US 3388866 A
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United States 3,388,866 CLOSED SYSTEM RECIRCULATING ASSEMBLY Gustave S. Levey, Houston, Tex., assigner to rlhe Spec- Flo Manufacturing Corporation, Houston, Tex., a corporation of Texas Filed Jan. 15, 1965, Ser. No. 425,808
7 Claims. (Cl. Z39- 127) This invention relates generally to liquid distribution systems and more particularly t-o a novel and improved recirculating pressure system for airless paint spraying devices and the like.
The present invention is directed to a recirculating system for paint spraying and the like, arranged to maintain a relatively high pressure in the paint at the spray gun normally in the order of tive hundred pounds per square inch to th-ree thousand pounds per square inch.
In order to maintain the desired pressure at the spray gun a system according to the present invention includes an adjustable back-pressure relief valve which remains closed unless the pressure in the return line and in turn at the spray gun is equal to the adjusted pressure and then opens to modulate the recirculating iiow, thus maintaining desired pressure. The system pump is provided with suiicient capacity to at least supply the maximum amount of paint required by the spray gun or guns at a pressure at least equal to the desired or adjusted pressure of the back-pressure relief valve. Normally the pump is selected to have excess capacity so that continuous recirculation is provided.
A heater is provided in the supply line from the pump to the spray gun which because of the recirculating flow maintains a uniform paint temperature even when the spray gun is intermittently operated. The relief valve is adjustable so that the user can select the correct operating pressure for the particular painting conditions and paint being used.
The adjustable back-pressure relief valve includes a valve element resiliently urged toward a seat by a spring, the compression of which is manually changed by turning an adjusting screw. A seal of the O-ring type seals against the adjusting screw preventing leakage. In order to maintain a positive pressure -on the seal to insure proper sealing, a fixed back-pressure relief valve is provided in the circuit downstream fr-om the adjustable back-pressure relief valve. This xed relief valve is totally enclosed and requires no external dynamic seals so leakage does not occur therein. It performs the dual function of preventing air from entering the pressure system when the system is initially pressurized and also maintains a positive pressure on the seal around the adjusting screw insuring proper sealing thereof during operation.
It is an important object of this invention to provide a novel and improved pressurized liquid recirculating system including adjustable back-pressure relief valve means and xed back-pressure relief valve means arranged to prevent air pollution of the system and leakage.
It is another important object of this invention to provide a recirculating pressure system for paint spraying and the like combining a pump, an adjustable back-pressure relief valve and separate pressure means for maintaining the discharge of the relief valve at a minimum pressure.
It is another important object of this invention to provide a novel and improved back-pressure system for recirculating pressure systems including an adjustable backpressure relief valve operable t-o prevent recirculating flow at pressures below an adjusted pressure in combination with a xed pressure back-pressure relief valve operable to maintain a minimum back-pressure in the adjustable valve.
3,385,866 Patented June 18, 1958 It is another important object of this invention to provide a novel and improved recirculating system for airless spray guns and the like, including a pump operable to provide an excess of liquid paint at operating pressures, an adjustable back-pressure relief valve operable to maintain adjusted operating pressures during normal operation, and a fixed back-pressure relief Valve operable to prevent discharge from the adjustable back-pressure relief valve at pressures below a minimum pressure.
It is still another object of this invention Ito provide a recirculating pressure system according to the last preceding lobject including heater means for controlling the temperature of the recirculating paint.
Further objects and advantages will appear from the following description and drawings wherein:
FIGURE 1 is a schematic illustration of the recirculating pressure system incorporating this invention; and
FIGURE 2 is an enlarged fragmentary view partially in section illustrating the structure of the back-pressure relief valve.
FIGURE 1 illustrates an embodiment of this invention utilizing a pump 10 operable to draw paint up an inlet line 15 from a paint container or drum |11. The pump illustrated is driven by a reciprocating air motor 12 and operates to supply paint under pressure to an outlet 13. The particular structure of the pump and its drive is disclosed in detail in my U.S. Patent No. 3,018,968. The particular pump structure is not critical to this invention except insofar as it cooperates with the remaining portions of the systems and it is merely necessary that the pump be operable to continuously provide a ow rate at least as great as that required for the operation of the spray gun at the required operating pressures of the spray gun.
The outlet 13 of the pump 10 is connected by a pres- 'sure line 14 to a heater 16 and from the heater 16 through a pressure line 17 t-o a spray gun 18. The spray gun 18 may be of any suitable type and reference may be made to my U.S. Patent No. 3,000,576, granted Sept. 19, 1961, for a detailed description of a preferred form of spray gun which may be used with a system incorporating this invention.
A return line 19 connects the spray gun 1S to a backpressure relief assembly 21 which discharges to the intake 23 of the pump 10. Preferably, the intake 23 is of the type which prevents mixing of the recirculated paint with the paint in the container 11 so that only the paint being pumped out of the container is heated.
The pump 10 operates to deliver paint at operating pressure with a volume at least equal to the volume Iof paint sprayed by the vspray gun 18 when the gun is operated. It should be understood that if desired more than one spray gun 18 may be connected to the pressure lines 17 Aand 19. In such installations the pump must have suflicient capacity for the combined operation -of the spray guns. The back-pressure relief valve assembly 21 in combination with the pump functions as a pressure regulator maintaining a pressure `at the spray gun equal to the operating pressure set by the adjustment of the 'back-pressure relief valve assembly.
Referring now to lFIGURE 2, the back-pressure relief valve lassembly 21 includes a main body 26 formed with an inlet chamber 27 and `au outlet passage 2S. The `upper end of the body 26 is formed with -a threaded opening 29 aligned with a bore 31 connecting the inlet chamber 27 and the 'outlet passage 28. An inlet port 32 is threaded to receive a fitting 33 connected through a T 34 4to the return line 19. Therefore, the recirculating flow through the return line is connected to the inlet chamber 27. A pressure gauge 36 is mounted on the T 34 adjacent to the back-pressure relief valve assembly so that the user can determine the operating pressure. A bleed port 37,
also open to the inlet chamber 27, is threaded to receive a bleed valve 38 which in turn is provided with a bleed hose 39.
A regulating valve assembly 41 includes fa v-alve body 42 threaded into the opening 29 and provided with 1a valve section 43 positioned Within the bore 31. A seal 44 prevents leakage therebetween. A valve seat element 46 is mounted in the valve section 43 and pressed against a seal 42S by .a threaded ring 47. A tubular Astern support i9 is threaded into the v-alve body 42 and is internally threaded adjacent to its outer end to receive the adjusting stern 51. An `O-ring 52, preferably formed of Teflon, provides a seal between the adjusting stem 51 and the inner wall of the stem support 49.
A ball valve 53 is carried by ka valve stem 54 which extends into 1and is guided by the Walls of an axial bore in the yadjusting stem 51. -A spring 56 extends between a thrust member 57 seated against the end face of the adjustable stem 51 and the valve stem 54 resiliently urging the valve stem fand in turn the ball valve 53 ltoward 4the valve seat with a resilient force which is the function of the adjusted position of the adjusting stem. Therefore, the pressure in the inlet kchamber 27 required to lift the ball valve 53 away from the seat 46 to allow flow through the device is a function of the adjusted position of the stem 51. If higher pressures are required the stem is rotated in ra clockwise direction to screw it down into the body Iand if lower pressures are required anticlockwise rotation of the stem 51 causes it to reduce the spring force. Seals 55 and 55a are provided between the stern support 49, the valve body 42, and the body 26 of the assembly.
In order to insure that 4a minimum back-pressure is provided in the outlet passage 27 a fixed relief valve `assembly 58 is threaded into Ian outlet opening 59. The assembly S includes a body 61 having a valve seat '62. A swivel nut 63 is mounted on the body 61 and threads onto a swivel fitting 64 mounted on the intake 23. A spring 66 extends between -a shoulder on the swivel fitting 64 and a ball valve 67 resiliently `urging the ball valve against the seat 62. Preferably, the elements of the fixed relief valve assembly are proportioned so thaty a pressure in the outlet passage 28 is in the order of twenty-five pounds per square inch before `the ball valve 67 `is lifted off of the seat 62 to allow flow. Therefore, the fixed relief valve Iassembly maintains a minimum pressure in the order of twenty-five pounds per square inch on the low pressure side of the adjustable relief valve t1 thereby maintaining a positive pressure on the seal 52 to insure its proper operation. Also, when the system is first pressurized lair in the system is not permitted to flow into the system from the relief valve, even when vacuums occur.
In operation the pump is started with the bleed valve 38 open to permit the air to escape from the system as the paint flows through the lines to `the spray gun 18 and back to the relief valve. When all of the air is out of the lines and any required flushing is completed the bleed valve 38 is closed yand continued pumping causes the pressure in the lines, the Igun and the inlet chamber 27 to build up to a pressure determined by the setting of the `adjustable stem 51. During the bleeding and normal operation of the system the pump produces a vacuum at the intake 23 since the paint level in the container is below the intake 2-3. During bleeding land initial pumping the valve assembly 58 remains closed and the vacuum Iat the intake 23 is not ytransmitted to the valve :assembly 41.
As soon as operating pressure is reached the ball valve 53 is lifted away fro-m `the seat and the paint Iecircul-ates through the system with the pressure in the lines 14, 17 and 19, and in the spray gun 18 maintained at operating pressure. The pressure in the outlet passage 28 is maintained yat a minimum of Iabout twenty-five pounds per square inch due to the -action of the ball valve `67.
If the fixed relief assembly 58 were not provided a vacuum would occur in the outlet passage 28. This vacnum or low discharge pressure, which would occur in the absence of the fixed pressure relief valve assembly 58, would cause working on the seal 52 and would result in leakage. However, back-pressure relief valve 58 prevents the intake vacuum of the pump from being transmitted lto the adjustable relief valve assembly 41 Iand leakage at the seal 52 does not occur.
Although a preferred embodiment of this invention is illustrated, it is to be understood that various modifications and rearrangements of parts may be resorted vto without departing from the scope of the invention as defined in the following claims.
What is claimed is:
1. A liquid pressure system comprising a source of liquid, a pump operable to pressurize liquid from said source and deliver it to an outlet, a liquid dispersing device, a supply pressure line connecting said outlet to said dispersing device, and return means connected to said dispersing device operating to return excess liquid for recirculation by said pump, said return means including first relief valve means adjustably operable to control operating pressure at said dispersing device, second relief valve means operable to restrict How from said first relief valve means when the discharge pressure therefrom is below a predetermined minimum pressure, and a manually operable bleed valve in said return means upstream from said second relief valve means.
2. A recirculating pressurized system comprising a source of liquid at substantially atmospheric pressure, a pump having an intake connected to said source and being operable to deliver liquid under pressure to an output, a dispersing device, pressure lines connecting said output to said dispersing device and said dispersing device to said intake, adjustable back-pressure means in said pressure lines between said dispersing device and inlet operable to restrict fiow therethrough when the pressure of liquid at said dispersing device is less than a predetermined adjusted presure; said back-pressure means including an external control for adjusting the value of said predetermined pressure, and a seal preventing leakage therealong, secondary back-pressure means in said lines between said adjustable back-pressure means and intake operable to restrict flow therethrough when the pressure in said secondary back-pressure means is below a minimum pressure, said minimum pressure being above atmospheric pressure and below saidpredetermined pressure, said secondary back-pressure means being free of external dynamic seals.
3. A fiow control assembly for use in recirculating paint spray systems comprising a body formed with an inlet adapted to be connected to a recirculation line, an outlet in said body, a relief valve in said body preventing flow between said inlet and outlet when closed and permittingflow therebetween when open, and adjusting stem threaded into said body from the exterior thereof and movable toward and away from said valve, a seal preventing leakage along said adjusting stem, a spring between said releaf valve and said adjusting stem operable to urge said relief valve closed with a force determined by the position of said adjusting stem in said body, pressure in said inlet opening said relief valve when the pressure therein reaches a pressure determined by the position of said adjusting stem relative to said body and a pressure responsive ow control restricting flow from said outlet at pressures below a predetermined minimum pressure, said pressure responsive flow control being free of external dynamic seals.
4.' A flow controly assembly for use in recrculating paint spray systems comprising a body formed with an inlet adapted to be connected to a recirculation line, an outlet in said body, a rst relief valve in said body preventing ow between said inlet and outlet when closed and permitting flow therebetween when open, an adjust- U,assess ing stem threaded into said body from the exterior thereof and movable toward and away from said first relief valve, a seal preventing leakage along said adjusting stern, a spring between said first relief valve and said adjusting stern operable to urge said rst relief valve closed with a force determined by the position of said adjusting stern in said body, pressure in said inlet opening said first relief valve when the pressure therein reaches a pressure determined by the position of said adjusting stem relative to said body, and a second relief valve mounted in said outlet, said second relief valve including a spring-hiased valve element restricting ow from said outlet at pressures below a predetermined minimum pressure, said second relief valve being free of external dynamic seals.
5. A ow control assembly for use in recirculating paint spray systems comprising a body formed with an inlet adapted to be connected to a recirculation line, a bleed valve mounted on said body connected to said inlet, an outlet in said body, a relief valve in said body preventing flow between said inlet and outlet when closed and permitting flow therebetween when open, an adjusting stem threaded into said body and movable toward and away from said valve, a seal preventing leakage along said adjusting stem, a spring between said relief valve and said adjusting stem operable to urge said relief valve closed with a force determined by the position of said adjusting stern in said body, pressure in said inlet opening said relief valve when the pressure therein reaches a pressure determined by the position of said adjusting stern relative to said body, and a pressure responsive ow control mounted in said outlet restricting ilow from said outlet at pressures below a predetermined minimum pressure.
6. A paint spray system comprising a source of paint, a pump operable to produce a vacuum at its intake to withdraw paint from said source and deliver paint under pressure to an outlet, a spray gun, a supply pressure line connecting said outlet to said spray gun, and return means connected to said spray gun operating to return excess paint to the intake of said pump, said return means including rst relief valve means adjustably operable to control operating pressure at said gun, second relief valve means operable to prevent flow from said rst relief valve means when the discharge pressure therefrom is below a predetermined pressure, and bleed valve means in said system ahead of said relieffvalve means, said bleed valve means being operable to an open condition to bleed air from said system and being closable to seal the pressure side thereof.
7. A flow control assembly as set forth in claim 6 wherein said iirst relief valve includes an adjusting member extending into said body from the exterior thereof and a seal preventing flow along said adjusting member, and said second relief valve is free of external dynamic seals.
References Cited UNITED STATES PATENTS 152,765 7/1874 Perkes 137-512 1,505,331 8/1924 Gold 239-533 1,934,296 11/ 1933 Dorner 239-570 2,461,766 2/1949 Peeps` 239-127 2,754,228 7/1956 Bede 239-124 2,729,228 l/ 1956 Stevenson 137-199 2,578,334 12/1951 Ashbaugh 137-506 3,000,567 9/1961 Levey et al. 239-499 3,018,968 1/1962 Levey et al. 239-127 FOREIGN PATENTS 807,165 1/1959 Great Britain.
EVERETT W. KIRBY, Primary Examiner.