US3720373A

US3720373A - Recirculating paint system or the like

Info

Publication number: US3720373A
Application number: US00176226A
Authority: US
Inventors: G Levey
Original assignee: Individual
Current assignee: Individual
Priority date: 1971-08-30
Filing date: 1971-08-30
Publication date: 1973-03-13
Anticipated expiration: 1990-03-13

Abstract

A recirculating pressure system for supplying a plurality of spray guns or the like is disclosed. A single pump supplies pressurized liquid to one end of a single recirculating loop, and the recirculating liquid, after passing through the loop, returns to the pump intake. A plurality of spraying stations are located in the loop and are connected in series. Each spraying station includes an adjustable automatic flow restriction which operates to produce a pressure drop at the associated station. A spray gun is connected to the loop at each station in parallel with the associated flow restriction. The supply line is connected upstream from the flow restriction, and the return line is connected downstream thereof. The flow restrictions function to produce sufficient-pressure drop to insure recirculating flow to the associated gun while permitting a major portion of the liquid to bypass the associated gun.

Description

Levey ]Mareh 13, 1973 1 RECIRCULATING PAINT SYSTEM OR THE LIKE [75] Inventor: Gustave S. Levey, Houston, Tex.

[73] Assignee: GustaveS. Levey, trustee, Houston,

Tex.

221 Filed: Aug.30, 1971 21 App1.No.: 176,226

[52] US. Cl ..239/127 [51] Int. Cl. ..B05b 9/00 [58] Field of Search.... ..239/l24-127 [56] References Cited UNITED STATES PATENTS 3,023,968 3/1962 Mitchell ..239/125 2,091,166 8/1937 Shiels i t r ..239/l27 2,244,686 6/1941 Garrison et a1 ..239/126 2,266,354 12/1941 Christensen et a1. ..239/l26 2,461,766 2/1949 Peeps "239/127 2,727,786 12/1955 Bede ..239/l27 3,018,968 l/l962 Levey ..239/l27 Primary Examiner-Lloyd L. King Attorney-Harold F. McNenny et a1.

[57] ABSTRACT A recirculating pressure system for supplying a plurality of spray guns or the like is disclosed. A single pump supplies pressurized liquid to one end of a single recirculating loop, and the recirculating liquid, after passing through the loop, returns to the pump intake. A plurality of spraying stations are located in the loop and are connected in series. Each spraying station includes an adjustable automatic flow restriction which operates to produce a pressure drop at the associated station. A spray gun is connected to the loop at each station in parallel with the associated flow restriction. The supply line is connected upstream from the flow restriction, and the return line is connected downstream thereof. The flow restrictions function to produce sufficient-pressure drop to insure recirculating flow to the associated gun while permitting a major portion of the liquid to bypass the associated gun.

15 Claims, 5 Drawing Figures PATENTEDMAM 3l975 720,373

' sum 1 ur 3 i 24 INVENTOR.

6057 4145 J. zel/gv RECIRCULATING PAINT SYSTEM OR THE LIKE BACKGROUND OF THE INVENTION This invention relates generally to liquid distribution systems and more particularly to a novel and improved recirculating distribution system for supplying liquid under pressure to a plurality of airless paint spraying devices or the like.

PRIOR ART Recirculating pressure systems for paint spray devices are known. Such systemsare normally used when the material being sprayed is heated or when the material tends to settle or separate if continuous flow is not maintained. My prior U.S. Pat. Nos. 3,018,968 and 3,388,866 both disclose recirculating systems for supplying a single airless spray gun with a pressurized heated coating material such as paint or the like. In the system disclosed in the latter of these patents, the paint is pressurized by a pump and is delivered to the spray gun through a heater and a supply line. A return or recirculating line is provided through which the heated and pressurized paint is returned to the pump. An adjustable back pressure regulator is provided in the return line to maintain the desired pressure at the spray v gun.

In many instances it is desirable to use a single pumping system to supply two or more spray guns. In such systems where recirculation is required, it is known to provide a pump which supplies paint under pressure to a high pressure line. The high pressure line is connected to each spray gun and when heated paint is required, a heater is usually provided in the high pressure line upstream from the spray guns. A recirculating or return line is connected to each gun and returns the excess or recirculating paint to the pump. Examples of such systems are illustrated in the U.S. Pat. Nos. 2,022,481; 2,244,686; 2,266,354; 3,023,968; 3,385,522; and 3,561,645.

Because such systems provide spray guns connected in parallel between the high pressure supply line and the return line, it is necessary for the supply and return lines to extend to each station at which a gun is provided. Further, since theguns are in parallel, a malfunction in a given portion of the system can cause flow to. be interrupted in such portion. Still further, sufficient volume of pressurized paint must be provided to insure the desired flow rates are maintained in each branch of the system.

In other instances, systems have been provided in which a'plurality of guns are connected in series with all ofthe recirculating material passing from one gun to the next, less only the amount released in the spraying from each gun. Such a system is objectionable because of the accumulated pressure drop which occurs, particularly in systems having a relatively large number of spray guns.

, SUMMARY OF THE INVENTION Located in the loop at each spray gun station is a flow restriction and a pair of valve fittings with one on each side of the associated flow restriction. The supply line of the associated gun is connected to the fitting upstream of the flow restriction and the gun return line is connected to the associated fitting downstream of the flow restriction. Therefore, each gun is connected in parallel with an associated flow restriction and in series with the other flow restrictions and associated guns.

In one illustrated embodiment, the spray guns are airless and the flow restrictions are adjustable pressure regulators which create a pressure drop that is automatically maintained at an adjusted value. In practice, the pressure regulators are adjusted to just create sufficient pressure drop to insure that the desired flow rate is maintained through the supply and return lines which connect the associated guns to the recirculating loop in order to maintain material temperature at the gun comparable to main line temperature.

In another embodiment, air spray guns are utilized and a gun mounted pressure reducing regulator is provided at each gun to control the pressure of the paint supplied to the gun. v

Because only a single loop is required, the total amount of piping, when compared to the parallel systems previously employed, is reduced in many installations without encountering excessive pressure drops. Further, the recirculating flow is reliably maintained through all portions of the system, and it is not necessary to provide excessive quantities of pressurized paint to maintain the desired flow rates in all portions of the system. I

BRIEF DESCRIPTION OF THE DRAWINGS FIG. I is a schematic illustration of a preferred embodiment of this invention in which a single pump is connected through a recirculating loop to three airless spray guns;

FIG. 2 is a fragmentary schematic illustration of the structural detail of the back pressure regulator and bleed system located at the intake of the pump;

FIG. 3 is a fragmentary schematic illustration of the structural detail of the automatic pressure regulator provided at each spray gun station along the recirculating loop;

FIG. 4 is a fragmentary schematic illustration of the structural detail of a second embodiment of back pressure regulator which maybe provided at the pump intake in place of the embodiment illustrated in FIG. 2;

and

FIG. 5 is an enlarged fragmentary view of an air spray gun with a pressure reducing regulator which may be utilized in a system in accordance with this invention.

The present invention is disclosed in an embodiment in which a single recirculating system supplies three separate paint spray devices with heated paint under pressure. However, it should be understood that this system is equally applicable for supplying other types of coating materials and that the invention is not limited to painting per se or the application of paint per se. Further, it should be understood that this system in accordance with this invention is suitable for supplying substantially any number of devices and that the system incorporating three spray devices is only illustrated by way of an example on a system incorporating this invention.

FIG. 1 illustrates this invention applied to an airless paint spray system. The system includes a pump provided with an inlet 11 and an outlet 12. The illustrated pump is a reciprocating pump driven by a compressed air motor 13. Reference may be made to my US. Pat. No. 3,0l8,968 for a more detailed description of such an air motor. Any suitable pump may be used, but the illustrated pump is preferred since it is capable of utilizing relatively low pressure compressed air, which is available in many industrial installations, to pressurize paint or the like to relatively high pressures in the order of 500 to 3,000 psi. The particular pump illustrated is arranged so that the pressure and volumetric output is substantially equal on both the extension and retraction strokes.

Connected to the output 12 is a pressure line 14 which supplies the paint at the output pressure to a heater schematically illustrated at 16. From the heater, a second line 17 supplies the paint under pressure to a first adjustable flow restriction 180. After passing through the flow restriction 18a, the paint still under pressure passes through a pressure line 19 to a second flow restriction 18b which is similar in structure to the flow restriction 18a. Paint flowing past the second flow restriction 18b flows through still another line 21 to a third flow restriction 18c and thereafter through a line 22 and a back pressure regulator 23 to the pump inlet 11. The various pressure lines therefore provide a single recirculating loop through which paint flows from the pump outlet 12 back to the pump inlet 11 in which the three flow restrictions 18a, 18b, and 180 are connected in series in the recirculating loop. The back pressure regulator 23 determines the exit pressure from the recirculating loop and, consequently, determines the pressure maintained in the recirculating loop.

The system also includes a supply line 24 which connects the pump 10 to a supply of paint schematically illustrated by the container 26. In addition, a bleed line 27 and bleed valve 28 are provided for bleeding the system to eliminate air therein and to facilitate flushing of the system.

Three similar airless spray guns 29a, 29b, and 29c are respectively connected in the system adjacent the associated flow restrictions 18a through 180. Each spray gun is provided with a supply line 31 which connects through a shutoff valve 32 to the recirculating loop immediately upstream from the associated flow restriction. A return line 33 connects each spray gun through a shutoff valve 34 to the loop immediately downstream from the associated flow restriction. Consequently, each spray device is connected in parallel with an associated flow restriction and each spray gun and associated flow restriction assembly is connected in series with the other assemblies in the recirculating loop.

FIG. 2 illustrates the structural detail of the back pressure regulator 22 and its associated apparatus. Return flow passing through the line 23 enters a fourway fitting 36 and is connected through a fitting 37 to the body 38 of the back pressure regulator 23. A pressure gage 39 is also connected to the fitting 36 to provide a visual indication of the back pressure maintained by the back pressure regulator 23. The bleed valve 28 also connects with the fitting 36 and in normal operation, it is maintained closed as illustrated. The function of the bleed valve 28 is discussed in detail below.

The inner end of the fitting 37 is provided with a valve seat 41 adapted to be engaged by a ball valve 42 carried by a valve stem 43. The valve stem is inturn carried by an adjusting stem 44 which is threaded into a gland nut 46 mounted on the body 38. A spring 47 extends between a thrust member 48 and the valve stem 43 providing a force which resiliently urges the ball valve 42 toward the seat 41. The value of the spring force is adjusted by threading the adjusting stem 44 either inward or outward with respect to the body 38.

When the pressure of the returning fluid upstream of the valve seat 41 reaches a pressure determined by the force of the spring 47, it overcomes the action of the spring and causes the valve element 42 to lift away from the seat 41 and permits return flow to the inlet 11 of the pump. On the other hand as flow occurs and pressure drops, the spring overcomes the pressure-induced forces and moves the valve toward the seat to throttle the flow. Consequently, the regulator automatically functions to maintain a return pressure, the value of which is determined by the adjusted force of the spring 47. When the spray guns are operated, the recirculating flow is not sufficient to supply the pump and makeup flow is automatically drawn through the line 24 in the pump inlet 11.

FIG. 3 illustrates the structural detail of the flow restrictions 18. It should be understood that each of the flow restrictions 18a through 18c is provided with the structure illustrated in FIG. 3. The inlet line through which the paint under pressure is supplied to the flow restriction is connected through a fitting 51 to a tee 52. The shutoff valve 32 is also connected to the tee 52 through a fitting 53. The third port of the tee 52 is connected to a fitting 54 provided with a valve seat 56 at its inner end. In the illustrated embodiment, the fitting 54 forms part of a pressure regulator 57 which includes a spring 58 urging a ball valve 59 toward the seat with a force having a value determined by the adjustment of the regulator stem 60. This regulator operates to automatically produce a relatively low pressure drop as the paint flows therethrough but must be able to withstand the relative high pressure existing in the recirculating loop.

The shutoff valve 32 connects with the supply line 31 to the associated gun, and the return line 33 connects through the shutoff valve 34 to the regulator downstream from the ball valve 59. The flow passing through the valve seat 56 along with the return flow through the line 33 passes out of the assembly through the downstream line of the recirculating loop which is connected through a fitting 65.

In operation, the pump 10 pressurizes the paint and pumps it through its outlet 12 to the recirculating loop. After the paint passes through the heater 16, it reaches the first flow restriction 18a. The flow then is divided with most of the flow passing directly through the automatic pressure regulator 57 and the other part of the flow passing through the supply line 31 to the spray gun 29a and then back to the loop through the return line 33. During operation, the

valves

32 and 34 are open to permit flow to the gun. The pressure regulator 57 of the flow restriction 18a is adjusted to provide a relatively low pressure drop usually in the order of 3 to 5 psi. This pressure drop is adjusted to be sufficient to cause the required recirculating flow through the supply line to the gun 29a and back through the return line 33 from the gun. Preferably, the regulator 57 is adjusted to the lowest possible pressure drop which will produce the required flow rate through the circuit connecting the gun 29a.

When the

lines

31 and 33 are long or smaller in diameter or when the viscosity of the paint being pumped is high, the regulator 57 is adjusted to provide a higher pressure drop to insure proper flow to the gun. However, excessive pressure drops are not desirable since the power loss resulting from the flow through the regulator increases with higher pressure drops.

From the first spray gun 29a and flow restriction 18a, the paint under pressure continues through the line 19 to the second spray gun 29b and flow restriction 18b. Here again, the flow is divided with sufficient flow passing through the supply and return

lines

31 and 33 to insure proper recirculating flow to the gun 29b. The remaining flow passes directly through the regulator 57 of the second flow restriction 18b.

The flow then continues through the line 21 of the third flow restriction 180 wherein the flow is again divided with a portion of the flow passing through the supply and return

lines

31 and 33 to the gun 29c and the remaining flow passing directly through the regulator 57 of the third flow restriction 180.

The recirculating flow then passes through the line 22 and back to the inlet 11 through the back pressure regulator 23. The back pressure regulator 23 is adjusted to automatically maintain the desired recirculating pressure in the system. For example, the back pressure regulator is usually adjusted to maintain a back pressure in the order of 500 to 3,000 pounds when the system is used for operation of airless spray guns. Because the pressure drop occurring at each of the flow restrictions is relatively small, the operating pressure available at each spray gun is fully adequate, and the difference in pressure between the upstream guns and the downstream guns is insignificant.

The

shutoff valves

32 and 34 are provided to permit the removal of the connected supply and return lines from a particular operating station without requiring an interruption in the operation of the system. When such removal is required, the two associated

valves

31 and 34 are closed and the full flow in the system occurs through the associated pressure regulator 57. If such removal is likely to continue for a substantial period of time while the system continues to operate, it is preferable to adjust the associated pressure regulator to provide a minimum pressure drop so that the power loss created by flow through such flow restriction will be minimized.

Although automatic pressure regulators of the adjustable type illustrated are preferred at each of the painting stations, in some instances where such adjustment is not required a fixed orifice may be provided. In such a system, however, adjustability and automatic response is not provided.

The bleed valve and connected bleed line 27 are normally used only during the flushing of the system and during the start-up of the system. Flushing of the system is usually accomplished by connecting the line 24 to a source of solvent or the like while connecting the line 27 to return the solvent to such source. During the flushing operation, the bleed valve 28 is opened to allow a solvent to be drawn into the system for circulation therethrough followed by discharge of the solvent through the bleed valve 28 and bleed line 27.

The elimination of air from the system is accomplished in a similar manner in that the bleed valve 28 remains open during the initial operation of the pump to allow air to be bled out of the system. During such bleeding operation, it is customary to adjust the back pressure regulator 23 to provide a sufficient pressure drop to insure that the flow occurs out through the bleed valve 28. After bleeding is completed, the bleed valve 28 is closed and the recirculating flow occurs in the manner described above.

FIG. 4 illustrates a second back pressure regulator structure which may be substituted for the regulator 23 where desired. The back pressure regulator illustrated in FIG. 4 is disclosed and claimed in my U.S. Pat. No. 3,388,866 referred to above, and reference may be made to that patent for a more detailed description of the structure and mode of operation of such a regulator. When the regulator of the type illustrated in FIG. 4 is utilized, the return line 22 is connected through a tee fitting 6l'to the inlet 62 of the back pressure valve 63. A pressure gage 64 is mounted on the tee 61 to provide a visual indication of the back pressure present in the system. In this embodiment, the bleed valve 28 is connected to the valve 63 in a manner so that it is in direct communication with the return line 22. A pressure regulating assembly 64 is provided to adjustably regulate the back pressure in the line 22. Here again, a spring-biased ball valve 66 is resiliently urged toward engagement with a valve seat 67 with a force which is adjustable. This valve automatically operates to maintain a back pressure at a value of which is determined by the adjustment of the regulator 63. Downstream of the regulator 63, a second pressure reducing valve assembly 67 is provided. This regulating valve or assembly is not adjustable, but provides a ball valve 68 which is urged by a spring 69 toward a valve seat 71 with a constant spring force. Preferably, the valve assembly 67 is constructed so that it provides a minimum back pressure in the order of 10 to 20 pounds on the pressure regulator 63. Such minimum back pressure maintains a load on the seal 72 and functions to prevent leakage and induction of air into the system as described in my U.S. Pat. No. 3,388,866. The downstream side of the valve assembly 67 is connected to the inlet 1 l of the pump 10 along with the supply line 24.

This embodiment of a back pressure regulator has the advantage of providing greater reliability in preventing induction of air into the system and is particularly desirable in combination with the present system since the present system involves substantially greater volume in the recirculating loop and, therefore, greater bleeding problems than small systems employing a single gun and a small recirculating path.

Preferably, the lines l4, l7, 19, 21, and 22 are sized to provide a relatively low pressure drop during flow therethrough. The supply and return

lines

31 and 33 connecting the loop of each of the guns, however, may be smaller since all of the flow does not pass through such lines. Of course, smaller lines are desirable since they are easier to handle. For example, in systems in which the recirculating loop is 350 feet long or less and the liquid being sprayed has a viscosity of not more than 100 seconds Zahn 2, it is desirable to form the recirculating loop of lines having an inside diameter of at least one-half inch. Because the flow through the

lines

31 and 33 is not the full flow through the system, smaller diameter lines can and are preferably used for such portions of the system. When greater length is present in the recirculating loop or greater flow rates are required due to the presence of larger numbers of spray guns, the recirculating loop should be formed of larger diameter lines. Also, when higher viscosity materials are being handled, larger line diameters are required.

The present invention is also applicable to conventional air spray guns. In such a system, air spray guns are connected to the system in substantially the same manner as illustrated in FIG. 1. In air spray systems, the recirculating loop is normally maintained at a much lower pressure than in an airless spray system. In many instances, the working pressure of the paint supplied to an air spray gun is in the order of 75 psi. In such a system, the exit pressure from the recirculating loop is adjusted to maintain the required working pressure at the last gun in the loop. The upstream guns, because of the pressure drop at each spray station, therefore, are supplied with paint at higher pressures than required. If the system utilizes the relatively small number of guns so that the accumulated pressure drop through the recirculating loop is insufficient to produce problems at the upstream guns, a pressure reducing regulator is not provided. The guns are connected in the system in the manner illustrated in FIG. 1.

In instances where the accumulated pressure drop in the recirculating loop is such that is produces excessive pressure at the upstream guns, for example in systems employing a large number of guns in the single recirculating loop, a gun mounted pressure reducing valve may be provided to automatically reduce the pressure supplied to the guns to the desired value. FIG. illustrates an air spray gun 81 with such gun mounted regulator. The air spray gun is connected to the supply and return

lines

31 and 33 through a regulator 82 and is separately supplied with compressed air through an air line 83. The regulator includes a housing assembly 84 having an inlet 86 connected to the two

lines

31 and 33. The gun 81 is connected through an outlet passage 87 separated from the inlet 86 by a valve assembly 88. The valve assembly 88 includes a valve seat member 89 and a valve poppet 91 supported by a flexible diaphragm 92. A spring 93 urges the valve poppet toward the closed position illustrated, and an adjustable spring 94 urges the poppet valve toward an open position with a force which is adjusted by a valve stem 96.

This regulator operates automatically to maintain the outlet pressure to the gun at a pressure determined by the setting of the valve stem 96. When the outlet pressure drops below the required pressure, the force of the paint on the diaphragm 92 decreases allowing the spring 94 to open the valve. 0n the other hand, when the pressure in the outlet builds up to the regulating pressure, the force of the paint on the diaphragm causes the diaphragm to move the valve toward the seated position. The regulator therefore functions to reduce the pressure of the paint supplied to the gun from the pressure at the adjacent portion of the recirculating loop to the working pressure required by the gun.

In a recirculating system of the type illustrated generally in FIG. 1 in which air spray guns of the type illustrated in FIG. 5 are installed, the recirculating pressure is adjusted to supply at least the required working pressure at the downstream gun, for example psi. In such a system, the pressure at an upstream gun is higher due to the pressure drops occurring at the various units 18 and due to the pressure drop resulting from the resistance to flow provided by the lines. Consequently, the pressure at the upstream guns may be substantially higher than 75 psi and may be, for example, in the order of psi or more when the system is provided with a large number of guns. In such a system, the pressure reducing regulator 82 is adjusted to reduce the pressure supplied to the upstream guns to a pressure in the order of 75 psi.

Although preferred embodiments of this invention are illustrated, it is to be understood the various modifications and rearrangements of parts may be resorted to without departing from the scope of the invention disclosed and claimed herein.

I claim:

1. A liquid distribution system comprising pump means having an inlet and an outlet, a recirculating loop connected at one end to said outlet and at its other end to said inlet, said pump means operating to recirculate liquid under pressure through said loop, at least two stations each provided with a flow restriction connected in the loop in series with each other, at least two liquid dispersing devices each provided with a supply line and a return line, and means for connecting the supply line of each liquid dispersing device to said loop at the associated station upstream from its associated flow restriction and for connecting the associated return line to said loop at the associated station downstream from its associated flow restriction, each flow restriction being operable to permit flow therethrough while providing sufficient pressure drop between the associated supply and return lines to cause a flow through such lines.

2. A liquid distribution system as set forth in claim 1 wherein back pressure means are provided in said loop downstream from said stations.

3. A liquid distribution system as set forth in claim 2 wherein said back pressure means is an adjustable automatic regulating valve.

4. A liquid distribution system as set forth in claim 3 wherein said back pressure means is adjusted to maintain a pressure having a value which is many times the value of the pressure drop produced by said flow restrictions.

5. A liquid distribution system as set forth in claim 4 wherein said liquid dispersing devices are airless spray guns.

6. A liquid distribution system as set forth in claim 5 wherein each flow restriction is adjustable.

7. A liquid distribution system as set forth in claim 6 wherein each flow restriction is an automatic pressure regulating valve.

8. A liquid distribution system as set forth in claim 7 wherein said back pressure means includes two pressure reducing valves connected in series only one of which is adjustable.

9. A liquid distribution system as set forth in claim 2 wherein each flow restriction is an automatic pressure regulating valve.

10. A liquid distribution system as set forth in claim 9 wherein a shutoff valve is provided in each supply and return line allowing such lines to be removed while said loop is pressurized.

11. A liquid distribution system as set forth in claim 10 wherein a heater is provided in said loop upstream from said stations.

12. A liquid distribution system as set forth in claim 9 wherein said loop is formed of first conduit means and said supply and return lines are formed of second conduit means, said second conduit means having a substantially smaller internal cross sectional area than said first conduit means.

13. A liquid distribution system comprising a recirculating loop, pump means connected to pressurize liquid in said loop and recirculate such liquid around said loop, a plurality of liquid dispersing devices connected to said loop in series with each other, and a flow restriction connected in parallel with each dispersing device operable to cause a portion of the liquid flowing around said loop to bypass the associated dispersing device.

14. A liquid distribution system as set forth in claim 13 wherein each flow restriction is an adjustable automatic pressure regulating valve.

15. A liquid distribution system as set forth in claim 14 wherein said dispersing devices are airless spray guns.