US2969926A - Airless spray guns - Google Patents

Description

Jan. 31, 1961 n.1. PEEPS 2,969,926

AIRLESS SPRAY yGUNS Filed Oct. 50, 1956 2 Sheets-Sheet 1 BY h 1 @g4 y 2M HTTOR N EYJ Jan. 31, 1961 D. J. PEEPs 2,959,926

AIRLESS SPRAY GUNS Filed oct. so, 195e 2 Sheets-Sheet 2 INVENTOR. Dana/0 d Peeps BYQMAQQL United States Patent AIRLESS SPRAY GUNS Donald J. Peeps, Rossford, Ohio, assigner to The De Vilbiss Company, Toledo, Ohio, a corporation of Ohio Filed Oct. 30, 1956, Ser. No. 619,183

"4 Claims. (Cl. Z39- 526) This invention relates to spray guns lfor the airless Vapplication of viscous materials and is particularly directed to a contro-l valve mechanism for such a spray gun.

It has :heretofore been proposed to spray heated liquid materials without the use of an atornizing air stream, and theoretically atomization which takes place as a result of a sudden pressure release should give a more uniform coating than one deposited with the aid of entrained air. One of the diiculties with airless spray guns has been that the very high pressure on the liquid has made it difficult to operate the material control valve. In many instances the valve has opened and closed so slowly that a substantial portion of the stream failed to disperse immediately after opening and immediately prior to closing of the valve. This sluggish valve action has resulted in non-uniform and unacceptable coatings. p It has been proposed to provide an auxiliary, air operated piston to open the valve of an airless spray gun, and it has also been proposed to provide a complex series of toggle mechanisms foi the purpose of imparting a snap action to the rearward or opening excursion of the material control valve. Such attempts have been unsatisfactory for various reasons and have not been widely adopted.

The present invention Ahas for its primary object to provide a material valve control mechanism for an airless spray gun in which pressure differentials in the heated liquid itself are utilized to impart a rapid and positive motion to the valve parts.

Another object of the invention is to provide a material valve control mechanism in which undesired pressure differences are balanced out, leaving only those pressure differences which are required for the proper fast operation of the valve.

Other objects and advantages of the invention will become apparent from the following description of a preferred form thereof, reference being had to the accompanying drawings, in which- F-ig. 1 is a fragmentary central vertical sectional view of a spray gun embodying the present invention;

Pig. 2 is a front elevational view with parts in section; and

Fig. 3 is a fragmentary, somewhat enlarged and diagrammatic sectional view showing the control valve of the present invention in an open position.

Briey stated, the present invention comprises a spray gun for the airless discharge of liquid materials comprising a gun body having two liquid chambers therein,

together with means to supply liquid under pressure to ice shown in an embodiment including a gun lbody 10 having a handle 12 depending therefrom, a trigger 14 being pivotally attached to the body by a pintle 16 in the usual manner. A front body portion 18 is attached to the main body 10 by a bolt 20 extending longitudinally of the gun and the mating surfaces of the body portions are insulated from each other by a suitable heat resisting washer 22 which is preferably of a plastic material.

The front body portion 18 has a longitudinal discharge passage or chamber 26 which is threaded at its front end to receive a stationary valve seat member 28. The stationary member 28 has an opening or spray nozzle 30 in its front wall through which heated liquid may flow under high pressure to expand and atomize during operation. This opening 30 is closed by a material control valve 32 which may be of any suitable form, a simple at faced surface type valve being shown in the drawings. Such a valve is advantageous because it gives a maximum valve opening with a minimum longitudinal excursion. The valve itself is preferably formed of a heat resistant plastic material and is carried at the end of a valve operating rod 34.

The rear end of the valve carrying rod 34 is attached as by a threaded connection to a head 38 to which is welded or otherwise fixed a longitudinally resilient sealing member such as a bellows seal 40. The bellows 40 contains air at atmospheric pressure in its interior since its outermost end, remote from the head 38, is fixed in position to seal the end of bore 26. Since the head of the bellows 40 is exposed to whatever pressure exists in chamber 26, a valve opening force is exerted on the annulus defined by the area of the bellows head minus the area of the valve 32. This force is utilizedy as hereinafter described. A plug 42 may be threaded into the gun body and used to seat the bellows wall against an adjacent surface of the body in a uid tight joint. The rearward movement of the rod 34 may be limited in any suitable manner as by a stop pin 43 inserted in the plug 42.

An adjusting rod 44 extends rearwardly inside the bellows 40 from the head 38 and may, if desired, be made integral with the head. Ilhe adjusting rod passes freely through the plug 42 and extendsinto a spring retainer 46 carried in the main gun body 10. The bellows 40 acts as a substantially frictionle'ss fluid tight packing around rod 44. An adjusting spring 50 is disposed Within the retainer and is compressed between a head 52 on the rod 44 and a threaded cup 54 extending outwardly from the rear of the retainer into an exposed position where a nut-like head thereof can be readily grasped by the operator to turn the cup 54 in or out and thus increase or decrease the force of spring 50 against the adjusting rod 44.

The present invention is particularly directed to a novel means to control the admission of fluid into chamber 26 in such a manner that an extremely rapid increase and decrease in pressure in that chamber is available for opening and closing valve 32. To this end, the front gun body portion 18 is provided with a vertical iluid conduit 60 which may be conveniently formed in an insert 62. threaded into the body. The insert 62 is ground dat on its lower face 64 to act as a valve seat for a resilientV annular valve 66. Valve 66 is carried by a holder 68 which has a spherically formed outer surface lying closely adjacent the walls of the bore of the body which form the fluid passage. The spherical portion of the valve holder is slotted at spaced points so that fluid can ow easily from below the holder to the valve 66, yet the spherical surface can act as a rocking guide for the holder.

A stem 70 depends from the valve holder 68 and straddles an operating rod 72. Rod 72 is connected on each side to a balancing bellows, the interiors of which escasas are at substantially atmospheric pressure. The front bellows, designated 74 in the drawings, has its open or outer end held in place by a threaded plug 76 and is guided for reciprocation by a center stem 78 the end of which is inserted into a bore or recess in the plug. The rear bellows, designated 80 in the drawing, is 'similarly held in place by a 'sealing plug 82 and encases a guiding and operating rod 84 which is either integral with, or attached to a, the rod 72. The operating rod extends through the rear plug 82 and is operatively connected with the trigger 14. It will thus be seen that the bellows 74 and 80 constitute a substantially frictionless sealing means for the valve operating rod 72 and that the seal is balanced because the eiective area of the front or exposed portion of each bellows is the same and is exposed to the same fluid pressure. y

Fluid enters the front gun body by a iirst chamber or lateral passage 86 in open communication with the vertical passage 60, intersecting the same at the bore which contains the sealing bellows. The passage 86 extends on each side of the center of the gun and is in turn intersected by vertical inlet and outlet passages 88 and 90 so that fluid may be circulated into and out of the gun in preparation for a spraying operation as hereinafter described. In some instances it is not necessary to circulate heated fluid through the gun, as where a iluid heating hose is used, and .in these cases there will be required only a single vertical passage opening directly into the iirst chamber formed by passage 66 and the volume surround ing the bellows 74 and 80. v

In operation, heated paint or other duid material is circulated through the gun until such time as the front gun body portion 18 is suiciently heated that operation can commence withoutdanger of cooling the liquid to the point that 'sluggish or ','u'nsatisfacto'ry operation will result. Liquid at a pressure of 250 'to9OQpoi1nds per square' vicl'i (depending an 'the material) is thus, present in the here 86 and exerts its pressure against the head of bellows 74 and 80. The operator iirst moves the trigger 14 rearwardly thus pulling rod 72 rearwardly. It will be seen that since both bellows 74k and 80 are attached to rod 72 the pressure of the liquid is balanced out and thus exerts no force, either forwardly or rearwardly, on rod 72.

Moving rod 72 rearwardly causes the depending valve stems 70 to rockthe control valve 66 Varound a'point on the rear of its circumference and causes the valve to move away from its seat rst at the` front edge. Assoon as the valve 66 cracksV away from itsseat, liquid flows fromY the irst chamber in which it has been circulating and enters the passage 60 and commences to buildv up a pressurek therein, which pressure tends to open the control valve 66 more fully by increasing the pressure on theY top thereof to a value nearly equal to the pressure on the lower face. The full pressure of the heated liquid thus appears quite rapidly in the second or discharge chamber 26 formed by the longitudinal bore of the gun and closed by the discharge valve 32. This pressure is exertedrearwardly in a direction tending to open the valve, on the annulus at the head of the bellows 40, above described. This pressure is resisted only by spring 50 so that valve 32 opens when the pressure times the area of annulus exceeds the force of the spring. As soon as valve 32 opens slightly,

the full pressure in chamber 26 is exerted against the front.

face thereof andthe rearward force tending to moveV the valve to a fully opened position and to hold it there is increased. l

Spraying thus proceeds with the liquid atomized by the release of pressure beyond the orice 30. By reason of the fact that liquid is flowing rapidly around the circum ference of control valve 66 there is an area of reduced pressure above this valve due to the velocity of the liquid so that the operator must hold trigger 14 in valve opening position.

When it is desired to close the discharge valve 32 the operator releases the trigger 14. The aforementioned pressure dilerence on control valve 66 immediately causes the valve to move towards a closed position. Since valve 32 is still fully open the large pressure reduction caused by continued ilow of even a very small quantity of duid from chamber 26 is sufcient to seat valve 66 very iirmly by reason of the pressure difference above and below it. Further, since there is now no continuous supply of liquid to chamber 26 the pressure therein drops to atmospheric pressure almost instantaneously and spring 50 can easily heat valve 32 against the plate or stationary valve member 28 and close olf the discharge orifice 30. i,

It will thus be seen that the discharge valve 32 is operated by pressure in chamber 26 and that this pressure is controlled by fluid flowing past control valve 66 which, in turn, is opened mechanically and is closed by a difference in pressure on its upper and lower faces.

While the invention has been shown in conjunction with a specific form and disposition of the parts it should be expressly understood that it is capable of numerous modifications and changes without departing from the scope of the appended claims.

What I claim is:

1. A spray gun for the airless spraying of liquid coating materials, said spray gun comprising a gun body having rst and second liquid chambers and a passage therebetween, means for supplying coating liquid under pressure to said lirst chamber, a control valve associated with said passage to close and to open said passage to theilow of coating liquid from said first chamber to said second chamber, ysaid control valve having a stem projecting into and located wholly within said first chamber, a pressure-balanced, trigger-actuated mech-A anism carried by said Vbody and operatively connected to said stem and movablein a direction laterally of said Stein to move said sftem laterally and to cause lsaid valve t rock about a point on its periphery thereby lto open said valve, trigger means located outside said first chamber and associated with vsaid spray gun body for manually operating said mechanism, means forming a spray nozzle in communication with said second chamber, a discharge valve between said second chamber and said spray nozzle, means normally urging said discharge valve toward a closed position, and means operatively connected to said discharge valve and responsive to liquid pressurein said second chamber to open said discharge valve rapidlyV when pressure in said second chamber exceeds a predetermined value, whereby said coating liquid will be substantially instantaneously sprayed from said spray nozzle when liquid pressure in said second chamber builds up above said value when said control valve is opened to supply coating liquid under pressure from said rst chamber through said passage to said second chamber.

2. A spray gun for the airless spraying of liquid coating materials, said spray gun comprising a gun body having first and second liquid chambers and a passage therebetween, means for supplying coating liquid under pressure to said rst chamber, a control valve associated with said passage to close and vto open said passage to the flow of coating liquid from said rst chamber to said second chamber, said control valve having a stem projecting into and located within` said first chamber, triggeractuated mechanism carried by said body and operatively connected at an intermediate portion topsaid stem andV movable in a direction laterally of said stem to move said stem laterally and to cause said valve to rock about,

a point on its periphery thereby to open said valve, a pair of balancing bellows, the interior of which is subjected to atmospheric pressure, said bellowsencompassing said trigger-actuated mechanism withinsaid iirst chamber on each side ofv said intermediate portion to balance out the effect of duid pressure in said first chamber on said trigger-actuated mechanism, trigger means located outr` side said r'st chamber and associated with said spray gun body for manually operating said mechanism, means forming a spray nozzle in communication with said second chamber, a discharge valve between said second chamber and said spray nozzle, means normally urging said discharge valve toward a closed position, and means operatively connected to said discharge valve and responsive to liquid pressure in said second chamber to open said discharge valve rapidly when pressure in said second chamber exceeds a predetermined value, whereby said coating liquid will be substantially instantaneo-usly sprayed from said spray nozzle when liquid pressure in said second chamber builds up above said value when said control valve is opened to supply coating liquid under pressure from said iirst chamber through said passage to said second chamber.

3. A spray gun for the airless spraying of liquid coating materials, said spray gun comprising a gun body having first and second liquid chambers and a passage therebetween, means for supplying coating liquid under pressure to said first chamber, means forming an annular valve seat around an end of said passage communicating with said irst chamber, an annular control valve adapted to seat on said valve seat to close and to open said passage to the ow of the coating liquid from said first chamber to said second chamber, said control valve having a stem projecting into and located wholly within said first chamber, a pressure-balanced, trigger-actuated mechanism carried by said body, having means operatively engaging opposite sides of said stem, and movable in a direction laterally of said stem to move said stern laterally to cause said valve to rock about a point on its periphery thereby to open said valve, trigger means located outside said irst chamber and associated with said spray gun body for manually operating said mechanism, means forming a spray nozzle in communication with said sccond chamber, and a pressure-responsive discharge valve between said second chamber and said spray nozzle and adapted to open rapidly when pressure in said second chamber exceeds a predetermined value, whereby said coating liquid will be substantially instantaneuosly sprayed from said spray nozzle when said control valve is opened.

4. A spray gun for the airless spraying of liquid coating materials, said spray gun comprising a gun body having first and second liquid chambers and a passage therbetween, means for supplying coating liquid under pressure to said iirst chamber, a control valve associated with said passage to close and to open said passage to the ow of coating liquid from said iirst chamber to said second chamber, said control valve having a stem projecting into and located wholly within said first chamber, a pressure-balanced, trigger-actuated mechanism carried by said body and operatively connected to said stem and movable in a direction laterally of said stem to move said stem laterally and to cause said valve to rock about a point on its periphery thereby to open said valve, trigger means located outside said first chamber and associated with said spray gun body for manually operating said mechanism, means forming a spray nozzle in communication with said second chamber, a discharge valve located between said second chamber and said spray nozzle and normally closing said second chamber from said spray nozzle, an operating rod connected to said discharge valve, said ro-d having one end subjected to atomspheric pressure and the other end connected to said discharge valve, a portion of the valve end of said operating rod being subjected to liquid pressure in said second chamber to urge said discharge valve toward an open position, and means associated with said operating rod for urging said discharge valve to a closed position, whereby said discharge valve will be opened when pressure of coating liquid in said second chamber is built up to a point at which the force of the coating liquid on said operating rod exceeds the force of said urging means.

References Cited in the iile of this patent UNITED STATES PATENTS 36,238 Shaw Aug. 19, 1862 1,722,985 Kling July 30, 1929 1,782,238 Kirchhan Nov. 18, 1930 1,865,390 Ballard June 28, 1932 2,552,033 Bradbury May 8, 1951 2,626,186 Nakken Jan. 20, 1953 2,719,533 Smith Oct. 4, 1955

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