US2763513A

US2763513A - Spray painting system

Info

Publication number: US2763513A
Application number: US373722A
Authority: US
Inventors: Francis C Paradise
Original assignee: Stewart Warner Corp
Current assignee: Stewart Warner Corp
Priority date: 1953-08-12
Filing date: 1953-08-12
Publication date: 1956-09-18
Anticipated expiration: 1973-09-18

Description

@Wb 18, 1956 F. c. PARADISE; 2,763,5M

SPRAY PAINTING SYSTEM Filed Aug.. l2, l955 2 Sheets-Sheet l @W- 18, 1956 F. c. PARADISE 763,53

SPRAY PAINTING SYSTEM Filed Aug. l2, 1953 2 Sheets-Sheet 2 SPRAY PAINTIG SYSTEM Francis C. Paradise, Libertyville, Ill., assgnor to Stewart- Warner Corporation, Chicago, Ill., a corporation of Virginia Application August 12, 1953, Serial No. 373,722

3 Claims. (Cl. 299-86) The present invention relates to spray painting systems, and more particularly to the type of spray painting system in ywhich the paint or other liquid material is fed to the spray gun by a liquid pump rather than from a tank placed under `air pressure.

One of the objects of the present invention is to provide an improved spray painting system in which the liquid material is pumped directly to the spray gun, and in `which the system, including the pressure in the liquid line, is completely under the control of the operator simply through manipulation of the trigger of the spray gun.

nited States Patent O An additional object is to provide a novel spray painting system of the above type, in which there are special arrangements to prevent surges of the liquid material when the spray is turned on and off by the 'operator through manipulation of the trigger at the spray gun.

Yet another object is to provide a novel system having the above characteristics, land in which the liquid line to the spray gun is not under pressure excepting during actual functioning of the `spray gun in applying the paint or other liquid materia-l.

-another object is to provide a novel system of the type set out above, which prevents spurting of paint when the spray gun trigger is pulled.

Still another object is to accomplish the above at relatively low cost, by means of equipment which will function in a trouble-free manner.

Other objects will become apparent from the following description, reference being had to the accompanying drawings, in which Fig. l is a diagrammatic :representation of the system showing the paint tank and associated mechanism, and

the connections between this mechanism and a spray gun; i

Fig. 2 is a vert-ical sectional View through a surge control valve incorporated in the mechanism of the present invention. The plane of this ligure is substantially parallel Ito the plane of Fig. 1 of the drawings;

Fig. 3 is a vertical sectional View through the surge control mechanism illustrated in Fig. 2. The view of Fig. 3 is taken at substantially right angles to the view of Fig. 2;

Fig. 4 is an elevational view of a portion of the mechanism incorporated in Fig. l, which serves the purpose of releasing the liquid pressure in the -line to the spray gun when liquid under pressure at the gun is not needed; and

Fig. 5 is a vertical sectional View through the device of Fig. 4, and may be considered :as taken in the direction of the arrows substantially along the line 5--5 of Fig. 4.

Spray painting systems are known in which the paint, lacquer, enamel, or other liquid, referred to generally hereafter as paint, is pumped directly from a reservoir to the paint inlet connection of .the spray gun rather than being supplied to the spray gun from 1a reservoir kept under an appropriate air pressure. The arrangement of pumping the paint directly to the spray gun 2,763,513 Patented Sept. 18, 1956 has advantages, but the use of such systems is usually accompanied by the disadvantage that the sudden movement of paint through the hose line, accompanied by the sudden stoppage thereof, as the trigger ot the spray gun is -operated on and off, results in surges being imposed upon the system which are disconcerting and somewhat destructive of the equipment.

The lsystem of the present invention overcomes these disadvantages by preventing surges in the paint line. In addition, when ordinary spray painting equipment of the liquid pump type is used, release of the spray gun trigger leads to higher pressures at the paint connection to the spray g-un, with the result that there is likely to be some spurt-ing of paint when the operator next Worlcs the spray gun trigger. This disadvantage is also overcome by the present invention.

Referring to Fig. l of the drawings, which shows a system in which the present invention is incorporated, a conventional spray gun is indicated at 10, the spray gun being operated by working the customary trigger 12. Compressed air is supplied to the spray gun through a hose 14, while the paint is brought to the gun by a hose 16. Compressed air lfor operating the equipment is supplied by way of a pipe yline or hose 18 which is connected to the apparatus indicated generally at 2l). This apparatus may conveniently be mounted upon and serve as the top for the paint reservoir 22.

Compressed air arriving at the equipment enters an automatic valve which tor convenience will be referred to as the control valve. lt is indicated generally by the numeral 24. From the control valve, air is supplied to the hose 14 leading to the spray gun and to a pipe 26 leading to a compressed air motor incorporated in a unit-ary structure 28 which includes the motor and a paint pump driven thereby. The compressed `air motor and liquid pump may be conventional in construction, and therefore need no description. It is sufficient to 'note that the pump driven by the compressed air motor withdraws iluid paint by 'way of a pipe 30 leading into the reservoir 22 to a position `near the bottom thereof and forces the paint or other liquid outwardly through a connection 32 to a fluid pressure relief valve 34. From this relief valve the paint passes to the previously mentioned paint hose 16. There is also a paint return line 36 `leading from the pressure relief valve 34 back to the reservoir v22.

The pressure relief valve 34, actuated by a compressed air connection represented by the hose 38, leads between the `control -valve and the pressure relief valve.

Referring now more specifically to the control valve which `.forms the subject matter of Figs. 2 and 3, this device is formed of a cor-ed land machined casting i0 to which another small casting, screw machine parts, and other valve elements are fitted. The main casting 40 has lan air inlet chamber 42 which contains a cylin drical screen element `i4 to the center of which air is admitted by `way of an air inlet lfitting 45. From the screen `44 the compressed air passes into a distributing chamber 46. This chamber is `formed :as a recess in one of the faces of the main casting 4d and `the `opening of this recess, which is generally circular at the `face of the casting, is closed by 'a llexible diaphragm 48 secured in place around its periphery by a cap Si). The main casting, the cap, `and the flexible diaphragm, are retained by several screws 52.

At its center, the diaphragm 48 is secured to a tting 54 which has a piloting stem 56 at the outer side of the diaphragm 48. This stem slides within a recess S3 formed in the cap 50 and maintains alignment of the parts. The diaphragm 43 and fitting 54 are biased away from the cap 50 by a coil spring 60 which bears with one end against the fitting 54, while its opposed end is based against the cap 50.

The right-hand side of the diaphragm 48 as seen in Fig.

3, carries a poppet valve stem 62 threaded into the fitting 54, and this poppet stem extends through a passage 64 leading from the recess 46 to the atmosphere, The casting is so formed that valve seats 66 and 68, respectively, are formed at the inside and atmospheric ends of the passage 64.

The valve stem 62 carries two poppet valves 70 and 72 for operation against the seats 66 and 68. Preferably, these valve poppets have resilient faces and are so arranged that when the diaphragm 48 and valve stem 62 are moved toward the left, the outside valve poppet 70 will be brought against the valve seat 68 at the atmospheric end of the passage 64. When the diaphragm 48 and valve stem 62 are moved in the opposite direction, that is, toward the right as seen in Fig. 3, the poppet 72 will be brought against the valve seat 66 at the inner end of the passage 64, thereby shutting off communication between this passage and the air chamber 46.

It is apparent, therefore, that whenever the pressure in the chamber 46 exceeds that in the space 74 between the diaphragm 48 and the cap 50 by a predetermined amount, the diaphragm 48 will move toward the left, thereby admitting air from the space 46 to the passage 64. On the other hand, at some pressure differential when the pressures within the

spaces

46 and 74 are more nearly equal, the spring 60 will cause the diaphragm 48 to move toward the right, thereby unseating the poppet 70 and closing poppet 72. Under these conditions, communication is cut olf between the chamber 46 and the passage 64 and the passage 64 is vented to the atmosphere.

There is a passage 76 which intersects the passage 64 and leads to the previously mentioned control air line 38 attached to the pressure relief valve. This passage 76 also has a branch 78 which ends at a one-way ball type check valve 80 urged against a seat at the outlet end of the passage 78 by a coil spring 82, this coil spring being retained in place by a cap 84 threaded into the casting 40 in alignment with the passage 78. The downstream side of the check valve 80 is in communication with a cavity 86 which is connected to the pipe 26 which leads to the pump motor.

The previously mentioned air distribution chamber 46 also has an outlet opening 88 which leads to a cylindrical chamber 90 connected to an outlet passage 92 for attachment to the hose air line 14 leading to the spray gun. The opening 88 between the

chambers

46 and 90 is flared outwardly at the top so as to provide a tapered valve seat 94 where it enters the chamber 90. A tapered valve plug 96 fits into this seat and is attached to a reciprocable valve stem 98, the upper end of which extends through a hole 100 in a shallow cup 102 which is retained in place by a threaded bushing 104. A coil spring 106 surrounds the valve stem 98 and bears with one end against the enlarged head at the plug 96. The opposite end of this spring bears v against a shoulder 108 at the upper end of a sleeve 110 ,which is slid over the valve stem 98. The spring 106,

therefore, urges the sleeve 110 upwardly against the lower surface of the cup 102, whereas the opposite end of this spring urges the valve 96 Yinto its seat so as to close the passage 88.

There is a vent passage 112 which extends from the recess 90 through a hole in the edge of the flexible diaphragm 48 and has its opposite end in communication with the chamber 74. This passage is for the purpose of maintaining the chamber 74 at the same pressure as the cavity 90.

The threaded bushing 104 which closes the exterior end of the cavity 90 is formed to provide an inwardly facing cylindrical recess 114 which contains a piston 116 having a downwardly opening cavity 118 therein for the purpose of clearing the upper end of the valve stem 98. Between the upper end of the piston 116 and the interior surface of the cap 104, there is a small soft acting coil spring 120 which urges the piston 116 downwardly. The lower end of the piston 116 is reduced in diameter externally so as to lit into a shallow cylindrical recess 122 in the upper face of the cup 102. Internally, the lower end of the piston 116 is flared outwardly as indicated at 124, so as to provide a tapered space for an annular row of steel balls 126 which surround the upper portion of the valve stem 98.

Downward movement of the piston 116 under the inlluence of the spring brings the tapered conical surface 124 at the lower yend of the piston against the balls 126 and wedges them inwardly against the valve stem 98. Because the spring 120 is comparatively soft in its action, however, the wedging action of the balls 126 against the valve stem is not great enough to prevent the valve 98 from being seated under the influence of the spring 106.

There is a passage 128 which leads from the upper end of the cylinder 114 at a position above the piston 116 to the cavity 86 upstream of the ball check valve 80. The upper end of the piston 116, therefore, is subjected to whatever pressure prevails at the motor for the paint pump.

In addition to the above, the valve body 40 also contains a small passage 130 which connects the air distribution chamber 46 with the cavity 90 above the valve 96. As will appear presently, the purpose of this passage is to equalize ythe pressures in the

chambers

90 and 46 after a short time delay. The amount of the delay will depend upon the size of the passage 130.

Referring now to the pressure relief valve illustrated in Figs. 4 and 5, it will be seen that this valve also is comprised of a cored and machined casting with various tittings attached thereto and located therein. At the lower end of this Valve structure there is a passage which extends therethrough for connection at one end to the outlet pipe 32 from the paint pump. The opposite end of this passage is connected to the hose 16 which supplies paint to the spray gun 10. Near its center the passage 140 intersects a vertically extending'cylindrical bore 142 which is drilled into the valve body from the lower end. Within this bore 142 there is an annular ring 144 retained against a shoulder near the upper end of the passage which is machined at its upper surface to provide a seat for a valve ball 146. This seat forming member 144 is supported by a sleeve 148 which in turn is held in place by a cap 150 threaded into the lower end of the bore 142. The sleeve 148 has a port 152 through one side thereof in communication with the passage 140, and in order to orient the port 152 with the passage 140, the opposite side of the sleeve 142 has a small opening 154 cut therethrough into which the end of a screw 156 projects. This screw, which is threaded through the main body casting,

' can also be removed to provide for the attachment of a .connection for flushing the interior paint passages of the valve 34.

The downstream side of the ball valve 146 is located within a chamber 157 which communicates with the pipe 36 leading back to the paint reservoir 22. Thus', when the valve ball 146 is free to move, paint from the pump entering through the pipe 32 is free to pass upwardly around the ball valve 146 and back to the paint reservoir by wayof the pipe 36. Under these conditions, there is substantially no pressure in the paint hose 16.

Directly above the valve ball 146 there is a plunger 153 the upper end of which is attached to a piston 160 which tits within a pneumatic cylinder 162 provided within a cap 164 threaded at 166 to the main casting. This pneumatic .cylinder 162 isI in communication through the top center thereof with the hose 38 which leads to the control valve. Normally the piston 160 and plunger 158 vare urged upwardly by a coil spring 168 which bears against the lower surface of the piston at one end, with its opposite end based in an annular groove 170 formed within the upper surface of the main body casting. So as to prevent paint from leaking into the pneumatic cylinder, a ring of packings 172 is provided around the plunger 1 ,58'at the upper end of the recess 157, and is retained in place by a packing nut 174 which is slid over the plunger 158 and threaded into the top surface of the main body casting at the center thereof.

With the elements of the system connected as shown and described, the apparatus `operates in the following manner.

When compressed air is supplied to the line 18, it passes through the screen 44 into the distribution chamber 46. This pressure operating against the end of the valve 96 will raise it off its seat so that air can ow into the chamber 9i) and fill the hose line 14 to the spray gun. The valve 96 will soon seat, however, because if the trigger at the spray gun is in the released position air cannot flow from the hose line 14 and therefore the air fiowing around the valve 96 and that liowing through the bypass 130 will soon equalize the pressures in the

chambers

46 and 90.

Inasmuch as the chamber 90 is in communication with the chamber 74 at the left side of the diaphragm 48, the pressures on the two sides of this diaphragm will balance and poppet 72 will be held against its seat 66 by the spring 60. Therefore, air cannot flow to the passage 64. No air pressure is imposed upon the upper surface of the pneumatic piston 16u, nor does air pass through the line 26 to the pump motor. The system therefore comes to rest with only the air line to the spray gun 10 being under pressure.

If. now, the trigger is pulled by the operator, air will flow through the hose 14 and from the spray gun 1t). This drops the pressure within the chamber 90 and causes the valve plug 96 to move upwardly inasmuch as the air capacity of the spray gun is far greater than that of the passage 130. The pressure developed by the spring 106 is such that with air flowing from the chamber 46 to the hose line 1 4 around the valve plug 96, the restriction offered by this valve will be enough so that the pressure in the chamber 9i) will be about 7 p. s. i. less than it is in the chamber 46. This causes the pressure in the diaphragm chamber '74 to be about 7 p. s, i. less than in the chamber 46, because of the communication provided by the passage 112.

Under this pressure differential, the diaphragm 48 moves toward the left, thereby closing the valve poppet 7i) against its seat and moving the valve poppet 72 toward the left as seen in Fig. 3, thereby permitting air to enter the passage 64 and by way of pass-age 76 to arrive at the line 33 leading to the pneumatic cylinder 162. The increase in pressure in the pneumatic cylinder 162 forces the piston 160 and plunger 158 downwardly, thereby clamping the valve ball 146 tightly against its seat so as to shut off the reservoir return line 36 from communication with the paint pump outlet.

Simultaneously, air passes upwardly from the passage 76 around the ball check valve Sil to the chamber 86, and thence to the motor for the paint pump. The pump `therefore starts operating and passes paint from the reservoir through the passage 14@ of the valve 34 to the paint line 16 and thence to the spray gun 1i). Under these circumstances the customary spray pattern is produced by the spray gun lil, since both paint and air are supplied thereto at the appropriate pressures.

As soon as air reaches the chamber 36 above the ball valve 80, this pressure is communicated by way of the passage 128 to the upper end of the piston 116, thereby forcing this piston downwardly so as to Wedge the balls 126 inwardly against the stem 9S of the valve 96. This therefore locks the valve 96 in the open position and prevents hunting, or other unevenness in flow therethrough, and also provides a closing time delay as will appear presently.

The system continues in operation in the fashion just described until the trigger 12 is released. As soon as this happens, flow will cease through the air line 14, thereby permitting the pressure in the chamber 90 to rise to the level of that in the chamber 46 almost instantly. This causes the pressure in the diaphragm chamber 74 to rise similarly and thus the spring 60 urges the diaphragm 48 and valve stem 62 toward the right, as seen in Fig. 3. This closes poppet valve 72 and opens poppet 70.

Air, therefore, ceases to iiow to the pump motor or to the control line 3S leading to the pneumatic cylinder 162. Opening of the poppet 7l) immediately drops the pressure of the control connection 38 to the pneumatic cylinder to atmospheric, thereby permitting the piston 160 and plunger 158 to rise with the result that the pressure in the paint hose 16 leading to the gun, and the pressure at the pump outlet, that is, the pipe 32, immediately drops to atmospheric or thereabouts inasmuch as the passage 140 is now freely in communication with the line 36 leading back to the reservoir.

It should be noted that whereas the pressure in the passage 76, and therefore the pressure at the pneumatic cylinder 162, drops to atmospheric immediately, there is some delay in the pressure drop within the chamber 86 leading to the pump motor, because the ball check valve prevents reverse flow from the pump rnotor through `the passage 78. The pump motor therefore will `run for a very brief interval. During this interval, or a portion thereof, the piston 116 will be held downwardly because of the communication between the piston cylinder 114 and the chamber 86 afforded by the passage 128. The valve plug 96 is therefore momentarily locked in its open position.

The result of this is that if the operator releases the trigger 12 only for an instant, as often happens, the pump motor and pump will continue in operation, and the valve 96 will remain open. However, since the pneumatic cylinder 162 operates almost instantly, the pressure in the paint line to the gun will drop somewhat before the trigger 12 is again actuated. This has the advantage of preventing spurting of paint from the spray gun when the trigger is again pulled.

The system, therefore, automatically turns on the pump and its motor which supplies paint to the spray gun whenever the trigger 12 is pulled, and shuts off the pump motor and relieves the pressure in the paint line to the gun almost instantly Whenever the trigger 12 is released for an appreciable interval of time. If the trigger is released only momentarily, the pressure in the paint line drops somewhat so as to prevent spurting, but the pump motor continues in operation during this short interval.

While I have shown and described a preferred embodiment of my invention, it will be apparent that numerous variations and modifications thereof may be made without departing from the underlying principles of the invention. I therefore desire, by the following claims, to include within the scope of the invention all such variations and modifications by which substantially the results of my invention may be obtained through the use of substantially the same or equivalent means.

I claim:

' l. A liquid supply system for use with a paint spray gun comprising, an air fitting for connection to said gun, a liquid fitting for connection to said gun, a compressed air motor, a liquid pump driven by said motor, a liquid reservoir, said pump being connected for withdrawing liquid from said reservoir and supplying said liquid under pressure to said liquid fitting when said motor receives air under pressure, means forming a bypass between said liquid fitting and said reservoir, a valve in said bypass, pressure responsive means for closing said by--pass valve when said pressure responsive means is supplied with air under pressure, means forming a chamber having an air inlet connection for supplying air thereto, said chamber having a first outlet passage leading to said air fitting and a second outlet passage leading to said pressure responsive means, a resiliently loaded valve in said first outlet passage, the last said valve being oriented to be opened by flow from said chamber to said air fitting and being adapted to restrict said flow to produce a pressure differential across the last said valve when air is flowing from said air fitting,

means forming a restricted bypass around said resiliently loaded valve for slowly equalizing the pressure on the two sides of the last said valve when the last said valve is closed, a pressure differential actuated two-position valve in said second outlet passage, said two-position valve being adapted when subjected to pressure differential to open to connect said chamber to said pressure responsive means and when not subjected to `a pressure differential to close said second outlet passage and to vent said pressure responsive means to the atmosphere, means for imposing said pressure differential on said pressure differential actuated valve, means forming a connection from said pressure responsive means to said air motor, a check valve in the last said connection, said check valve being oriented to permit flow to said air motor `and to prevent fiow in the opposite direction, pressure actuated means for clamping said resiliently loaded valve to prevent movement thereof, and means for subjecting said pressure actuated means to the pressure prevailing at said air motor.

2. A liquid supply system for use with a paint spray gun comprising, an air fitting for connection to said gun, a liquid fitting for connection to said gun, a compressed air motor, a liquid pump driven by said motor, a liquid reservoir, said pump being connected for withdrawing liquid from said reservoir and supplying said liquid under pressure to said liquid fitting when said motor receives air under pressure, means forming a bypass between said liquid fitting and said reservoir, a valve in said bypass, pressure responsive means for closing said bypass valve when said pressure responsive means is supplied with air under pressure, means forming a chamber having an air inlet connection for supplying air thereto, said chamber having a first outlet passage leading to said air fitting and a second outlet passage leading to said pressure responsive means, a resiliently loaded valve in said first outlet passage, thellast said valve being oriented to be opened by fiow from said chamber to said air fitting and being adapted to restrict said fiow to produce a pressure differential across the last said valve when air is fiowing from said air fitting, a pressure differential actuated twoposition valve in said second outlet passage, said twoposition valve being adapted when subjected to a pressure differential to open to connect said chamber to said pressure responsive means `and when not subjected to a pressure differential to close said second outlet passage and to vent said pressure responsive means to the atmosphere,

means for imposing said pressure differential on said pressure differential actuated valve, means forming a connection from said pressure responsive means to said air motor, a check valve in the last said connection, said check valve being oriented to permit flow to said airfmotor and to prevent fiow in the opposite direction, pressure actuated means for clamping said resiliently loaded valve to prevent movement thereof, and means for subjecting said pressure actuated means to the pressure prevailing at said air motor. l

3. A liquid supply system for use with a paint spray gun comprising, an air fitting for connection to said gun, a liquid fitting for connection to said gun, means for supplying liquid under pressure to said liquid fitting when said means receives air under pressure, means forming a low pressure outlet for said liquid fitting, a valve in said outlet, pressure responsive means for closing said valve when said pressure responsive means is supplied with air under pressure, means forming a chamber having an air inlet connection for supplying air thereto, said chamber having a first outlet passage leading to said air fitting and a second oulet passage leading to said pressure responsive means, a

resiliently loaded valve in said first outlet passage, the last said valve being oriented to be opened by flow from said chamber to said air fitting and being adapted to restrict said fiow to produce a pressure differential across the last said valve when air is fiowing from said air fitting, a pressure differential actuated two-position valve in said second outlet passage, said two-position valve being adapted when subjected to a pressure differential to open to connect said chamber to said pressure responsive means and when not subjected to a pressure differential to close said second outlet passage and to vent said pressure responsive means to the atmosphere, means for imposing said pressure differential on said pressure differenti-al actuated valve, means forming a connection from said pressure responsive means to said liquid supplying means, a check valve in the last said connection, said check valve being oriented to permit fiow to said liquid supplying means and to prevent fiow in the opposite direction, pressure actuated means for clamping said resiliently loaded valve to prevent movement thereof, and means for subjecting said pressure actuated means to the pressure prevailing at said liquid supplying means.

4. A liquid supply system for use with a paint spray gun comprising, an air fitting for connection lto said gun, a liquid fitting for connection 'to said gun, means for supplying liquid under pressure 'to said liquid fitting when said means receives air under pressure, means forming a flow pressure outlet for said liquid fitting, a valve in said outlet, pressure responsive means for closing said valve Iwhen said pressure responsive means is supplied with air under pressure, means forming a chamber having an air inlet connection for supplying air thereto, said chamber having a first outlet passage leading to said air `fitting and a second outlet passage leading to said pressure responsive means, a resilien-tly loaded valve in said first youtlet passage, the last said valve being oriented to be opened by ffow from said chamber to said air fitting and being adapted to restrict said flow to produce -a pressure differential vacross the llast said valve when air is fiowing from said air fitting, means 'forming a restricted |`bypass around said resiliently loaded valve `for slowly equalizing the pressure on `the two sides `of the last said valve when the last said valve is closed, a pressure differential actuated 'two-position valve in said second outlet passage, said ytwo-position valve being adapted when subjected to pressure differential to open to connect said chamber to said pressure responsive means and when not subjected to a pressure differenti-al to close said second outlet passage and to vent said pressure responsive means to the atmosphere, means for imposing said pressure differential on said pressure differential actuated valve, means forming a connection from said pressure responsive means to said liquid supplying means, a check valve in the last said connection, said check valve being oriented 'to permit ow to said liquid supplying Imeans and to prevent fiow in lthe opposite direction, pressure actuated means for clamping said resiliently loaded valve to prevent movement thereof, and means lfor subjecting said pressure |actuated means to the pressure prev-ailing a-t said liquid supplying me-ans.

5. A liquid supply system for use with a paint spray gun having 1an lair supply line and .a liquid supply line comprising, means for supplying liquid under pressure to said liquid `supply line when said means receives air under pressure, means forming a low pressure outlet for said liquid supply line, a valve -for closing said outlet, pressure responsive means for closing said valve when said pressure responsive means is supplied with air under pressure, means forming a chamber having -an air inlet connection, said chamber having a first outlet passage `lea-ding to said air supply line and a second outlet passage leading to said pressure responsive means, means 4to produce a pressure differential when -air is fiowing to said air supply line, a pressure differential actuated two-position valve in said second outlet passage, said two-position valve being ladapted when subjected to a pressure differential Ito open to connect said chamber to said pressure responsive means and when not subjected to a pressure differential to close said second outlet passage and to vent said pressure responsive means to the atmosphere, means for imposing said pressure differential on said pressure differential actuated valve, means forming an air supply connection between said second outlet passage and said liquid supplying means, and check valve means interposed in said air supply connection Ito prevent the reverse flow of air past the check valve Ifrom said liquid supplying means thus providing for limited continued `operation of the latter by air held against return `flow through `the check valve `after the air supply has been terminated by operation of said two-position valve.

6. A liquid supply system for use with a paint spray `gun `having an air supply line and a liquid supply line comprising, means 'for supplying fliquid under pressure to said liquid supply line when said means receives air under pressure, means forming a low pressure outlet for said liquid supply line, a valve for closing said outlet, pressure responsive means for closing said valve when said pressure responsive means is supplied with air under pressure, means forming a chamber having an `air inlet connection, said chamber having an outlet passage leading to said pressure responsive means, air supply means connected to said air supply line, -means in said air supply means for producing a substantial pressure diierential therein as an incident to the flow of air therethrough to said air supply line, a pressure differential actuated two-position valve in said outlet passage, said two-position valve being adapted when subjected to a pressure differential to open to connect said chamber lto said pressure responsive means and when not `subjected lto a pressure diierential to close said `outlet passage and to vent said pressure responsive means to the atmosphere, means for imposing said pressure differential of said air supply means on said pressure dilerential actuated valve, means forming an air supply connection between said outlet passage and said liquid supplying means, and check valve means interposed in said air supply connection `to prevent the reverse iiow of air past the check valve from said liquid supplying means, thus providing for limited continued operation of the latter by air held against return flow lthrough the check v-alve after the air supply has been terminated by loperation of said two-position valve.

7. For use with 1a spray gun having separate air and liquid `supply inlets, an air and liquid supply system comprising, in combination, pump means for supplying liquid under pressure, means adapted to connect the outiet of the pump means Yto ythe liquid supply inlet of a spray gun, uid pressure control means `connected with 'the outlet of the pump Ito unload the liquid output pressure therefrom in response to ya critical change in the pressure of a controlling iluid medium supplied to the control means, means for supplying air under pressure to said pressure responsive pump outlet control means and including a valve operable to sharply change the pressure cf air [applied to said pump loutlet control, -an operator for said valve formed for actuation by dilerential uid pressure applied thereto, means adapted to supply air under pressure to the air inlet of the spray gun and including a flow orifice therein, a `flow restriction member movably disposed adjacent the downstream side of said orifice, biasing means acting on said ilow restriction member to urge the latter toward closing relation with said orifice, the biasing means yielding to reduce the restrictive effect of the liow restriction member to permit Widely varying rates of iiuid flow through the orifice while providing for a relatively stabilized diierential pressure on Iopposite sides of the oriiice for the different flow rates, and means connecting the diiferentia'l fluid pressure on opposite sides of the orifice tothe diterential iluid pressure valve yoperating means.

8. For use with a spray gun having separate -air and liquid supply inlets, an air and liquid supply system comprising, in combination, pump means for supplying liquid under pressure, -means adapted to connect the outlet `of the pump means to the liquid supply inlet of a spray gun, uid pressure con-trol means connected with the outlet of the pump -to unload the liquid output pressure therefrom in response to a critical change in the pressure of a controlling fluid medium supplied to the control means, means for supplying air under pressure to said pressure responsive pump outlet control means and including a valve operable to sharply change the pressure of air applied Ito said pump outlet control means, an operator for said valve formed for actuation Iby differential 'liuid pressure `applied thereto, means adapted `to supply air under pressure to the air inlet of the spray gun and including an orifice therein, a ow restriction member movably disposed adjacent the downstream side of said orifice, biasing means Iacting on said iiow restriction member to urge the latter toward closing relation with said oriiice the biasing means yielding to reduce the restrictive efect of the flow restriction member to permit widely differing rates of air iiow through the orifice While providing for a relatively stabilized diierential pressure on Iopposite sides of fthe orice for 4the dilerent :dow rates, means connecting the diierential iiuid pressure on opposite sides of the orifice tothe dierential fluid pressure valve `operating means, and fluid pressure actuated retaining means communicating with the downstream side of said valve land mechanically connected with said ow restriction member to temporarily hold the latter away from said orifice against the lforce of said biasing means when fluid ow through said valve is momentarily interrupted.

References Cited in the ile of this patent UNITED STATES PATENTS