Note: Descriptions are shown in the official language in which they were submitted.
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Description
FOAM GENERATING APPARATUS
Technical Field
The present invention relates to devices for generating foam for use in
fire fighting and spf;cifically to a foam generator which provides for
automatic
balancing of pressure differentials between incoming pressurized water and
pressurized air.
Background Art
Foam generators utilizing pressurized water and pressurized air in
combination with a surfactant are useful in fire fighting. There are certain
well
known means of mixing air, water, and a surfactant to generate foam,
including mixing chambers, venturis, and nozzles.
U.S. Patent No. 4,981,178 issued to Bundy on January 1, 1991
discloses an apparatus for generating fire-fighting foam using a mixing
chamber.
U.S. Patent No. 4,505,431 issued to Huffman on March 19, 1985 for
"Apparatus for Discharging Three Commingled Fluids" and U.S. Patent No.
4,474,680 issued to Kroll on c~ctober 2, 1984 for "Foam Generating Apparatus
and Method" disclose venturi-type foam generators.
It has been very difficult in the past to produce a simple device for
generating foam from the mixing of pressurized air and pressurized water.
(The foam also requires the presence of a soap or surfactant which is
introduced into the water prior to the foam generator.) Pressure balancing
between incoming pressurized air and incoming pressurized water requires
elaborate measures to control both the air volume and pressure and the water
volume and pressure. It has generally been necessary to use very
complicated devics;s to balance the volumes and pressures or to require the
operator to manually adjust the volumes and pressures on a continuous basis
during operation to maintain a balance. Thus a skilled operator is typically
required to operate such systems.
SUIBSTITUTE SHEET (RULE 26)
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If a balanced pressure is not maintained, the quality of the foam being
generated can be .affected. 9larious types of foam may be desirable for
particular applications. In some situations a dry foam is desirable; in other
situations, a wetter foam is desirable. Too much water or too much air can
result in a foam that is not efficient for the intended purpose. For example,
in
some situations; the most desirable type ofifoam contains sufficient moisture
to aid in smothering a fire while it is sufficiently dry to cling to surfaces.
If a
balanced pressure and volume of water and air is not maintained, the result
can be a foam thaft is either too wet or too dry or that has other
deficiencies
with respect to the desired quality. The volume of water in relation to the
volume of air determines the consistency of the generated foam, so the
control of both pressure and volume is necessary to assure the desired foam
quality.
The prior art emphasizes the importance of maintaining balanced
pressures between the water and air supplies. Bundy, at column 3, beginning
at line 12, discusses the problem of achieving the proper combination of air
pressure and volume with water pressure and volume to achieve the desired
quality of foam. Bandy also discusses the desirability of maintaining equal
pressure in the air and water supplies.
The prior art has addressed the problem of, balancing the air and water
supply pressure in a foam generator by various expedients as mentioned
above. Even with the fairly complex and expensive means employed, the
operation of a foam generating apparatus for fire fghting requires the
services
of an experienced operator and even then much experimentation is
necessary. For example, even the simple act of changing a hose attached to
the apparatus often requires difficult and time consuming rebalancing of the
system.
It has been suggested that a high degree of turbulence may contribute
to the quality of foam produced in that a finer foam structure is obtained.
Foam comprised of large bubbles is less useful for typical fire-fighting
applications. It many therefore be desirable to both balance the pressures of
the incoming water and air and do so in a way that maximizes turbulence.
Prior foam generating systems lack a means to automatically cut off the
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flow of water and air into the system's hose when the hose nozzle is turned
off. This may create an unsafe condition if system air and water pressures are
not precisely balanced. if the system water pressure exceeds the system air
pressure, closing the nozzle may cause a "slug" of water to build inside the
hose. When the operator again opens the nozzle and expects a relatively low-
density foam to emerge, the slug of water that squirts forth may cause the
operator to lose control of the hose. Conversely, if the system air pressure
exceeds the system water pressure, a pocket of air may build in the hose
when the nozzle is closed. Subsequent opening of the nozzle may send forth
a burst of oxygen onto a flame thereby aiding the spread of a fire rather than
extinguishing it. Elither a slug of water or burst of air may thus result in
serious
injury to the hose operator or bystanders. Given the difficulty in prior art
foam
generating systems of maintaining a precise balance between system air and
water pressure, it has been difficult to prevent these unsafe conditions.
The problerns and limitations of the prior art are overcome by the
present invention as summarized below.
Disclosure of Invention
The present invention is an apparatus for generating foam for use in
fire fighting. The invention utilizes a unique mixing chamber designed to
automatically balance the dynamic pressure of incoming air and water
streams and thereby produce high-quality foam even if the incoming static air
and water pressure vary significantly. This allows the foam generator to work
in a wide variety of situations and environments, even with makeshift
compressor and pump equipment, without the necessity of complicated
calibration steps. Such versatility is highly desirable for firefighting,
especially
in rural areas where specialized equipment may be unavailable.
In the present invention, pressurized water (including a surfactant) and
pressurized air arE; introduced in such a way as to automatically achieve the
desired balance between water and air pressures, and also produce a highly
turbulent environment which conduces to the formation of a high quality foam.
The apparatus includes an automatic regulator that stops the flow of air and
water when the nozzle is turned off, thereby preventing the safety hazard
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created if the hose were to fill with unmixed water or air. This automatic
regulator also prevents the backpressure in the hose from exceeding either
the incoming air or water pressure.
The water and air pressures in a foam generator derive from three
components: a static or head pressure, which is the input pressure from the
water pump and air compressor of the system; a dynamic pressure within the
mixing chamber, which is determined by the flow rate of water and air input
into the chamber; <~nd a residual pressure or backpressure from the hose.
Prior art foam generators have attempted to balance the static water and air
pressure. In conventional systems, this balance is necessary since if either
pressure exceeds 'the other, it will prevent the formation of high-quality
foam.
Thus conventional foam generators are only effective for firefighting purposes
if the input air and water are at precisely the same pressure.
The present invention, by contrast, focuses on dynamic pressure as a
means to both balance the water and air pressure within the mixing chamber
and to achieve a highly turbulent environment conducive to excellent foam
quality. In the present invention, water is introduced into a restricted area
in
the mixing chambs;r with an ever-widening area for expansion as it travels
farther toward the air source. The water pressure falls as the water travels
through the widening area approaching the air inlets, such that a point is
eventually reached where the water pressure falls to equal the air pressure it
encounters. If either the static air or water pressure is changed, the
equalization point may move further or cioser to the air or water inlets, but
will
still lie somewhere between the two inlets so that mixing will occur. Thus
equalization of dynamic pressures takes place automatically due to the design
of the mixing charr~ber. As long as the static pressures are maintained within
a certain range, the system will automatically readjust and still deliver
excellent-quality foam since an equalization pressure will still be reached.
The
energy lost as the water and air lose energy is converted into turbulence that
serves to thoroughly mix the water and air and thereby produce high-quality
foam.
In order to .achieve this rapid conversion of the dynamic pressures of
the incoming water and air into turbulent energy, the incoming water and air
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streams should be directed onto a surface which stops or splatters the
streams, or against another stream. In addition #o balancing the water and air
pressures, the "splattering" effect also produces the highly desirable
turbulent
environment and separates the incoming water into fine droplets to speed ,.
mixing with the incoming air.
In the prefeirred embodiment of the invention, the heart of the foam
generator is two plates housed in a chamber where pressurized air and water
are introduced into the restricted area between the two plates. Although the
word "plate" is used throughout this disclosure, it should be understood that
the invention is not limited to plates that are flat, but may also include
"plates"
that have slots, arE: concave or convex, or otherwise have varying surfaces.
In one embodiment, the pressurized water is introduced through an opening in
one plate. The pressurized air is introduced into the restricted area through
a
number of channells bored through the other plate. The air channels may
appear in an annullar grove, placed on the surface of the plate, that
circumscribes the water inlet. While introducing the pressurized air into an
annular groove is not necessary to the practice of the present invention, it
does serve to improve mixing of the water and air by producing still more
turbulence upon e;Kit of the water and air from between the two plates.
In the preferred embodiment, the two plates are in close proximity to
each other. The narrow restricted area between the plates provides part of
the mechanism that helps to equalize the pressure between the incoming
water and the inca~ming air. Preferably the two plates are placed in such
proximity that the i;urbulence effect created by the plate walls is
significantly
enhanced.
The waterlsurfactant solution and the air will intermingle in this
restricted area in a highly turbulent fashion, and upon exiting the restricted
area will produce a foam. The consistency of the foam can be adjusted by the
operator by adjusting the incoming water pressure or volume, the incoming air
pressure or volume, or by moving the plates relative to one another.
In some embodiments the air inlets may be set at an angle, such that
the air inlets are turned somewhat toward the water inlet. It is believed that
forcing the pressurized air between the plates at this angle, which preferably
is
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about a 45°, creatEa even greater turbulence when the air and water
meet,
thus improving the quality of the resulting foam.
It is therefo~~re an object of the present invention to provide for a self-
balancing, foam-generating mechanism using pressurized water and
pressurized air. A further object of the present invention is to provide for a
foam-generating mechanism using pressurized water and pressurized air
which is simple and economical to construct and easy to operate. An
additional object of the present invention is to provide for a foam-generating
mechanism using pressurized water and pressurized air which produces
varying qualities and quantities of foam and accepts varying lengths and types
of hoses without rE:quiring complicated and delicate rebalancing of air and
water pressures. .A further ~bject of the present invention is to provide far
a
foam-generating rr~echanism using pressurized water and pressurized air that
may be used with a wide assortment of different compressors and water pump
mechanisms and rnay be operated by less skilled persons. A still further
object of the present invention is to provide for highly turbulent mixing of
the
pressurized water and air to produce an exceptionally high-quality foam. Yet
another object of the present invention is to pravide a foam-generating
mechanism with a regulator that automatically cuts off the flow of pressurized
air and water into ~~the system when the nozzle is closed, thus preventing the
dangerous situation of a slug of water or burst of air emerging from the hose
when the nozzle is reopened. Further objects and advantages of the present
invention will be apparent from a consideration of the following detailed
description of the preferred embodiments in conjunction with the appended
drawings as briefly described following.
Brief Description c~f Drawings
Fig. 1 is an exterior perspective view of a chamber containing the foam
generating plates and having incoming lines for pressurized water and air and
an exit for foam gE:nerated in the chamber. Fig. 2 is a sectional elevation
view
of the chamber of Fig. 1 showing the pressurized water plate and the
pressurized air plate attached to the top and bottom respectively of the
chamber with the 'foam generating area therebetween. Fig. 3 is a sectional
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plan view of the chamber showing the pressurized air plate and the annular
groove thereon. Fig. 4 is a schematic diagram showing the components of a
complete foam generating system employing the present invention. Fig. 5 is a
perspective view of a second embodiment of the present invention for use in
high pressure situations in which the plates are carried on respective plugs
which are held to i,he chamber by bolts. Fig. 6 is a sectional view of the
embodiment of Fig. 5. Fig. 7 is a sectional plan view of a third embodiment of
the present inventiion with an adjustable distance between the plates and a
foam exit tube that is perpendicular to the air and water inlets. Fig. 8 is a
sectional plan vievv of a fourth embodiment of the present invention having a
fixed distance between the plates and a water inlet and foam outlet that are
in
line with one another. Fig. 9 is a schematic diagram showing a preferred
embodiment of thE; regulator and automatic cut-off system of the present
invention. Fig. 10 is a schematic diagram of a detail section from Fig. 9
showing the operation of the pressure regulator cylinder and automatic cut-off
microswitch.
Best Mode for Cairvinq Out the Invention
The present invention may be described with reference to Figs. 1 and
2. A chamber 10 is provided which accepts an incoming pressurized water
line 20 and pressurized air tine 30. Foam generated in the chamber 10 exits
through the outlet 40.
The heart of the present invention is found in the provision, for two
plates 50, 60 where the incoming water and air are introduced to each other.
The shape of the chamber 10 in which the foam is generated is not critical to
the invention, although the chamber 10 should allow space around the plates
50, 60 for the generated foam to exit. Furthermore, it is desirable to avoid
shaping the chamber 10 such that a spiraling action is induced in the foam.
Such action can separate foam into its primary constituents by centrifugal
force.
The pressurized water plate 50 is simply a circular disc 51 with a bore
52 through the center for the introduction of pressurized water to a
restricted
area 70 between 'Ihe plates 50, fi0. The bore 52 may be reduced by an orif ce
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for better control of the pressure and for adjustment of the volume of the
incoming water. A,s will be discussed hereinafter, the pressurized water
contains an admixture of surfactant which is introduced to the pressurized
water prior to the chamber 10 by various means well .known in the art.
As shown in Figs. 2 and 3, the pressurized air plate 60 is likewise a
circular disc 61 having a restricted area-facing surtace 62 on which an
annular
groove 63 is disposed on the surface 62 and may be located at various radial
distances from the periphery of the surface 62. In some embodiments, it may
be desirable to place surface roughening features such as ripples or grooves
between the annullar groove 63 and the periphery of the surface 62 in order to
enhance turbulence and mixing. The annular groove 63 is fed pressurized air
from a plurality of radial passages 64 communicating with an inlet bore 65.
The inlet bore 65 in turn communicates with the incoming pressurized air line
30: Alternatively, "the radial passages 64 may be replace by a plenum
receiving pressurized air and communicating with the annular groove 63 by
simple openings. When a plenum is employed it maybe desirable to have the
pressurized air enter the plenum at right angles to the openings
communicating with the annular groove fi3 in order to ensure an even
pressure among the openings and therefore at all points on the annular
groove 63.
Fig. 4 is an overall schematic of a complete system incorporating the
present invention ahowing an air compressor 80 connected by air line 81
leading to the air inlet 30 of the chamber 10, and a water pump 82 connected
to water reservoir 84 and to water line 83 leading to the water inlet 20 of
the
chamber 10. Not shown are valves in the air line 81 and the water fine 83 for
setting the volume: and pressure of the incoming water and air. Also shown in
the schematic is a soap reservoir 85 and dispenser 86 into the water inlet
line
83.
Figs. 5 and 6 show a second preferred embodiment of the present
invention. There .are three primary pieces to the preferred embodiment of the
foam generator of the present invention. The assembled foam generator is
shown in perspective in Fig. 5. First, there is a housing 90, which is
preferably
constructed of stainless steel. The housing is a T-shaped hollow chamber
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having an water inlet section 91 and air inlet section 92 across the top of
the
'T" and a foam outlet section 93 at the base of the'T". The foam outlet
section 93 at the base of the T-shaped chamber is reduced to a pipe which is
the nozzle opening 94 or connection point for a hose. While the prior art
normally uses the hose as part of the foam generating apparatus, the present
invention requires only a minimal length of hose. Foam is generated in the
housing 90 and available in close proximity to the nozzle opening 94.
Fitting into the housing 90 are two plugs 95, 96, preferably of plastic,
which fit in respective open ends 97, 98 of the water inlet section 91 and air
inlet section 92, rEapectively, at the top of the T of the housing 90. These
two
plugs 95, 96 incorporate the plates 100, 101, which introduce pressurized
water and air into the restricted area 104 between the two plates 100, 101.
A section a~f the embodiment of Fig. 5 showing the two plates 100, 101
is given in Fig. 6. Each plug 100, 101 is provided with a flange 102, 103;
respectively, whic'~h fits against the respective open ends 97, 98, and serve
to
fix the plugs into position so as to form a restricted area 104 of the
requisite
width. Each plug 95, 96 is reduced to a middle section 105, 106 sized to fit
tightly in either open end 97, 98. Each plug is further reduced to an inner
section 107, 108. When the two plugs 95, 96 are assembled into the housing
90, the restricted area 102 between the two plugs 95, 96 is set at the desired
distance.
Plate 100 introduces pressurized water into the restricted area 102
through a bore 112 which is connected to the inlet water supply by an integral
water inlet connection 113. Likewise, plate 101 introduces pressurized air
into
the restricted area 102 through an annular groove 114 fed by radial passages
115 from an inlet I'~ore 116 provided with an integral air inlet connection
117.
The generation of foam is otherwise identical to that described above for the
embodiment of Figs. 1-4
A device siized to deliver foam to a 1 112 inch hose from a 100 psi water
supply and 100 p:>i air supply would have inlets 91, 92 about 3 inches in
diameter. The foam outlet section 93 at the base of the T-shaped chamber is
reduced to a pipe approximately the diameter of the hose. In this sized
embodiment, the outermost part of each flange 102, 103 is about 6 inches in
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diameter. Each phug 95, 96 is reduced to a 3 inch diameter middle section
105, 106 to fit tightly in either open end 97, 98. Each plug is further
reduced
to an inner section 107, 108 of about 2 inches in diameter. In this
embodiment, when the two plugs 95, 96 are assembled into the housing 90,
the restricted area 102 between the two plugs 95, 96 is preferably about 3/16
inch.
As shown in Figs. 5 and 6, the two plugs 95, 96 are held to the housing
90 by four bolts 110 through holes in the flanges 102, 103. Although not
critical, it is desirable that a space 111 be left around the plates 100, 101
and
the restricted area 102 to allow the free exit of foam generated between the
plates 100, 101.
A third preferred embodiment of the present invention is shown in Fig.
7. This embodiment uses a chamber of generally cylindrical shape, with a
water inlet 120 dirE:cted into the center of one end of the chamber. Air inlet
122 passes through this same end of the chamber, allowing pressurized air to
pass into the chamber and then through air orifices 132 in first plate 133.
Air
orifices 132 are angled toward the center of the chamber and thus toward the
direction that water will travel when it enters through water inlet 120 and
strikes second plate 131. Second plate 131 includes an adjustment feature
130, which may bE; in the form of a threaded bolt that extends through the
opposite end of the chamber. Adjustment feature 130 allows the operator to
vary the width of the restricted area between first plate 133 and second plate
131 which will affect the type of foam that is produced. In this way the
operator may create whichever type of foam is necessary for a given
application, such as when a dryer foam is needed to adhere to vertical
surfaces, or a wetter foam is needed for spraying foam long distances against
a wind. The foam exits the chamber at foam outlet 124.
A fourth prE:ferred embodiment of the present invention is illustrated in
Fig. 8. Like the ernbodiment of Fig. 7, this embodiment uses a chamber of
generally cylindrical shape, with a water inlet 134 directed into the center
of
one end of the chamber. Air inlet 136 allows pressurized air to pass into the
chamber and them through air orifices 144 in first plate 145. Air orifices 144
are angled as in the embodiment of Fig. 7. In this embodiment, second plate
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143 is fixed in posiition relative to first plate 145 by bolts. The foam exits
the
chamber through foam outlet 138, which extends from the opposite end of the
chamber through which water inlet 134 passes.
The system by which air and water pressure is regulated in the
preferred embodiment of the foam generator apparatus is illustrated in Figs. 9
and 10. Water is drawn from water reservoir 194 and pressurized by water
pump 146. A surf<~ctant from soap reservoir 148 is added to the pressurized
water by soap dispenser 150. The mixture is pumped through water manifold
152, then through water check valve 154 which prevents backflow of water or
air through the system. Flow sensor 156 feeds flow information to flow
indicator 192, which may be used by the operator to adjust the system to
reach a desired volume of water per unit time. The water then flows through
water valve 158 (the function of which will be described below) and into
mixing
chamber 160.
Turning now to the pressurized air side of the system, compressor 196
forces pressurized air through air manifold 162 and through air valve 164 (the
function of which will be described below), then through flow control valve
166
and air flow meter 168. Based on the reading on air flow meter 168, the
operator may adjust flow control valve 166 to reach a desired air flow volume
per unit time. Air then flows through air check valve 170, which prevents the
backflow of air or water through the system, and into mixing chamber 160.
Foam created in mixing chamber 160 travels through hose 172 and out
through nozzle 174.
Pressure regulator 182 (shown in detail in Fig. 10) is used to cut off the
flow of air and water automatically when nozzle 174 is closed, thereby
preventing the buildup of either a slug of water or burst of air in hose 172.
When nozzle 174 is closed, backpressure builds in the hose and back through
the chamber, which quickly exceeds the system static air pressure. This
backpressure forces diaphragm 200 in pressure regulator 182 upward. The
arm extending vertically from diaphragm 200 thus presses against contact arm
198 of microswitch 180, causing contact arm 198 to bridge the two electrical
contacts of microswitch 9 80 and close the electrical circuit formed thereby.
Closing this circuit activates electric solenoid 186, which in turn actuates
shut-
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off control valve 188, which simultaneously closes both water valve 158 and
air valve 164. This prevents the flow of either water or air to mixing chamber
160, thus preventing the buildup of a slug of water or burst of air in hose
172
when nozzle 174 its closed.
Once nozzle 174 is opened again, the system backpressure will fall,
thereby allowing cliaphragm 200 to fall and opening the electrical circuit
previously closed by contact arm 198 of microswitch 180. Spring return 190
will then simultaneously open water valve 158 and air valve 164. This will
allow water and alit to again enter chamber 160 and thus the system will begin
generating foam again automatically.
Alternatively, the pressure regulator could use a controller (not shown)
in communication with microswitch 180 that activates microswitch 180 when
the system backpiressure rises above a threshold value. Once microswitch
180 is activated, vvater valve 158 and air valve 164 will simultaneously
close.
When the system backpressure falls below the threshold value, the controller
deactivates microswitch 180 thereby allowing spring return 190 to
simultaneously open water valve 158 arid air valve 164. The controller can be
preset to a certain threshold pressure value, or can include means (such as a
dial or keypad) to enter the threshold pressure desired by the operator.
in operation of the preferred embodiments described herein, the
incoming static water pressure is generally set to a level in excess of the
incoming static air pressure. The difference is not critical. The pressure at
the
periphery of the plates is determined by the outlet back pressure due to the
chamber size, ths: hose, nozzle, and any orifice or restriction in the outlet
side
of the system. The pressure at the center of the plates is determined by the
inlet water pressuire, and the pressure available at the annular grooves is
determined by thE: inlet air pressure. The back pressure at the periphery of
the plates is at some level higher than atmospheric, but lower than either the
pressure at the water inlet or the air inlet. Air is of course compressible,
while
water is not. It is believed therefore that due to the lower air pressure and
the
compressibility of the air, a balanced pressure between the air and water is
reached at some radial point between the air inlet at the annular groove and
the water inlet at the central bore. This radial equilibrium point will shift
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radially between the air and water inlets depending on the incoming volume
and pressure of water, thus automatically balancing the two. As the back
pressure changes, the pressure at the balance point will change
proportionally. The balancing of the dynamic water pressure and air pressure
is therefore automatic without the need for intervention by the user. This
mechanism is believed to explain the operation of the present invention but
the invention is not limited thereto. Additional adjustment of the mechanism
to
enhance the quality and quantity of the foam is possible through adjustment of
the size of the restricted area between the two plates.
Furthermore, it is desirable that the proximity of the plates be such as
to induce a high degree of turbulence into the mixing. This is accomplished by
putting the two plates in close proximity. Thus a large proportion of the
mixing
takes place betwf:en the plates and the hose is not as necessary to act as a
turbulent mixing chamber. 'This frees the operator from any problems involved
in rebalancing thE; system when hoses or lengths of hoses are changed.
Furthermore; since the hose is not occupied by unrestricted air, the hose may
be operated at p~:ak capacity resulting in maximum flow and increased
trajectory for the ifoam exiting from the nozzle of the hose. Better mixing
before the hose also allows better foam quality with finer structure when such
is desirable. In those embodiments of the present invention utilizing plates
that are movable relative to one another so as to vary the size of the
restricted
area between them, the water pressure within the mixing chamber may also
be regulated by movement of the plates.
The present invention also has the advantage that it allows more
flexibility in the use of pumps and compressors. As an example, one large
pump might supply several foam lines independently of each other. Oversize
pumps and compressors may be utilized without alteration. The present
invention allows i;he air pressure to fluctuate which enables the compressor
to
cycle without adverse effect on the foam.
Although the preferred embodiment has been described with respect to
a version of the present invention in which two plates are used and each plate
introduces only water or air to the restricted area between for mixing, an
alternative embodiment may employ two plates in which one plate serves as
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the impingement surface and the other plate contains passages for
introducing both pressurized air and a pressurized solution of water and
surfactant. This arrangement utilizes the same principles for operation, but
may have advantages allowing a compact design.
The present invention has been described with reference to certain
preferred and alternative embodiments which are considered exemplary only
and not limiting to the full scope of the invention as set forth in the
appended
claims.
