US3000576A

US3000576A - Spray gun

Info

Publication number: US3000576A
Application number: US12092A
Authority: US
Inventors: Gustave S Levey; Stanton F Harvey
Original assignee: SPEE FLO Co
Current assignee: SPEE FLO Co; SPEE-FLO Co
Priority date: 1960-03-01
Filing date: 1960-03-01
Publication date: 1961-09-19
Anticipated expiration: 1978-09-19
Also published as: BE600751A; DE1218322B; CH393148A; GB933706A; DE1858891U

Description

Sept. 19, 1961 G. s. L EVEY ETAL l3,000,576

SPRAY GUN Filed March 1, 1960 4 sheets-sheet 1 INVENTORS 6057A VE 5- EVA-'Y SMA/70N f'.- HA RvE Y.

BY R/CHE y, MSNM/NYA FA RIP/Na To/v A TTOFNEYS sept. 19, 1961 Filed March l, 1960 G. s. I EvEY E11-A17 SPRAY GUN 4 Sheets-Sheet 2 IN VEN TORS GUSTA VE' SLL-VFY STANTON F- HAVEY lP/CHENS/vE/v n? FAHR/Nauw, y?

ATTORNEYS Sept 19, 1961 G. rs. Lr-:vEY Erm. 3,000,576

SPRAY GUN I Filed March l, 1960 4 Sheets-Sheet 3 "l l' I UMH,

WIW"VW"' ,W ,www lll" Il TQ W" WHW'. 4

IN V EN TORS GUSTA VE 5 Evi-"Y s7ANro/v AHARVEY.

BY R/{HE Y, NSNENA/V FA RRI/VG TON Sept. 19, 1961. i G. s. LEVI-:Y ETAL SPRAY GUN Filed March 1, 1960 4 Sheets-Sheet 4 fw 6L N2 INVENTOR-S GUSTA VE' 5- EVEY STANTON F- HAPVEK BY l? /c HE Y, MSNE/v/v Y FA RR/A/GTO/v A TTORNEYS United States Patent Oiiice Patented Sept. 19, 1961 3,000,576 SPRAY GUN Gustave S. Levey and Stanton F. Harvey, Houston, Tex.,

assignors to The Spee-Flo Company, Houston, Tex., a corporation of Texas Filed Mar. 1, 1960, Ser. No. 12,092 8 Claims. (Cl. 239-499) This invention relates to a spray gun for paint and the like, more particularly a gun for hydraulically atomizing and spraying paints and other liquids.

Heretofore paints have been sprayed by entraining paint in a jet of high pressure air escaping through a spray nozzle, the air serving to atomize and propel the paint against a surface to which it is to be applied. Such air spray guns have been capable of applying paint at substantially uniform density over surfaces of any configuration. The compressed air escaping through the nozzle breaks up the paint into a mist of substantially uniform density which is applied to the surface being painted as an elliptical pattern with a marginal portion feathering out to a decreased density of paint. This pattern permits a continuous spray from the gun to be progressed along the surface being painted, in the direction of the short `dimension of the elliptically-shaped pattern, to produce a uniform strip having lateral margins feathered out so that subsequent parallel passes with the spray gun with the feathered margins of the patterns over-lapping permits the application of a uniform coating of the desired density over the entire surface.

The principal objection to the use of air spray guns resides in the fact that the compressed air serving as the atomizing and carrying medium must escape and carries with it a substantial quantity of paint and' paint solvents. This results in an excessive waste of the paint and also produces a large volume of air mixed with flammable paint and solvent vapor which must be conducted away with hoods, stacks and the like from the area in which the paint is being applied.

Efforts have been made to eliminate this over-spray by forcing the liquid paint at high velocity through atom-izing nozzles having sharp outer Vedges'without the use of air. Such airless spraying requires pumping the liquid paint under high pressure to produce the necessary velocity through the nozzle to obtain hydraulic atomization. The difliculty of breaking up and atomizing the paint depends, among other factors, upon the viscosity, surface tension and density of thepaint. -Correct atomization has not heretofore been achieved with many materials. Efforts to improve the atomization and distribution have included heating the paint which tends to reduce viscosity and surface tension but does not change the density and also by the use of increased hydraulic pressures. None of these expedients solved the problem particularly for high quality finishes.

All of these prior efforts to eliminate the disadvantages of air spraying, however, have resulted in non-uniform spray patterns having thickened portions or pig-tails near the opposite ends of the oval sprayV patterns and lacking the feathered marginal portion produced by the air spray guns which are necessary to permit lapping of successive passes to obtain a uniform film. The typical airless spray nozzles heretofore used have a small orifice usually of an elliptical shape with sharp edges. rSuch a nozzle inherently creates a vena contracte or restriction caused by the rapid acceleration of the lquidas it passes through the orifice. As the typical airless spray nozzle orifice is elliptically shaped with vertices at the top and bottom which are necessary to produce the elliptical spray pattern, the creation of Ithe vena contracta tends to prevent the passage of the liquid over the Sharp vertices and, therefore, to prevent the full atomization quality which is necessary. This poor atomization at the top and bottom of the orice creates the pig-tail or thickened edges already referred to. Efforts to eliminate this common diflcultyrwith standard airless guns include reduction of viscosity, by thinning or an increase in pressure which is similarly a disadvantage because such pressure increase is accompanied by a volume increase through the center of the nozzle which results in liooding of the work as a result of excessive material flow. `4As it is impossible to eliminate the vena contract by streamlining the orifice because the orifice shape as presently designed must remain, we have eliminated it by accelerating the fluid jet prior to its introduction into the spray nozzle to a velocity approximately equal to that ofthe velocity of the liquid moving through the nozzle itself. By controlling the liquid in this manner we have eliminated any tendency to form a vena contracta and have obtained substantially uniform pressure and velocity across the area of the spray nozzle, so that the liquid is uniformly atomized and distributed across the spray pattern with a uniform reduction in density or feathering at the margins of the pat-tern. All ofthe advantages of the prior air and airless methods are thereby realized with the elimination of the disadvantages of each.

Known forms of spray guns embody passageways adapted to be connected to a source of paint under high pressure, a valve body in the passageway with a valve port extending therethrough, a needle or ball pointed valve member movable in the passageway and arranged to seat on the upstream side of thevalve body to interrupt the flow and a spray nozzle secured to the gun on the downstream side of the valve plate. Conventional spray nozzles have elongated or oval-shaped nozzle openings, the area of the opening varying from an area equal to that of a circle of .011 of an inch in diameter, to an area equal to that of a circle of about .035 of an inch in diameter. Thus the area of all of these openings is less ,than .001 square inch. The valve port and al1 other passages upstream from the nozzle openinghave been maintained substantially larger than the area of the nozzle opening to minimize pressure drop and flow restriction, and to impose high pressure on the nozzle, in an effort to obtain atomization.

In the prior spray guns, the paint reached the nozzle under high pressure and with relatively low velocity, and was accelerated in the nozzle opening to the high velocity and low pressure of the spray fan, resulting in a vena contracta, which contributed to the undesirable distribution and atomization characteristic of the prior airless spray guns.

In accordance with the present invention, the paint moves as a submerged jet at high velocity and low pressure into the nozzle opening, spreading sufiiciently to fill the opening. The vena contracte is eliminated, and uniform, complete atomization is effected. Y

In a preferred embodiment of the present invention a restricted orifice is provided between the valve and the nozzle so as to accelerate the paint to the desired high velocity. The orifice is aligned with the central axis of the nozzle opening and discharges a submerged jet into a space of substantially larger diameter than the orifice, through which the jet travels and spreads sufficiently to fill the nozzle opening with high velocity paint.

In another embodiment of the present invention, the relatively large diameter valve por-t of the prior spray guns is retained unchanged, and a hole is bored into the large diameter chamber between the valve plate and the nozzle and connected to a return hose leadingl to the intake side of the pressure pump, so that the paint passes through the valve port at the same high velocity and low pressure with which it Passes .threyah and emerges from the nozzle opening, the excess quantity passing through the valve port because of its larger area being returned through the bleed hole to the intake side of the pump.

Each of these embodiments achieves the principal bjects of this invention of uniformly atomizing and distributing the paint in the spray fan, and producing a spray pattern with feathered margins.

Other objects and advantages will appear from the following detailed description of preferred embodiments of this invention.

ln the accompanying drawings,

FIG. 1 is a vertical section through an airless spray gun embodying the present invention;

FIG. 2, is a greatly enlarged cross-section through the valve port and spray nozzle of a gun constructed according to this invention;

FIG. 3 is an enlarged end elevation taken on the line 3-3 of FIG. 2 looking in the direction of the arrows;

FIG. 4 is a cross-section taken on the line 4 4 of FIG. 3 looking in the direction of the arrows;

FIG. 5 is a detailed cross-section through the spray nozzle taken on the line 5 5 of FIG. 4 looking in the direction of the arrows;

FIG. 5A is a further enlargement of the central portion of FIG. 5 showing the spray nozzle opening;

FIG. 6 is a view similar to FIG. 2 on a somewhat smaller scale showing another embodiment of the present invention;

FIG. 7 is a view similar to FIG. 6` showing further modification;

FIG. 8 is a similar cross-section through a spray nozzle showing another embodiment of lthe present invention; and

FIG. 9 is a representation of a painted strip produced by a spray gun embodying the present invention with a second spray pattern over-lapping the first strip.

Referring to the drawings, the spray gun illustrated in FIG. 1 embodies a handle portion 10 having a forwardlyextending stock portion 11 to which is secured a spray portion 12 by means of a bolt 13.

The spray portion 12 has an axial bore 14 having an internally threaded portion 15 at its forward end and a reduced counterbore 16 at its rearward end. Threaded fitting boss 17 opens into the lower side of the bore 14 and is formed to receive a combined swivel fitting and strainer holder 1S. The fitting 18 includes an enlarged passage containing a strainer or filter 19 and at its lower end is threaded to receive a nut 2.@ within which is rotatably secured a swivel coupling member 21 adapted to be connected to the end of a flexible hose leading from a high pressure paint pump. The coupling member 21 may be rotatably secured to the nut 2t? in any suitable manner as by a metal ring 2,2 and the inner end of the coupling member 21 is sealed against fluid leakage as by the gaskets 21a which engage and seal against the member 21 and the innerwall of the fitting 18. The fitting 13 is formed with wrenching flats 18a so that it may be removed by holding the handle portion l0 and applying a wrench to the flats 18a thereby permitting the strainer 19 to be removed and replaced. The swivel may be disconnected for repacking and the like by applying one wrench to the ats 18a and another to the nut 20. By this arrangement it is possible to remove, clean or replace the strainer 19 quickly and easily with a single wrench without opening the swivel connection itself which requires less frequent attention.

The hose connected to `the fitting 2d may be branched, with a return line leading through a pressure reducing valve to the intake of the pump if it is desired to use a heater in the supply line. A suitable pump and circulating system is disclosed in a co-pending application Serial No. 853,638, filed November 17, 1959, to which reference is made for a more complete disclosure of the structure and operation ofthe pump and arrangement of hoses and a heater. When no re-circulation is needed or desired, the coupling 21 may be connected to a single hose leading to a source of paint under pressure, such as the outlet side of a pump.

A nut 23 is secured in the threaded end 15 of the bore 14 and secures a valve body 24 in position at the forward end of the bore 14. The valve body 2.4 has an axial valve port Z5 extending therethrough, the inner or upstream end of which is adapted to be closed by a ball -valve 26 carried on an axially extending valve stem 27. The valve stem is guided in the counterbore 16 and extends through a gland knut 2,8 which seals the free end of the counterbore 16. The valve stem 27 is biased forwardly in any suitablev manner into position to seal the valve port 25.

In the illustrated arrangement a tubular member 3i) is adjustably threaded into a sleeve 31, the latter being secured in the handle portion 10. The tubular member 3f! encloses a spring 32 arranged to urge forwardly a pusher sleeve 33 adjustably secured to the valve stem 27. The forward end of the sleeve 33 has an abutment flange 34 adapted to be engaged by a pivoted trigger 35. Pressing the trigger 35 toward the handle portion 10 retracts the valve stem 27, opening the valve port 25.

The spray portion 12 at the forward end of the bore 14 is also external-ly threaded to receive a nut 36 which secures a spray nozzle assembly to the forward end of the gun. As best shown in FIG. 2, the valve body 24 has a reduced portion 40 at its forward end which fits in a counterbore 41 in the nut 23 The valve body 214 may have a press fit within the nut 23 so that it is secured in place and sealed against fluid leakage, and the valve body itself is preferably made of hard erosion resistant material such as tungsten carbide. As shown in FIG. 2 the valve port 25 terminates in a flared seating surface 42 to engage the ball valve 26 and at its opposite end the port 25 communicates with a restricted orifice 43. The orifice 43 is preferably a straight cylindrical hole with an axial. length from about two to ten times its diameter.

'Ihe spray nozzle assembly 37 includes a holder 44 having an external flange 45` to be engaged by an internal flange on the nut 36. A spray tip 46 has a reduced forward end portion 47 and is press-fitted into a correspondingly shaped axial opening 4S in the holder 44. The tip 46 is preferably formed of hard erosion resistant material such as tungsten carbide and has a relatively large bore 49 extending inwardly from the rearward end thereof. A small bore 50 is formed through the forward portion of the tip 46 to form the spray nozzle opening. Preferably the bore 49 terminates in a substantially perpendicular Wall or shoulder as illustrated.

A spacer sleeve 51 is fitted within the holder 44 and abuts against the rearward end of the tip 46 and against the forward face of the nut 23, being secured in leakproof relation by the nut 36, The spacer sleeve 51 has an internal bore 52 which, as illustrated, is larger in diameter than the bore 49 in the tip 46 and is preferably at least as large in diameter as the bore 49.

The spray opening itself is formed as illustrated in FIGS. 3 to 5A. Projecting forwardly from the reduced portion 47 of the tip 4f is a boss 55 which, as shown, may have flat side faces S6 and 57 and a curved end face 58. A tapered slot S9 is cut transversely across the boss 55, the slot tapering to a narrow width equal to the desired width of the oval-shaped spray nozzle opening. The bore 50 is initially formed as a blind bore terminating in a spherically-shaped end 6l) and the slot 59 is cut through the boss 55l far enough to intersect the bore 50. rIhus the spray opening is an oval-shaped or elongated slot 61 having a long dimension equal to the diameter of the bore 50 and a short dimension equal to the minimum width of the tapered slot 59.

In an optimum arrangement the restricted orifice 43 formed in the forward end of the valve body 24 is a circular bore' of a diameter such. that its area is equal to the area of the oval-shaped spray opening 61. Thus the bore 50 leading to the spray opening is larger in diameter than the orifice 43. When paint under high pressure is delivered to the gun through a hose connected to the fitting 21 and the valve 26 is in open position the paint fiows under high pressure through the valve port 25 and is then accelerated, with a consequent drop in pressure, through the restricted orifice 43. The space within the

bores

49 and 52 is filled with paint, and paint emerges through the bore 50 and the oval-shaped spray opening 61. A high velocity stream or jet of paint moves axially out of the orifice 43, travels through the center of the space in the

bores

49 and 52 as a submerged jet and enters the bore 50, spreading sufficiently in its passage through the

bores

49 and 52 to fill completely the bore Sti.

The area of the orifice 43 being equal to the area ofY the nozzle opening 61, the pressure through the orifice 43 drops from the relatively high pressure existing in the valve port 25. The paint is driven through the bore 50 and the spray nozzle 61 by the velocity of the submerged jet, with a relatively small pressure drop, rather than being driven through the nozzle opening by a high pressure-head on the upstream side of the nozzle as in the spray guns used heretofore. The liquid paint in the

bores

49 and 52 is likewise at a relatively low static pressure and is given a toroidal rolling action by lthe -action of the submerged jet, being driven forwardly with the jet near the axis and flowing rearwardly around the periphery of the

bores

49 and 52. Since the surrounding liquid is free to move or roll over it offers relatively little frictional resistance to the submerged jet delivered from the orifice 43 and thus does not substantially reduce the volume of paint that can be delivered through a particular nozzle opening 61 by a given pressure-head in the bore 14.

With this arrangement the paint delivered through the nozzle opening 6.1 is completely and uniformly atornized as it passes the sharp outer edges of the nozzle opening and is driven forwardly in an oval-shaped spray fan. The spray fan is completely or substantially free of any vena contracta and instead spreads uniformly in all directions as it moves away fro-rn the spray nozzle opening. The spray fan produces a pattern such as illustrated diagrammatically in FIG. 9 with a central oval-shaped portion 62 constituting a paint film of uniform thickness and a feathered margin portion 63 in which the quantity of paint reduces uniformly towards the extreme edge of the pattern. Thus the operator can direct the spray fan against a surface to be painted and by moving the gun downwardly, or in the'direction of the narrow dimension of the pattern, can produce a uniformly painted strip such as 64 of any desired length. A subsequent strip can be applied adjacent the first strip with the feathered margin portions over-lapping so that the thickness of the film is substantially uniform completely across the surface to be painted, the over-lapped marginal portions reinforcing each other as indicated at 65.

As stated above, the optimum arrangement is one in which the cross-sectional area of the orifice 43 is equal to the area of the nozzle opening 61. However, it is desirable to use a substantial number of different sized and different shaped spray nozzle openings, depending upon the liquid volume requirement of `the particular material that is being sprayed. Thus, a slow drying enamel which must be applied in a thin coat to avoid runs and sags requires a nozzle opening having an area equal to the area of a circle .011 or .013 of an inch in diameter, whereas other materials require or permit openings with a larger area or with a smaller proportionate difference between the long and `short dimensions of the oval opening.Y i

It is customary to change spray tips as needed by simply removing the nut 36 and replacingv the spray tip assembly 37 with a different assembly. Since it is difficult to replace the restricted orifice 43 each time a different spray tip assembly is secured to the gun we have found that satisfactory results can be obtained with three different sizes of the orifice 43. We have found that when the orifice 43 is made as a circular hole with a diameter of about .O12 of an inch satisfactory results are secured with spray nozzles in which the area of the nozzle opening 61 varies vfrom an area equal to that of a round hole of a diameter of .()ll of an inch to the area of a round hole of .015 of an inch. For the larger sized nozzle openings in which the area of the nozzle opening 61 varies from the `area of a circle of .015 of an inch in diameter to the area of a circle of .021 of an inch, We have found that satisfactory results are secured by using `an orifice such as the orifice 43 having a diameter of .018 of an inch. For nozzles with areas equalto circles of .021 through .031 of an inch in diameter, satisfactory results are secured with an orifice with a diameter of .025 of an inch. ln each of these arrangements the area of the nozzle opening and of the orifice is less than..001 square inch. These three steps cover the present commercial range. Y

When the area of the orifice 43 exceeds the area of the nozzle opening 61 the velocity of the submergedjet delivered by the orifice 43 is less than thevelocity through the nozzle opening 61. When this difference in velocities becomes great enough it tends to produce a vena contracta in the spray fan and to interfere with the uniform atomization and distribution achieved'by this invention. We have found that the critical limit is reached when the area of the orifice 43 is as much as twice the area of the nozzle opening 61. When the area of the orifice 43 is smaller than thearea of the nozzleopening 61 uniform atomization and distribution may nevertheless be secured, but a smaller amount of paint is delivered than would otherwise be obtained through the particular nozzle with a given pressure in the supply. When the jet delivered by the orifice is too small, however, the jet does notiill the bore S0 and the desired spray fan is not produced. We have found that the critical limit in this direction is reached when the area of the orifice 43 is as small at 1A the area of the nozzle opening 61.

It is also necessary that the orifice 43 be sufficiently long to establish a submerged jet which persists as a jet until it reaches and fills the bore 50 leading to the nozzle opening 61. At the same time it is desirable to keep the length of the orifice as short as possible so that it does not substantially reduce the volume of paint delivered from the nozzle opening under a given pressure-head. We have found that the optimum axial length of the orifce 43 is about three times its diameter but that satisfactory results are obtained if its axial length is not less than two diameters. An axial length of the orifice 43 up to about ten times its diameter does not seriously interfere with the volume of paint or require excessively high pressures in the supply lines.

It is also necessary to maintain the orifice 43 aligned with and co-axial with the bore 50 or the central axis of the nozzle opening 61 so that the submerged jet delivered by the orifice 43 uniformly fills the nozzle opening 61. We have found that an enlarged space, or chamber such as that provided by the

bores

49 and 52 between the orifice 43 and the bore 5t), is likewise essential for the best results. We have found that the axial length of this chamber is preferably about 1;/4 of an inch for average materials and orifice and nozzle areas within the range given above. For spraying materials with higher than average density and/or surface tension this distance is preferably greater to permit the submerged jet to spread sufficiently to fill the nozzle opening, Without overfilling. For materials below averagein densityrand/or surface tension a shorter axial length gives optimum results. .An excessive length tends to increase the spreading of the submerged jet delivered by the orifice 43 with consequent increase in pressure and reduction in velocity. An insufficient axial length of this space tends to prevent complete filling of the nozzle opening particularly at the ends of the long dimension of the nozzle opening 61.

A modified form of the invention is illustrated in FIG. 6. In this form the spray portion 112 of the gun and the nozzle assembly 137 are substantially identical with the

parts

12 and 37, in the embodiment first described. The restricted orifice, however, is provided by an additional member instead of being formed in the end of the valve body 24. As shown in FIG. 6, the valve body 124 has a straight cylindrical bore 125 extending completely therethrough and closed at its inner end by a ball valve 126. The nut 123 is formed with a reduced counterbore 141 providing a shoulder abutting against the forward end of the valve body 124 and is formed on its face with a recess snugly receiving a wafer 170. The wafer 170 is made of hard material such as tungsten carbide and is formed at its center with the restricted orifice 143. The wafer 170 abuts the spacer sleeve 151 which in turn abuts the spray tip 146, all of these parts being secured in leak-proof relation by the nut 136.

The orifice 143 is preferably a straight hole circular in cross-section with an area substantially equal to the cross-sectional area of the spray opening in the spray tip 146, the relation of the areas and spacing of the parts being the same as in the embodiment first described. The wafer 170 may be made of a thickness to provide the desiredl axial length of the opening 143 which, as previously stated, may be from two to ten times the diameter of the orice. While a particular wafer 170 with a given sized orifice 143 may be used with a range of sizes of spray nozzles within the limits described in connection with the first embodiment, it is also possible with this arrangement to provide a wafer 170 for each different size spray opening. In this way the optimum relation may always be maintained between the area of the spray opening and the area and axial length of the orifice 143.

A further embodiment of the invention is illustrated in FIG. 7. In this form the restricted orifice 243 is formed in a Wafer or disc 270 having a central pilot 271 adapted to fit within the bore 249 in the spray tip 246. The pilot 271 may be formed to fit snugly in the bore 249 so as to insure maintairing the orifice 243 exactly co-axial with the nozzle opening. This pilot may, of course, be used in either of the embodiments previously disclosed and as explained in connection with FIG. 6 the disc 270 may be made interchangeable so as to provide the correct size and length of' orifice 243l for each different size of nozzle opening to be used on the gun.

A further embodiment of the invention is illustrated in PEG. 8. In this form no restricted orifice is used between the valve and the spray opening and instead the paint is accelerated to the desired velocity by forcing a greater volume through the valve body than is delivered through the spray opening. In this formV the nut 323 is secured in the forward end of the bore 314 in the gun and supports the valve body 324. The Valve body is provided with a straight cylindrical opening 325 which is preferably substantially larger in area than the largest spray nozzle to be used with the gun. The nut 323 has a counterbore 341 which may be substantially the same diameter as the bore 325 in the valve body and forms a continuation thereof. The counterbore 341 opens into the interior of the spacer sleeve 351 which in turn communicates with the enlarged bore 349 in the spray tip 346 in substantially the same way as the embodiment in FIGS. 1 to 5. A radial hole 373 is drilled through the front fiange of the nut 323 leading from the counterbore 341 to the annular space 374 between the periphery of the nut 323 andthe interior of the nut 336. Another radial hole 375 extends throughI the side wall of the nut 336 and is connected to a return line such as a hose 376 open substantially to atmospheric pressure, as by being connected to the intake side of the pressure pump or the like. The radial holes- 373 and 375 are large enough in diameter to produce no substantial back-pressure, so that the pressure in the counterbore 341 is reduced substantially to atmospheric pressure.

With this arrangement when the ball valve 326 is open high pressure paint flows from the bore 314 through the valve port 32S with a velocity determined by the pressurehead and the diameter of the bore 325, the pressure dropping substantially to atmospheric when the paint reaches the counterbore 341. The high velocity submerged )et emerging axially from the counterbore 341 is thus driven through the spray opening in the spray tip 346 at substantially the same velocity, the excess volume resulting from the large diameter of the bore 325 passing ofi through the radial bores 373 and 375 at substantially atmospheric pressure. Y

This arrangement sho-wn in FIG. 8 4thus permits a. single valve body to be used with any of a wide range of different sizes of spray nozzle openings and delivers the paint through the nozzle opening without substantial change in velocity so that no vena contracta is formed in the spray fan and uniform atomization and the desired distribution of the paint is obtained in the same manner described in connection with the embodiments in FIGS. l to 7.

While preferred embodiments of the invention have been described in considerable detail it will be understood that various rearrangements and modifications may be resorted to without departing from the scope of the invention as defined in the following claims:

What is claimed is:

l. Means for hydraulically atomizing and spraying liquids comprising a body formed with a passageway adapted to be connected to a source of liquid under pressure and completely filled with such liquid, a spray tip secured to said body and having a nozzle opening extending therethrough, said nozzle opening being elongated in cross-section and being defined by converging Walls of said spray tip intersecting in a non-circular sharp edge, said nozzle opening having a cross-sectional area equal to the area of a circle having a diameter no greater than .035 of an inch and communicating with a portion of said passageway constituting a chamber having a crosssectional area substantially greater than that of said nozzle opening, means in said passageway forming a restricted orifice circular in cross-section and opening into said chamber and co-axial with said nozzle opening, said restricted orifice having an area no greater than about twice the area of said nozzle opening and having a uniform diameter no greater than about .035 of an inch through an axial length at least about twice its diameter, said orifice being arranged to accelerate liquid from said source and direct the same as a submerged jet through said chamber and co-axially into said nozzle opening, whereby the liquid emerges from said nozzle opening as an atomized mist substantially uniformly distributed in an oval shaped pattern with feathered edges.

2. Means for hydraulically atornizing and spraying liquids comprising a body formed with a passageway adapted to be connected to a source of liquid under pressure and completely filled with such liquid, a spray tip secured to said body and having a nozzle opening extending therethrough, said nozzle opening being elongated in cross-section and being defined by converging walls of said spray tip intersecting in a non-circular sharp edge, said nozzle opening having a cross-sectional area equal to the area of a circle having a diameter no greater than .035 of an inch and communicating with a portion of said passageway constituting a chamber having a cross-sectional area substantially greater than the area of said nozzle opening, means in said passageway forming a restricted orificev circular in cross-section and opening into said chamber and co-axial with said nozzle opening,lsaid restricted oriiice having an area between one-fourth and twice the area of said nozzle opening and having a uniform diameter no greater than about .035 of an inch through an axial length at least about twice its diameter, said oriiice being arranged to accelerate liquid from said source and direct the same as a submerged jet through said chamber and co-axially into the inner end of said nozzle opening, whereby the liquid emerges from said nozzle opening as an atomized mist substantially uniformly distributed in an oval shaped pattern with feathered edges.

3. In an airless paint spray gun of the type having a spray tip with a transversely elongated sharp-edged opening therethrough and a passageway in the gun for paint under pressure leading to said spray tip, a valve in said passageway to control the flow of paint to the spray tip, means to provide a feather-edged pattern for the spray comprising a disc in said passageway between said valve and said spray tip, a cylindrical projectio-n on the face ot said disc adjacent the spray tip, said projection having a paint discharge orifice therein aligned with the said opening in the spray tip, said spray tip having a cylindrical recess adjacent the cylindrical projection on said disc, said recess having an inner diameter corresponding to the outer diameter of said projection and fitting around the projection to maintain the paint discharge orifice therein aligned with the spray tip opening, said paint discharge orifice and said spray tip opening being spaced to form a paint chamber within said recess around the discharge jet going from the orifice in the projection to the opening in the spray tip.

4. Means for hydraulically atomizing and spraying paint comprising an airless spray gun having a passageway with an inlet adapted to be connected to a source of liquid paint under pressure, said passageway leading to a spray tip having a nozzle opening extending therethrough, said nozzle opening being elongated in cross-section and being defined by converging walls of said spray tip intersecting in a non-circular sharp edge, said nozzle opening having an area no greater than about .001 square inch, a valve body in said passageway having a valve seat surrounding a valve port, said valve port having a substantially larger area than said nozzle opening, a valve .member movable in said passageway for controlling the `flow of paint through said valve port, said gun including an enlarged chamber between said valve port and said nozzle opening, and means between said valve port and said nozzle opening, including an axially extending circular bore with a diameter substantially smaller than said chamber connecting said valve port with said chamber, said means creating a compact submerged jet of liquid paint moving axially through said chamber and into said nozzle opening with a velocity and pressure substantially equal to the velocity and pressure of the paint passing through said nozzle opening, whereby the paint emerges from said nozzle opening as an atomized mist substantially uniformly distributed in an elongated spray pattern having feathered edges.

5. Means for hydraulically atomizing and spraying paint comprising an airless spray gun having a passageway with an inlet adapted to be connected to a source of liquid paint under pressure, said passagewayleading to a spray -tip having a nozzle opening extending therethrough, said nozzle opening being elongated in crosssection and being defined by converging walls of said spray tip intersecting in a non-circular sharp edge, a valve body in said passageway having a valve seat surrounding a valve port, said valve port having a substantially larger area than said nozzle opening, a valve member movable in said passageway for controlling the flow of paint through said valve port, said gun including an enlarged substantially cylindrical chamber between said valve port and said nozzle opening, and means between said valve and pressure of the paint passing -through said nozzle opening, said -means including an axially extending circular bore constituting the .inlet to said chamber from said valve port, said bore having an area no greater than about twice the area of said nozzle opening and having an axial Vlength greater than about twice its diameter, whereby the paint emerges from said nozzle opening as an atomized rnist substantially uniformly distributed in an elongated spray pattern having feathered edges.

6. Means for hydraulically atomizing and spraying paint comprising an airless spray `gun having a passage' l lway with an inlet adapted to be connected to a source of liquid paint under pressure, said passageway leading to a spray tip having a nozzle opening extending therethrough, said nozzle opening being elongated in cross-section'and being defined by converging walls of said spray tip intersecting in a non-circular sharp edge, a valve body in said passageway having a valve seat surrounding a valve port, said valve port having a substantially larger area than said nozzle opening, a valve member -movable in said passageway for controlling the flow of paint through said valve port, said gun including an enlarged chamber between said valve port and said nozzle opening, and a separate member in said passageway between said valve body and said chamber formed with an axially extending circular bore having an axial length greater than about twice its diameter and no greater than about twice the area of said nozzle opening, said member creating a compact submerged jet of liquid paint moving axially through said enlarged chamber and into said nozzle opening with a velocity and pressure substantially equal to the Velocity and pressure of the paint passing through said nozzle opening, whereby the paint emerges from said nozzle opening as an atomized mist substantially uniformly distributed in an elongated spray pattern having feathered edges.

7. Means for hydraulically atomizing and spraying paint comprising an airless spray gun having a passageway with an inlet adapted to be connected to a source of liquid paint under pressure, said passageway leading to a spray tip having a sharp-edged elongated nozzle opening extending therethrough, said nozzle opening having an area no greater than about .001 square inch, a valve body in said passageway having a valve seat surrounding a valve port, said valve port having a substantially larger cross-sectional area than said nozzle opening, a valve member movable in said passageway for controlling the flow of paint through said valve port, said -gun including an enlarged chamber between said valve port and said nozzle opening, and means between said valve port and said nozzle opening including an axially extending circular bore with a diameter substantially smaller than said chamber and substantially larger than said nozzle opening connecting said valve port with said chamber, and a bleed opening connecting said chamber with a low pressure zone having substantially atmospheric pressure, said means maintaining the static pressure in said chamber substantially atmospheric and creating a compact submerged jet of liquid paint moving axially through said chamber and into said nozzle opening with a velocity and pressure substantially equal to the velocity and pressure of the paint passing through said nozzle opening, part of the paint entering said chamber from said bore passing out of said chamber through said bleed opening and the remainder emerging from said nozzle opening as an atomized mist substantially uniformly distributed in an elongated spray pattern having feathered edges.

8. Means for hydraulically atomizing and spraying liquids comprising a body formed with a passageway adapted to be connected to a source of liquid under pressure and completely filled with such liquid, a spray tip secured to said body and having a nozzle opening extending therethrough, said nozzle opening being elongated in cross-section and being defined by converging Walls of said spray tip intersecting in a non-circular sharp edge, said nozzle opening having a cross-sectional area equal to the area of a circle having a diameter no greater than .035 of an inch and communicating with a portion of said passageway constituting a chamber having a cross-sectional area substantially greater than that of said nozzle opening, means in said passageway forming a restricted orifice circular in cross-section and opening into said chamber and co-aXial with said nozzle opening, said restricted orifice having an area substantially equal to the area of said nozzle opening and having a uniform diameter no greater than about .035 of an inch through an axial length at least about twice its diameter, said orice being arranged to accelerate liquid from said source and direct the same as a submerged jet through said chamber and co-aXially into said nozzle opening, whereby the liq- 20v 2,754,228-

uid emerges from said nozzle opening as an atomized mist substantially uniformly distributed in an oval shaped pattern with feathered edges.

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