Patent GB-887848-A (GB)
Title: Improvements in or relating to the control of autoclaves
IPC: A61L2/24
Filed: 1959-09-21
Abstract: 887,848. Control apparatus for autoclaves. DRAYTON REGULATOR & INSTRUMENT CO. Ltd., HENFREY, K. M., and MARCH, A. A. C. Sept. 21, 1959, No. 32131/59. Class 81 (1). [Also in Group XXXVII] Control apparatus for controlling the operation of an autoclave 1 comprises a valve 14 for controlling the admission of steam thereto and means responsive to the absolute pressure in the autoclave for causing the valve to admit steam thereto when the absolute pressure therein reaches a predetermined value and means responsive to the temperature within the autoclave chamber for determining the period of time during which the steam is admitted to the autoclave in order to achieve substantially complete sterilization and effective at the end of the period to cause closure of the steam-admitting valve. The pressure-responsive means comprises an absolute pressure switch having switch contacts connected in a circuit of electricallyoperated control means for effecting operation of the steam-admitting valve; contacts being operated to close a circuit of the control means when the absolute pressure in the autoclave chamber reaches the predetermined value. The temperature-responsive means comprises a time temperature integrating device including an energy regulator for effecting a switching operation after a predetermined time period, a thermostatic device responsive to the temperature within the autoclave chamber for an initiating operation of the energy regulator when the temperature in the chamber reaches a desired value and an operative connection between the thermostatic device and the energy regulator for adjusting the time period of the regulator according to variation in temperature within the chamber. As shown in Fig. 1, an autoclave 1 is provided with steam through a steam line 13 and pressurecontrol valves 14, 15, the latter being rendered inoperative when required by operation of an electromechanically-controlled valve 16, and via steam-controlled valve 19 and a line 20 which is also connected to the absolute pressure switch 23 (further described below). Air is admitted via a filter 22 and controlled by a valve 21 and water is supplied via a line 24 and control valve 25 and line 26 to a condenser 7, the operating chamber of a pressure-operable valve 9 and via a line 30 to an electromagnetically-operated three-way valve 31 connected to the operating chamber of a pressure-operable valve 32 controlling the connecting of a vacuum pump 5 to condenser 7. The steam-controlled valve 19, the air-controlled valve 21 and the water control valve 25 are arranged to be operated or non- operated in sequence by cams (not shown) mounted on a common shaft indicated in broken line at 34, and driven by a four-position electric motor 35a, which is under the control of a controller 35 connected through an electrical connection 36 to a start switch 37 and an electrical connection 39 to a time-temperature integrator 40, the temperature-responsive element of which is connected through tubing 41 to a bulb 42 inserted in the pipe-line 8. A further electrical connection 43 connects the absolute pressure switch 23 to the electromagnetically-operated three-way valve 31. As shown in Figs. 2 and 3 the absolute pressure switch comprises a base 44 having secured thereto a bracket 45 adapted to mount two bellows units 46 and 47, respectively, the base 48 of the bellows unit 46 being formed with a collar 49 which receives a connecting nipple 53 for effecting a connection of the bellows unit to the autoclave through the line 20 (Fig. 1). The bellows unit 47 is evacuated and sealed and is thus responsive to atmospheric pressure. A beam 56 mounted on pivot member 55 and having slots at each end through which screw-threaded spindles 61, secured to the end-plates 62 of each bellows unit, may have its angular position adjusted by rotation on the screw-threaded spindle 61 and pivot member 64. A pair of switch-carrying members 68 is mounted above the beam and each is supported by springs 72, 77, and the angular position of each may be varied by turning an adjusting-nut 76. On each switch-carrying member 68 is mounted a micro-switch 79, one being operated upon a predetermined angular displacement of a beam in one direction and the other on the displacement of a beam in the other direction. Thus when the bellows unit 46 is connected to the autoclave, the angular position of the beam 56 will be a function of the difference in the respective pressures in the two bellows units, i.e. the absolute pressure, and that at one predetermined value of absolute pressure, one of the micro-switches 79 operates and at any predetermined value of absolute pressure, the other micro-switch. In operation, e.g. in the sterilizing of surgical dressings, the electromagneticallyoperated valve 16 is open to drain, so that the pressure-reducing valve 15 is rendered inoperative and steam is supplied to the chamber at the higher pressure determined by the pressurereducing valve 14. The start switch 37 is then operated and through the control apparatus 35 causes the motor 35a to rotate to its first or pre-vacuum position, in which the cams on the cam-shaft 34 effect closure of the air valve 21 and opening of the water valve 25, the steam valve 19 remaining closed. Closure of the air valve 21 seals the chamber from the atmosphere and opening of the water valve 25 causes water to flow through line 26 to the cooling coil 29 of the condenser 7 and to the valve 9 to operate the valve to the open position. Water also flows through line 30 and valve 31 to operate valve 32 to the open position, thereby connecting the vacuum pump 5 to the condenser 7. The pump thus evacuates the chamber 2 through line 33, valve 32 open, condenser 7, line 8 and valve 9 open. The evacuation of the chamber proceeds until the absolute pressure reaches a predetermined value, for example, 20 mm. Hg, when the absolute pressure switch 23 operates and through the electrical connection 38 and control apparatus 35 causes the motor 35a to move to its second or sterilizing position. The camshaft 34 is correspondingly rotated to a second position in which the cams mounted thereon effecting opening of the steam valve 19 and closure of the water valve 25, the air valve 21 remaining closed. Closure of the water valve 25 causes pressure-operable valves 9 and 32 to close, thereby isolating the vacuum pump and condenser from the chamber 2 and the opening of the steam valve 19 admits steam from main steam supply line 13 through the pressurereducing valves 14, and 15, line 17, valve 19 open, and line 20 to the chamber 2. Steam pressure then builds up in the chamber 2 and when the required sterilizing temperature is reached, the thermo-responsive element of the time-temperature integrator 40 operates to initiate the timing period of the time-temperature integrator, which period is preset according to the sterilizing temperature employed. At the end of this period, the time-temperature integrator operates a switch means in the electrical connection 39 which, through the control apparatus 35 causes the motor 35a to move to its third or post-vacuum position, the cams on the cam shaft 34 effect closure of the steam valve 19 and opening of the water valve 25, the air-valve 21 remaining closed. The opening of the water valve 25 effects consequential opening of the valve 9, but valve 32 is prevented from opening by operation of the electromagneticallyoperated valve 31 by the absolute pressure switch over connection 43, whereby the water line 30 leading to the valve 32 is shut off and the operating chamber of the valve 32 is connected to drain. The chamber 2 is connected by the opening of the valve 9 to the condenser 7 and the steam in the chamber is condensed, until an absolute pressure of, for example, 50 mm. Hg is reached when an interval timer 119 (Fig. 6, not shown) causes the valve 31 to operate to the through position to connect line 30 to the valve 32 which thereupon operates to the open position and connects the vacuum pump 5 to the condenser 7 and after a short period of, for example, one minute, the absolute pressure switch causes the motor 35a to be rotated to its fourth or process end position in which the air valve 21 is opened and the water valve 25 closed, the steam valve 19 remaining closed. Air is thus admitted from the filter 22 through line 20 to the chamber and the sterilizing cycle is complete. As shown in Figs. 4, 5, the timetemperature integrator comprises a sealed housing 84 enclosing a bimetallic strip-operated timing device 85 which consists of a synchronous motor coupled by an electromagnetic clutch to a cam, which after a predetermined angular rotation actuates a micro-switch and serves to control the duration of the shortest sterilizing period that is required at a sterilizing temperature of 275‹ F., the longer times required at lower temperatures being produced by periodically interrupting the supply to the timer motor by means of a thermal switch referred to as an energy regulator, which regulator includes a temperature-responsive bellows unit 86 adapted to be connected by the tubing 41 to the bulb 42 (Fig. 1), a linkage indicated generally at 87 connecting the bellows of the unit 86 to the timing device 85 and a micro-switch 88 operable by an " L "-shaped lever 89 forming part of the linkage. A bimetallic strip 91 carrying a heater 90 is connected in parallel with the load to be controlled and is so arranged that on heating up it operates a switch 120 to break the circuit to the load. The heater then cools and the switch 120 remakes the circuit and repeats the heating cycle. The ratio of time " on " to time " off " is adjusted by a mechanical stop 121 which determines the movement of the bimetal which must take place before the switch operates, the position of the stop 121 being determined by the temperature-sensitive system including the bellows unit 86