Forced water fill and drainage for an unplumbed sterilizer

An unplumbed sterilizer (10) with a self-contained heater (34, 35) has a fill system (32) that includes a pump (82) to pump liquid from a sterilizer reservoir (26) to the sterilizing chamber (22). By utilizing the pump (82) in the fill system (32), a precise volume of water is filled into the sterilizing chamber (22) with each sterilizing cycle, and further, the pump pressure flushes the fill system (32) of particles that may otherwise partially or fully clog the fill system (32). A sterilizing chamber drain cycle is executed immediately prior to the fill cycle by operating the pump (82) to pump liquid from the sterilizing chamber (22) to the reservoir (26). The operation of the drain cycle permits the fill cycle to be executed without any residual liquid in the sterilizing chamber (22); and further, the subsequent fill cycle will flush any particles from the fill system (32) introduced by the drain cycle.

FIELD OF THE INVENTION 
This invention relates generally to the field of sterilizers and, more 
particularly, to an improved method and apparatus for filling an unplumbed 
sterilizer with liquid. 
BACKGROUND OF THE INVENTION 
For purposes of this specification and claims, an "unplumbed sterilizer" is 
herein defined as a sterilizer having an internal liquid reservoir fluidly 
connected to a sterilizing chamber which is charged or filled with a 
preset volume of liquid from the reservoir. A heater operatively connected 
with the sterilizing chamber converts the liquid in the sterilizing 
chamber into a sterilizing fluid. Since the sterilizing fluid is generated 
within the sterilizer, an unplumbed sterilizer is not connected to an 
external source of steam or other sterilizing fluid. While the description 
herein will often refer to the liquid in the reservoir as water and the 
sterilizing fluid as steam, other liquids and sterilizing fluids may be 
used. In unplumbed sterilizers, the charging or filling of the sterilizing 
chamber with the preset volume of water is an important part of the 
sterilizing cycle. The preset amount of water is dependent on the physical 
characteristics of the sterilizing unit, the load, that is, of media, 
articles, utensils or the like to be sterilized, and the particular 
sterilizing cycle. Typically, in unplumbed sterilizers, often referred to 
as bench top sterilizers, the sterilizing chamber is physically located 
below or lower than the water reservoir within the sterilizer. When it is 
desired to fill the sterilizing chamber with water, a timer-controlled 
solenoid valve is opened; and gravity feeds the desired volume of water 
from the reservoir to the chamber during the time the solenoid valve is 
maintained open. While such gravity feed systems have the advantage of 
simplicity, they also have several inherent disadvantages. 
One problem with gravity feed fill systems is the potential for 
contaminants to partially or fully clog the valve of the fill solenoid. 
Although this seldom occurs, it is potentially the most troublesome of 
problems. Often the source of fill valve contamination is the articles or 
media being sterilized. During the sterilization process, some media may 
evaporate from a culture; and when the sterilizing chamber is vented back 
to the reservoir, the media condenses into the reservoir water. During 
subsequent fill cycles, small particles of media or other contaminants 
which are in the fill water can become lodged in the fill solenoid valve 
and restrict the flow of water into the sterilizer while the valve is 
open. Since the fill cycle is timer-controlled, restrictions in the fill 
valve will result in the sterilizing chamber being filled with less than 
the desired volume of water. The smaller volume of water presents a 
smaller load to the heaters that convert the water to steam, and 
therefore, the heaters may overheat. The heaters have over-temperature 
protection, that is, high temperature thermostats, to turn the heaters OFF 
in the event of overheating. However, continued operation of the heaters 
at the over-temperature limit is detrimental to the life of the heaters. 
Further, to remove the valve contamination may require some disassembly of 
the sterilizer which is inconvenient and time consuming. 
Another problem with some gravity feed systems is the variation in 
reservoir head pressure from different levels of water in the reservoir. 
After the reservoir is filled, the level of water in the reservoir 
continuously drops with subsequent sterilizing cycles. When the reservoir 
reaches a low water limit, the reservoir is refilled. Different water 
levels in the reservoir produce correspondingly different head pressures 
during the gravity feed fill cycle of the sterilizing chamber. Therefore, 
executing the constant time water fill cycles with different water levels 
in the reservoir will result in different volumes of water being filled 
into the sterilizing chamber. Overfilling of the sterilizing chamber can 
result in overflow, or spillage when the door of the sterilizer is opened, 
or difficulties in drying. Conversely, under-filling, or a short fill of 
water in the sterilizing chamber, causes the heating element to overheat. 
As illustrated in U.S. Pat. No. 4,865,814, this problem can be eliminated 
by providing a second water reservoir that is used for filling the 
sterilizing chamber with water. Before any fill cycle is executed, the 
second reservoir is filled, thereby guaranteeing that each fill cycle will 
fill the sterilizing chamber with the same volume of water. However, the 
use of a second reservoir has several disadvantages. First, the time 
required to fill the second reservoir increases the overall sterilizing 
cycle time. Second, the provision for a second reservoir and the 
associated valves and plumbing increases the overall cost of the 
sterilization device. 
A still further problem relates to the drainage of water from the 
sterilizing chamber after a sterilizing cycle. The desired volume of water 
filled into the sterilizing chamber is a volume that, to the greatest 
extent possible, will be converted into steam so that a minimum of water 
remains in the chamber after the sterilizing cycle. However, with 
successive sterilizing cycles, liquid contained in the material being 
sterilized may be evaporated from the material and condensed within the 
sterilizing chamber. Alternatively, during a sterilization cycle, all of 
the liquid filled into the chamber may not be converted into sterilizing 
steam. In either case, the result is that liquid remaining from prior 
sterilizing cycles can accumulate within the sterilizer; and over a number 
of sterilizing cycles, the liquid accumulation can result in liquid 
overflowing or running out of the sterilizer when it is opened to remove 
the sterilized material. Such an overflow is a significant inconvenience. 
To avoid or minimize the problem of such water accumulation and overflow, 
immediately after the completion of the sterilizing cycle, many 
sterilizers open the fill solenoid valve, and the pressure in the 
sterilizing chamber causes any water that remains in the sterilizing 
chamber to be forced back through the fill line, through the fill valve 
and into the reservoir. While this reverse flush of water through the fill 
line is effective in removing the excess water, it does present problems 
of its own. For example, if the water that has accumulated in the bottom 
of the sterilizing chamber is contaminated with particles of the media 
being sterilized, that contamination can accumulate in the fill line or in 
the fill valve, potentially clogging either the fill line or the fill 
valve. Further, if the sterilizer is not used again for a period of time, 
for example, overnight, the media that has accumulated in the fill line or 
the fill valve will harden, which will prevent it from being flushed or 
washed away by the next fill cycle. Media that has hardened in the fill 
line or fill valve often must be physically removed, requiring the partial 
disassembly of the sterilizer for cleaning. Such a cleaning operation is a 
substantial inconvenience to the user. 
From the above, it is clear that sterilizers having gravity feed fill 
cycles exhibit several deficiencies which may lead to the over-filling or 
under-filling of water into the sterilizing chamber with the consequential 
disadvantages of either water spillage or high temperature heater 
operation which reduces the useful life of the heater. Further, known 
attempts to provide a more consistent water fill volume have the 
disadvantages of a longer fill cycle time and increased cost and 
complexity in the sterilizer design. Consequently, there is a need to 
provide an improved, more efficient and reliable apparatus and method for 
filling for an unplumbed sterilizing chamber with water. In addition, 
known drainage techniques for removing water after a sterilizing cycle 
have the disadvantage of potentially restricting or clogging the fill line 
or fill valve. Consequently, there is a need for providing a better, more 
reliable drainage system for the sterilizing chamber. 
SUMMARY OF THE INVENTION 
The present invention provides an unplumbed sterilizer provided with a 
self-contained heater, that fills the sterilizing chamber with a desired 
volume of water from a reservoir without underfilling or overfilling. 
Further, the unplumbed sterilizer of the present invention reliably and 
repeatedly fills the sterilizing chamber with the desired volume of water 
during successive sterilizing cycles without overfilling or underfilling. 
The volume of water input to the sterilizing chamber is independent of 
variations of water level in the reservoir and further operates more 
reliably to provide the desired water fill in the presence of 
contamination in the fill line or the fill valve. In addition, the 
sterilizer of the present invention drains excess water from the 
sterilizing chamber prior to a fill cycle so that the fill cycle cleans 
the fill system of particulate matter remaining from the drain cycle, 
thereby minimizing the potential for uneven fills and more consistently 
filling the sterilizing chamber with a known volume of water. Therefore, 
the unplumbed sterilizer of the present invention has the advantages of 
operating more reliably and being self cleaning so that partial 
disassembly and physical cleaning is generally not required. 
In accordance with the principles of the present invention and in 
accordance with the described embodiments, the unplumbed sterilizer 
includes a chamber for receiving items to be sterilized which has an inlet 
for receiving water. A heater is operatively connected to the chamber for 
heating the water to produce the steam used for sterilization. A pump is 
fluidly connected to the reservoir. A control operates the pump in a 
predetermined controlled manner to pump a predetermined volume of water 
from the reservoir into the sterilizing chamber. In another aspect of the 
invention, an electro-mechanical valve with a flow restricting orifice is 
located between the pump and the sterilizing chamber. 
In another embodiment of the invention, the control provides a method of 
operation in which a control signal operates the pump to pump the desired 
volume of water into the sterilizing chamber. In one aspect of the 
invention, the pump is operated for a predetermined period of time. In 
another aspect of the invention, a positive displacement pump is operated 
over a predetermined pump cycle of operation. In a still further aspect of 
the invention, the control opens a valve with an orifice or flow 
restrictor that is located between the pump and the sterilization chamber. 
The pump operates at a known pressure to pump the water through a flow 
restricting valve orifice of a known size over a predetermined period of 
time, thereby providing a desired volume of water to the chamber. 
The pump consistently and reliably provides the same volume of water to the 
chamber over successive fill cycles. With the pump, the desired volume of 
water is provided to the chamber in much less time than with gravity feed 
systems and is independent of variations in head pressure within the 
reservoir itself. Further, the pressure of the pump is effective to unclog 
the valve of any contaminant particles that may have lodged therein. 
Therefore, the water fill system for a sterilizer utilizing the pump has 
the advantages of providing shorter and more accurate water fill cycles 
that, in turn, result in more efficient and reliable sterilizer operation 
by eliminating the adverse effects of underfilling or overfilling the 
sterilizing chamber. The water fill system utilizing the pump has the 
advantage of being generally self cleaning. 
In another embodiment of the invention, the control executes a drain cycle 
immediately prior to the above-described fill cycle and may be considered 
a part of the fill cycle. Upon initiating the drain cycle, the solenoid 
valve is opened; and the pump is operated to produce a pressure 
differential that forces water remaining from a previous sterilizing cycle 
from the chamber, through the open fill valve and back into the reservoir. 
The drain cycle removes accumulated liquid from the chamber so that each 
fill cycle is started with a known and predictable quantity of water in 
the chamber. Depending on the location of the physical drain within the 
chamber, the known quantity of water may be little or none. Therefore, the 
invention has the advantage of preventing overflow from accumulated water. 
In addition, knowing the quantity of water with which the fill cycle 
starts, permits a more predictable and reliable fill cycle with the 
advantages previously discussed. 
Further, if the drain cycle introduces any particles or other contaminants 
into the fill line and the fill valve, the execution of a fill cycle 
immediately after the drain cycle is effective to wash such contamination 
out of the fill line and the fill valve before it has an opportunity to 
coagulate or harden. Therefore, the invention has the advantage of 
providing even more reliable operation because the drain cycle is 
self-cleaning.

DETAILED DESCRIPTION OF THE INVENTION 
Referring to FIG. 1, a sterilizer 20 has a sterilizing chamber 22 having a 
hinged door 23 on the front thereof through which articles or material to 
be sterilized are placed into and removed from the sterilizing chamber 22. 
Often, the sterilizing chamber 22 is mounted at a slight incline with 
respect to the horizontal so that any liquid within the sterilizing 
chamber will flow to the rear bottom portion 24 of the sterilizing chamber 
22. The sterilizer 20 further includes a reservoir 26 which is filled with 
water 28. The reservoir can be filled manually or is filled automatically 
in response to outputs from a water level detection switch 30 that detects 
high and low water levels within the reservoir 26. 
Prior to a sterilizing cycle, a volume of water is transferred from the 
reservoir 26 through a fill system 32 and into the sterilizing chamber 22. 
The water collects at the bottom rear section 24. A main, steam generating 
electrical heater 34, which is in the range of 1500 watts, is turned on to 
vaporize the water into sterilizing steam which pressurizes the 
sterilizing chamber 22 and sterilizes items within the chamber 22. An 
electrical drying heater 35, in the range of 400 watts, is used to dry the 
sterilized articles or material in a known manner. A pressure sensor 36 
and a temperature sensor 38 provide respective pressure and temperature 
output signals to an analog interface and switch circuit 40 that, in turn, 
provides the temperature and pressure signals to a controller 42. The 
controller 42 is preferably a microprocessor-based programmable controller 
with arithmetic and logic capabilities. The controller 42 controls the 
sterilizing cycle in accordance with the temperature and pressure output 
signals. In addition, a pressure relief valve 43 will respond to 
excessively high pressure in the sterilizing chamber 22 and open the 
chamber to the reservoir 26 in response to the pressure exceeding the 
pressure relief valve setting. In a known manner, the controller 42 
provides a control signal to an I/O controller 44 to operate a vent 
solenoid valve 45 at the end of the sterilizing cycle to vent the 
sterilizing steam back to the reservoir. 
A heater power source 46, for example, a source of AC power, is connected 
to an overheat relay 48. Under normal conditions, the overheat relay 48 is 
operated by the circuit 40 to connect power from the heater power source 
46 to a main heater relay 52 and drying heater relay 54. The relays 52, 54 
are preferably solid state relays and have input control signals connected 
to outputs of the controller 42. If the controller provides a main heater 
ON signal on line 56, the main relay 52 closes connecting power to the 
main heater 34. Similarly, if the controller 42 provides a drying heater 
ON signal on line 58, the drying heater relay 54 connects heater power to 
the drying heater 35. A printer 60, keyboard 62 and display 64 may be 
connected to the controller 42 depending upon the requirements of the 
sterilizer 20. The keyboard 62 is used by an operator to provide process 
information to the controller 42. For example, parameters for different 
types of sterilization cycles with associated pressures, temperatures and 
timing parameters can be input or programmed into the controller 42 using 
the keyboard 62. The display 64 is used to display the information being 
input by the operator and also displays the active cycle and associated 
parameters during a sterilization cycle. The printer 60 can be used to 
print out the process variable values that are used during a sterilization 
cycle. 
The water fill system 32 of the present invention utilizes an 
electro-mechanical valve 66 having a solenoid 68 operating a valve stem 70 
that selectively opens and closes a flow restricting orifice 72 within the 
fill valve 66. The fill valve 66 has a first port 74 connected to an inlet 
76 of the sterilizing chamber 22. Further, the fill valve 66 has a second 
port 78 connected to a first port 80 of a pump 82. The pump 82 has a 
second port 84 connected to an outlet of the reservoir 86. Therefore, the 
fill system 32 provides a fluid connection from the reservoir 26 through 
the pump 82 through flow restricting orifice 72 of the fill valve 66 to 
the sterilizing chamber 22. The operation of the solenoid 68 and pump 82 
are controlled by the controller 42, providing respective control signals 
to the I/O interface 44 which in turn is connected to the pump 82 and the 
solenoid 68. 
In use, the sterilizer 20 has the capability of executing many different 
sterilizing cycles depending on the articles or media to be sterilized. In 
each of those sterilizing cycles, it is necessary for the sterilizing 
chamber 22 to be filled with a precise volume of water which the main 
heater 34 converts to sterilizing steam. Variations in the size of that 
volume of water adversely affect the operation of the sterilizer and the 
sterilizing process. For example, a "short-fill", which is less than the 
desired volume of water filled into the chamber 22, provides less than the 
desired thermal load for the main heater 34. Consequently, the main heater 
34 may overheat, causing the overheat relay 48 to disconnect power from 
the main heater relay 52, thereby interrupting the sterilizing cycle. 
Further, continued overheating of the main heater 34 will shorten its 
useful life. On the other hand, providing too great a volume of water to 
the sterilizing chamber 22 may require a longer time for the main heater 
34 to convert the water to steam, may reduce the quality of the steam for 
sterilization purposes and/or may saturate the media being sterilized. 
Therefore, providing the precise volume of water to the sterilizing 
chamber is important for consistent and reliable high quality sterilizing 
cycles. 
FIG. 2 illustrates the steps of a water fill cycle in accordance with the 
principles of the present invention. FIG. 2 is representative of a process 
that is executed within the operating program of the controller 42. The 
subroutine of FIG. 2 at 200 awaits the command to begin a water fill 
cycle. The command may represent the setting of a flag or other state 
within the controller 42 in response to running a sterilizing cycle. 
Further, the command may be generated by an operator input through the 
keyboard 62. If no fill cycle start is detected the water fill cycle 
subroutine returns to the main program and remains inactive. Upon 
detecting a fill cycle start, the subroutine at 202 will cause the 
controller 42 to produce a signal through the I/O interface 44 to the 
solenoid 68 to operate the solenoid 68 so that the flow restricting 
orifice 72 of the fill valve 66 is opened. Thereafter, the subroutine at 
204 will cause the controller 42 to produce another output signal to the 
I/O interface 44 which is also connected to the pump 82. The controller 42 
turns the pump 82 ON so that the pump 82, which is preferably a diaphragm 
pump, produces a pressure and pumps water from the reservoir 28 through 
the pump 82 to the fill valve 66. The pressure produced by the pump 82 and 
the diameter of the orifice 72 are known; and therefore, the period of 
time that the pump must operate to provide the desired volume of water 
within the sterilizing chamber 22 is readily determined. The operating 
time of the pump is measured by the system by the subroutine at 206, 
simultaneously with starting the pump 82, starting a fill timer 
immediately after turning the pump 82 ON. Thereafter, on a periodic basis, 
the subroutine at 208 checks whether the fill timer has expired. When the 
subroutine at 210 detects the expiration of the fill timer, the controller 
42 changes the signal to the I/0 interface 44 to turn the pump 82 OFF. 
Thereafter, at 212, the controller changes the state of the signal to the 
I/O interface 44 to operate the solenoid 68 to close the orifice 72 within 
the fill valve 66. Preferably, the pump 82 is a small diaphragm pump that 
produces a pressure in the range of approximately 8-15 pounds per square 
inch ("psi"). 
By utilizing the pump 82 within the fill system 32, the volume of water 
filled into the sterilizing chamber 22 can be more accurately controlled 
not only within a single fill cycle but over successive fill cycles. 
Further, the pump pressure will result in the sterilizing chamber being 
filled with the desired volume of water in approximately 15-20 seconds. 
With a gravity feed system, a comparable fill cycle duration is often 
60-90 seconds. Therefore, the pump 82 permits shorter water fill cycle 
that with resulting advantage of a more efficient sterilizing cycle. In 
addition, the pressure produced by the pump is effective to dislodge 
particles or other contaminants that may have collected around the orifice 
72 that would otherwise restrict flow of the water through the orifice 72. 
Therefore, the fill system 32 utilizing the pump 82 has a self cleaning 
capability. The fill system 32 has the advantages of providing the 
sterilizer 20 with a more reliable operation and potentially a longer 
life. 
If successive sterilizing cycles are run for liquid loads, the drying 
heater 35 is not used, and the sterilizing process will often evaporate 
liquid from the load and condense that liquid in the sterilizing chamber. 
With successive sterilizing cycles, the liquid from previous sterilizing 
cycles may accumulate within the sterilizing chamber to the point that it 
overflows when the door 23 on the sterilizing chamber 22 is opened. 
Further, the accumulation of liquid in the sterilizing chamber with 
successive sterilizing cycles changes the volume of liquid to be converted 
to steam which may affect the quality of sterilizing steam produced by the 
heater 34. 
To overcome the problem of liquid collecting in the sterilizing chamber 
over successive cycles, the water fill cycle has a second embodiment 
illustrated in the flow chart of FIG. 3. In a manner identical to that 
previously described, the controller 42 executing the subroutine of FIG. 3 
at 302 and 304 detects the start of a fill cycle and operates the solenoid 
68 to open the orifice 72 of the fill valve 66. Next, at 306, the 
controller 42 provides a signal to the I/O interface 44 to turn the pump 
82 ON so that a pressure is created to pump the liquid from the 
sterilizing chamber 22 through the orifice 72 of the fill valve 66 and 
into the reservoir 26. That action, in essence, starts a drain cycle in 
which liquid is drained under pressure from the sterilizing chamber 22. 
The controller at 308 simultaneously with starting the pump 82 starts a 
drain timer; and thereafter, at 310, the controller periodically checks 
whether the drain timer has expired. Upon expiration of the drain timer, 
the controller 42 proceeds to execute the steps 312-320 of the subroutine 
of FIG. 3. Those steps are identical to the previously described steps 
204-212 with respect to FIG. 2 and operate to fill the reservoir with a 
predetermined volume of water for the next sterilizing cycle. 
By using the pump to drain liquid from the sterilizing chamber, the 
sterilizing chamber always has the identical volume of liquid in it prior 
to initiating a fill cycle. That volume may range from no liquid to a 
small volume of liquid depending on the location of the inlet 76 with 
respect to the lowest point in the area 24 of the sterilizing chamber 22. 
Consequently, the utilization of a pressurized drain cycle provides for 
more consistent fill cycles as well as a more consistent sterilizing 
process. In addition, the drain cycle drains the accumulation of water 
within the sterilizing chamber, and therefore eliminates the potential for 
overflow from the chamber upon opening the door. Further, by executing the 
drain cycle immediately prior to the fill cycle, any particles that are 
brought into the fill system 32 by the drain cycle are immediately flushed 
back out of the fill system 32 by the subsequent fill cycle. Therefore, 
the unique combination of drain cycle-fill cycle has the advantage of self 
cleaning the fill system 32. 
While the invention has been set forth by a description of the preferred 
embodiment in considerable detail, it is not intended to restrict or in 
any way limit the claims to such detail. Additional advantages and 
modifications will readily appear to those who are skilled in the art. 
While the pump 82 is preferably a diaphragm pump, other types of pumps, 
for example, a gear pump, a vane pump or other positive displacement pump 
may be used. 
Further, if pump 82 is a positive displacement pump, the valve 66 having 
the flow restricting orifice 72 can used as previously described. However, 
alternatively, the flow restricting orifice 72 in the valve 66 can be 
eliminated because the head pressure of a positive displacement pump is 
sufficiently constant to provide the desired liquid fill from the 
reservoir 26 to the sterilizing chamber 22 over a cycle of operation. 
Alternatively, the solenoid operated fill valve 66 described with respect 
to FIG. 1 could be replaced with a motorized ball valve or other remotely 
controllable valve. In another embodiment utilizing a positive 
displacement pump, for fill cycle operations, the valve 66 could 
implemented with a simple check valve that operates as a function of 
pressure differentials and is not operated by the controller 42. 
Since a positive displacement pump provides a liquid volume output that is 
proportional and linear to the pump operation, the preset volume of liquid 
can be controlled by operating the positive displacement pump over a 
predetermined period of time. In that case, the a fill timer as described 
in steps 206, 208 of FIG. 2 and steps 314, 316 of FIG. 3 can be used to 
measure a predetermined period of time for operating the positive 
displacement pump. Alternatively, as will be appreciated, the operation of 
fill timers can be replaced by operating cycle counters that are operative 
to command operation of the positive displacement pump over whole or 
partial pump cycles. Further, the pump control can be open loop, in that 
the pump is commanded to operate through one or more whole or partial 
cycles. Alternatively, the controller 42 can control the pump as a 
function of a feedback signal derived from the pump operation in which the 
feedback signal represents a measure of angular or linear motion of the 
positive displacement pump. The above also applies to using the positive 
displacement pump to drain the sterilizing chamber as described at steps 
306-310 of FIG. 3. 
The pump 82 has a preferred pressure range of approximately 5-40 pounds per 
square inch {"psi"}, however, a fill cycle could be performed with a 
pressure head as low as 2-3 psi. The controller 42 can also operate with 
the water level detection switch 30 and a fill valve (not shown) connected 
to a liquid supply to automatically maintain the reservoir filled with a 
desired level of liquid or water. The invention, therefore, in its 
broadest aspects, is not limited to the specific details shown and 
described. Consequently, departures may be made from the details described 
herein without departing from the spirit and scope of the claims which 
follow: