US3198439A - Airless spray gun with variable output - Google Patents

Description

Aug. 3, 1965 J. H. MGNINCH, JR, ETAL 3,193,439

AIRLESS SPRAY GUN WITH VARIABLE OUTPUT Filed May 10, 1963 2 Sheets-Sheet 1 Fag L7.

INVENTOR. Josa u H. McNman J! gygzrr J. DELLA F'Lmu AT? 02 Ni-YS Aug. 3, 1965 J. H. MONINCH, JR.. ETAL 3,198,439

AIRLESS SPRAY GUN WITH VARIABLE OUTPUT JOSEPH H. McNmca J2. OBER'T J. DELLA FLou QMW A TORNEYS United States Patent 3,198,439 AIRLES gPRAY GUN WITH VARIABJE ()UTEUT Joseph H. McNinch, IL, and Rohert J. Della Flora, To-

ledo, Ohio, assignors to The De Vilhiss Qompany, Toledo, Ohio, a corporation of llhio Filed May 16, 1963, Ser. No. 279, :3l 13 Claims. (l. 239-332) This invention relates to spray gun which utilizes low pressure coating material, raises its pressure, and ejects it as an airless spray, and more particularly to an improved means for varying the .coating material output of such a spray gun.

Spray guns capable of airless atomization of coating material provide good control of the coating material and substantially reduce overspray. With airless spray guns heretofore known, however, the coating material is placed under high pressure by means of a pump or other device located at some distance from the spray gun. Consequently, the pump, hose, and other components of the system between the pump and the spray gun contain coating material at high pressure. These components, therefore, must be of heavy, expensive construction to safely contain the high pressure coating liquid.

The spray gun according to the present invention atomizes coating material by means of high pressure and without air, but employs coating material from a relatively low pressure source and increases the pressure only after the material has entered the spray gun. Consequently, only an ordinary low pressure source, hose, and related components are required for the coating system.

The pressure of the coating material is raised within the new spray gun by means of air or other suitable power fluid which itself is only at moderate pressure and can be supplied to the spray gun from a conventional a-ir compressor. The relatively low pressure power fluid raises the pressure of the relatively low pressure coating material by means of a reciprocating piston assembly which includes a large diameter power piston and a small diameter coating material piston to achieve the desired pressure rise. The coating material is then ejected or sprayed in rapid pulses which provide a substantially continuous flow of atomized coating particles. The new spray gun in particular employs improved means for varying the coating material output more effectively than heretofore and accomplishes this by changing the stroke length of the power piston. The quantity of coating material sprayed thus can be changed in the new spray gun even though the pressure of the power fluid remains constant. Further, the length of the stroke can be changed by means 'of a simple adjusting member easily controlled by the operator. The new spray gun also has more effective means for controlling the coating material pressure than heretofore.

It is, therefore, a principal object of the invention to provide an airless spray gun of the type described which has improved means for adjusting the coating material output and for controlling coating material pressure.

Other objects and advantages of the invention will be apparent from the following detailed description of a preferred embodiment thereof, reference being made to the accompanying drawing, in which:

FIG. 1 is a schematic view in elevation of a spray gun and supply equipment embodying the invention;

FIG. 2 is an enlarged, fragmentary view in longitudinal cross section of the spray gunslrown in FIG. 1; and

FIG. 3 is a view in cross section taken along the line 3-3 of FIG. 2.

Referring to the drawings, and more'particularly to FIG. 1, a spray gun embodying the inventionis indicated 3398,43? Patented Aug. 3, 19%?) at it) and includes, a main body 12, a handle 14, and a relatively low pressure by air supplied through a line 24 from a storage tank 26 and a compressor 28.

Coating material under relatively low pressure is supplied to the spray gun 10 from the line 20 through a sup- .ply passage 3% (FIG. 2) and an annular manifold 32. A

plurality of valve passages 34 communicate with the annular manifold 32 and also with a coating material chamber or cylinder extension 36 and acoating material cylinder 38. The valve passages 34 normally are blocked by .a check valve ring 40 which .is-urged against the ends of the passages 34 by means of a spring 42. The passages 34, the ring 49, and the spring 42 constitute check valve means which enable'coating material to enter the chan1 ber 36 from the supply opening 30 but not to flow in the reverse direction.

A coating material piston 44 to raise the pressure of the coating material extends through the coating material cylinder 38 and into the chamber 36. When the piston 44 is retracted, by means to be discussed subsequently, the pressure in the cylinder 38 and the chamber 36 is reduced, enabling the coating material in the manifold 32, which is under some-pressure,to overcome the force of the spring 42 and open the valve ring 49. With the coating material chamber 36 filled, when the piston 44 moves forwardly again, the coating material is placed under. rapidly increasing pressure and must eventually be able to escape from the chamber 36. For this purpose, a group of outlet passages 46 are located at a forward end of the chamber 36 and communicate with a central outlet passage 45 in an outlet valve member 50. Coating material flow to the passage 4% depends on the position of the outlet valve member 50 which can be seated near the group of outlet passages 46 to prevent flow or can be moved forwardly by the coating material pressure to permit flow. A suitable seal 52 prevents" leakage of coating material outside the valve memberSll. V

The valve member 50 normally is held against the seat adjacent the outlet passages 46 by means of power fluid pressure in a pressure cylinder 54 which acts on a valve piston 56. The power fluid is supplied to the cylinder 54 by a supply passage 58 in the end of the spray gun 10, which passage is connected by any suitable tube or passage means 60 to a power fluid supply passage 62 in the handle 14 upstream of a power fluid valve V operated by the trigger 16. The passage 62 communicates with the supply line v18. The power fluid pressure in the cylinder 54 holds the valve member 50 against its seat until the force of the pressurized coating material acting upon the end of the member 50 exceeds the force of the power fluid on the piston56, whereupon the member 50 will move quickly away from the seat and enable coating material to-flow from the outlet passages 46 through the passage 48 and to a suitable nozzle cap 64. The nozzle of the cap 64 can be' designed in accordance with high pressure spray nozzles known in the art and does not constitute a novel part of the present invention. The'rear of the pressure cylinder 54 is suitably vented through a vent passage 65.

The force of the air or other power fluid acting on the piston 56 of the valve member 50 not only determines the pressure which the coating material in the chamber 36 must reach before being sprayed from the gun 10, but also determines the cut-off pressure, below which no coating material will issue from the gun. In this manner, spattering or random flow of poorly atomized coating material particles is substantially eliminated, thereby eliminating a problem common to high pressure coating material spray guns heretofore known. The piston and cylinder arrangement also causes the valve member 50 to open at a given percentage of operating pressure, regardless of the amount of the pressure. A wide range of pressure thus can be used while maintaining a high cut-oft pressure.

From the above operation, it will be apparent that the coating material is supplied to the nozzle cap 64 in pulses, one during each reciprocatory cycle of the coating mateterial piston 44. These pulses are so frequent, however, that they establish a substantially continuous spray when the trigger 16 is pulled. The off time of the spray gun, namely that time in which the coating material is not being discharged, will determine the gaps between the individual sprays emitted from the nozzle, and this oif time should be uniform and held to a minimum. In practice, the piston 44 preferably reciprocates at a rate of 2000 to 6000 times per minute, which provides from 2000 to 6000 pulses or spray patterns per minute. From a practical standpoint, this almost constitutes a continuous spray.

The operating mechanism for the coating material piston 44 will now be explained. The piston 44 is connected through an intermediate, enlarged member or stem 66 to a power piston 68 so that the power piston 68 and the coating piston 44 are functionally integral. The power piston 68 is located in a power cylinder 70 formed by a cylindrical wall 72 in the rear of the gun 10. A spring chamber 74 opens into the cylinder 70 and holds a return spring 76 which is compressed between an end of the chamber 74 and the forward side of the piston 68, thereby urging the piston 68, the stem 66, and the coating material piston 44 toward rear positions. spring 76 provides a simple means for returning the piston and preferably has a small preload so that the piston will be returned in a constant amount of time regardless of the length of stroke. In this manner, the off time will be relatively constant under all conditions.

The piston 68 is moved forwardly against the force of the spring 76 by the pressure of the power fluid supplied through the line 18 and the passage 62. This fluid is admitted through a power fluid inlet '78 to an annular fluid supply manifold 80. From the manifold, the power fluid can flow through four flow control openings 82 (FIG. 3) in an annular valve plate 84, the openings being formed by notches or flat peripheral portions in the plate 84. Unless the valve plate 84 is against a supply valve seat 86 formed at the end of the cylinder wall 72, the power fluid I will then fill the rear end of the power cylinder 70, overcoming the force of the spring 76 and moving the power piston 68 forwardly in the cylinder 70, thereby similarly movingthe coatingmaterial piston 44. As the high pressure fluid fills the power cylinder 70, it also passes through minute valve passages 88 and into a power fluid valve chamber 90, with this power fluid. then tending to urge the valve plate 84 against the seat 86. This pressure, however, will be more than offset by the pressure in the cylinder 70, until the pressure in the cylinder 70 drops substantially. Hence,,until the pressure drops, the valve plate 84 will remain away from the seat 86 and power fluid can continue to enter the cylinder 70.

A cylindrical exhaust projection 92 extends rearwardly from the piston 68 and moves therewith. The projection 92 cooperates with a cylindrical exhaust opening or port 94 in a threaded stroke control member 96. The projection 92 blocks and closes off the opening 94 during most of the travel or stroke of the piston 68, until the piston 68 reaches a position near the forward end of its stroke.

'At that time, the projection 92 moves out of the opening 94, as shown, to enable the high pressure power fluid in the rear end of the cylinder 70 to escape through the control member 96. The pressure of the fluid in the valve chamber 90 and in the manifold 80 then forces the valve plate 84 forwardly against the seat 86 to prevent further entry of high pressure fluid into the cylinder 70. With the sudden drop of pressure in the rear end of the cylin- The return 7 4 turn stroke. During this time, fluid in the chamber 90 blee 3 through the holes 88 so that pressure in the chamber 90 is substantially at atmospheric by the time the piston 68 completes its return stroke. As the piston 68 moves rearwardly, the projection 92 again closes the exhaust port 94, but, with the valve plate 82 in the forward position against the supply valve seat 86, exhaust passages 98 are opened, with the valve plate 84 having moved away from an annular exhaust valve seat 100. Remaining power fiuid in the cylinder 70 can then exhaust through the passages 98 to rear vents 102. When the piston 68 approaches the rear end of the cylinder 70 adjacent the vaive plate 84, an exhaust control shoulder 104 adjacent the piston 68 cooperates with the inner diameter of the valve plate 84 to block further flow of power fluid from the cylinder 70 through the exhaust passages 98. Thus, the remaining fluid is trapped between the piston 68 and the valve plate 84 to act as a cushion for the end of the stroke of the piston 68 and also to force the valve plate 84 rearwardly again, away from the supply valve seat 86 and against. the exhaust passage seat 100. Pressurized power fluid is then again admitted between the valve plate. 84 and the seat 86 to the cylinder 70 to. again drive the piston 68 forwardly.

The operator can adjust the stroke, of the piston 68 by turning the stroke control member 96 toward or away from the cylinder '70 and the exhaust projection 92. By screwing the member 96 into the spray gun body 12 and toward the cylinder 70, the operator can increase the length of stroke of the piston 68. The exhaust opening 94 is thus moved toward the cylinder 70 and the exhaust projection 92 does not uncover the opening 94 until the piston 68 moves farther toward the front end of the spray gun. The length of the stroke thereby is increased since the opposite end of the stroke always remains at the same point, adjacent the valve plate 84.

The operator can also screw the member 96 out of the gun body and away from the cylinder 70 to similarly move the exhaust opening 94, whereby the exhaust projection 92 will move out of the opening sooner and enable the escape of pressurized fluid from the rear of the cylinder 70 earlier than otherwise. The fluid is thereby exhausted sooner and the length of the stroke of the piston 68 is correspondingly shortened.

in each case that the stroke of the power piston 68 is lengthened or shortened, the stroke of the coating material piston 44 is correspondingly lengthened or shortened thereby to increase or decrease the amount of coating material sprayed from the gun upon each complete cycleof the piston 68.

While the overall operation of the spray gun should be apparent from the above description, it will be reviewed for the sake of clarity. When spraying is to begin, air or other power fluid from the tank 26 is supplied to the source 22 to place the coating material therein under some pressure. The material, under a pressure of 100 pounds per square inch, for example, is then fed through the line to the inlet passage and the manifold 32. At the same time, the power fluid is supplied through the line 18 and the supply passage 62 to the manifold 80. The fluid also is supplied through the passage to the inlet passage 58 and the chamber 54.

The fluid in the annular manifold 80 passes between the valve plate 84 and the valve seat 86 and into the rear end of the power cylinder thereby moving the piston 68 forwardly against the force of the spring 76. As this movement occurs, the exhaust projection 92 also moves with the piston 68. Movement continues until the projection 92 is out of the opening, at which time the pressurized power fluid in the rear of the cylinder 70 is exhausted through the opening 94, this fluid being exhausted much faster than it can be admitted to the cylinder through the openings 82 of the valve plate 84. Pressure of fluid in the chambers and then forces the valve plate 88 to move forwardly and engage the valve seat 86 to prethen predominates to move the piston 68 toward the rear.

At this time, the valve plate 84 continues to be held in its forward position against the seat 86 mainly because of the force of the power fluid in the chamber 80 so that the fluid in the cylinder 70 can exhaust through the vent passages 98. When the shoulder 104 cooperates with the inner edge of the valve plate 84, the remaining fluid in the rear of the cylinder 70 is trapped, which helps the piston 68 to reverse direction and also forces the valve plate 84 to the rear position, overcoming the force of the fluid in the chamber 80. Once again, fluid can flow through the openings 82 between the valve plate 84 and the seat 86 to start another forward stroke of the piston 68.

During the return stroke of the piston 68, the coating material piston 44 moves rearwardly to tend to establish a negative pressure in the coating material chamber 36. The pressure differential across the check valve plate 40 is then suflicient to overcome the relatively light force of the spring 42 and move the valve plate 40 away from the passages 34. Coating material then flows from the annular manifold 32 into the chamber 36 and the cylinder 38 until the piston 44 reaches the rear end of its stroke. As the coating material piston 44 again moves forwardly along with the power piston 68, the coating material pressure in the chamber 36 rises until the force of the coating material acting on the valve member 50 overcomes the force of the power fluid in the chamber 54 acting on the piston portion 56 of the valve member 50. The valve member 50 then moves away from its seat to enable coating material in the central outlet chamber 48 to move into the passage 52 and be supplied to the nozzle cap 64. By way of example, the force of the power fluid on the piston 56 of the valve member 50 keeps the valve member closed until the coating material pressure exceeds 80% of the desired pressure for the coating material. The outlet pressure remains the same even though the length of the piston stroke is shortened or lengthened and the output of the gun can be varied while maintaining the pressure of the power fluid constant.

Various modifications of the above described embodiment will be apparent to those skilled in the art, and it is to be understood that such modifications can be made without departing from the scope of the invention, it they are within the spirit of the depending claims.

We claim:

1. An airless spray gun comprising a spray gun body, means forming a power cylinder, a power piston located in said power cylinder, passage means in said spray gun body connected to a rear portion of said power cylinder, means for supplying power fluid to said passage means, fluid valve means to regulate flow of power fluid to said power cylinder, rear exhaust port means in said body communicating with the rear portion of said power cylinder, exhaust valve means for opening and closing said rear exhaust port means, and additional exhaust means for the rear portion of said power cylinder and opened when said power piston travels forwardly a predetermined distance in said power cylinder.

2. A power unit according to claim 1 characterized by means for adjusting said additional exhaust means to change the predetermined distance at which said additional exhaust means will exhaust power fluid from said power cylinder, thereby changing the length of stroke or said piston.

3. An airless spray gun comprising a spray gun body having a power cylinder, a power piston located in said power cylinder, coating material spray means including coating material pressurizing means located outside said power cylinder, means connecting said power cylinder to said pressurizing means, passage means in said spray gun body connected to the rear portion of said power cylinder, means for supplying power fluid to said passage 6 means, fluid valve means associatedwith said passage means to regulate flow of power fluid to said power cylinder, rear exhaust port means in said body communicating with the rear portion of said power cylinder, exhaust valve means for opening and closing said rear exhaust port means, additional exhaust means for said power cylinder and opened when said power piston travels forwardly a predetermined distance in said power cylinder, means for adjusting said additional exhaust means to change the predetermined distance at which the exhaust means will exhaust power fluid from said power cylinder, thereby changing the length of stroke of said power piston, and means for controlling said fluid valve means to control the supply of power fluid to said power cylinder.

4. An airless spray gun comprising a spray gun body having a power cylinder, 21 power piston located in said power cylinder, coating material spray means including coating material pressurizing meanslocated outside said power cylinder, stem means extending through an end wall of a front end of said power cylinder and-connecting said power piston to a portion of said pressurizingrneans, passage means in said spray gun body connected to the rear end of said power cylinder, means for supplying power fluid to said passage means, valve means associated with said passage means for controlling the flow of power fluid from said passage means to said power cylinder, said valve means being opened when said piston is near the rear end of said cylinder, rear exhaust passage means in said body located near the rear end of said power cylinder, second valve means located in said exhaust passage means and being open when said power piston is moving in a rearward direction, additional exhaust means effective to exhaust power fluid from said power cylinder when said power piston has moved forwardly in said cylinder a predetermined distance, and means for adjusting the position of said additional exhaust means to change the predetermined distance atwhich the exhaust means will exhaust power fluidfrom said power cylinder, thereby changing the length of stroke of said power cylinder.

5. An airless spray gun comprising a spray gun body having a power cylinder, a power piston located in said power cylinder, coating material spray means including coating material pressurizing means located outside said power cylinder, stern means extending through an end wall of a front end of said power cylinder and connecting said power piston to a portion of said pressurizing means, said stern means passing through an intermediate chamber formed by said gun body beyond the end wall of said power cylinder, resilient means in said intermediate chamber urging said power piston toward the rear, passage means in said spray gun body connected to the rear end of said power cylinder, means for supplying power fluid to said passage means, valve means associated with said passage means for controlling the flow of power fluid from said passage means to said power cylinder, said valve means being opened when said piston is near the rear end of said cylinder, rear exhaust passage means in said body located near the rear end of said power cylinder, second valve means located in said exhaust passage means and being open when said power piston is moving in a rearward direction, an exhaust projection functionally integral with said power piston and extending rearwardly therefrom, means forming an exhaust opening communieating with said power cylinder beyond the rear end of a travel of said power piston, said projection extending through and blocking said exhaust opening throughout most of the travel of said power piston and being out of said exhaust opening at a forward portion of the travel of said power piston to exhaust power fluid from a rear portion of said power cylinder, and means for adjusting the position of said exhaust opening means in a direction parallel to the direction of travel of said power piston-to adjust the length of travel of said power piston. v

6; An airless spray gun comprising a spray gun body having a power cylinder, a power piston located in said power cylinder, coating material spray means including coating material pressurizing means located outside said power cylinder, means connecting said power piston to a portion of said pressurizing means, valve means at a rear end of said power cylinder opposite said pressurizing means, passage means in said spray gun body connected to the rear end of said power cylinder, means for supplying power fluid to said passage means, means forming a valve seat associated with said passage means and positioned to be engaged by said valve means to prevent flow of power fluid into said power cylinder from said passage means, means effective to urge said valve means toward said first valve seat, a rear exhaust port in said body located near the rear end of said power cylinder, a rear exhaust passage communicating with said exhaust port, means forming an additional valve seat positioned to be engaged by said valve means and to close said rear exhaust passage, an exhaust projection functionally integral with said power piston and extending rearwardly therefrom, means forming an exhaust opening communieating with said power cylinder beyond the rear end of the travel of said power piston, said projection extending through and blocking said exhaust opening through most 'of the travel of said power piston and being out of said exhaust opening at a forward portion of the travel of said power piston to exhaust power fluid in said power cylinder through said exhaust opening, and trigger means for controlling the supply of power fluid to said passage means.

7. An airless spray gun comprising a spray gun body having a power cylinder, a power piston located in said power cylinder, coating material spray means including coating material pressurizing means located outside said power cylinder, means extending through an end wall of a front end of said power cylinder and connecting said power piston to a portion of said pressurizing means, a valve plate at a rear portion of said power cylinder opposite the end wall, passage means in said spray gun body connected to the rear portion of said power cylinder, means for supplying power fluid to said passage means, means forming a valve seat associated with said passage means and positioned to be engaged by said valve plate to prevent the flow of power fluid into said power cylinder from said passage means, means efiective to urge said valve plate toward said valve seat, a rear exhaust passage in said body communicating with the rear end of said power cylinder and effective to exhaust power fluid between said valve plate and said power piston when said power piston moves in a rearward direction, means forming an additional valve seat positioned to close said rear exhaust passage when contacted by said valve plate, an exhaust projection functionally integral with said power piston and extending rearwardly thereform, means foring an exhaust opening communicating with said power cylinder beyond the rear end of the travel of said power piston, said projection extending through and blocking :said exhaust opening through most of the travel of said power piston and being out of said exhaust opening at .a forward portion of the travel of said power piston to exhaust power fluid in said power cylinder through said exhaust opening, means located outside said cylinder 1 eyond said end wall and cooperating with said connecting means between said piston and said pressurizing means to urge said piston toward the rear end of said power cylinder, and trigger means for controlling the supply of power fluid to said passage means.

8. A airless spray gun comprising a spray gun body having a coating material chamber, a coating material piston reciprocable in said chamber, power means connected to said piston for reciprocating the same, a coating material supply passage communicating with said coating material chamber, check valve means enabling the flow of coating material from said supply passage to said coating material chamber and blocking the flow of coating material in thereverse direction, nozzle means spaced from said chamber, outlet passage means connecting said chamber and said nozzle means, pressure means preventing the flow of coating material from said chamber to said nozzle ,means through said outlet passage means when the pressure of coating material in said chamber is below a predetermined amount, said pressure means enabling the'flow of coating material from said chamber to said nozzle means when the pressure of the coating material exceeds the predetermined amount, said pressure means including a valve member in said outlet passage means and communicating with said coating material chamber so as to be urged toward an open position by coating material in said chamber, means forming a power fluid chamber communicating with a portion of said valve member, and means for supplying power to said chamber to act on said pressure valve member and urge it toward a closed position, whereby coating material cannot flow to said nozzle means until the force of the coating material acting on said valve member overcomes the force of the power fluid in said power fluid chamber acting on said valve member.

9. An airless spray gun comprising a spray gun body having a coating material chamber, a coating material piston reciprocable in said chamber, power means connected to said piston for reciprocating the same, coating material supply means communicating with said coating material chamber, check valve means enabling the flow of coating material from said supply means into said coating material chamber and blocking the flow of coating material in the reverse direction, an out-let port in said body communicating with said coating material chamber, nozzle means conected with said outlet port, a pressure valve member between said outlet port and said nozzle means and controlling flow of coating material to said nozzle means, said pressure member communicating with said chamber and positioned to be urged toward an open position by the pressure of coating material in' said chamber, means forming a power fluid chamber communicating with a portion of said valve member, means for supplying power fluid to said power fluid chamber to act on said pressure valve member and urge it toward a closed position, whereby coating material cannot flow to said nozzle means except under high pressure.

10. An airless spray gun comprising a spray gun body having therein a power cylinder and a coating material cylinder, a coating material piston in said coating material cylinder, a power piston in said power cylinder and having means connecting said power piston to said coating material piston, a valve plate at a rear portion of said power cylinder opposite the coating material cylinder, passage means in said spray gun body connected to the rear end of said power cylinder, means for supplying power fluid to said passage means, means forming a fluid control valve seat associated with said passage means and positioned to be engaged by said valve plate to prevent the flow of power fluid into said power cylinder from said passage means, means effective to urge said valve plate toward said first valve seat, a rear exhaust passage in said body communicating with the rear end of said power cylinder and effective to exhaust power fluid between said valve plate and said power piston when said power piston moves in a rearward direction, means forming an exhaust valve seat positioned to block said rear exhaust passage when contacted by said valve plate, an exhaust projection functionally integral with said power piston and extending rearwardly therefrom, means forming an exhaust opening communicating with said power cylinder beyond the rear end of the stroke of said power piston, said projection extending through and blocking said exhaust opening throughout the majority of the travel of said power piston to prevent the escape of power fluid from said power cylinder through said exhaust opening, means located outside said power cylinder cooperating with said connecting means between said power piston and said coating material piston to urge said power piston toward the rear of said power cylinder, coating material supply means communicating with said coating material cylinder, check valve means enabling the flow of coating material from said coating material supply means into said coating material cylinder and blocking the flow of coating material in the reverse direction, an outlet port in said body communicating with said coating material cylinder, nozzle means connected with said outlet port, a pressure valve member blocking said outlet port, means urging said pressure valve member toward the blocking position, said urging means being yieldable to enable said pressure valve member to move to an open position when pressure of the coating material Within said coating material cylinder rises above a predetermined amount, whereby coating material can flow to said nozzle means under high pressure.

11. An airless spray gun comprising a spray gun body, means forming a power cylinder in said body, a power piston located in said power cylinder, passage means in said spray gun body connected to a rear portion of said power cylinder, means for supplying power fluid to said passage means, a supply valve plate, means forming a supply valve seat effective with said supply valve plate to regulate flow of power fluid through said passage to said power cylinder, rear exhaust port means in said body communicating with the rear portion of said power cylinder, means forming an exhaust passage seat eflective with said supply valve plate to open and close said rear exhaust port means, means forming a valve chamber contiguous with said valve plate, and means for supplying power fluid to said valve chamber to urge said supply valve plate toward said supply valve seat.

12. An airless spray gun comprising a spray gun body,

means forming a power cylinder in said body, a power piston located in said power cylinder, passage means in said spray gun body connected to a rear portion of said power cylinder, means for supplying power fluid to said passage means, a supply valve plate, means forming a supply valve seat effective with said supply valve plate to regulate flow of power fluid through said passage to said power cylinder, rear exhaust port means in said body communicating with the rear portion of said power cylinder, means to open and close said rear exhaust port means, means forming a valve chamber contiguous with said valve plate, means for supplying power fluid to said valve chamber during a power stroke of said piston to urge said valve plate toward said supply valve seat when the power stroke is completed and for bleeding power fluid from said valve chamber during a return stroke of said piston to substantially eliminate the urging force by the time the piston has completed the return stroke.

i3. An airless spray gun comprising a spray gun body, means forming a power cylinder in said body, a power piston located insaid power cylinder, passage means in said spray gun body connected to a rear portion of said power cylinder, means for supplying power fluid to said passage means, fluid valve means to regulate flow of power fluid through said passage to said power cylinder, rear exhaust port means in said body communicating with the rear portion of said power cylinder, exhaust valve means carried by said power piston for opening and closing said rear exhaust port means, and a spring acting on said piston to move said piston toward the rear of said power cylinder when said rear exhaust port means are opened.

References Cited by the Examiner UNITED STATES PATENTS 1,604,043 10/26 Hansen 9l240 1,852,591 4/32 Smith, et a1. 913l7 1,949,497 3/34 Stafford, et a1 222334 1,965,038 7/34 Hartman 222334 2,540,357 2/51 Stanley 239-329 2,941,726 6/60 Szczepanski 239329 3,018,968 1/62 Levey 239329 3,061,202 10/62 Tyler 239-330 3,120,347 2/64 Duke 239332 EVERETT W. KIRBY, Primary Examiner.

Claims (1)

1. AN AIRLESS SPRAY GUN COMPRISING A SPRAY GUN BODY, MEANS FORMING A POWER CYLINDER, A POWER PISTON LOCATED IN SAID POWER CYLINDER, PASSAGE MEANS IN SAID SPRAY GUN BODY CONNECTED TO A REAR PORTION OF SAID POWER CYLINDER, MEANS FOR SUPPLYING POWER FLUID TO SAID PASSAGE MEANS, FLUID VALVE MEANS TO REGULATE FLOW OF POWER FLUID TO SAID POWER CYLINDER, REAR EXHAUST PORT MEANS IN SAID BODY COMMUNICATING WITH THE REAR PORTION OF SAID POWER CYLINDER, EXHAUST VALVE MEANS FOR OPENING AND CLOSING SAID REAR EXHAUST PORT MEANS, AND ADDITIONAL EXHAUST MEANS FOR THE REAR PORTION OF SAID POWER CYLINDER AND OPENED WHEN SAID POWER PISTON TRAVELS FORWARDLY A PREDETERMINED DISTANCE IN SAID POWER CYLINDER.

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