US2774583A - Apparatus for producing fire extinguishing foam - Google Patents

Description

E. HAFTKE Dec. 18, 1956 APPARATUS FOR PRODUCING FIRE EXTINGUISHING FOAM Filed Aug. 14, 1953 United States Patent APPARATUS FOR PRODUCING FIRE EXTINGUISHING FOAM Edward Haftke, Ealing, London, England Application August 14, 1953,'Serial No. 374,387

Claims priority, application Great BritainFebruary 3, 1953 Claims. Cl. 261-76) The invention relates to fire extinguishing apparatus of the kind which projects a foam consisting of liquid and entrained air onto the fire and more particularly to means of improving the construction of the foam-making device.

Known foam making devices consist of an ejector member through which a dispersed jet of liquid, usually water and a foaming agent, is forced into an injector nozzle to which air from the atmosphere is freely admitted. The air is entrained by the liquid flowing at high velocity, and is mixed with the atomized particles of the liquid to form bubbles of foam.

It is desirable that the amount of air entrained per unit mass of liquid flowing should be as large as possible, in order to obtain the highest possible output of foam. The entrained air must however, be intimately mixed with the liquid in such manner that the bubbles are of the smallest size aud are of uniform size, since, only such bubbles will form a stable foam effective to extinguish a fire. The efficiency of the mixing of air and liquid depends largely upon the turbulence created in the suction space, but the extent of the turbulence must not be as great as to reduce the velocity of flow of the foam from the nozzle, and thus shorten the range of the jet of foam.

It has been found that the output of effective foam generated by such branchpipes can be considerably increased by forcing the jet of the liquid (which is stabilised by the addition of a foam-making agent) through two or more cylindrical suction tubes or chambers mounted in immediate succession coaxially at the inlet portion of the branchpipe in a tube, each of the suction tubes or chambers entraining air from the atmosphere admitted to it through separate inlets provided in the wall. By such means in the limited space of reduced pressure at each of the suction tubes or chambersv the turbulence can be adjusted to the amount of air entrained by the liquid, the size of which varies in the successive tubes.

To ensure a uniform and gradual mixing of air and liquid it is advantageous that the main portion of air should be entrained by the last suction tube in the direction of flow, while each of the preceding tubes should entrain less than half of the amount of air passing through the succeeding tube. The amount of air entrained by each tube can be to a large extent predetermined by the cross-sectional area of the tube, and the total area of the air inlets.

Only by correlating the dimensions of the tubes in a suitable manner is it possible to maintain throughout all of the tubes sufficient velocity of flow of the liquid in order to entrain the required amount of air and also to deliver the foam to a substantial distance.

It is essential that the liquid discharged from the ejector into the air-suction chambers should be in the form of an atomised stream. This not only increases the suction surface of the stream but also facilitates the intimate mixing of the liquid with the entrained air. The

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2 smaller the particles of the atomised liquid, the finer the foam bubbles and the better will be the fire extinguishing properties of the foam produced.

It has been found that, for foam making nozzles with multi-stage air intake, the most suitable ejector member is of the kind which consists of a turbulence chamber formed as a tubular conduit of a relatively short length and provided at its respective ends with an inlet orifice and an outlet orifice mounted co-axially with the conduit which in turn is concentric with the nozzle. The smallest cross-sectional area of the turbulence chamber is substantially larger than that of either of the orifices, so that considerable turbulence and eddy currents are created by the high velocity liquid stream on its passage through the chamber. The hitherto streamline flow of the liquid is thereby set in a turbulent state which causes the stream on emergence from the chamber to break up into small particles forming. a conical spray with its area expanding in the direction of flow.

The atomisation of the liquid depends primarily on the I extent of turbulence imparted to the stream which in turn is governed by the dimensions of the turbulence chamber. The best results are obtained if the length of the turbulence chamber is at least three times the diameter of its inlet orifice and the cross-sectional area of the chamber is six to nine times larger than the area of the inlet orifice. Means can be provided in the conduit forming the turbulence chamber for varying the distance between the inlet and outlet orifice, which distance controls the length of the chamber and varies the degree of atomisation of the liquid and thereby the consistency of generated foam.

The outlet orifice of the turbulence chamber, forming the ejector, consists of a centrally apertured thin plate and its area, primarily controls the angle of divergence of the cone of liquid spray on its emergence from the ejector. The cross-sectional area of the outlet orifice is not critical for the rate of flow of the liquid and it can vary for the same output, according to the area of the inlet orifice and the dimensions of the turbulence chamber. It is essential that the angle of divergence of the spray should be adjusted to the diameter of the suction tubes providing the air-intake, in such a manner, that the smallest possible loss of stream velocity is caused by the impingement of the boundary of the core of spray upon the walls of the tubes and in particular upon the wall of the last downstream tube, which provides the largest airsuction chamber. It has been found that the best performance is obtained when the ratio of the cross-sectional area of at least one of the air-suction chambers, preceding the last one downstream, and the cross-sectional area of the outlet orifice of the ejector lies between 5:1 and 10:1. The choice of the chamber in the sequence best suitable for correlation with the outlet orifice depends on the number of chambers in the air-intake arrangement, which number is governed primarily by the liquid output of the ejector, the assumed initial water pressure and the aimed foam texture.

The foam making nozzle, constructed in accordance with the stated principles, consists of a tubular housing comprising a cylindrical portion which extends downstream at a divergent angle and forms a frustum-like portion of a progressively increasing cross-sectional area and ends in a discharge orifice of a reduced cross-section, the three parts being co-axial. The upstream part of the cylindrical portion provides the intake section of the nozzle and it comprises a connection to the supply of water under pressure to which a foam agent is admixed, an ejector member for the atomisation of the liquid and air-suction chambers for introducing into the liquid stream the whole amount of air required for the generation of chamber of the described kind arranged co-axially with the nozzle. Adjacent to the ejector outlet and co-axially with.it are mounteitwb or more. airesuction chambers, eachfornledas a cylindrical tube. The suction chambers are arranged in immediate successionand in overlapping relation to eachother, each of thecharnbers. being of a larger diameter in accordance with its distance from the ejector and the. last suction chamber upstream being formed by the wall; of the cylindrical portion of the nozzle. The air-suction chambers preceding the last one upstream-are each of relatively short length, none exceeding twice its own diameter. A'ir-inletsare provided in the wall-of the tubes forming the air-suctionchambers which admit toitfreely atmospheric air entrained by the liquid in stages, as the stream flows through the successivesuction chambers creatingin each of the chambers reduced pressure. Due to the restricted length of such an air-intake arrangement, the whole. amount of air requiredfor the production of the foam is admixed to the liquid, while its viscosity is still lowand its stream velocity high, both conditions essential for providing a uniform and efiective liquid-air mixture.

The progressively expanding portion of the nozzle increases to a cross-sectional area three to four times larger than the area of the cylindrical portion and it houses one or more screens of wire gauze or perforated sheet mounted at the enlarged end of the portion. While the foam flows through the screen or screens with its velocity reduced by the enlarged space of the portionof the nozzle, the uniformity of the foam bubbles is,considerably improved and their sizedecreased.

The discharge orifice, is formed as an extension of the large end of the expanding portionof the nozzle and its downstream end is of a decreased cross-sectional area for the purpose of shaping the foam into a streamline jet and increasing its velocity, prior to its projection onto the-seat'of the fire.

The invention is diagrammatically illustrated by way of; example in the accompanying drawings, in which:

Figure lis a sectional elevation of a nozzle constructed according to the invention, and,

Figure 2 is an enlarged sectional elevation of the ejector member illustrated in Figure l.

The foam generating tube 1 is provided at one end with a coupling 2 by means of which it is connected to the hose which delivers water under pressure, the water being stabilised by having a foaming agent in solution or in admixture. An ejector member 3 is mounted centrally of the coupling 2, the member 3 being formed as a cylinder with end plates 4 and 5. The end plates 4and 5 are each providedwith a central orifice t and 5' respectively, the outlet orifice 5 being of the same or greater diameter than the inlet orifice 4.

A suction chamber 6, formed as a cylindrical tube, surrounds and extends beyond theend 5 of the ejector member 3 and is mounted on or inthe coupling 2. The wall of the suction chamber 6 is provided with a number of circumferentially spaced, circular air inlets 7. At substantially coincident positions with the air inlets '7, a series of air inlets 8 of larger diameter are provided in the wall ofthe foam generating tube 1. The air inlets 8 open directly to the atmosphere.

A-second suction chamber 9 provided as a tube of larger diameter and length than the first suction chamber 6, is mounted coaxially with the chamber 6. The chamber 9 overlaps, to a smallextent, that'end of the suctionchamber 6; remote from the ejector member 3. The end of the suction chamber 9 encircling the chamber 6 is provided with an inwardly directed annular flangelt) which is a trally in thepipe 1' and'coaxially with the chamber 6.-

spacsd eries q xz rcu ar a r l ll re P 'Q lQQ the cylindrical wall of the chamber 9 near the lower end.

Beyond the outlet end of the suction chamber 9, the wall of the tube 1 is provided with a further series of circumferentially spaced, air inlets 13 which are open to the atmosphere.

The tube 1 is of uniform circular cross-section from the ejectorrnemberfi to aposition beyond theouter end of the section chamber 9, after which the tube 1 increases progressively in cross-section to form a bell-mouth, until a position near the outlet at which it is constricted to form a delivery nozzle 15. The cylindrical part of the tube 1 beyond the endvof the suction chamber 9, serves to form a third suction chamber, the length as well as the diameter of which chamber is greater than that of the second suction chamber 9.

In the bell-mouth of the tube 1 there are provided two screensof wire or of perforated sheets of metal 14 spaced apart. The screens orsheets 14are advantageously of dish-form with their concave surfaces directed towards the delivery nozzle 15, andare formed-integral with suitably supported on the walls of the tube 1.

The foamgenerating tube 1 operates as follows: The liquid, namely the water and foaming agent, passes under pressure through the inlet 4' into the ejector member 3,- and dueto the restricted inlet 4' and outlet 5' is caused to whirlin the member 3. The liquid is set in a turbulent state in the member 3 and after passing through the orifice 5', enters the suction chamber 6 in the form of a spray. The spray of liquid, in its passage through the first suction chamber 6, draws in air through the inlets 7, which inlets are in the region of reduced pressure caused by. the flow of the liquid spray. The air becomes entrained with the spray during its passage through the suctioncharnber 6.

The liquid/ air mixture formed into a cylindrical stream passes from the firstsuction chamber 6 into the second suction chamber 9, in which further quantities of air are drawn into the suction chamber 9 through the air inlets 12 and are entrained in the liquid/air mixture in its passage through the chamber 9; As in the first suction chamber 6, the air inlets 12 of the second suction chamber 9,are formed in the region of reduced pressure. The greater diameter of the chamber 9 as compared with the diameter of the chamber 6 provides the space required for intimate. admixture of the further quantity of air drawn inthrough the inlets 12, with the liquid/ air mixture received from the chamber 6.

Fro m the second suction chamber 9, the liquid/air mixture in the form of a cylindrical stream of enlarged diameter passes into thesuction chamber which is formed by the tub e 1, the third suction chamber being of greater diameter and length than the diameter and length of the chamber 9.- Further quantities of air are drawn into the third suction chamber through the inlets 13 and are entrained in the, liquid/air mixture, the inlets 13 being formed inthe region ofireduced pressure.

The liquid/ air mixture in the form of an initial foam then passes into the enlarged portion of the tube 1 and through the screens or perforated sheets 14. Passage through the screens 14 serves to decrease the size and improve theuniformity of the foam bubbles. The foam thus formed passes out through the delivery nozzle 15 in the form of-a solid jet. 9 i

It will be noted that the end plate 4 of the ejector member 3 is, in Figure 2, shown in a different position to that which itoccupies in Figure 1, the volume of the chamber being less in Figure 2 than in Figure 1. Any suitable means may be provided to permit alteration of the volume ofthe chamber 3 by movement of the end plate 4. Such means maycomprise an end plate 4 having its circumferentialsurface suitably threaded to engage a similar thread-on the inner surface of-the wall of the chamber 3. One or both of -theendplates 4 and 5, advantageously the rear plate 4, may be provided: so as to be removable from the ejector member 3 in order to vary the consistency of the foam.

1 claim:

1. A nozzle for producing a fire extinguishing foam and projecting it as a substantially streamline jet, formed as a continuous tube having air inlet openings in its walls and including at its upstream end cylindrical portions which extend downstream at a divergent angle to provide a progressively increasing cross-sectional area and ends in a discharge orifice of a reduced cross-sectional area, the inlet end of the tube comprising a connection to a supply of water under pressure to which a foam agent is admixed, an ejector member coaxial with the tube for the atomisation of the liquid stream and two or more airsuction chambers in co-axial alignment with said ejector member for introducing into the liquid the Whole amount of air required for the production of the foam, said ejector member consisting of a turbulence chamber formed as a tubular conduit provided at its upstream end with an inlet orifice and at its downstream end with an outlet orifice formed as a centrally apertured thin plate, said orifices being aligned axially of said tube, the smallest crosssectional area of said tubular conduit being substantially larger than the cross-sectional area of either of said orifices, the air-suction chambers each consisting of a cylindrical tube having air inlets in its walls arranged in immediate succession in overlapping relation to each other and the last air-suction chamber downstream formed by the wall of said tube, each of the air-suction chambers being of larger diameter in accordance with its distance from said ejector member and each communicating freely with the atmosphere through said air inlets, whereby the ratio of the cross-sectional area of at least one of the airsuction chambers preceding the last one upstream and the cross-sectional area of the outlet orifices of the ejector member lies between 5:1 and :1 and the length of any of the same air-suction chambers does not exceed twice its diameter and wherein each upstream end of said cylindrical tubes is closed about the adjacent cylindrical tube and ejector member, respectively.

2. In a nozzle for producing a fire extinguishing foam and projecting it as a substantially streamline jet formed as a continuous tube having air inlets in its walls and an apertured closure defining an inlet end to which a supply of water under pressure to which a foam agent is admixed may be connected, an ejector member in said apertured closure defining a turbulence chamber having axially aligned apertured end plates, one of which is movable toward and away from the other, for atomising liquid directed therethrough, a cylindrical member having air inlets in its walls secured at one end to said closure and positioned about said ejector member and extending inwardly of said tube therefrom, a second cylindrical member of larger diameter than said first mentioned cylindrical member and having air inlets in its walls positioned in said tube in partially overlapping relation to said first mentioned cylindrical member and means forming a closure between said second cylindrical member and said tube, and a secondary apertured closure on said second cylindrical member with said first mentioned cylindrical member extending through the aperture therein, said cylindrical members forming progressively larger airsuction chambers progressively downstream from said ejector member.

3. A nozzle according to claim 1, in which the length of the ejector between the inlet and outlet orifices is numerically at least three times -the diameter of the inlet orifice of the ejector.

4. A nozzle according to claim 1, in which the ejector is formed as a cylinder having a cross-sectional area six to nine times the cross-sectional area of the inlet orifice of the ejector.

5, A nozzle according to claim 1, in which the crosssectional area of the portion of the nozzle of progressively increasing diameter at the widest part is three to four times the cross-sectional area of the uniform part of the nozzle.

References Cited in the file of this patent UNITED STATES PATENTS 2,373,009 Bedford Apr. 3, 1945 2,556,239 Tuve et a1. June 12, 1951 2,597,913 Webster May 27, 1952 2,630,183 Fowtz Mar. 3, 1953 2,651,546 Palm Sept. 8, 1953 FOREIGN PATENTS 468,687 Great Britain July 6, 1937 1,014,293 France May 28, 1952 860,144 Germany Dec. 18, 1952

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