US3007647A

US3007647A - Pressure supply system for spray guns

Info

Publication number: US3007647A
Authority: US
Inventors: Frank C Woelfer
Original assignee: Balcrank Inc
Current assignee: Balcrank Inc
Priority date: 1959-08-14
Filing date: 1959-08-14
Publication date: 1961-11-07
Anticipated expiration: 1978-11-07

Description

Nov. 7, 1961 F. c. WOELFER 3,0 7

PRESSURE SUPPLY SYSTEM FOR SPRAY suns Filed Aug. 14, 1959 2 Sheets-Sheet 1 INVENT OR.

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Nov. 7, 1961 F. c. WOELFER 3,007,647

PRESSURE SUPPLY SYSTEM FOR SPRAY GUNS Filed Aug. 14, 1959 2 Sheets-Sheet 2 I /A P 12 4 34 W 34 17% 5 INVENTOR.

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ATTORNEYS.

3,007,647 PRESSURE SUPPLY SYSTEM FOR SPRAY GUNS Frank C. Woelfer, Cincinnati, Ohio, assignor to Balcrank, Inc., Marhurg, Cincinnati, Ohio Filed Aug. 14, 1959, Ser. No. 840,487 Claims. (Cl. 239-329) This invention relates to a distribution system for spray guns, wherein paint or other viscous liquids are pumped from a reservoir and advanced to one or more spray guns to be projected in spray form upon the surface to be treated.

Systems of this type are in extensive use in industrial plants in applying paint, lacquer, and other surface finishing compounds to the manufactured parts. In most instances, the spray guns are operated in a special enclosure having air exhaust means to prevent the paint fumes from spreading throughout the plant. The supply reservoir is usually located at some point remote from the spray booth and the paint is advanced under pressure to the spray guns by way of a conduit which may be from 25 to 100 feet or more in length.

According to the conventional supply systems to which the present improvements are particularly directed, the reservoir is provided with an air-operated pump for forcing the paint under pressure from the reservoir, through the supply line to the spray gun. The spray gun includes a trigger-operated valve for regulating the flow of paint and also includes an air supply line which creates an air blast for projecting the paint in spray form from the discharge nozzle of the gun. For simplicity of control,

the air-operated pump of the reservoir is of the stall type, that is, the pump is stopped under back pressure in the supply line when the valve of the spray gun is closed. Because of viscosity and flow resistance, it is necessary to supply the paint under fairly high pressure to the supply line; hence, when the spray gun valve is closed to stall the pump motor, the back pressure which builds up in the supply line causes the line or conduit to expand slightly. When the spray gun valve is re-opened, the back pressure creates a momentary gush or surge of paint through the spray gun, due to rapid contraction of the expanded supply line. This surge has too much volume and velocity to be atomized by the air blast; as a consequence, it issues as a solid high velocity stream from the nozzle and spoils the surface finish of the work and is also wasteful of paint.

One of the primary objectives of the present invention has been to provide a surge eliminator of simple construction adapted to be installed in the distribution system to eliminate the surge problem without requiring extensive changes in the system or in the pump itself.

According to the present invention, the surge eliminator is inserted in the supply line at some point between the pump and spray gun. The surge eliminator blocks the flow of paint from the pump in response to predetermined back pressure in the supply line which is substantially less than the output pressure of the pump and insufficient to cause expansion of the supply conduit. Accordingly, when the valve of the spray gun is closed, the surge eliminator immediately responds to the back pressure to stall the pump, and when the valve is reopened, the paint immediately is supplied to the gun but at sufficiently low pressure to eliminate the gush of paint. When the line pressure drops sufficiently, the valve of the surge eliminator opens to allow the pump to resume operation.

The present surge eliminator is somewhat similar to the pressure control unit shown in Patent No. 2,726,790, issued on December 13, 1955 to Frank C. Woelfer, the present applicant. According to the patent, the pressure control unit is mounted upon a grease gun and includes dfihlhd? Patented Nov. 7, 196i.

a manually shiftable sleeve which, in one position, provides high pressure grease delivery and in a second position, provides a low pressure delivery. The present surge eliminator differs from the control unit in that it provides automatic operation, as distinguished from manual, and also differs structurally to adapt it to its particular use.

Briefly, the surge eliminator of this invention comprises an external shell or housing adapted to be inserted in the supply line, and a one-piece combined floating plunger and valve slidably confined within the shell, the plunger having two diameters which act as differential pistons. The shell is bored internally to provide two cylinder bores for the respective pistons and the intake end of the shell forms a valve seat which coacts with the end of the small diameter piston to control the operation of the pump. When the spray gun valve is opened, the plunger is shifted to an intermediate balanced position to allow the paint to flow, and when the flow of paint through the line is blocked off at the spray gun, the end of the small piston immediately engages its valve seat to stall the pump.

A further objective has been to provide a simplified structure and one which reduces turbulence and flow resistance through the surge eliminator.

For this purpose, the small diameter piston has a tapered nose which coacts with the valve seat and includes a series of radially spaced apertures formed in the nose rearwardly of the seat-engaging portion of it. The apertures communicate with an axial bore formed in the plunger, the arrangement being such that the paint flowing through the valve seat enters the small cylinder and flows without much change in direction, about the tapered nose and through the radial apertures and through the central aperture to the discharge end of the shell.

By virtue of its structural features, the surge eliminator is also adapted to be installed in supply systems for highly viscous compounds, such as undercoating and sealing compounds of various kinds, which by reason of flow resistance, must be pumped through the lines at higher pressures than paint and the like. In such installations, the surge eliminator may be installed between the outer end of the supply line and the spray gun so as to maintain the supply line at full pump pressure for immediate flow when the spray gun valve is opened. According to this arrangement, the viscous material may cause expansion of the supply line at full pump pressure; however, the surge eliminator prevents surging of the material through the spray gun when the valve is opened. The various features and advantages of the present invention will be more clearly apparent to those skilled in the art from the following detailed description taken in conjunction with the drawings.

In the drawings:

FIGURE 1 is a diagrammatic view showing a typical paint delivery system including a paint pump and spray gun, the surge eliminator being inserted in the supply line adjacent the paint pump.

FIGURE 2 is a side view of a spray gun similar to FIGURE 1, but showing the surge eliminator inserted in a second position, between the end of the conduit and spray gun.

FIGURE 3 is an enlarged longitudinal sectional view of the surge eliminator, with the plunger in its unseated position during operation of the spray gun.

FIGURE 4 is a sectional view similar to FIGURE 3,

I but showing the plunger shifted to valve closing position in response to back pressure when the spray gun is shut off.

FIGURE 5 is a cross sectional view taken along line 55 of FIGURE 4, detailing the tapered nose of the plunger.

Described generally with reference to FIGURE 1, the paint reservoir, indicated generally at 1, includes an air-operated pump motor 2 mounted at its upper end, the motor having a pump cylinder 3 projecting downwardly toward the bottom of the reservoir. A paint pump of this type includes a piston slidably mounted within the cylinder 3 and connected means of a piston rod to an air-actuated piston within the motor 2. Air pressure is supplied to the cylinder of the pump motor by an air conduit 4 and is conducted by way of a suitable reversing valve arrangement to the motor cylinder to reciprocate the pump piston.

The internal construction of the air motor and pump does not form a part of the present invention and has therefore been omitted from the disclosure. It will be understood at this point however, that the motor is of the stall type arranged to advance the paint or other material under pressure to the supply conduit 5 which leads to the spray gun 6. When the spray gun valve is closed, it blocks the flow of paint through conduit 5 and stalls the air motor under back pressure. In the example shown in FIGURE 1, the surge eliminator, which is indicated generally at 7, is inserted between the delivery fitting 8 of the paint pump and the conduit 5.

The spray gun 6 is a conventional structure especially designed to handle paints and other more viscous compounds, such as undercoating compounds for automobile bodies, roofing compounds, sealing compounds and materials of the type used in Waterproofing the foundation of buildings. The word paint, as used in the specification and claims, is intended to also include these liquids and semi-liquids. These materials are forced from the reservoir to the spray gun at pressures which depend upon the viscosity of the material and the length of the conduit. The delivery pressure is adjusted by suitable regulating means on the delivery pump.

By way of example, in handling highly viscous materials such as an undercoating compound, Where the delivery conduit is fairly long, a pump delivery pressure in the neighborhood of 400 p.s.i. may be required to advance the material through the conduit, due to the flow resistance of the material. On the other hand, in handling lighter liquids such as ordinary paints and lacquer, considerably less delivery pressure is required. In either case, in the absence of a surge eliminator, the conduit 5 expands slightly under back pressure when the spray gun is shut off, with the pump stalled under back pressure. When the spray gun valve is re-opened, the conduit contracts rapidly and as a consequence, projects a gush or surge stream of paint through the nozzle 10 as conduit pressure drops to normal. The surge eliminator of this invention prevents this surge by reducing the back pressure in the conduit 5 sufliciently to prevent expansion of the conduit under back pressure.

In general, the spray gun comprises a body having a spray nozzle 10, a control handle 11, and an air conduit 12 which supplies air pressure for projecting the paint in the 'form of a spray for application to the surface to be coated. The spray gun is provided with suitable valves (not shown) interconnected with the control handle 11 to regulate the flow of air and paint through the gun, both valves normally being closed and being opened only when the operator actuates the handle 11. When the valves are opened, the paint enters the gun and is picked up in a blast of air and projected as a fine mist from the nozzle 10. When the valves are closed, the flow of air and paint are blocked off, as noted above, thus creating back pressure in conduit 5 so as to stall the pump.

When the surge eliminator 7 is installed at the point shown in FIGURE 1, the eliminator responds to a given back pressure in the conduit 5 to stall the pump which delivers at a higher pressure. The surge eliminator therefore decreases the back pressure in the conduit to a point below that at which conduit expansion occurs. As a consequence, the paint in the conduit is maintained at all times under a predetermined normal delivery pressure to provide immediate response when the spray gun valve is opened, but sufliciently low to eliminate the surge when the spray gun is started.

Surge eliminator Referring now to FIGURES 3-5, the surge eliminator in general comprises a cylindrical housing or shell 13, having a differential plunger, indicated generally at 14, and a closure cap 15 screw threaded as at 16 upon the outlet end of the shell 13. The inlet end of the shell comprises an externally threaded nipple 17 which is screwed into the delivery fitting 8 of the pump, as indicated earlier. The intake nipple 17 leads to a valve seat 18 which communicates with a small cylinder bore 20. The opposite end of the small cylinder 20 is delineated by a tapered shoulder 21 which leads to a large cylinder bore 22. The closure cap 15 includes an internal shoulder 23 which delineates the outer end of the large cylinder 22. Shoulder 23 leads to a delivery fitting 24 which is internally threaded as at 25. The conduit 5 is provided with a fitting which includes a nipple 26 threaded into the fittings 24. In order to provide wrench engagement for tightening the closure cap 15 upon the shell 13, both parts are provided with flats 27 (FIGURE 5) which are machined across the cylindrical outside diameter of these parts.

The floating valve plunger, indicated previously at 14, is free to float axially within the shell 13, being slipped in place before the closure cap 15 is applied. The plunger comprises a small piston 30 interfitting the small cylinder bore 20, and a large piston 31 interfitting the large cylinder bore 22. The small diameter piston 30 has a tapered nose 32 projecting toward the intake nipple I7 and adapted to interfit the valve seat 18, thereby to block the flow of paint, as indicated in FIGURE 4.

The plunger includes an internal bore 33, and the tapered nose is provided with apertures 34 communicating with bore 33. It is to be noted that the apertures 34 are located inwardly of that portion of the nosepiece which engages the valve seat 18. As viewed in FIGURE 5, the apertures 34 are equally spaced about the periphery of the nose 32 and have axes residing at right angles to the tapered surface of the nose, such that the apertures partially face the valve seat 18. When the valve is open (FIGURE 3) the paint flowing through the valve seat is deflected outwardly by the tapered nose and enters the small diameter cylinder 20 then is deflected by the cylinder wall inwardly through the apertures 34 and into the bore 33 of the plunger. The arrangement is such that the paint flows with little interference or turbulence through the valve seat and plunger to the outlet end of the unit, as indicated by the arrows.

The

pistons

30 and 31 each include a peripheral groove 35 having seated therein an O-ring 36 formed of synthetic rubber or other appropriate material. These rings provide a seal with the surface of the respective cylinder bores, while permitting the plunger to slide freely therein. An annular space 37 is delineated within the shell 13 by the juncture of the two pistons and their cylinder bores. A small aperture 38 communicates with the annular space to permit the escape of any paint which may leak past the seal n'ngs during operation of the valves, and to prevent aid from being trapped therein.

In its full open position shown in FIGURE 3, the rearward end of the plunger seats against the internal shoulder 23 of the closure cap 15. This portion of the plunger is counterturned externally as at 40 and is provided with a lateral aperture 41 to provide communication between the cylinder and annular space delineated by the counterturned portion of the piston.

Although the plunger is shown in FIGURE 3 at its limit of motion toward the left, in actual practice, it will shift to an intermediate position, as explained below.- The differential piston diameters, in the example illustrated, provide a pressure ratio of 2 to 1 in pump delivery pressure to conduit pressure. By way of example, if the pump is set to deliver paint at 400 p.s.i., the valve will remain open until a back pressure of approximately 200 p.s.i. exists in conduit 5. At this pressure, the differential areas of the two pistons are effective to shift the plunger toward the right, causing the nose to establish a seal with the valve seat 13 thereby to stall the pump. During operation of the spray gun, there is always a tendency for the plunger to shift toward closing position under the back pressure acting upon the large piston 31. On the other hand, the pump pressure acts upon the small piston 3t) in the opposite direction to keep the valve partially open and in a state of equilibrium, with greater pressure acting upon the small piston in the ratio of the diiference in piston diameter. However, when the plunger shifts to closed position, the forces acting upon the plunger consist of the pump pressure multiplied by the area of the nose which engages the valve seat, opposed to the back pressure acting upon full diameter of the large piston.

When the spray gun valve is opened, the back pressure in the conduit immediately starts the flow of paint to the nozzle, and at the same time, the back pressure on the large piston 31 decreases, permitting the plunger to shift again toward the left so as to reestablish the supply to the conduit.

In handling heavy viscous compounds, such as semiliquid compounds which have a great deal of flow resistance, a higher pressure is required to force the compound through the conduit, as noted earlier. In such cases, the surge eliminator is interposed between the end of the conduit and the spray gun, as indicated in FIGURE 2. In this arrangement, the full pump pressure is available to force the compound through the conduit 5, while on the other hand, the surge eliminator prevents any gush of material when the spray gun is started. During actual operation, the flow resistance of the material causes the pressure to drop substantially as the material advances toward the end of the conduit. Accordingly, if the surge eliminator were interposed at the pump end of the conduit, the flow resistance would retard the build-up of pressure in the conduit and thereby introduce a lag in the operation of the spray gun.

The surge eliminator is also introduced in the outer end of the supply line in those instances where the line must be extended for a substantial distance beyond the pump, as is the case in certain industrial installations. In this instance, even tho-ugh paint of average consistency is being pumped, the length of the supply conduit will create sufiicient flow resistance to introduce a time lag in the pressure build-up. With the unit at the outer end of the line, the back pressure maintained in the line is available for immediate response to operation of the spray gun.

Having described my invention, 1 claim:

1. A supply system for paint and the like comprising a paint reservoir, a supply conduit, a power pump associated with the reservoir and adapted to deliver paint from the reservoir to the conduit under pressure, a spray gun in communication with said conduit for projecting the paint in the form of a spray, said spray gun having a valve for blocking the flow of paint through the spray gun, said power pump adapted to stall under back pressure when said spray gun valve is closed, a surge eliminator in communication with said conduit between the pump and spray gun, said surge eliminator comprising a housing having an inlet passageway at one end thereof including a valve seat, said housing having an outlet passageway at the opposite end thereof, an axially floating one-piece pressure-responsive plunger residing within said housing, said plunger having a pair of axially aligned dilferential diameter pistons at opposite end portions thereof slidably confined in said housing in sealed engagement therewith, the larger of said pistons being presented to said outlet passageway, and a tapered nose element on the smaller piston of said plunger adapted to engage said valve seat, said plunger shifting said nose element am'ally into engagement with said valve seat in response to back pressure when the spray gun valve is closed, said back pressure being substantially less than the delivery pressure of the power pump, said nose element thereby stalling said pump under back pressure which is insufiicient to create a surge of paint through the gun when the valve thereof is opened.

2. A supply system for paint and the like comprising, a paint reservoir, a supply conduit, 9. power pump associated with the reservoir and adapted to deliver paint from the reservoir to the conduit under pressure, a spray gun in communication with said conduit for projecting the paint in the form of a spray, said spray gun having a valve for blocking the flow of paint through the spray gun, said power pump adapted to stall under back pressure when said spray gun valve is closed, a surge eliminator interposed between the inlet end of said conduit and the pump, said surge eliminator comprising a housing having a pair of axially aligned differential diameter cylinder bores formed therein, said housing having an inlet passageway at one end thereof including a valve seat communicating with the smaller of said cylinder bores, said housing having an outlet passageway at the opposite end thereof communicating with the larger of said cylinder bores, an axially floating pressure-responsive plunger residing within said housing, said plunger having differential diameter pistons slidably confined in said cylinder bores, and a tapered nose element on the smaller of said pistons, said tapered nose adapted to engage said valve seat, said plunger having an axial bore extending to said tapered nose, said nose having a plurality of apertures communicating with the bore of the plunger, said apertures having axes inclined toward said valve seat, said plunger shifting said nose element axially into engagement with said valve seat in response to back pressure in the conduit when the spray gun valve is closed, said back pressure being substantially less than the delivery pressure of the power pump, said nose element thereby stalling said pump under back pressure which is insufficient to create a surge of paint through the gun when the valve thereof is opened.

3. A supply system for paint and the like comprising a paint reservoir, a supply conduit, a power pump associated with the reservoir and adapted to deliver paint from the reservoir to the conduit, a spray gun connected to said conduit for projecting the paint in the form of a spray, said spray gun having a valve for blocking the flow of paint through the spray gun, said power pump adapted to stall under back pressure in said conduit when said valve is closed, a surge eliminator interposed between the outlet end of the conduit and spray gun, said surge eliminator comprising a housing having a pair of axially aligned differential diameter cylinder bores formed therein, said housing having an inlet passageway at one end thereof including a valve seat communicating with the smaller of said cylinder bores, said housing having an outlet passageway at the opposite end thereof communicating with the larger of said cylinder bores an axially floating pressure responsive plunger residing within said housing, said plunger having differential diameter pistons slidably confined in said cylinder bores, and a tapered nose element on the smaller of said pistons, said tapered nose adapted to engage said valve seat, said plunger shifting said nose element axially into engagement with said valve seat in response to back pressure in the spray gun when the valve thereof is closed, said back pressure being substantially less than the delivery pressure of the power pump while the pressure in said conduit is equal to the pump delivery pressure, said nose element thereby stalling said pump under back pressure which is insufiicient to create a surge of paint through the gun when the valve thereof is opened.

4. A surge eliminator for a supply system for paint and the like including a supply conduit, a power pump adapted to deliver paint to the conduit under pressure, and a spray gun connected to said conduit and having a valve for blocking the flow of paint therethrough, said surge eliminator comprising, a housing having a pair of differential diameter cylinder bores in end-to-end relationship, said housing having an inlet passageway at one end communicating directly with the smaller of said cylinder bores and an outlet passageway at its opposite end communicating with the larger of said cylinder bores, said housing adapted to be inserted in said conduit between the pump and spray gun for the passage of paint through the housing from the inlet passageway to said outlet passageway, said inlet passageway having a valve seat facing the end of the smaller cylinder, a one-piece axially floating pressure-responsive plunger having a pair of differential diameter pistons slidably confined in said differential cylinder bores, the larger of said pistons being presented to the outlet passageway and adapted to be shifted therefrom in response to predetermined back pressure in said outlet passageway, and a tapered nose on the smaller of said pistons adapted to engage said valve seat, said tapered nose including a series of apertures having axes inclined toward the inlet passagewa, said plunger having an axial bore communicating with said apertures and providing for the flow of paint generally in a straight line from the inlet passage, about said tapered nose and through said apertures when the nose is spaced from the valve seat with the spray gun valve open, said plunger adapted to shift said nose into engagement with the valve seat in response to back pressure in the conduit which is less than the delivery pressure of said pump, said back pressure being insufficient to create a surge of paint through the gun when said valve is re-opened.

5. A surge eliminator for a pressure supply system for paint and the like including a supply conduit, a power pump adapted to deliver paint to the conduit under pressure, and a spray gun connected to said conduit and having a valve for blocking the flow of paint therethrough, said surge eliminator comprising, a housing having a pair of differential diameter cylinder bores in end-to-end relationship, said housing having an inlet passageway at one end communicating directly with the smaller of said cylinder bores and an outlet passageway at its opposite end communicating with the larger of said cylinder bores, said housing adapted to be inserted in said conduit between the pump and spray gun for the passage of paint through the housing from said inlet passageway to said outlet passageway, said inlet passageway having a valve seat adjacent said smaller cylinder and facing the same, and an axially floating pressure-responsive plunger having differential diameter pistons slidably confined in said cylinder bores, the larger of said pistons being presented to the outlet passageway and adapted to be shifted therefrom in response to predetermined back pressure in said outlet passageway, the end portion of the smaller of said pistons being tapered from the full diameter of the smaller cylinder bore toward the valve seat, said tapered end portion adapted to engage said valve seat, said tapered portion having a plurality of apertures located inwardly from the portion thereof which engages the valve seat, said plunger having an axial bore communicating with said apertures and extending toward said outlet passageway for the passage of paint generally in a straight line from the inlet passageway about the said tapered portion and through said apertures when the nose is spaced from the valve seat with the valve of the spray gun open, said plunger adapted to shift said tapered portion into engagement with the valve seat in response to back pressure which is less than the delivery pressure of said pump, said back pressure being insufficient to create a surge of paint through the gun when said valve is re-opened.

References Cited in the file of this patent UNITED STATES PATENTS 922,986 Westaway May 25, 1909 1,971,659 Ruthven Aug. 28, 1934 2,266,354 Christenson Dec. 16, 1941 2,404,548 Thomas July 23, 1946 2,687,739 Shelburne et al Aug. 31, 1954 2,793,075 Gulick May 21, 1957