Note: Descriptions are shown in the official language in which they were submitted.
spec if ica tion
This lnvention is concerned with methods and apparatus
for cqmbined ultrasonic washing and biocidal treatment of
articles such as surgical instruments, utensils, and devices
in a unitized shell pressure vessel.
Surgical instruments constitute a significant portion
of hospital cleaning, decontamination and sterilizing require-
mentS. The complexity of instrument design and nature o
surgical soil compound the problems of suryical instrument
processing. Surgical instruments usually have multiple joints,
hinges, crevices or serrated edges which may harbor large amounts
of soil. The soil itself is usually composed of protein or
other organic material which often has been fixed in place
by heat or chemicals. Furthermore, the necessity for decon-
tamination of soiled instruments with a minimum of risk to
the staff adds to the complexity of the problem.
Commercially available apparatus for preparing
surgical instruments for reuse has required multiple handling
steps and separate pieces of equipment. An example of a
standardly practiced method of processing surgical instruments
calls for placements of the instruments in a washer/sterilizer
which has a cleaning phase which removes the gross soil and
decontaminates the instruments with high temperature steam
(normally 270 F). Since soil which is not removed tends to be
fixed in place by the steam, the instruments are then trans-
ferred to a sonic cleaner. Following sonic cleaning the
instruments are terminally sterilized. This technique requires
multiple handling of instruments and mu~tiple pieces of
equipment.
~1
.
The present invention clrcumvents these problems of
the prior art by makiny possible ultrasonic removal of all soil
before subjecting the articles to biocidal treatment. Further,
to accomplish the multiple processing steps of ultrasonic
cleaning and decontamination, disinfection, or sterilizativn,
only direct insertion Df the articles into a single chamber is
involved.
These contributions of the invention increase avail-
able options in hospital practice for handling of suryical
instruments. For example, open-tray handling and processing
of surgical instruments is made possible. Trays of surgical
instruments can be cleaned by ultrasonic washing and sterilized
directly, without leaving the surgical floor and without
requiring instrument handling or muslin wrapping of instruments
before reuse. Or, surgical instruments directly from surgery
can be cleaned by ultrasonic washing and decontaminated or
disinfected for handling or storage with no hazard to
personnel.
A concept, suggested in prior literature, for sonic
washing in a sterilizing chamber was limited to placement of
sonic transducers internally of a chamber or placement of
sonic transducers on a transducer plate which was isolated by
gasket mounting from the remainder of the shell. Both
approaches have serious disadvantages. Internal chamber
mounting of sonic transducers reduces chamber volume, requires
-2-
moisture-proofiny which is difficult to maintain under the
harsh requirements of ultrasonic c:Leaning and sterilization,
requir,es passage of electrical conductors throuyh the vessel
walls to the transclucers inside the enclosure, and makes
repair or replacement of transducexs expensive and difficult;
internal mounting of transducers in sterilizing chambers has
not been commercially practical. ~lso, use of the separate
gasket mounted transducer plate has not been accepted as
eommercially praetical possibly because of longevity and other
problems in the gas~et area under the harsh conditions
encountered. Therefore, hospital practice has continued to
require multiple handliny steps or conveyor systems utilizing
multiple pieces of equipment for decontamination, sonic
washing, and disinfecting or sterilizing.
Impractical and inoperative aspects of the prior art
have been overcome by combining improved structural features
for a unitized shell with physical steps and proper sequencing
of such steps to accomplish the cavitation required for effective
and efficient ultrasonic washing within a pressure vessel
capable of carrying out hospital biocidal procedures.
Shell material having good sonic transmission
capabilities is selected. The material is also selected to
have high corrosion resistance to biocidal agents and resist-
ance to cavitation-induced erosion and pitting; the latter
requirement substantially eliminates composites such as the
nickel-clad carbon steel used in many sterilizersO The shell
configuration and material provide for direct, rigid, and
reliable external mounting of sonic transducers. Reinforcing
; -3-
is selected to facilitake use of rela-tively thin gage metal
plate for the unitized shell while maintaining strenyth
requir,ements for the pressure vessel, minirnizing interference
with sonic energy transmission, and facilitating transducer
placement for uniformity Df cavitation within the chamber
volume established for placement of articles.
The ultrasonic washing liquid is exposed to deep
vacuum conditions in the unitized shell chamber. Combining
deep vacuum and the transmitting of ultrasonic energy into the
washing liquid produce a synergistic effect achieving rapid
degassing of the liquid and cavitation for efficient ultra-
sonic cleaning. Such deep vacuum facilitates the ultrasonic
cavitation which in turn facilitates rapid removal of
substantially all gases. As a result, effective and efficient
ultrasonic washing is made possible with the transfer of
ultrasonic energy being through a unitized shell wall of a
pressure vessel approved for hospital sterilizing practice.
Rapid processing of surgical instruments is a direct
advantage with ultrasonic cleaning and decontamination, dis-
infection, or sterilizakion being carried out in a singlechamber. Use of substantially the full volume of the chamber
and economies in manufacture and maintenance result fr~m the
external surface mounting of transducers. Ultrasonic energy
transmission and utilization of transmitted sonic energy are
enhanced to a degree that multiple level sonic washing, e.g.
permitting stacking of trays of surgical instruments in
multiple tiers, is accomplished effectively and efficiently.
--4--
Becau~e of the completeness and efficiency of the
cycles available, surgical instruments can be completely
processed directly after use merely by insertion into the
chamber. The instruments are ultrasonically washed, rinsed,
and either sterilized and readied or reuse in the same
chamber or decontaminated or disinfected for transfer or
storage. Structuxal features of the chamber and exterior
mounting of the transducers provide for long life and
economical operation.
Other advantages and contributions o-f the invention
are set forth in describing a specific embodiment Df the
invention shown in the accompanying drawings. In these
drawings:
FIGURE 1 is a schematic illustration of ultrasonic
washing and biocidal treatment apparatus of the invention;
FIGURE 2 is a perspective view of rectangular
cross section pressure vessel structure for carrying out the
invention;
FIGURE 3 is a longitudinal sectional view, in
elevation, of pressure vessel apparatus of the invention;
FIGURE 4 is a sectional view taken on line 4-4 of
FIGURE 3;
FIGURE 5 is a fragmentary sectional view, on an
enlarged scale, taken on line 5-5 of FIGURE 2; and .
FIGURE 6 is a graphic representation of a time-
pressure cycle for ultrasonic washing and sterilization of
surgical instruments in accordance with the invention.
A pressure vessel, manufactured in accordance with
teachings of the invention, is capable of operating at
internal pressure levels utilized in sterilizing, i.e.
45 psig, while meeting established safety requirements.
Re~erring to FIG. 1, pressure vessel 10 preferably j'
has its longitudinal axis disposed horizontally. A chamber
for holding articles to be treated is partially defined b~
unitized shell 12 which, within the present teachings, can !,
be relatively thin metal plate selected for transmitting
desired levels of ultrasonic energy.
One longitudinal end of the unitized shell 12 can be
closed by a rigidly welded end wall 14 and the other end sealed
utilizing a suitable door operating assembly 16. The latter
provides access to an interior washing and biocidal treatment
chamber 18. Alternatively, both ends of the shell 12 can have
a door to provide dual access to the interior chamber 18 when
the vessel is wall mounted between rooms.
Articles to be cleaned are placed in the chamber 18;
a closure-operating assembly 16 closes door 19 and seals the
chamber before addition o~ a washing liquid. Wa~er from a
suitable source such as reservoir 20 is delivered, through
solenoid-actuated control valve 21, by pump 22 into the
chamber 18 via a suitable conduit 24. Detergent may be
injected into the water delivered to the chamber by suitable
means, not shown. An electrically operated flow control valve
26 and one-way chec~ valve 28 are provided in conduit 24
between pump 22 and the chamber 18.
Conduit 24 is connected through a wall oE the
pressure vessel to a spray bar 30 having a plurality of spray
S heads 32 which direct the washing :Liquid in a spray encompass-
ing substantially the entire interior of the chamber 18
established for placement of artic:Les by racks or shelves
(not shown). When two or more racl~s of instruments are to be
supported one above the other in the chamber, spray heads 32
may also be posltioned to direct spray inwardly. The flow
control valve 26 can be a solenoid-actuated, normally-closed,
energized-open valve connected, through conductor 34, to a
master control 36.
Washing liquid admitted to chamber 18 normally con-
tains substantial ~uantities of dissolved and entrained gas
which inhibits cavitation. It has been found that a relatively
deep vacuum, combined with the ultrasonic energy which can be
transmitted through the unitized shell 12, makes possible both
effective and efficient cleaning oE surgical instruments~
The invention provides for rapidly removing sub- -
stantially all gas from the washing liquid. The admission of
washing liquid into the chamber 18 is controlled to a pre-
determined depth, sufficient to cover articles to be cleaned.
~ void space can be left in the chamber above the surEace of
the liquid or a standpipe communicating with the chamber can
be provided to expose the washing liquid to the deep vacuum
taught. The chamber can thus be rapidly evacuated to a
relatively deep vacuum which, together with the ultrasonic
energy, rapidly removes gas from the liquid.
', Desired evacuation of the chamber can be accom-
plished in an economically practical manner by a water ejector
5apparatus. Referring to FIG. 1, this apparatus includes a
supply pipe 38 connected, through conduit 24, to -the outlet
of pump 22, and to an ejector assembly 40 having a reduced
diameter venturi section 42. Outlet from khe ejector 40
discharges through a suitable sump or drain 44. A second pipe t
1046 has one end connected to an outlet opening 48 in the upper
portion of the chamber 18 and its other end terminatiny in the
throat 42 of the ejector 40.
An electrically actuated control valve 50 and a
one-way check valve 52 connected in line 46 control the flow
15of air and gases from the void in the top of chamber 18 to
the ejector 40. Valve 50 is connected, through conductor 54,
to the main cor~trol 36 which actuates the valve to control the
flow of gas through pipe 46.
An electrically actuated valve 56 in water supply
20line 38 is connected to and actuated by con-trol 36, via line
58; this controls the supply of water to the ejector 40.
Thus, opening of valves 50 and 56 will result in gas being
drawn from chamber 18 by an aspiration effect to rapidly
reduce the pressure above -the washing li~uid to a deep vacuum.
Evacuation can commence simultaneously with the
admission of water into the chamber and continue for a
sufficient time to achieve the desired vacuum level after the
3~3
filling operation has been completed. Alternatively, the
evacuation can commence after the filliny operation is
partially or completely accomplished. It has been found that
an optimum level of cavitation, with a resultiny increase in
cleaning efficiency, is achieved by maintaininy substantially
the desired deep vacuum exposure of the liquid duriny ultra-
sonic treatment.
In order to transmit desired ultrasonic energy, a
plurality of ultrasonic transducers 60 are rigidly mounted on
an external surface of unitized shell 12. The transducers 60
are connected, through a conductor harness 62, to a power
source 64. The latter, in turn, is connected through line 66
to control 36 for driving the transducers. Transducers 60 are
arranged in a pattern on the vessel shell to apply ultrasonic
energy throughout the liquid in chamber 1~ providing sub-
stantially uniform cavitation while minimiziny wave eneryy
cancellation. The eneryy level and pattern assure cavitation
throuyhout the liquid to make possible uniform cleaniny of
articles, such as surgical instruments, supported in trays
submerged at multiple levels in the cleaning liquid.
Established cleaning tests have been used to verify
the effectiveness of ultrasonic cleaning with the present
invention. However, the level of cavitation achieved provides
a faster quantitative indication of cleaning effectiveness and
efficiency. Cavitation can be evaluated quantitatively by
known methods, e.g. utilizing an iodine release test which
measures iodine liberation from potassium iodide in the presence
.. ..
of carbon tetrachloride. The rela-tionship between iodine
release and vacuum level, when combined with ultrasonic
energy transmission as taught, is exponential; for apparatus
of the type under consideration this relationship can be
expressed:
I = 1.3 x 10~53V
where I equals iodine release in mg/liter and V equals
vacuum level in inches of mercury.
Ultrasonic energy transmission combined with vacuum
levels in excess of approximately 15" Hy. is effective in
producing functional cavitation. Vacuum levels of about 20"
Hg. and higher up to about 30" Hg. are preferred; e.g., pulling
a vacuum of about 25" Hg. significantly multiplies (by a factor
of about 10) the iodine release over that available without a
vacuum. Maintaining a high vacuum throughout application of
ultrasonic energy further multiplies cleaning effectiveness
as indicated by the iodine release available.
Formal data on the utilization of iodine release
as an indicator of effective and efficient ultrasonic washing
of surgical instruments is not available in the literature;
however, it has been verified through established cleaning
tests that an iodine release of about twenty (20) to about
thirty (30) mg/l indicates a cavitation level providing
effective cleaning, within commercially acceptable time
periods, of dual tier stacks of surgical instrument trays.
Also, that iodine release in excess of thirty (30) mg/l,
which is readily available with the present lnvention,
-- 10 --
indicates a cavitation level providing for effective and
efficient cleaning of three tier stacks of surgical instrument
trays within a sterilizing chamber.
Iodine release values in the above range are readily
achieved in a 16"x16"x26" vessel utilizing 25" Hg. vacuum and
between twenty-four and thirty-six transducers, operating at
a frequency between forty and forty-five Khz, with total
power input in the range of 1000 to 1500 watts. Iodine
release levels approaching 60 mg/l are available in such a
chamber with the present invention by utilizing forty-eight
transducers. ~hese values are accomplished while maintaining
~oise level readings, at multiple locations within 6" to 5'
of the ultrasonic washer-sterilizer, below those permitted
by Federal regulations (OSH~) for continuous operation without
ear protection.
Upon completion of the deep vacuum, ultrasonic
degassing, cavitation, and cleaning, the washing liquid is
drained from chamber 18 through a drain pipe 68 connected to
a drain outlet 70 in the bottom of the unitized shell. Flow
through the drain pipe 68 to drain 72 is controlled by a suit-
able electrically operated valve 74 and a one-way check valve
76. Actuation of valve 7~ is controlled by the main control
36 through conductor 78.
In order to drain liquid from the chamber 18 how-
ever, it is necessary to first release the vacuum in the
void above the liquid. This can be accomplished by admitting
gas, such as steam or air, into the chamber in sufficient
3~
quantities to break the vacuum. In the embodimen-t illustrated,
steam can be supplied Erom a suitable source such as a boiler
80 thrpugh a pipe 82. Multiple inlets can be provi~ed with
inlet 83 in the lower portion of the chamber or inlet 84 in
the top portion.
When steam is utilized to break the vacuum, an
electrically actuated flow control valve 86 and a one-way
check valve 88 control the flow of steam Erom boiler 80 to the
chamber 18. A pressure regulator 90 can be connected in line
82 to control the steam pressure admitted into the chamber.
Actuation oE valve 86 is controlled by main control 36
through line 92. Upon completion of the ul-trasonic washing,
valve 86 can be opened to admit a contr~lled flow of steam into
chamber 18 to break the vacuum and, if desired, to build up a
positive pressure to assist in forcing the washing liquid
from the chamber 18.
As an alternative, air at atmospheric pressure may be
employed to break the vacuum. Air, which may be filtered by a
suitable bacterial filter 106, passes into chamber 18 through
conduit 108 having an electrically actuated control valve 110
and a one-way check valve 112 connected therein. Valve 110 is
controlled by main control 36 through line 114.
When washing liquid is removed from the chamber,
soil materials which have been dislodged from the articles may
be redeposited. Provision should be made for removal of
redeposited material before biocidal treatment. As the washing
liquid is drained to a level exposing the washed articles,
valve 26 can be openecl while drain valve 74 is maintained
open to provide for flow of rinsing liquid from the spray
nozzles 32 over the articles within the chamber to remove
dislodged soil directly to drain. Additional nozzles can be
positioned internally of the chamber for spraying from
different directions as may be required for adequate removal
in multiple tier operation.
Upon completion of the r:insiny operation, valves 26
and 74 are closed and the biocidal treatment phase is started.
In a steam sterilizing treatment, steam supply pipe 94 is
connected in pipe 82 upstream of valves 86, 88 and the pressure
regulator 90. An electrically actuated flow control valve 96
and a one-way check valve 98 are connected in pipe 94 to
control the flow of steam through this line to the chamber 18
either through inlet 83 or, if desired, through inlet 84 in
an upper portion of the chamber. A pressure regulator 100 is
connected in the pipe 94 and set a-t a pressure to provide the
desired steam sterilization temperature, generally between
about 250F. and 285F. at pressures in a range of about 15
to about 45 psig; at 270~F. an internal steam pressure of about
30 psig is provided. Control 36 maintains valve 96 in the open
position, with pressure regulator 100 controlling the pressure
within the chamber for a sufficient time to complete -the
sterilizing operation.
Aternatively, a temperature, pressure, or combination
temperature-pressure sensor, indicated generally at 102,
can be located within the chamber and connected, through
- 13 -
3~
conductor 10~, to main control 36 to conti.nuously monitor
the actual pressure and/or temperature within the chamber,
with the signal from sensvr 102 being employed by main
control 36 to control the flow of steam throuyh valve 96
into the chamber.
An advan-tage of vacuum capability is that, at the con-
clusion of steam sterilization, a vacuum can be applied to
remove steam and dry the instruments before openiny of -the
chamber; the instruments will then be reacly or use.
Alternatively, valve 96 can be closed and the drain valve 74
opened to permit the pressure within the chamber to return
to ambient. A holding tank can be substituted for drain 72
if ET0 or other-chemical biocidal agents are used. With
venting of the sterilizing fluid from the chamber, air can
be admitted into the chamber 18. When sterilized instruments
are to be left in the chamber for substantial times, for
example until they are again required for a surgical proce-
dure, or when it is desired to flow air through the chamber
to flush residual sterilizing gas from the chamber, filtered
air can be supplied to the chamber at the end of the steri-
lizing procedure. To this end, the filter 106, having a
filter element sufficiently fine to remove essentially all
bacteria from air passing therethrough, may be utilized to
assure against contamination of the instruments in the chamber.
Inlet to the filter 106 may be through an opening to atmosphere
or, alter.natively, a suitable source of air pressure may be pro-
vided if it is desired to circulate air through chamber 1~ at
the conclusion of the washing and sterilizing operation.
~" ' ' .,' ~ "
Data presented on the 16"x16"x26" chamber relates
to a shell 12 constructed of 3/16" stainless steel plate.
Stain~ess steel, type 316L, is a representative metal having
desired stre.ng-th, ultrasonic transmission capabilities, and
desired corrosion resistance. Low carbon content in the metal
facilitates -transmission of ultrasonic energy, other
characteristics which facilitate -transfer of ultrasonic energy
are known so as to enable selection of shell material by those
skilled in the art.
For a rectangular cross section sterilizer, the
metal plate is rigidly welded at longitudinal corners of the
shell to form a completely unitized chamber body. End wall
14 can be constructed of the same stainless steel material and
can, preferably, be of slightly heavier gage to add reinforc-
ing strength. End wall 14 is rigidly welded to one longitudinal
end of the plate making up the unitized body. The opposite end
of the unitized shell 12 is welded around its periphery to a
conventional end ring which reinforces the open end of the shell
and provides for mounting of door assembly 16.
~eferring to FIG. 5, end ring 116 is in the form oE
an inwardly open channel having outer and inner, inwardly
directed flanges 118, 120, respectively, integrally formed
with an axially extending web portion 122~ The inner flange
120 is rigidly welded to the end of the unitized shell 12 and
projects inwardly a distance substantially greater than flange
118, with the outwardly directed surface 12~ forming a sealing
surface. Closure operating assembly 16 can be ~f conven-tional
-15-
'
33~i~
construction and can be mounted by hinyes 176 on one side of
the end ring 116. The door 19 (FIG. 3) comprises a rigid flat
closure plate dimensioned to overlie the sealiny surface 124
of the flange 122 around its entire periphery to seal the
chamber 18. A suitable sealing gaskek, not shown, can be
carried on the door surface to assure a good seal.
Locking arms 136 can be extended by an actuating
lever mechanism 138 to project into the inwardly directed
open channel of the end ring (FIG. 3).
In the embodiment illustrated ln FIGS. 2-5, the
unitized shell 12 presents, in vertical cross section, a flat
bottom plate 126 with parallel vertical side plates 128, 130
and a horizontal top plate 132. This rectangular cross-
sectional configuration provides maximum usable space within
the chamber 18 and conventional rack support structure can be
provided. An external surface is provided as part of the
unitized shell concept to facilitate reliable mounting of
transducers; bracing is preferred with an alloy capable of
withstanding the temperature gradient. Generally a substanti-
ally flat external surface is provided for ease of mounting.
Other cross-sectional configurations for the chamber and
external surface can be used, e.g. curvilinear, if provisions
are made for securing the transducers and for avoiding undue
interference or cancellation of wave energy within the chamber.
A plurality of transducers 60 are arranged in a
selected pattern over substantially the entire bottom wall and/or
on the side walls of the shell to facilitate uniform distribution
-16-
.
3~
o~ ultrasonic energy throughout the volume of washing liquid
established for placement of articles and to eliminate or
minimize sonic wave interference. If transducers are mounted
on multiple walls, sequential energization of the transducers
can be utilized to avoid or minimize sonic wave interference
within the chamber.
In the specific embodiment of the invention shown,
the bottom wall 126, the side walls 128, 130 and the top wall
132 have bPen construct~ from 3/16" gage 316L stainless steel.
Chamber 18 is 16"x16" in cross section with alongitudinal
dimension of 26". Reinforcing ribs were placed at spaced
intervals along the length of the chamber to enable the chamber
to withstand internal pressures for steam sterilizing and
vacuums approaching 30" Hg., with safety factors as required
by A.S.M.E. specifications.
As shown in FIGS. 2-4, the unitized shell 12 is
reinforced by a plurality of steel bars 134 rigidly welded to
the external surface of the shell 12. The reinforcing bars
134 at each position are arranged and welded together to form
a complete ring 135 circumscribing the shell. Four reinforcing
rings are employed in this embodiment with the spacing between
adjacent circumscribing rings 135 and between the respective
ends ~f the chamber and the adjacent ring 135 being substanti-
ally e~ual. A total o-E thirty-six ultrasonic transducers
rigidly mounted on the external surface of the bottom wall 126,
operating at -Eorty-one Khz and total power input of approxi-
mately 1500 watts, was found to be adequate to provide the
necessary cavitation for effective and efficient cleaning.
-17-
.
'
~"~a~
The transducers were arranged in a uniform pattern includiny
a plurality of transducers between each adjacent pair Oe
reinforcing rings 135, and between the end rings and the
respective ends of the unitized shell.
In FIG. 6, a commercially practical cycle of
operation of a sonic washer-steam sterilizer is schematically
presented in terms of chamber pressure vs. time. A void space
is preferably left in the chamber above the surface of the
liq~id at the completion of the filling operation; filling
may re~uire about two minutes for a 16"x16"~26" washer-
sterilizer chamber. An added advantage of the combination
washer-sterilizer of the present invention is that steam from
the sterilizing process can be used directly for heating the
washing liquid within the chamber. The steam is discharged
beneath the surface of the washing liquid for a time sufficient
to heat the washing liquid to the desired temperature; about
80F. to about 120F. is utilized for protein matter soil.
Alternative heating means such as submersible electric resist-
ance heaters may be employed~ Heating of the washing liquid
helps in providing rapid degassing as does the use of a
detergent which reduces surface tension.
The pressure in chamber 18 may remain substantially
at atmospheric, or increase slightly during the filling operation
and during the heating of the water. ~Ieating of the washing
liquid with steam may require another two minutes of cycle time.
Upon completion of the in-chamber heating, the water
ejector apparatus is actuated to evacuate the void in the chamber
.
-18-
18 to the desired deep vacuum. The syneryistic action of the
deep vacuum and the ultrasonic energy are required to achieve
both t,he degassing and the cavitation taught by the present
invention within acceptable times for use in hospital steri-
S lization and other institutional biocidal treatment. ~either
the deep vacuum nor the ultrasonics alone will suffice. When t
the desired vacuum level .is reached in the chamber, control 36 Ç
energizes the power source 64 to d:rive the ultrasonic trans~
ducers 60 to apply ultrasonic energy to the washing liquid
through the bottom wall 126 of the unitized shell 12 and effect
desired degassing, cavitation, and cleaning. Sensor 102 may
be employed to signal the desired vacuum level or, alternatively,
the evacuator may be operated for a predetermined time which has
been empirically determined to be sufficient to attain the
desired vacuum level.
The ultrasonic energy transmitted in coDperation
with the deep vacuum established acts quickly to substantially
completely degas the liquid with cavitation at a level not
otherwise available. The combined effect produces a profuse
removal of gas and agitation within the solution caused by such
profuse removal; both aid in the cleaning and both are readily
apparent if the apparatus is viewed through an observation glass
in the door.
As one aspect of a pre~erred cycle, operation Df
evacuating apparatus 40 is continued for at least a portion of
the time during which ultrasonic energy is applied to the washing
liquid to continue withdrawal of gas liberated from the liquid
--19--
3~
and to assure that the desired vacuum level is maintained
until degassing is complete~ The vacuum level can be maintained
thereafter by closing the valve 50. Alternatively, the
evacuator can be operated continuously throughout the ultra-
sonic cleaning phase of the cycle.
In the preferred sequence, evacuation to the deepvacuum level takes place pxior to application of ultrasonic
energy; i.e. ultrasonic energy transmission is not initiated
until the desired deep vacuum level is reached, or approximated.
Tests show that this sequence produces better cavitation and
more efficient cleaning than initiation of sonic energy signi-
ficantly above the desired deep vacuum level. utilizing
f~rty-eight transducers at a t~tal power input of 2000 watts
at fvrty-one ~hz after drawing a vacuum of at least 25" ~g.
resulted in an iodine release of 57 mg/l; thus indicating
extremely efficient degassing and a high level Df cavitation.
With the deep vacuum established, the liquid media is
"shocked" by the ultrasonic energy; gas bubbles are violently
released producing a visible foaming action which travels to
the surface. This contrasts with the result~ achieved when
ultras~nics are applied priDr to reaching deep vacuum. In
the latter sequence, a large number of gas bubbles attach to
the walls and bDttom of the chamber; while iodine release under
this latter c~ndition indicates adequate cavitation, being
approximately 25 mg/l, the preferred sequence optimizes the
cavitation as indicated by the iodine release test results.
-20-
As shown in F~G. 6, ultrasonic cleaning can be
completed within about fifteen minutes from the start of the
filling operation; such a time period is within desired com-
mercial efficiency. Upon completion of the ultrasonic cleaniny
phase of the cycle, main control 36 acts to deenergize khe
ultrasonic transducers and to close valves 50 and 56 if these
valves have not been previously closed. Control 36 then admiks
either steam or air into the chamber for a time tD reaease the
vacuum in the chamber. Drain valve 74 is then opened to permit
the washing liquid to drain from the chamber. Approximately
two minutes can be required to break the vacuum and drain a
chamber of the size described.
As washing liquid is drained from chamber 15,
control 36 opens the valve 26 to spray liquid downwardly from
nozzles 32 to rinse the cleaned articles and remove any dislodged
particles which may have been floating on the surface of the
washing liquid and settled on the axticles during draining.
During this rinsing operation, drain valve 74 remains open.
About two minutes is sufficient time for the removal of loose
debris; at the conclusion, rinse water supply valve 26 and
drain valve 7~ are closed.
Steam valve ~6 is then opened to admit live steam
to increase the pressure in chamber 18 to, e.g., approximately
30 psig to produce a temperature of approximately 270~F. The
temperature is maintained at this sterilizing level for a time
sufficient to completely sterilize the articles, generally in
the range of three to five minutes. Lower pressures can be used
for other biocidal treatments.
-21-
A preferred cycle of operation according to the
present invention may thus involve loadlng articles to be
treated into the chamber and sealing the chamher, admitting
ultrasonic washing liquid and detergent into the chamber to
a level covering the articles to be cleaned, injecting steam
into the washing liquid to heat the liquid, evacuating the
chamber to expose the washing liqu:id to a deep vacuum in
excess of about 15" Hg. and preferably about 20" Hg. to about
30" Hg., transmitting ultrasonic energy through the unitized
shell of the chamber while maintaining the deep vacuum during
at least a portion of the time o~ application of ultrasonic
energy to degas the washing liquid and to ultrasonically clean
the articles in the charnber, releasing the vacuum in the
chamber, draining the washing liquid from the chamber, spraying
rinsing liquid into the chamber to remove redeposited soil
material from the articles, purging the chamber with steam,
sterilizing the articlesin the chamber with steam at a pressure
in the range of about 15 to 45 psig., and exhausting the steam
and applying vacuum to the chamber to remove steam from the
chamber and dry sterilize articles, the steps of admitting
washing liquid and detergent into the chamber, evacuating the
chamber, and applying ultrasonic energy to the chamber to
complete degassing and ultrasonic cleaning being accomplished
in a predetermined time and not substantially in excess of
about fifteen (15) minutes, and the complete process from
commencement of admission of the washing liquid and detergent
into the charnber to completion of exhaust of steam being
carried out in about thirty (30) minutes.
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.
At the conclusion of biocidal treatment, drain
valve 74 is opened to permit the pressure in the chamber to
retur~ to atmospheric. The vessel may then be opened to remove
the articles from the chamber 18; however, if desired, the
chamber 18 may remain sealed to further assure the sterile
condition of the articles until next needed. If the articles
are to remain in the charnber 18, valve 110 should be open to
permit filtered air to maintain the pressure at substantially
atmospheric level as the chamber cools.
It should be understood that various ccnfigurations
and sizes can be employed for the pressure vessel by utilizing
the above teachings of the invention on transfer of the sonic
energy and use of deep vacuum levels to obtain desired cavi-
tation within a unitized shell meeting necessary pressure
vessel strength requirements. Also, in the light of these
teachings, method step modifications can be made which fall
within the principles of the invention. Therefore, the scope
of the invention should be determined by reference to the
appended claims.
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