Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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NOZZLE FOR USE WITH FIRE-FIGHTING FOAMS
BACKGROUND OF THE INVENTION
In the design and operation of air-foam nozzles of the
type used for flammable liquid firefighting, there are a
number of problems that must be solved. Over the years many
nozzles have been developed attempting to overcome one, or
more, of the following problems: (1) provide a simple means
to inject firefighting foam concentrates into the water
stream at the nozzle; (2) provide a means to,insure thorough
mixing of water and foam concentrate within the nozzle; (3)
provide a means to control the amount of air entrained into
the water-foam solution; and (4) provide a means of
increasing the discharge range of aerated foam solution.
Conventional air-foam nozzles can easily be divided
into two broad groups based on the "expansion ratio" of the
nozzle. "Expansion ratio" is a term describing the final
volume of air-foam bubbles when compared to the original
volume of foam solution. As the expansion ratio of a foam
sample increases, it indicates a greater ability of the
nozzle to mechanically agitate and aerate the foam solution.
A nozzle with a higher expansion ratio generates foam having
a lighter weight per unit of volume, with smaller, more
homogeneous, thinner-walled bubbles which are longer lasting
due to their greater ability to retain foam liquid in the
bubbles.
Air-foam nozzles designed for use with synthetic based
foam concentrates know as aqueous film forming foams (AFFF)
customarily have low expansion ratios, less than 4 to 1.
AFFF foams are very effective on flammable liquid spill
fires, and were originally developed for aircraft crash
firefighting, where a rapidly spreading, low expansion foam
blanket is preferred to give rapid knockdown of flames so
that passengers and crew can be quickly rescued from a
burning aircraft. This effectiveness is due in large part
to an aqueous film that spreads on the surfaces of the
flammable liquid as the foam bubbles break, thereby slowing
vaporization from the surface of the liquid and helping
prevent re-ignition. A low expansion, quick draining foam
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is preferred for this application.
Nozzles designed for use with AFFF concentrates may be
subdivided into two additional types: (1) those in which
foam solution is pumped to the nozzles through fire hose or
piping as shown by the nozzle 10 of Figs. 1A and 1B; and (2)
those where foam solution is formed in the nozzle by water
being pumped to the nozzle through fire hose or piping and
foam concentrate being supplied to the nozzle through a
separate conduit as shown by the nozzle 20 of Figs. 2A and
2B.
In nozzles where foam solution is pumped to the nozzle
as in the nozzle 10 of Figs. 1A and 1B, water and
concentrate have ample time for thorough mixing while
traveling through the hose or piping. In nozzles where the
water and foam concentrate must mix at the nozzle as in the
nozzle 20 of Figs. 2A and 2B, mixing may not be uniform,
especially if the concentrate is injected on the inside of
the cylinder formed by the water discharge.
This non uniform distribution of foam concentrate in
the water stream will have a negative impact on the foam
quality produced by the nozzle. The foam bubbles will not
be uniform in size and as a result the expanded (aerated)
foam will deteriorate rapidly. Foam with rapid
deterioration (typically called fast draining) is not
optimized and therefore is not likely to be suitable for the
intended application.
Air can only be entrained on the outer surface of the
discharge pattern when either type nozzle is adjusted at or
near the straight stream setting as shown in Figs. 1A and 2A
when a pattern selection sleeve 12, 22 is adjusted to the
outward position. This limited aeration results in low
expansion ratios. Lower expansion foam is heavier than foam
with higher expansion ratios, and generally has a greater
ability to travel through the air over longer distances for
a given discharge velocity.
Nozzles designed for use with protein based foam
concentrates are of the air-aspirating type. Exemplary
nozzles 30 and 32 are shown in Figs. 3A and 3B,
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respectively. These nozzles have expansion ratios greater
than 6 to 1. Protein based foam concentrates require more
energy than do synthetic based concentrates for aeration of
the foam solution into expanded fire-fighting foam. Protein
based foams depend on a thick blanket of bubbles, not an
aqueous film, for extinguishment.
These nozzles may also be subdivided into two
additional types: (1) those in which foam solution is pumped
to the nozzle through fire hose or piping as shown in Fig
3A; and (2) those where water is pumped to the nozzle
through fire hose or piping and foam concentrate is supplied
to the nozzle through a separate conduit as shown in Fig.
3B.
Nozzles with the ability to pick up concentrate through
a separate conduit by use of a built-in-venturi as shown in
Fig. 3B have been in widespread use since they were
developed in the 1940's. These "self educting" nozzles
offer good mixing of the water and foam concentrate,
however, the kinetic energy required to assure good mixing
and air aspiration reduces the velocity of the discharge
stream, thereby shortening the discharge range that can be
achieved. On the other hand, nozzles of the variable-
pattern fog type with a built-in venturi as shown in Figs.
2A and 2B, do not offer mixing as good as the air-aspirating
type, but because they use less kinetic energy for mixing
and air-aspiration their discharge range is enhanced.
Existing nozzles with a built-in means of foam
concentrate pick-up as shown in Figs. 2A, 2B and 3B are all
designed so that concentrate enters through a conduit in the
side of the nozzle. This conduit then typically connects
with a conduit along the central axis of the nozzle bore and
inside the main waterway. The conduit may be equipped with
a venturi suction chamber, or the end of the conduit may be
sealed. If the concentrate conduit is
sealed on the inlet end of the nozzle, concentrate must
be pumped to the nozzle by a separate pump which could be of
the
water powered venturi type. Although designs may differ,
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the basic principle has remained unchanged since its inception.
SUMMARY OF THE INVENTION
It is therefore desirable to provide a single firefighting nozzle design
addressing all four of these problem areas. A nozzle is provided which can
discharge
a solution consisting of fresh, brackish, or sea water, mixed with small
amounts of
firefighting foam concentrate. This solution can be then aerated to form
expanded
firefighting foam suitable for use by those skilled in the flammable liquid
firefighting
art. The characteristics of the fire or hazard determine the type and percent
concentration of the foam concentrate used, the desired foam expansion ratio,
and the
1 o type discharge device selected.
According to an aspect of the present invention, there is provided a nozzle
assembly for combining a liquid foam concentrate with a liquid to produce a
fire
extinguishing foam solution, the nozzle assembly comprising: a tubular body
having
axially aligned inlet and outlet openings; wall means for internally
subdividing the
15 body into an axial passageway surrounded by an annular chamber, opposite
ends of
the passageway being in communication with the inlet and outlet openings to
accommodate a flow of the liquid through the body; a sleeve surrounding the
outlet
opening and extending axially from the body; means for introducing a supply of
the
foam concentrate into the annular chamber; a plurality of openings in the wall
means
2o spaced around the passageway; jet nozzles for diverting a portion of the
liquid
flowing through the passageway into the openings to mix with and educt foam
concentrate in the annular chamber for delivery into the interior of the
sleeve; and
guide means for directing an annular exiting flow of the liquid from the
outlet opening
outwardly towards the interior of the surrounding sleeve to additionally mix
the
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liquid with the educted foam concentrate and to thereby produce a dilute
mixture of
foam solution within the sleeve.
There is also disclosed a nozzle assembly including a nozzle body having an
inlet at a first end and an outlet at a second end. A first fluid passageway
is defined
within the nozzle body for first fluids passing between the inlet and outlet.
Second
and third fluid passageways for respective second and third fluids are also
defined
within said nozzle body. A discharge mixing unit is provided at the second end
and is
in fluid communication with the first, second and third fluid passageways for
mixing
the first, second and third fluids to produce a discharge solution. The
discharge
1o mixing unit includes one or more mixing chambers provided on the interior
surface of
the second end of the nozzle body. The mixing chambers are defined between a
plurality of inwardly extending blades from the interior surface of the second
end. The
second end of the nozzle body has an adjustably extending pattern selection
sleeve.
The third passageway includes a variable fluid flow control device which is
operable
15 for varying the expansion ratios of the discharge solution.
BRIEF DESCRIPTION OF THE DRAWINGS
Figs. 1A and 1B show cross sections of a conventional nozzle with a pattern
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for straight stream discharge and inwardly for fog stream
discharge, respectively;
Figs. 2A and 2B show cross sections of a conventional
nozzle using a separate foam concentrate conduit with a
pattern selection sleeve adjusted outwardly for straight
stream discharge and inwardly for fog stream discharge,
respectively;
Fig. 3A shows a cross section of a conventional
aspirating nozzle in which a foam solution is supplied to
the nozzle; Fig. 3B shows a cross section of a conventional
aspirating nozzle in which water and foam concentrate are
supplied to the nozzle via different conduits;
Fig. 4 shows a cross section of a nozzle in accordance
with the present invention having a pattern selection sleeve
adjusted outwardly for straight stream discharge;
Fig. 5 shows a cross section of the nozzle of Fig. 4 in
a disassembled state;
Fig. 6 shows a frontal view of the nozzle of Fig. 4
taken along line 4-4; and
Fig. 7 shows an exploded cross section view of the jet
nozzles and discharge tube assembly openings from the nozzle
of Fig. 4.
DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS
An exemplary nozzle 40 in accordance with the present
invention is shown in Figs. 4-6. The nozzle 40 includes a
nozzle body 42 having a feed-in conduit 41 and an internal
main waterway 43. A swivel inlet coupler 44 accommodates
the attachment of the nozzle to a desired source, e.g. hose,
of water or foam.
In accordance with an exemplary embodiment of the
present invention, water is pumped through the conduit 41 to
the base of the nozzle where it flows into the main waterway
43. The main waterway has therein a discharge tube assembly
45 which changes having a central short cylindrical tube
opening 46 that curves outward to an annular orifice 47
formed by a nozzle discharge head 48 and a baffle plate 49.
The discharge tube assembly 45 is held in place by the
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discharge head 48 when the discharge head is screwed into the nozzle body.
The discharge tube assembly 45 includes a plurality of discharge openings 62.
Fluid from
the main waterway 43 is fed to the openings 62 via a plurality of jet nozzles
63.
The interaction between the jet nozzles and openings serving as a jet pump
will be described in
more detail hereinafter.
A first conduit 50 in the nozzle body communicates with a chamber 51, which is
concentrically defined around the outside of the main waterway 43. A coaxially
displaced
cylindrical wall 52 is positioned within the nozzle body in order to separate
the main waterway 43
and chamber 51. In accordance with an exemplary embodiment o:f the present
invention, the
1o conduit 50 serves as an entryway for foam concentrate to the nozzle.
A second conduit 53 in the nozzle body communicates with a chamber 54, which
is
concentrically defined within the main waterway 43. A coaxially displaced tube
55 is positioned
within the nozzle body in order to separate the main waterway 43 .and chamber
54. The tube 55
extends through the main waterway and through the discharge head 48, and
includes an outwardly
15 flared end which defines the baffle plate 49. In accordance with an
exemplary embodiment of the
present invention, the conduit 53 serves as an entryway for air to the nozzle.
The nozzle body also includes an adjustable pattern selection sleeve 56. The
pattern
selection sleeve is slidable between a fully extended outward position as
shown which promotes
straight stream discharge of fluids from the nozzle, and an inward position
which promotes fog
2o stream discharge of fluids from the nozzle.
In accordance with the present invention, a plurality of blades 57 extend
radially inwardly
from the inner circumferential end surface of the pattern selection sleeve 56.
The plurality of blades
57 in turn define a plurality of mixing chambers 58 therebetween. 'The mixing
chambers are in fluid
communication with both the main waterway 43 and the chamber 51 associated
with the first
25 conduit 50 via a
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chamber 59. The chamber 59 is defined between the inner
surface of the pattern selection sleeve 56 and the discharge
head 48.
The nozzle configuration shown in Fig. 4 gradually
increases the velocity head of the water stream, thereby
decreasing the pressure head. In the situation where a
water stream from the main waterway 43 passes through the
annular orifice 47 and is discharged to atmosphere, all of
the available kinetic energy has been converted to velocity
head. Water passes over the outer edge of the discharge
head 48 and enters the multiple mixing chambers 58 formed by
the blades 57 on the pattern selection sleeve. Within the
mixing chambers 58, the water mixes with foam concentrates
flowing from conduit 50 and chamber 51.
With reference now to Fig. 7, a more detailed
description of the jet pump action of the openings 62 and
jet nozzles 63 is provided. The jet nozzle 63 includes an
inlet 70 for fluid communication with the main waterway 43.
A suction chamber 71 is defined at the outlet of the nozzle
jet and the opening 62, which in turn are in fluid
communication with the chamber 51. The opening 62 includes
a cylindrical parallel section 72 which feeds to a
diffuser/discharge area 73 which coincides with earlier
described chamber 59.
The ability of the jet pump formed by jet nozzles 63
and opening 62 to educt a fluid is based on the same
principle found in all nozzles of the self educting type.
This same principle is used in air aspirating nozzles to
pick up air and aspirate the foam solution. The inlet 70 is
the area where fluid enters the jet pump nozzle. The
suction chamber 71 is an area where fluid being pumped
enters the jet pump, and where high velocity fluid from the
jet pump nozzle entrains fluid being pumped from suction.
The parallel section 72 is an area where fluid being pumped
mixes with fluid from the jet pump nozzle, thereby acquiring
energy from the nozzle discharge. The diffuser/discharge
area is an area where fluids loose velocity pressure and
regain static pressure due to velocity change so that fluids
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can enter pressurized area in the mixing chambers 58 formed by the blades 57.
According to a preferred embodiment, it is critical that the included angle of
the discharge
head 49 is 90° or less. If this included angle is greater, pressure
rises excessively in chamber 59 so
that the jet pumps are no longer capable of operating. The jet pumps will
operate up to a back
pressure equal to 10% of the nozzle operating pressure, and if the included
angle is greater than 90°,
the back pressure in chamber 59 will exceed this 10% limit.
With reference back to Figs. 4-6, a variable air flow control device 60, e.g.
a conventional
air flow valve, may be opened to allow air to flow through the conduit 53 and
chamber 54 along the
nozzle axis. Air exits the central chamber 54 into a low pressure area 61
which exists behind the
l0 baffle plate 49 at the end of the tube 55. The low pressure area 61 is
created by water flow out of
the annular orifice 47 being deflected by the pattern selection sleeve 56 to
flow parallel, or nearly
so, to the axis of the nozzle. Air enters mixing chambers 58 and mixes with
the foam solution to
form finished foam for discharge.
The variable air flow control device 60 may be closed completely to provide
lower
15 expansion ratios when AFFF foams are used for spill fires. Alternatively,
the air flow
control device may be fully opened to provide higher expansion ratios when
protein based foams
are used.
In situations where foam solution is pumped to the nozzle feed-in conduit 41
through .the
main waterway 43, it is not necessary to use the conduit 50 and chamber 51 for
entering foam
2o concentrate to the nozzle. Instead, the conduit 50 and chamber 51 c;an be
used for additional
aeration. In this manner, air is allowed to enter the chamber 51, where it can
flow through the
chamber 59 into the mixing chambers 58, thus allowing greater aeration and
higher expansion ratios
for the discharged foam solution.
Accordingly, the present invention provides a firefighting nozzle for use in
flammable liquid
25 firefighting and has a unique combination of benefits not available in
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conventional nozzle designs. The invention combines several
desirable characteristics in a cost effective design. For
example, when adjusted at or near the straight stream
patterns, aeration takes place on the outside of the stream
as in existing nozzles, but the unique central air passage
allows the option of selecting higher expansion ratios by
allowing air to enter the low pressure area created inside
the discharge pattern.
The use of the blades 57 located on the inside of the
outer pattern selection sleeve 56 serve multiple functions.
The blades act as straightening vanes to cancel the twisting
currents developed inside the nozzle and the negative effect
these currents have on the discharge pattern, thus tending
to increase the discharge range capability with aerated
foams. The blades 57 separate the discharge area into the
plurality of mixing chambers 58 to enhance mixing of the
water and foam concentrate when the liquids must mix in the
nozzle. The separate mixing chambers formed by the blades
allow greater agitation and aeration of the solution when
the central airway is opened and the nozzle is adjusted at,
or near the straight stream pattern. If foam solution is
pumped to the nozzle and the concentrate chamber around the
main conduit is left open to atmosphere, more air enters the
mixing chambers formed by the blades and additional aeration
occurs.
Furthermore, when water and foam concentrate are
supplied through separate conduits, good mixing will occur
in the mixing chambers, regardless of the pattern selected.
The foregoing description has been set forth to
illustrate the invention and is not intended to be limiting.
Since modifications of the described embodiments
incorporating the spirit and substance of the invention may
occur to persons skilled in the art, the scope of the
invention should be limited solely with reference to the
appended claims and equivalents thereof. What is claimed
is:
