Abstract:
The invention is a method of monitoring a filter for absorbing paint particles produced during spray painting with a spray gun in a paint spray booth coupled to an exhaust pump, the method includes the steps of: 1) installing a filter between the booth and exhaust pump; 2) determining the initial pressure drop across a filter prior to use of the spray booth; 3) determining the maximum allowable pressure drop for the filter prior to the requirement that spraying activities must be terminated by adding the initial pressure drop of the filter to the maximum allowable increase in pressure drop across the filter before the of spraying activities must be terminated; 4) providing a warning when a first portion of the maximum allowable pressure drop is reached; and 5) preventing the use of the spray gun when a second portion, greater than the first portion, of the maximum allowable pressure drop is reached.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to the field of paint spray booths and, in particular, to a filter monitoring system for the spray booth that insures that the maximum available filter life is obtained. 
     2. Description of Related Art 
     Environmental regulatory agencies requires self-disclosure of violations to the appropriate Government Agency. Heavy fines are applied to companies that fail to meet the clean air standards. Under this law, paint spray booths equipped with filter systems are closely monitored to prevent over spray from reaching the atmosphere. In addition, the operator within the booth must be protected. Thus spray booth monitoring systems are available that provide alarm signals when the filter(s) is near the end of its useful life. 
     For example, in U.S. Pat. No. 5,356,334 “Apparatus And Method For Airborne Particulate Booth” by R. D. Gray uses sensors to monitor the pressure drop across filters. A signal is provided when the filters are near the end of their useful life. The apparatus is primarily designed for use in powder type spray operations. Therefore, it uses a filter pulsing system to periodically unclog the filter(s). When the pulse rate becomes almost constant, the alarm signal is activated. The system also provides for signaling when the end of filter life is approaching and shutting down the system should the filter become clogged to a point that it is ineffective. However, it is not desirable to completely shut down the spray booth. There may be a considerable amount of particulate matter still in the spray booth. 
     Another example can be found in U.S. Pat. No. 5,554,416 “Automated Air Filtration And Drying System For Waterborne Paint And Industrial Coatings” by F. G. Scheufler, et al. Pressure sensors upstream and downstream of the main filter are used to monitor pressure drop across the filter. As the pressure drop increases, signaling filter loading, a signal is sent to a blower to increase the flow rate to compensate therefore. A series of lights illuminate as the blower speed increases indicating filter condition. Thus adequate warning is provided to the operator to turn off the spray booth prior to complete filter failure. However, such a system depends upon the alertness of the operator to shut down the spray booth. Thus there is always a possibility that of operator error. In addition, the Scheufler, et al. system does not compensate for initial filter condition. 
     Another example can be found in Published Patent Application No.: US 2002/0062788 Al “Apparatus And Method For Configuring Spray Coating Application Systems” by D. M. Czech, et al. Here a system to remotely monitor the performance of a spray-coating booth via the Internet and the like, however, no specific mention of filter monitoring is made. 
     U.S. Pat. No. 6,168,646 “Flow Rate Control Of Temperature Controlled Fluids” by W. L. Craig, et al. discloses the use a filter assembly including a first roller of fresh filter material and a take up roller. The filter is disposed across the airflow path. As the exposed portion of the filter becomes clogged, the pressure drop there across causes the exposed portion of the filter to distort. This causes the exposed portion of the filter to make contact with a switch, which activates the rollers causing the take up roller to pull unexposed filter material off the first roller across the flow path and winding up the clogged portion on the take up roller. However, no warning device is provided for indicating that the last portion of the filter is clogged. 
     U.S. Pat. No. 6,040,777 “Device And Process For Indicating The Exhaustion Of A Fan Filter” by K. Ammann, et al. also discloses a device for determining filter life. However, the filter is designed to remove gases from the air. A gas detection device measures the level of the gas and if it rises to a predetermined level, indicating filter saturation, an alarm signal is provided. 
     Thus it is well-established practice to monitor filter performance in a paint spray booth and the like. However, none of the prior art discloses a system that takes into account the initial pressure drop across a new filter may very from filter to filter. For example consider a filter where the end of useful life occurs when the pressure drop increase across the filter is 3 PSI. If the initial pressure drop reading is 0.5 PSI, then a significant portion of the filter life is lost. Furthermore, none of the prior art devices constantly monitors the pressure drop across the filter, so that any unusual increases or decreases that indicate a problem in the spray booth can be investigated. None of the prior art devices address the problem of particulate matter that maybe still in the air after the spray booth has been shut down. 
     Thus, it is a primary object of the invention to provide a filter monitoring system for a spray painting booth. 
     It is another primary object of the invention to provide a filter monitoring system for a spray painting booth incorporating a system to indicated filter status. 
     It is a further object of the invention to provide a filter monitoring system for a spray-painting booth that provides automatic shut off of the operation of the spray gun at a predetermined percentage of the filter life. 
     It is a still further object of the invention to provide a filter monitoring system for a spray painting booth that takes into account the initial pressure drop across the filter prior to establishing the expected life of the filter. 
     It is another object of the invention to provide a filter monitoring system for a spray painting booth that provides a warning if there is a discrepancy between the reading at the end of one paint spraying shift and the beginning of another. 
     SUMMARY OF THE INVENTION 
     A typical paint spray booth comprises a closed off room having a bank of primary filters at one end. A blower assembly is in communication with the filters and draws air from the room through the primary filters. The output from the blower is coupled to one or more secondary filters. Thus with an operator spraying parts within the room by means of an air powered type spray gun, excess paint particles are collected on to the primary filters and vapors and smaller particles are collected on the secondary filters. 
     The invention is a method of monitoring a filter (either the primary or secondary filters or both) for absorbing paint particles or vapors produced during spray painting with a spray gun in a paint spray booth coupled to an exhaust pump. The method comprising the steps of:
         1. Installing a filter between the booth and exhaust pump.   2. Determining the initial pressure drop across a filter prior to use of the spray booth. This is accomplished with the use on pressure sensors on either side of the filters.   3. Determining the maximum allowable pressure drop for the filter prior to the requirement that spraying activities must be terminated by adding the initial pressure drop of the filter to the maximum allowable increase in pressure drop across the filter before the spraying activities must be terminated.   4. Providing a warning when a first portion of the maximum allowable pressure drop is reached; and   5. Preventing the use of the spray gun, while keeping the blower in operation when a second portion, greater than the first portion, of the maximum allowable pressure drop is reached.       

     Preferably, the spray gun is pneumatically (air) powered by pressurized air via a line. A solenoid valve is mounted therein for controlling the airflow there through coupled to the spray gun. Thus the step of preventing the use of the spray gun, while keeping the blower in operation, when a second portion, greater than the first portion, of the maximum allowable pressure drop is reached, includes the step of actuating the solenoid valve to the closed position cutting off airflow to the spray gun. 
     The first portion of the filter life is about 80 percent of the maximum allowable pressure drop, but can be adjusted depending on operation&#39;s requirements. The second portion is 90 percent of the allowable pressure drop, but can adjusted depending on the operation&#39;s requirements. It is preferred that the pressure transducers be connected to a computer with a display terminal. Thus the method further includes the step of monitoring the pressure drop across the filter on the display terminal. In addition, method also includes the step of sending an alarm signal to the computer and displaying the alarm signal on the display terminal. 
     The novel features which are believed to be characteristic of the invention, both as to its organization and method of operation, together with further objects and advantages thereof, will be better understood from the following description in connection with the accompanying drawings in which the presently preferred embodiment of the invention is illustrated by way of example. It is to be expressly understood, however, that the drawings are for purposes of illustration and description only and are not intended as a definition of the limits of the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a top view of a typical paint spray booth 
         FIG. 2  is a side view of the paint spray booth illustrated in  FIG. 1   
         FIG. 3  front view of a panel attached to an outer wall of the spray booth shown in  FIG. 2  taken along the arrow  3 . 
         FIG. 4  is a flow chart of the computer program for monitoring spray booth filters. 
         FIG. 5  is a typical computer screen for monitoring filter performance. 
         FIG. 6  is a typical computer screen for changing a filter. 
         FIG. 7  is a flow chart of the portion of the computer program for calculating the useful life of the filter. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring to  FIGS. 1 and 2 , the spray booth, generally indicated by numeral  10 , includes an air powered spray gun  12  coupled to a line  14 , which in turn is connected to a paint spraying apparatus  16 . The apparatus  16  includes a normally closed valve  20  that controls the flow of air to the spray gun  12 . It should be noted that, while a pneumatically powered spray gun is illustrated, any spraying system could be used in the booth  10 . Mounted at end  22  of the booth  10  is a bank of primary filters  24 , having first sides  25 A and second sides  25 B, designed to absorb particulate matter. The filters  24  divide the booth into a spraying area  26 A and small chamber  26 B. A blower  28  having and inlet duct  30  connected to the chamber  26 B and an exhaust duct  32  coupled to a secondary filter  34 . The secondary filter is a High Efficiency Particulate Air Filter (HEPA) that insures that small particulate matter is removed from the air prior to reaching the ambient. Thus during paint spraying operations the blower  28  draws the particulate matter through primary filters  24  and pumps the remaining small_particulate matter laden air through the secondary filter  34 . Such paint spray booths are in wide use throughout most industries. It is critical that a filter monitoring system be incorporated in order to meet Government mandated personnel safety and air quality requirements. The failure to do so can and will result in large fines and or criminal prosecution. 
     The filter monitoring system includes a manometer device  39  having pick up ports  40  and  42  positioned on each side  25 A and  25 B of the filter  24  and a second manometer device  43  having pickup ports  44  and  46  on each side of the filter  34 . The manometers  39  and  43 , as well as valve  20  are connected to a remotely located computer assembly  48  having a computer  49  display terminal  50  and keyboard  52 . Referring to  FIG. 3 , the manometer  40  includes a panel  56  having digital gage  57 A and analog gage  57 B. The panel  56  further includes a switch  58  for manually controlling valve  20 . In addition, a keypad  60  is provided to prevent unauthorized use. Thus should the computer system, to be subsequently discussed, fail, the valve  20  can be manually controlled. The blower  28 -control panel (including on/off switch) is indicated by numeral  59 . 
       FIG. 4  is a Process Flow Chart for the computer program to monitor filter performance. It comprises the following steps: 
     Step  60  Log in or out—The operator swipes their identification card or manually enters the data. When the operator logs on, the screen as depicted in  FIG. 5  appears on the terminal screen. The screen includes the following displays:
     Logged On and Off Indicator Light  60     Spray gun Air Condition Light (valve  20  open or closed)  62     Operator Name Window  64     Acknowledge Alarms Button  66  (Touch Screen Indicator)   Details and New Filter  68  (transfers to  FIG. 6  screen) which will be   subsequently discussed. Also a touch screen indicator.   Primary Filter Digital Read Out  70     Primary Filter Gauge  71     Secondary Filter Digital Read Out  72     Secondary Filter Gauge  73     Message Screen  74     Screen Setting Button  76     Log IN/OUT Button  77     Exit Program Button  78 .   

     Step  79  Determination Of Pressure Drops. If there is no pressure drop, the blower  28  is not running. Then the system automatically goes back to step  60 . If pressure drops are sensed, then to Step  80 . 
     Step  80  Enter Data—Time, Operator name and ID are recorded as well as an initial pressure drop reading across filters  24  and  34 . 
     Step  81  Determination If Operator Logging On Or Off—The existing pressure drop across the primary and secondary filters, is determined and recorded. If there is no pressure drop, then to step  83 . If there is a pressure drop, then to Step  84 . 
     Step  83  Shut Off Valve  20 —If Valve  20  is open, a signal is sent to the valve causing it to shut down cutting off air pressure to spray gun  12 . 
     Step  84  Activate Solenoid Valve  20 —A signal is sent to the valve  20  causing it to open and allow operation of the spray gun  12 . 
     Step  86  Monitor Pressure Drops—The program continues to monitor the pressure drops across the primary and secondary filters,  24  and  34 . These pressure drops are indicated on the Screen in FIG.  4 . 
     Step  88  Check Accuracy—The pressure drop determination across the primary and secondary filters  24  and  34  is compared to last reading made. If there is a significant change, a warning is provided in the message screen  74  in FIG.  5 . If no error is detected, then to Step  96 . For example, one of the filters could have had a structural failure or have blown out. This would result in a significant change in pressure drop readings. 
     Step  90  Display Alarm—An error signal is generated causing a “ALARM CONDITION” message to appear at the message screen  78  (FIG.  4 ). 
     Step  92  Send E-mail—Email notifications are sent to all effected departments. 
     Step  94  Record Information—Automatically back to Step  83  Shut off Valve  20 . As previously stated, that if there is not significant change recorded in the Step  88  Check Accuracy, Step  96  follows. 
     Step  96  Determine 90 Percent Point Of Primary Filter—The actual pressure drop across the primary filter  24  is compared to the point where the filter is completely filled and if the 90 percent point is reached then to Step  90 . If not, to step  98 . Note that the level at which the can be adjusted upward or downward. 
     Step  98  Determine 80 Percent Point Of Primary Filter—The actual pressure drop across the primary filter  24  is compared to the point where the filter is completely filled and if the 80 percent point is reached then to Step  106 , which will be subsequently discussed. The 80 percent warning can also be adjusted upward or downward. 
     Step  100  Determine 90 Percent Point Of Secondary Filter—The actual pressure drop across the secondary filter  34  is compared to the point where the filter is completely filled and if the 90 percent point is reached then to Step  90 . If not, to step  102 . 
     Step  102  Determine 80 Percent Point Of Secondary Filter—The actual pressure drop across the secondary filter is compared to the point where the filter is completely filled and if the 80 percent point is reached then to Step  106 . If not, return to Step  86 . 
     Step  104  Display Alarm—A signal is generated causing a “80 PERCENT FILTER READING” message to appear at the message screen  78  (FIG.  4 ). 
     Step  106  Send E-mail notification to all effected departments. 
     Step  108  Record Information—Return to Step  86  to continue monitoring. 
     Referring to  FIGS. 1-6 , when either the primary or secondary filters need to be replaced, the blower  28  of course is turned off at panel  59 . The filter is replaced. The operator then restarts the blower  28  and presses the screen at the “Detail and New Filter” button on the screen in FIG.  5 . This brings up the screen illustrated in FIG.  6 . This screen includes a time history section  112 , were the actions taken by operators are recorded. A comments section  114  where the operator can enter actions taken, etc. There is also a spray booth not working light  116  and an initiated by space  117  and date space  119 . In addition there is a spray booth not working acknowledgment button  120 . Additionally date and time windows  121  and  122  indicated the day and time. There is also a return to main menu button  124 , which returns the operator back to the screen in FIG.  5 . Thus a record of the spray booth down time is maintained. 
     Of most importance in the screen in  FIG. 6  are the filter change control panels  126 A and  126 B. The control panel  126 A includes a dial gauge  127 , and digital gauge  128 . A press to request filter change button  129 , with date and time windows  130  and  131  is also provided. Thus maintenance personnel will be contacted to replace the filter. However, in some cases the filter will already have been change. Assuming that the new filter is installed the press to reset new filter button  132  is pressed and date and time windows  134  and  135  will automatically record the time and date. This will automatically reset the gauges  71  and  72  in the screen in FIG.  5 . The Control panel  126 B operates in a similar manner and thus will not be further discussed. 
     When the operator presses button  132  press to reset filter, the program as illustrated in  FIG. 7  will automatically add the allowable pressure drop increase for the filter to the initial reading. This then becomes the starting point for the primary or secondary filter digital read out gages  70  and  74  and gages  72  and  76 , as the case may be shown in FIG.  5 . Thus referring to  FIG. 7  the steps are as follows: 
     Step  138  Install new filter—This requires that the old filters be removed and replaced with new ones. 
     Step  139  Determine Initial Pressure Drop—The blower  28  is turned on and readings are recorded. 
     Step  140  Add Allowable Pressure Drop Increase—This is the amount of pressure drop increase for the filter before it is considered ineffective. 
     Step  141  Adjust Gage Readings—The Initial pressure Drop and Allowable Pressure Drop Increase are added together to provide a Total Pressure Drop. This value is then used in determine the 80 percent and 90 percent values. 
     Thus it can be seen that the monitoring system compensates for the variation in initial pressure drop across the filter, increasing the useful filter life, provides a warning if an unusual pressure drop change occurs. Finally, only the spray gun is turned off, when filter limits have been reached and the blower will continue to operate insuring that and remaining paint particles or vapors are collected. 
     While the invention has been described with reference to a particular embodiment, it should be understood that the embodiment is merely illustrative, as there are numerous variations and modifications, which may be made by those skilled in the art. Thus, the invention is to be construed as being limited only by the spirit and scope of the appended claims. 
     INDUSTRIAL APPLICABILITY 
     The invention has applicability to the paint and coating application industry.