US3633822A

US3633822A - Liquid discharge nozzle with air injection feature

Info

Publication number: US3633822A
Application number: US52447A
Authority: US
Inventors: John O Hruby Jr
Original assignee: Rain Jet Corp
Current assignee: Rain Jet Corp
Priority date: 1970-07-06
Filing date: 1970-07-06
Publication date: 1972-01-11
Anticipated expiration: 1989-01-11

Abstract

A liquid discharge nozzle containing no moving parts and including a hollow body defining a liquid inlet opening at one end and a liquid outlet opening at the other end. The body has an internal chamber arranged in communication with both the inlet and outlet ends of the body. A plug is disposed across the chamber adjacent the body outlet end. Liquid flow passage means are defined through the plug by a plurality of grooves formed in the side walls of the plug, the grooves providing the only flow path of liquid from the liquid inlet opening to the exterior of the body. Means are provided for injecting compressed air into the grooves at locations between the ends of the grooves.

Description

United States Patent Inventor John O. I-Iruby, Jr.

Burbank, Calif.

Appl. No. 52,447

Filed July 6, 1970 Patented Jan. 11, 1972 Assignee Rain Jet Corp.

Burbank, Calif.

Continuation-impart of application Ser. No.

784,541, Dec. 9, 1968, which is a continuation-in-part of application Ser. No. 691,111, Dec. 8, 1967, now abandoned which is a continuation-impart 01 application Ser. No. 492,389, Oct. 4, 1965, now abandoned. This application July 6,

i970, Ser. No. 52,447

LIQUID DISCHARGE NOZZLE WITI-I AIR i9, 22, 428.5, DIG. l, DIG. 16, 416.5, 417.3, 552

[56) Reierences Cited UNITED STATES PATENTS 2,046,592 7/1936 Tracy 239/4173 X 1,565,996 12/1925 French 239/4173 X 3,485,452 12/1969 Sborlino 239/4173 X Primary ExaminerM. Henson Wood, Jr. Assistant Examiner-Thomas C. Culp, .lr. Attarney-Christie, Parker & Hale ABSTRACT: A liquid discharge nozzle containing no moving parts and including a hollow body defining a liquid inlet opening at one end and a liquid outlet opening at the other end. The body has an internal chamber arranged in communication with both the inlet and outlet ends of the body. A plug is disposed across the chamber adjacent the body outlet end. Liquid flow passage means are defined through the plug by a plurality of grooves formed in the side walls of the plug, the grooves providing the only flow path of liquid from the liquid inlet opening to the exterior of the body. Means are provided for injecting compressed air into the grooves at locations between the ends of the grooves.

LIQUID DISCHARGE NOZZLE WITH AIR INJECTION FEATURE CROSS-REFERENCE TO RELATED APPLICATION This application is a continuation-in-part of copending application, Ser. No. 784,541 filed Dec. 9, 1968 as a continuation-in-part of copending application, Ser. No. 691,1 1 1 (now abandoned) filed Dec. 8, 1967, as a continuation-in-part of Ser. No. 492,389 (now abandoned) filed Oct. 4, 1965.

BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to liquid handling and, more particularly, to nozzles for discharging aerated liquid in a predetermined pattern. Nozzles according to this invention are characterized by the absence of moving parts in the liquid stream.

2. Description of the Prior Art In ornamental fountain arrangements which are to be viewed during the day without illumination by artificial light, it is desired that the discharged water be aerated as fully as possible in order that the water discharge pattern may be readily visible. Aerating fountain heads or nozzles are known. Present fountain heads, however, produce only a limited number of water discharge patterns. Many existing aerating fountain heads do not produce sufficient aeration of the water discharged from them. Moreover, many existing aerating nozzles contain moving parts which wear as the nozzle is operated. In other cases, existing aerating nozzles require critical clearances in the nozzle openings to produce the desired aeration; these clearances either become worn by erosion as the nozzle is operated, or clogged by foreign particles in the liquid passing through the nozzle head, thus adversely affecting the nozzle aerating efficiency.

For efficiency of operation, an aerating fountain nozzle should produce the appearance of discharging a massive stream of water even though the quantity of water actually passed through the nozzle is relatively moderate. When this desired condition is obtained, a small pump may be used, thus resulting in a fountain which is economical to operate. Also, in order that they may be used in populated areas, aerating fountain nozzles should produce as little mist or fine spray as possible; mist is readily transported by slight breeze out of the fountain area to locations where viewers may be positioned. Mist also tends to mask the basic fountain discharge pattern and thus detracts from the aesthetic effect desired in the fountain.

The design of aerating liquid nozzles is often more of an art than a science, especially where it is desired that the aerated liquid discharged from the nozzle follow a predetermined path from the nozzle throughout a relatively wide range of liquid pressures applied to the nozzle, and where the discharge is to be used to produce an ornamental effect. The use of techniques and principles which are effective in gas-mixing nozzles, wherein two or more gases are mixed in the nozzle structure and are discharged as a mixture, is practical in only random situations in aerating liquid nozzles because of the widely different physical properties between gases and liquids.

SUMMARY OF THE INVENTION This invention provides a simple, rugged, effective and efficient aerating nozzle which is particularly useful in ornamental fountain arrangements. The nozzle contains no moving parts which may wear as the nozzle is operated. Moreover, no critically sized apertures are provided in the nozzle, and thus water erosion and the presence of foreign particles in the water passed through the nozzle have little effect, if any, upon the aerating efficiency of the nozzle. The nozzle produces the appearance of a massive discharge stream even though the actual volume of water passed therethrough is moderate. Moreover, nozzles according to this invention provide diverse and novel liquid discharge patterns which are essentially free of objectionable mist or fine spray and which are readily visible because of the high degree of aeration of the nozzle discharge and freedom from mist. The present nozzles provide unique dynamic displays not heretofore possible.

Generally speaking, the invention provides an aerating liquid discharge nozzle comprising an elongate body having opposite open ends defining a duct therethrough between a liquid inlet opening defined by one open end of the body and a liquid outlet opening defined by the other open end of the body. A plug is disposed across the duct along the body from the other open end of the body and is secured from movement along the length of the body. Liquid flow passage means is defined through the plug by a plurality of grooves formed in the sidewalls of the plug, the grooves and the inner walls of the body cooperating to define a plurality of liquid outlet passages, and the grooves providing the only flow path of liquid from the liquid inlet opening to the exterior of the body. Air duet means communicate through the plug to the grooves between the ends of the grooves for injection of compressed air into liquid flowing through the passages during use of the nozzle.

BRIEF DESCRIPTION OF THE DRAWINGS The above-mentioned and other features of the present invention are more fully set forth in the following detailed description of the invention, the description being presented in conjunction with the accompanying drawings, wherein:

FIG. 1 is a cross-sectional elevation view of a nozzle according to this invention;

FIGS. 2 and 3 are elevation views of water discharge patterns which may be produced by the nozzle shown in FIG. 1;

FIG. 4 is a top plan view of the nozzle of FIG. 1;

FIG. 5 is an elevation view of the nozzle shown in FIG. 2 mounted on an angle to the vertical and showing a discharge pattern which may be produced by the nozzle; and

FIG. 6 is a cross-sectional elevation view of another nozzle according to this invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT An aerating nozzle 10 according to this invention is shown in FIG. 2 and includes an elongate hollow body 12 defining a circularly cylindrical inner chamber 14. The body has an open, externally threaded 13 lower end 15 which defines a liquid inlet opening to the chamber and which adapts the body for connection to a water supply duct (not shown). The chamber opens to the exterior of the nozzle across its entire aerial extent at an open upper end 16 of the body. A plug 18, having a length between parallel opposite end surfaces 20 and 22 at least equal to one half the mean transverse dimension (the diameter) of the chamber, is disposed across the chamber between the inner walls of the body at a location spaced below the open upper end of the body. Preferably, the plug is spaced below the upper end of the body a distance at least equal to one-half the maximum transverse dimension of the chamber. A plurality of substantially identical grooves 24 are formed in the sidewalls of the plug and extend between, and open to the opposite ends of the plug. The grooves are spaced apart uniformly around the circumference of the plug and are parallel to the axis of the nozzle. The grooves open to the inner walls of the body and form water outlet passages through the plug. The sidewalls of the plug, between the grooves, are intimately engaged with the walls of chamber 14 so that the grooves provide the only paths for water flow from the nozzle inlet opening to the nozzle outlet opening.

Preferably the grooves have equal cross-sectional areas at corresponding locations along their lengths. As shown in FIG. 1, the grooves are tapered along their lengths to increase regularly in area proceeding upwardly along the grooves, the area of the groove at its upper end is about twice the area at its lower end. Also, it is preferred that the grooves be at least twice as long as they are deep. The grooves of nozzle 10 have semicircular cross-sectional configurations. The total cross sectional area of the grooves is not greater than and preferably is substantially less than the area of the chamber below the plug to and including the nozzle inlet opening. Nozzle 10 includes eight grooves 24 each of which has plug-defined walls which make substantial intersecting angles with the inner walls of the body, such substantial angles, preferably on the order of 90, assures that no water emerges from the grooves as thin sheets of water which readily degenerate into fine mist in the nozzle discharge pattern. Also, the upper surface of the plug, around each groove, is substantially normal to the lengths of the grooves and makes a sharp angle, preferably a right angle, with the groove walls, thereby further assuring that the discharge from the nozzle is as free of fine mist and spray as possible.

As shown in FIG. 1, the inner walls of the body above the plug are straight, i.e., parallel to the axis of the body.

A cavity 26 is formed in plug 18 centrally of the body. The cavity has a closed upper end, but communicates with plug lower surface 22. The upper end of a hollow tube 28 is received in the plug adjacent the lower surface of the plug so that the cavity and the interior of the tube are in communication with each other. The connection between the upper end of the tube and the plug provides an airand liquid-tight seal around the tube. The tube has a lower closed end 30 spaced below the plug.

A compressed air duct 32 extends from communication with tube 28 adjacent the lower end of the tube through body 12 below the plug into connection with a compressed air conduit 34 outside the nozzle. It is preferred that conduit 34 be provided by rigid metal or plastic tubing rather than by a flexible hose. Duct 32 is sealed around its exterior to the nozzle body. The compressed air conduit is connected to the outlet of an air compressor 36 via a valve 38 having an actuating or control lever 40. The valve is of the quick-open, quick-close type so that sharply defined pulses of compressed air may be applied to cavity 26 upon cyclic operation of the valve.

Cavity 26 is connected to each groove 24 via respective ones of a plurality of compressed air passages 42. Each passage connects with its respective groove at about or above the midlength of the groove through the plug. Each passage extends upwardly from the cavity to its respective groove, and preferably makes an angle of about 45 with the axis of the body.

When nozzle is vertically oriented above a water supply duct to which the nozzle is connected, the nozzle produces a vertical column of aerated water substantially as shown by column 44 in FIG. 2. When no compressed air is supplied to cavity 26 via duct 34, nozzle 10 produces a plume of water. When compressed air is supplied to nozzle, 10, however, by operation of valve 38 to operatively connect the compressor or other source of compressed air to the nozzle, the height of the column of water above the nozzle increases significantly. The introduction of the compressed air into the water outlet passages defined by grooves 24 substantially increases the exit velocity of the water from the passages. The introduction of the air into the water outlet passages also increases the aeration of the water emerging from the nozzle. The height change of the water column produced by nozzle 10 follows substantially immediately the opening or closing of valve 38; the more rapidly the valve is opened or closed, the more sharply defined the change in water column height.

Nozzle 10 may be operated to produce a novel shell-burst or skyrocket water discharge pattern shown in FIG. 3. The shellburst pattern is produced by passing water through the nozzle and simultaneously injecting air into the nozzle water outlet passages by opening valve 38 to establish the higher column of water producible by the nozzle. Thereafter, when desired, the valve is closed sharply, either manually or by some suitable mechanism (not shown) which forms no part of the present invention, to substantially instantaneously terminate the injection of compressed air into the water outlet passages. The water which has emerged from the water outlet passages has sufficient kinetic energy that it moves, or at least tends to move, to the height of the higher air-augmented column of water. The water passing through the passage as and after air injection is terminated has a kinetic energy attributable only to the nozzle geometry and the pressure of the water in the water main or supply duct to which the nozzle is connected.

Accordingly, the height of the water column above the nozzle is substantially instantaneously reduced to the height of the lower column producible by the nozzle. If the water column height is reduced sufficiently rapidly, the rising water which lies between the plug and the top of the air-augmented column continues to rise and defines a quantity of water in midair over the decreased column. This quantity of water tends to coalesce and fall back toward the nozzle as a single body of water. The production of this body of water is critical to the ultimate production of a sharply defined shell-burst pattern, and, thus, it is important that valve 109 be closed as quickly as possible.

Before the coalesced body of water, left in midair over the nozzle when the air injection to the water outlet passages is terminated, has fallen below the top of the lower column of water, valve 38 is opened as rapidly as possible to cause the column of water emerging from the nozzle to rise substantially instantaneously to its former height. The top of the rapidly rising column of water forcefully meets the falling coalesced body of water and shatters the body of water. Water drops produced by this impact radiate in all directions from the point of impact to produce shell-burst water discharge pattern 46. The faster the column of water rises to meet the falling body of water, the more sharply defined is the shell-burst effect. It is therefore important that valve 38 be opened as rapidly as possible when air injection is resumed.

The shell-burst pattern may be reproduced at any time desired merely by rapidly closing and reopening valve 38 after a delay lasting less than but approaching the time required for water to fall a distance equal to the difference between the higher and lower water column heights.

The shell-burst effect could be provided by rapidly closing and opening a valve in the water pipe to which nozzle 10 is connected. Such a practice, however, is extremely undesirable because of the hammer effect produced by a rapidly started or rapidly stopped quantity of water. Such a practice would rapidly cause the water pipe or the valve, or both, to rupture, and would also damage the noule. Air, on the other hand, is compressible and does not produce such hammering effects. The compressibility of the air, however, works against the generation of sharply defined pulses of compressed air in the water outlet passages of the nozzle; for this reason, it is preferred that duct 34 be essentially rigid between the valve and the nozzle, and that the valve be located as close to the nozzle as is practicable.

Shell-burst discharge patterns have been produced at will in a nozzle in accord with the foregoing description. The nozzle body has an inner diameter of 3,800 inches. Plug 18 in this nozzle is 2 inches thick and is disposed 1,950 inches below the upper end of the body. The plug defines around its circumference eight vertical untapered semicircular grooves three/eighteenths of an inch deep and three/eighteenths of an inch in radius. The air passages from cavity 26 to the grooves are one/fourth of an inch in diameter. This nozzle has a back pressure of 12 pounds per square inch when passing water at a rate of gallons per minute. The nozzle, when valve 38 is closed, produces a column of water approximately 20 feet high. When valve 38 is opened to supply compressed air at 60 pounds per square inch gage pressure to the nozzle, the height of the column of water increases to approximately 32% feet.

Shell-burst patterns have also been produced at will in a nozzle wherein the body has an inner diameter of 2 5/16 inches, the plug is 2 inches thick and is disposed 1,950 inches below the top of the body, the plug defines around its circumference eight vertical grooves one/fourth of an inch deep and one/fourth of an inch in radius, and the air passages to the grooves are three/sixteenths of an inch in diameter. This nozzle shows a back pressure of 20 pounds per square inch when water flow through the nozzle is 1 10 gallons per minute. The height of the lower column of water produced by this water fiowrate is about 25 /z feet. When air at a pressure of 60 p.s.i.g. is supplied to the noule, the height of the discharged water column increases to about 48% feet.

As shown in FIG. 5, nozzle may be disposed at a desired angle to a plumb line and operated in a manner similar to the operation which produces shell-burst pattern 46 to produce a serpentine discharge pattern 48.

Nozzle 50, shown in FIG. 6, is similar to nozzle 10 in all respects except that the upper end portion of body 52 above plug 18 defines a reducing bell portion 54. Untapered grooves 64 replace tapered grooves 24 of nozzle 10. At the same height above the plug as body end 16 of nozzle 10, the inner surfaces of the body of nozzle 50 are curved concave inwardly toward the nozzle axis, as at 56, and then recurved convexly, as at 58, away from the nozzle axis to an open upper end 60 of the body defining a nozzle outlet opening 62. Immediately adjacent the top end of the body, the inner surfaces of the body define a circular cylinder. Preferably, if water aeration is to be maintained, the area of opening 62 is no less and preferably is somewhat greater than the total cross-sectional area of grooves 24. Nozzle 50 has the feature that the difference between the heights of air-augmented and nonaugmented water discharge columns produced by it is greater than in nozzle 10; this difference is, in large part, attributable to the shape of body 52 above the plug rather than to the absence of taper in grooves 64. For example, in a nozzle 50 wherein the body has a nominal diameter of 2% inches at plug 18 and the nominal diameter of opening 62 is 2 inches, the height of the air-augmented water column is approximately three to five times the height of the water column when no air is applied to the nozzle. Thus, nozzle 50 is especially suitable for producing the shell-burst effect shown in FIG. 5 or the serpentine effect shown in FIG. 6.

From the foregoing, it is apparent that this invention provides novel and highly useful water discharge nozzles. These nozzles are particularly useful in ornamental fountain arrangements, but may be used in other applications as desired. For example, nozzle 10 may be used as a fire nozzle if desired. The nozzles described above produce a high degree of aeration in the liquid passing through it without relying upon any moving parts or critically sized openings to accomplish this aeration. Preferably, the nozzles are fabricated entirely from polyvinyl chloride or some similar plastic; thus these nozzles are highly resistant to the effects of water erosion and have long life expectancies under adverse conditions. The nozzles have in common the feature that the water discharge patterns produced by the nozzles are remarkably free of mist, fog, or fine spray.

In the foregoing description, specific geometrical arrangements and dimensional relationships, and even specific dimensions, have been set forth merely for the purposes of example and explanation of this invention; only in certain instances have specified features of the nozzles been stated to be critical. Accordingly, it will be apparent to those skilled in the art that modifications and alterations in the above-described nozzles may be made without departing from the scope of this invention. As noted above, it will also be apparent to those skilled in the pertinent art that features of one described nozzle may be applied to another described nozzle without departing from the teachings of the invention, especially where a characteristic of the one nozzle is desired in the other.

What is claimed is:

1. An aerating liquid discharge nozzle comprising:

a. an elongate body having opposite open ends defining a duct therethrough between a liquid inlet opening defined by one open end of the body and a liquid outlet opening defined by the other open end of the body;

b. a plug disposed across the duct adjacent the other open end of the body and secured from movement along the length of the body, the plug being engaged around its periphery with the inner walls of the duct;

. a plurality of liquid flow passages defined through the plug at regular intervals around the plug at locations proximate to the periphery of the plug and communicating between the opposite ends of the plug, the liquid flow passages providing the only flow path of liquid from the liquid inlet opening to the exterior of the body; and

d. means for injecting compressed air into the several liquid fiow passages at locations between the ends of the passages through the plug.

2. A nozzle according to claim 1, wherein the plug has a 5 length between the opposite ends thereof greater than about one-half the mean transverse dimension of the duct at the location of the plug along the duct.

3. A nozzle according to claim 1, wherein the liquid flow passages each have a length between opposite ends of the plug at least twice the maximum transverse dimension thereof.

4. A nozzle according to claim 1, wherein the duct has the configuration of a circular cylinder. and the liquid flow passages are spaced uniformly about the axis of the cylinder.

5. A nozzle according to claim 1, wherein the liquid flow passages are constant cross-sectional area along their lengths.

6. A nozzle according to claim I, wherein the liquid flow passages are comprised of a plurality of grooves formed in the sidewalls ofthe plug.

7. A nozzle according to claim 1, wherein the liquid flow passages extend through the plug substantially parallel to the length of the duct.

8. An aerating liquid discharge nozzle comprising: a. an elongate body having opposite open ends definin g a duct therethrough between a liquid inlet opening defined by one open end of the body and a liquid outlet opening defined by the other open end of the body; b. a plug disposed across the duct adjacent the other open end of the body and secured from movement along the length of the body, the plug being engaged around its periphery with the inner walls of the duct; c. a plurality of liquid flow passages defined through the plug at regular intervals around the plug at locations proximate to the periphery of the plug and communicating between the opposite ends of the plug, the liquid flow passages providing the only flow path of liquid from the liquid inlet opening to the exterior of the body; and d. means for injecting compressed air into the liquid flow passages at locations between the ends of the plug includmg i. a cavity within the plug centrally of and spaced from the liquid flow passages,

ii. a conduit communicating between the cavity and the exterior of the body,

iii. means adapting the conduit for communicating with a source of compressed air, and

iv. a passage communicating between each liquid flow passage at a location between the opposite ends thereof and the cavity.

9. A nozzle according to claim 8, wherein the plug is spaced toward the duct inlet opening from the outlet end of the body, and the body for a selected distance from the plug toward the outlet end of the body defines a right-circular cylinder.

10. A nozzle according to claim 9, wherein the cylinder extends from the plug to the outlet end of the body so that the cylinder opens without restriction to the exterior of the body.

11. A nozzle according to claim wherein the body at a location spaced between the plug and the outlet end of the body is smoothly curved around the axis of the cylinder to define a reduced diameter opening at the outlet end of the body concentric to the axis of the cylinder.

12. A nozzle according to claim 1 1, wherein the diameter of the reduced diameter opening is about one half the diameter of the cylinder at the location of the plug.

13. A nozzle according to claim 8, wherein each liquid fiow passage has a greater cross-sectional area between the intersection of the corresponding air passage therewith and the end thereof adjacent the duct outlet opening then between said intersection and the end of the liquid flow passage adjacent the duct inlet opening.

14. A nozzle according to claim 13, wherein the cross-sectional area of each liquid flow passage increases regularly from the intersection of the corresponding air passage therewith to the end of the plug adjacent the duct outlet opening.

15. A nozzle according to claim 14, wherein the cross-sectional area of each liquid flow passage increases regularly from the end thereof adjacent the duct inlet opening to its other end.

16. An aerating liquid discharge noule comprising:

c. a plurality of liquid flow passages defined through the plug at regular intervals around the plug at locations proximate to the periphery of the plug and communicating between the opposite ends of the plug, the liquid flow passages providing the only flow path of liquid from the liquid inlet opening to the exterior of the body;

d. means for injecting compressed air into the liquid flow passages at locations between the ends of the plug; and

e. the body of the plug being arranged so that the nozzle is devoid of structure spanning the duct between the plug and the other open end of the body.

t i l l

Claims

1. An aerating liquid discharge nozzle comprising: a. an elongate body having opposite open ends defining a duct therethrough between a liquid inlet opening defined by one open end of the body and a liquid outlet opening defined by the other open end of the body; b. a plug disposed across the duct adjacent the other open end of the body and secured from movement along the length of the body, the plug being engaged around its periphery with the inner walls of the duct; c. a plurality of liquid flow passages defined through the plug at regular intervals around the plug at locations proximate to the periphery of the plug and communicating between the opposite ends of the plug, the liquid flow passages providing the only flow path of liquid from the liquid inlet opening to the exterior of the body; and d. means for injecting compressed air into the several liquid flow passages at locations between the ends of the passages through the plug.

2. A nozzle according to claim 1, wherein the plug has a length between the opposite ends thereof greater than about one-half the mean transverse dimension of the duct at the location of the plug along the duct.

4. A nozzle according to claim 1, wherein the duct has the configuration of a circular cylinder, and the liquid flow passages are spaced uniformly about the axis of the cylinder.

6. A nozzle according to claim 1, wherein the liquid flow passages are comprised of a plurality of grooves formed in the sidewalls of the plug.

8. An aerating liquid discharge nozzle comprising: a. an elongate body having opposite open ends defining a duct therethrough between a liquid inlet opening defined by one open end of the body and a liquid outlet opening defined by the other open end of the body; b. a plug disposed acRoss the duct adjacent the other open end of the body and secured from movement along the length of the body, the plug being engaged around its periphery with the inner walls of the duct; c. a plurality of liquid flow passages defined through the plug at regular intervals around the plug at locations proximate to the periphery of the plug and communicating between the opposite ends of the plug, the liquid flow passages providing the only flow path of liquid from the liquid inlet opening to the exterior of the body; and d. means for injecting compressed air into the liquid flow passages at locations between the ends of the plug including i. a cavity within the plug centrally of and spaced from the liquid flow passages, ii. a conduit communicating between the cavity and the exterior of the body, iii. means adapting the conduit for communicating with a source of compressed air, and iv. a passage communicating between each liquid flow passage at a location between the opposite ends thereof and the cavity.

11. A nozzle according to claim 9, wherein the body at a location spaced between the plug and the outlet end of the body is smoothly curved around the axis of the cylinder to define a reduced diameter opening at the outlet end of the body concentric to the axis of the cylinder.

12. A nozzle according to claim 11, wherein the diameter of the reduced diameter opening is about one half the diameter of the cylinder at the location of the plug.

13. A nozzle according to claim 8, wherein each liquid flow passage has a greater cross-sectional area between the intersection of the corresponding air passage therewith and the end thereof adjacent the duct outlet opening then between said intersection and the end of the liquid flow passage adjacent the duct inlet opening.

16. An aerating liquid discharge nozzle comprising: a. an elongate body having opposite open ends defining a duct therethrough between a liquid inlet opening defined by one open end of the body and a liquid outlet opening defined by the other open end of the body; b. a plug disposed across the duct adjacent the other open end of the body and secured from movement along the length of the body, the plug being engaged around its periphery with the inner walls of the duct; c. a plurality of liquid flow passages defined through the plug at regular intervals around the plug at locations proximate to the periphery of the plug and communicating between the opposite ends of the plug, the liquid flow passages providing the only flow path of liquid from the liquid inlet opening to the exterior of the body; d. means for injecting compressed air into the liquid flow passages at locations between the ends of the plug; and e. the body of the plug being arranged so that the nozzle is devoid of structure spanning the duct between the plug and the other open end of the body.