US 3816025 A
A fluid circulation system for a paint spray installation or the like with a recirculating primary fluid circuit from a reservoir through the pump to the work stations and back to the reservoir. A secondary fluid circuit connected downstream of the pump through a safety control and return to the reservoir, with the safety control functioning to shut off the pump when a malfunction occurs in the primary circuit. A pressure sensitive valve for use as the safety control and incorporating a self-cleaning valve chamber suitable for use with a paint recirculating system.
Description (OCR text may contain errors)
United States Patent [191 ONeill 1 3,816,025 June 11, 1974 1 PAINT SPRAY SYSTEM  Inventor: William J. ONeill, 1504 Monlemar.
Palos Verdes Estates, Calif. 90274  Filed: Jan. 18, 19 73 21 Appl. No.: 324,571
Primary Examiner-William L. Freeh Assistant ExaminerRichard Sher Attorney, Agent, or Firml-larris, Kern, Wallen & Tinsley  ABSTRACT A fluid circulation system for a paint spray installation or the like with a recirculating primary fluid circuit from a reservoir through the pump to the work stations and back to the reservoir. A secondary fluid circuit connected downstream of the pump through a safety control and return to the reservoir, with the safety control functioning to shut off the pump when a malfunction occurs in the primary circuit. A pressure sensitive valve for use as the safety control and incorporating a self-cleaning valve chamber suitable for use with a paint recirculating system.
,5 Claims, 4 Drawing Figures RESEI? VOIR WORK 5TH T/ONS PAINT SPRAY SYSTEM This invention relates to recirculating fluid systems such as are used in large paint spray installations, and in particular, to a new and improved safety control system.
In a typical installation in an automobile assembly plane or the like, paint is maintained in constant circulation through long pipe lines between a reservoir and pump and one or more paint spraying stations. Constant circulation or recirculation of the fluid is desirable because of the nature of the fluid. For example, the pigments in paints tend to sludge and settle out and the paint tends to thicken when the fluid is not moving. Therefore present day systems maintain the paint in agitation and in motion and this is accomplished witha recirculating system. Also, it is highly advantageous to maintain continuous control of the paint at one central reservoir to obtain constant color control.
These recirculating systems with long conduits between the reservoir and pump and the work stations fluid with the likelihood of dumping large quantities of fluid out the openline, creating a severe fire hazard and entailing considerable loss'of material as well as time and expense in clean up.
Pump controlsoperated by pressure sensing devices in the recirculating fluid line have been utilized in the past in an attempt to sense the occurence of a line break for the purpose of shutting off the pump. However these systems have not been satisfactory. In a typical prior art installation the pressure sensing device is placed in the recirculating line between the pump and the work stations. If a break occurs in the line downstream of the pressure sensing device, i.e., between the pressure sensing device and the reservoir, the pump will produce a highervolume of output because of the drop in back pressure in the recirculating line and this higher volume of fluid flow through the pressure sensing device will maintain the system on.
If the reservoir becomes empty, the pump will continue to pump air through the pressure sensing device at a rate sufficient to maintain the system on and will fill the line with air.
The present invention provides a solution to this severe problem in the controlof recirculating fluid systems. Recirculation of the fluid is maintained through a conventional primary fluid circuit comprising the reservoir, pump, one or more work stations, and back pressure valve. Pressure sensing isachieved by meansof a secondary fluid circuit connected between the pump outlet and the back pressure valve outlet providing for circulation of a portion of the pumped fluid through the secondary circuit. A pressure sensor inthe secondary circuit provides the control for shutting off the pump.
Another problem encountered in the prior control systems is that of sludging or pigment buildup or retention in the pressure sensor despite the continuous recirculation of the fluid. This problem occurs on a longterm basis and is not immediately apparent in a new installation. However itis a severe problem, since the installation is designed to be a safety system and unless periodically cleaned and tested, there is no way of knowing whether or not the sensing unit is operating properly. It has been found in the past that the pressure sensors will operate satisfactorily for a period of time and then become fouled and unsatisfactory. The present invention incorporates a new and improved fluid chamber for the pressure sensing device.
Other objects, advantages, features and results will more fully appear in the course-of the following description. The drawing shows and the description describes the presently preferred embodiment of the invention which is given by way of illustration or example.
In the drawing:
FIG. 1 is a schematic diagram of a fluid circulating system incorporating the presently preferred embodiment of the invention;
FIG. 2 is a side view of a safety valve incorporating the presently preferredpressure sensing unit of the invention; a
FIG. 3 is a side view partly in section taken along the line 3-3 of FIG. 2; and
FIG. 4 is a sectional view taken along the line 4--4 of FIG. 2.
The system as shown in FIG. 1 includes a paint supply reservoir connected to the inlet of a pump 11 by a conduit 12. The pump output is connected to a plurality of work stations 13 by a line 14 which continues onto a back pressure valve 15 and a line 16 to the reservoir 10. A typical work station would be a paint spray booth, with the line 14 providing a supply of paint to the spray gun, with the compressed air for the spray gun being provided by a separate source'not shown.
The pump 11 may be driven by any conventional power unit'and in the embodiment of FIG. 1, the pump is driven by an air motor 20 provided with compressed air from an air supply 21 through an on-off valve 22. In an alternative embodiment, the pump could be driven by an electric motor controlled by'an on-off switch in place of the on-off valve 22.
' The reservoir 10, the pump 11, the line 14, the back pressure valve 15, and the line 16 provide a primary fluid circuit in which the paint from the reservoir is continuously recirculated past the work stations, this being a conventional fluid circulating system.
The valve 22 is turned to the on or open position when it is desired tostart paint circulation. A safety circuit is provided for turning the valve 22 to the off position when a break occurs in the primary circuit. The
safety system includes a flow reducer connected to the line 14 at point 31, a pressure sensor 32, and a back pressure valve 33, with the back pressure valve outlet connected to the line 16 at point 34. The flow reducer 30, the pressure sensor 32, and the back pressure valve 33 form a secondary circuit for fluid circulation for directing a portion of the pump output through the pressure sensor 32. Preferably, a suction tee is provided at the point 34 to insure that fluid does not back up from this point to the back pressure valve 33.
A preferred apparatus for the pressure sensor 32 and on-off valve 22 is shown in FIGS. 2-4. The pressure sensor includes a housing with a chamber 41 and a flange 42. A yoke 43 with a mating flange 44 is mounted on the housing by screws 45, with a diaphragm 46 therebetween. The diaphragm may be made of a conventional diaphragm material such'as a synthetic rubber, and may be protected from the fluid in the chamber 41 by a sheet 47 of a material resistant to The valve 22 is mounted on the yoke 43 by a threaded shaft 50 which passes through an opening'in the yoke,'with nuts 51, 52 locking the valve in place. These nuts permit adjustment of the position of the valve with respect to the diaphragm. The valve 22 may be conventional in design and includes a passage interconnecting an inlet 53 and an outlet 54, with a valve member 55 engagable with a valve seat for blocking flow through the valve. The valve member 55 is carried on a shaft 60 and is urged downward to the closed position by a spring 61.
A push rod 64 is slideably positioned in an inne bracket 65 of the yoke 43 between a cap 66 resting on the diaphragm and a spherical tip 67 of'a lever 68, the lever being typically mounted on the yoke 43 by a pin 69. A spring 70 is positioned about the push rod 64, urging the cap 66 and diaphragm 46 downward.
The chamber 41 of the housing 40 is in the form of a trough with a rounded bottom 74, with the longitudinal'axis of the trough parallel to the plane of the diaphragm. The chamber inclues an inlet passage'75 at one end of the trough and an outlet passage 76 at the opposite end of the trough, with the axes of the inlet and outlet passages perpendicular to the axis of the trough and preferably in planes parallel to the diaphragm, as illustrated in the drawing. Conduits 77 are connected at the inlet and outlet passages by conventional fittings 78.
This chamber configuration eliminates discontinuities and shoulders encountered in the chambers of conventional pressure sensitive safety valves. Further, with this chamber configuration, a swirling or scouring action is produced in the fluid as it flows. through the chamber and thereby prevents particle retention or particle buildup. This was a major problem in the earlier straight through flow chambers in paint recirculating systems where substantial pigment build-up occurred in a. relatively short time. On some occassions the safety valves were operating satisfactorily for only a few hours before they had to be shut down for cleaning.
- in operation, thelever=68 is pushed downward to move the valve stem 60 up and open the valve 22. This energizes the motor 20 which drives the pump 11 and circulates fluid through the primary circuit and through the secondary circuit. Fluid flowing through the chamber 41 exerts an upward pressure on the diaphragm 46 and maintains the valve 22 in'the open condition under normal operating pressures. If the pressure in 'the chamber 41 falls below a predetermined value as controlled by the'parameters of the unit, the spring forces will overcome the chamber pressure, move the diaphragm downward and permit the valve to close, shutting off air supply to the air motor. The same mode of operation will occur if an electrical switch is substituted for the valve 22.
It is not necessary that the unit of FIGS. 2-4 be adjustable for operating at various pressures. This is readily taken care of by adjusting the flow reducer 30 and the back pressure valve 33. The amount of flow through the flow reducer 30 is adjusted so that only a small portion of the pump output flows through the secondary circuit. Typical systems have volume flow rates in the range of to 18 gallons per minute. Present day automobile body paints have as much as six pounds of pigment per gallon and a flow velocity of 70'feetper minute is required in order to maintain the pigment in suspension. The volume flow rate in the secondary circuit'for such a system will be quite small, typically less than a pint per minute. At start up, the flow reducer'30 and back pressure valve 33 are initially closed. The pump is energized by actuating the lever 68 and the flow reducer is cracked open, permitting some flow into the chamber of the pressure sensing device 32.
This will maintain the pump on and the lever 68 can be released. The back" pressure valve is. then opened a small amount to where some downward movement of the rod 64' is noted. This indicates that the pressure sensing device is in a balanced condition, and a slight drop in-line pressure now will be sufficient to shut the system off.
I claim: i
1. In a fluid circulating system for paint spraying or the like, including a fluid supply reservoir, a fluid pump, at least one work station, and a first back pressure valve connected in a recirculating primary fluid circuit, theimprovement comprising in combination: acontrol for turning said pump on and off; and a secondary fluid circuit comprising an adjustable flow reducer, a sensing unit and a second adjustable back pressure valve connected between a first point in said primary circuit between said pump and work station, and a second point in said primary circuit between said first back pressure valve and reservoir, for circulating a selectable portion of the pumped fluid through said sensing unit and setting'said sensing unit in a pressure balanced condition for a particular rate of flow in said primary fluid circuit, said sensing unit including means for actuating said control to turn said pump off when the fluid pressure in said sensing unit falls below a predeter- .mined value. 2.'A system as defined in claim 1 wherein said control and sensing unit comprise a unitary structure with a pressure chamber, a diaphragm for said pressure chamber, a pump on-off unit, a push rod between said on-off unit and said diaphragm, spring means urging said onoff unit-and diaphragm to the off condition, and means for setting said on-off unit and diaphragm in the on condition, with said pressure chamber in said secondary fluid circuit.
3. A system as defined in claim 2 wherein said pressure chamber includes a trough with its longitudinal axis substantially parallel to the plane of said diaphragm and having a rounded bottom opposite said face, and inlet and outlet passages at opposite ends of said trough and substantially perpendicular to said longitudinal axis with said inlet and outlet passages in a plane substantially parallel to the plane of said diaphragm.
4. A system as defined in claim 1 including a suction tee connected in said primary circuit at said second point between said first back pressure valve and reservoir, with said secondary circuit connected at said suction tee, with the tee oriented such that the fluid flow of said primary circuit through said tee induces the fluid flow in said secondary circuit to said tee.
5. A method of protecting a paint spray recirculating system having a paint supply reservoir, a fluid pump, at least one work station, and a back pressure valve connected in a primary paint circuit, including steps of:
continuously recirculating paint through the primary paint circuit;
continuously bypassing a small portion of the recirculating paint through a secondary paint circuit from the pump to the reservoir;
continuously sensing the pressure in the secondary UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,816,025 Dated June 11, 1974 Inventor(s) William J. O'Neill It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:
On the Title page, Inventor's address should read:
--- 25314 Village 25 Camarillo, Calif. 93010 Signed and Scaled this Twenty-Six h D of September 1978 [SEAL] A ttest:
DONALD W. BANNER RUTH C. MASON Arresting Officer Commissioner of Patents and Trademarks