire assembly. The flattened section on the horizontal part of the graph at the 280 F. and 34 lbs/sq. inch abscissa is the result of the residual heat resisting initiation of condensation, and de-energizing of the heating elements at point A. At point B the condensing action of the fan, started at A, has overcome the override residual phenomena of the deenergized elements and temperature and pressure drop rapidly, said pressure-temperature relationship remaining in equilibrium until atmospheric pressure has been reached. V

It is obvious that the flattened section of the graph on abscissa 280 F. can be lengthened or shortened by interposition of timing devices delaying the energization of the accelerated condensing cycles without in any manner changing the basic concept of the process. Similarly,

the peak temperature can be increased or decreased as dictated by the required sterilization.

It is thus seen that the invention provides a contained system, all the condensate being collected so that there is no release of any of the generated steam into the at- 7 mosphere. Due to the accelerated condensing action, the

sterilizing and cooling cycle is completed in a minimum of time. The steam is maintained at all times in a satu-- rated condition, and no steam is lost. Since the closed system enables a fixed pressure and temperature drop relationship to be maintained after steam generation has been completed, equilibrium is constantly maintained within the chamber, so that there can be no boiling over of any bacteriological liquid when that is the material being sterilized. The only human judgment that is required with the apparatus of my invention. is that of observing the temperature reading of the gauge 111 in order to determine when the door can be opened. ,In lieu disclosed inventive concept within the scope of the appended claims.

What is claimed is: 1. In a sterilizing apparatus, a pressure vessel comprising an enclosed casing having a sterilizing compart-' ment therein, a steam condensing compartment having an exterior wall of high heat conducting material, an electric fan outside of said vessel and in adjacent facing relation to said exterior wall, a water reservoir at the bottom of said casing, means in said casing for storing goods to be sterilized, said compartments being regionally separated, a partition wall between said condensing and sterilizing compartments, port means in open com munication between said condensing compartment and said reservoir and sterilizing compartment, said reservoir being in open communication with both of said compartments, heating means coactively associated with said reservoir for generating steam from water stored therein, said heating means having an electric heating element, an electric circuit operatively connected to said element and said fan, a switch in said circuit movable between first and second operative positions, means to bring said switch to said first position, and automatic switch-actuating means connected to said switch and responsive to a predetermined peak temperature in said sterilizing compartment to bring said switch to said second position, the relation of said heating element, fan circuit and switch being such that the circuit through the fan is open and the circuit through the heating element closed when said switch is in said, first position, and said circuit through the fan is closed and the circuit through the heating element open when said switch is in said second position.

2. In a sterilizing apparatus, a pressure vessel com prising an enclosed casing having a sterilizing compartment therein, a rack in said compartment with an inner compartment and said jacketed passageway and said res ervoir, heating means coactively associated with said reservoir for generating steam from water stored therein, said heating means having an electric heating element, an

electric circuit operatively connected to said element and said fan, a switch in said circuit movable between first' and second operative positions, means to bring said switch to said first position, and automatic switch-actuating means connected to said switch and responsive to a predetermined peak temperature in said sterilizing compart I ment to bring said switch to said second position, the relation of said heating element, fan, circuit and switch being such that said circuit through the fan is openand the circuit through the heating element closed when said 7 switch is in said first position, and said circuit through the fan is closed and the circuit through the heating element open when said switch is in said second position.

3. In a sterilizing apparatus, a pressure vessel comprising an enclosed casing having a sterilizing compartment, a steam condensing compartment having a high heat conducting exterior wall, a water reservoir at the bottom of said casing, means in said casing for storing .7

goods to be sterilized, said compartments being regionally separated, a partition wall between said condensing and sterilizing compartments, port means in open communication between said condensing compartment and said reservoir and sterilizing compartment, said reservoir being in open communication with both of said compartments, an air escape conduit in communication with said sterilizing compartment, an air release valve operatively connected to said conduit, an electrically operated fan outside of said vessel and in adjacent facing relation to said exterior wall of said condensing compartment, an electric heating element coactively associated with said reservoir for generating steam from water stored therein, an electric circuit operatively connected to said element and said electrically operated fan, a switch in said circuit movable between first and second operative positions, means to bring said switch to said first position, and automatic switch-actuating means connected to said switch and responsive to a predetermined peak temperature in said sterilizing compartment to bring said switch to said second position, the relation of said heating element, fan, circuit and switch being such that said circuit through the fan is open and the circuit through the heating element closed when said switch is in said first position, and said circuit through the fan is closed and the circuit through the heating element open when said switch is in said second position.

4. Apparatus as in claim 1 in which said steam condensing compartment is spaced from said sterilizing compartment; and each of said condensing and sterilizing 5. A method for sterilization comprising the steps of: enclosing the items to be sterilized in a pressure chamber; generating steam; introducing the steam into the chamber at temperatures above atmospheric; maintaining the steam in the chamber until desired sterilization has been effected; establishing a cooling air stream in heat exchange relationship with the steam upon attainment of a given pressure temperature condition in said chamber; and collecting the condensed steam for subsequent reconversion to steam and reintroduction into the chamber.

6. A method as in claim 5 in which the quantity of heat input to generate the steam is selected to maintain the steam at a given temperature in the sterilizing chamber for a desired time.

7. A method as in claim 5 in which any air present in the chamber prior to introduction of the steam thereto is expelled to the atmosphere.

References Cited UNITED STATES PATENTS 1,217,113 2/1917 Darnall 21-85 2,093,334 9/1937 Meitzler.

2,613,130 10/1952 Jewell et a1 2196 2,715,251 8/1955 Vischer 2198 3,065,509 11/1962 Vischer 21-94 X MORRIS O. WOLK, Primary Examiner.

JOSEPH SCOVRONEK, Examiner.

I. ZATARGA, Assistant Examiner.

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