Abstract:
The present system uses a large volume of low pressure air to propel a free (i.e., physically unattached to any other component of the invention) boiler tube brush through a boiler tube. The system tank receives relatively high pressure from a conventional source, e.g. “shop air” from a standard compressor and tank. A pneumatic or electric switch shuts off incoming air at a relatively low pressure, and simultaneously sends a signal to a trigger switch at the delivery hose output nozzle. Operating the trigger allows the signal to return to the large capacity output valve to which the delivery hose is attached, sending a large volume, low pressure air pulse through the hose and nozzle to pneumatically propel the tube cleaning brush through the boiler tube without hazard. The brush comprises a series of loosely matted fiber discs assembled on a core. Each disc may have a different abrasive quality.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The present invention relates generally to devices and systems for cleaning various articles, and more specifically to a pneumatic device and system for cleaning out the fire tubes in an industrial boiler. The present cleanout system includes an apparatus for providing a source of low pressure air in a relatively large volume, a delivery nozzle or “gun” for discharging the volume of air through a boiler tube, and a specially configured brush which is pneumatically propelled through the tube to clean out the inner surface of the tube.  
         [0003]     2. Description of the Related Art  
         [0004]     Industrial boilers are used in a wide variety of applications, for producing heated water (or sometimes other fluid) for heating a building, steam production to turn electrical generators or for powering other equipment, etc. Such industrial boilers are generally arranged with a series of tubes passing through the internal volume of the device. The tubes either contain water (or other liquid) which is heated by combustion within the boiler shell and surrounding the tubes, or the boiler shell contains water or other working fluid and the interiors of the tubes are heated by combustion.  
         [0005]     The tubes of such industrial boilers eventually become coated internally with various contaminants, depending upon whether they are fire tube or water tube boilers. These contaminants restrict the heat transfer between the combustion within the tubes and the water surrounding the tubes (in fire tube boilers) or the combustion outside the tubes and liquid within the tubes (for water tube boilers). In either case, the buildup of foreign matter within the tubes can greatly reduce the efficiency of the boiler operation. In fact, studies have been made to determine the optimum point at which boiler operation should be shut down for tube cleaning, depending upon the size of the tubes and boiler, the thickness of the contaminant buildup, and perhaps other factors.  
         [0006]     The tubes of water tube boilers eventually become coated internally with calcium and other mineral buildup, which can be extremely difficult and time consuming to remove. The tubes of water tube boilers are often equipped with internal fins and the like for more efficient heat transfer, which prohibit any effective mechanical cleaning of the interiors of the tubes. Fire tube boiler tubes are also eventually coated internally with combustion byproducts, generally in the form of solid carbon particles (ash and soot). As the fire tubes do not include any inwardly protruding fins and the like for heat transfer, and the combustion byproducts coating the interiors of the tubes are generally relatively soft and do not adhere strongly to the interiors of the tubes, they can generally be removed by brushing.  
         [0007]     Accordingly, various techniques have been developed in the past for removing the soot and other combustion byproduct buildup from the interior walls of the tubes of fire tube boilers. Most such techniques involve the use of relatively long pushrods which are used to push a brush through the length of the tube running through the boiler. This process is tedious, and must be done for each tube of the boiler. A later improvement is the use of pneumatic pressure to blow a brush or similar device through each tube. However, such pneumatic devices of the prior art all use relatively high pressure, which can be hazardous to both the boiler tubes and other environment as well as to persons engaged in the operation and working in the immediate area.  
         [0008]     The present invention provides a solution to this problem by means of a system using relatively large volumes of low pressure air to propel a brush device through the tubes of a fire tube boiler, for cleaning the interiors of the tubes. The present boiler cleaning system includes a pneumatic tank having a series of valves which limit the amount of air pressure which may be built up in the tank, from a conventional source of relatively high air pressure (“shop air”). The present cleanout device also includes a series of rapidly acting valves which release the relatively low air pressure within the supply tank almost immediately, in order to provide a pulse of low pressure air to propel the cleaning tool harmlessly through the tube. The cleaning tool used with the present invention is also novel in that it preferably includes a series of brush elements thereon, each of which accomplishes a different aspect of the cleaning.  
         [0009]     A discussion of the related art of which the present inventor is aware, and its differences and distinctions from the present invention, is provided below.  
         [0010]     U.S. Pat. No. 650,451 issued on May 29, 1900 to James J. Byers, titled “Tube Cleaner,” describes a boiler tube cleanout brush having a specific configuration. The Byers brush includes cutting blades extending in opposite spiral patterns from a central shaft, with a wire brush disposed between the two spiral blades. The Byers brush is pushed through the boiler tubes by mechanical means (e.g., a long pushrod). Byers does not disclose any pneumatic means for propelling his brush through the boiler tubes, and in fact teaches away from such a system due to the porous nature of his brush which would allow any differential in air pressure on one side to pass through the brush, rather than propelling the brush through the boiler tube.  
         [0011]     U.S. Pat. No. 1,133,262 issued on Mar. 30, 1915 to James O. Casaday, titled “Rotative Boiler Tube Cleaner,” describes a mechanical device which somewhat resembles a cutting head used in well drilling operations. A series of peripheral cutting elements is disposed about a rotary shaft, with the assembly serving to break up and cut away scale deposits within the tubes of a water tube type boiler. The device must be rotated by mechanical means. It cannot be propelled pneumatically through the tube, due to the hard scale buildup within such water tubes. The Casaday device is unsuitable for use in cleaning fire tubes, as only mechanical cutting elements are provided on the tool; no brushes are provided.  
         [0012]     U.S. Pat. No. 1,598,771 issued on Sep. 7, 1926 to Charles C. Gerhardt, titled “Boiler Tube Cleaning Brush,” describes such a brush having a series of radially extending bristle groups. Gerhardt also provides a pneumatic seal at one end of his brush assembly, for air pressure to act upon in order to propel the brush through the boiler tube. However, Gerhardt does not describe any means of generating the required pneumatic pressure or volume for propelling his brush through a boiler tube. The present invention provides specific equipment for producing the desired high volume and low pressure charge of air for propelling the brush through the boiler tubes. The brush of the present invention is also novel, in that it may provide multiple abrasive grades for scouring and polishing the inside of the tube in a single pass through the tube.  
         [0013]     U.S. Pat. No. 2,631,113 issued on Mar. 10, 1953 to John V. O&#39;Brien, titled “Method Of And Apparatus Employing An Elongated Flexible Member For Cleaning Out Obstructions From Conduits,” describes the construction of a cable having a flexible core wrapped with a spiral spring wire. Such devices are commonly used for sewer and drain cleanout work, and require some form of manual or power rotation to be applied thereto in order to rotate the cutting elements at the distal end of the cable. The O&#39;Brien tool teaches away from the present cleanout system, as the O&#39;Brien tool cannot be propelled pneumatically through a tube or other passage.  
         [0014]     U.S. Pat. No. 2,631,114 issued on Mar. 10, 1953 to John V. O&#39;Brien, titled “Method Of Cleaning Out Obstructions From Conduits,” is a divisional patent from the &#39;113 U.S. Patent to the same inventor, discussed immediately above. The same points of difference noted in that discussion, are seen to apply here as well.  
         [0015]     U.S. Pat. No. 3,354,490 issued on Nov. 28, 1967 to Don G. Masters et al., titled “Boiler Tube Cleaning Apparatus,” describes an auger drive system for rotating and driving a flexible cable through a tube or the like. The drive system includes horizontal and vertical tracks, for aligning the driving device with the various tubes of the boiler. The device of the Masters et al. &#39;490 U.S. Patent is more closely related to the devices of the &#39;113 and &#39;114 U.S. Patents to O&#39;Brien discussed above, as it provides for the rotation of an elongate flexible shaft. Masters et al. do not disclose any form of pneumatic propulsion for a tube cleanout brush, nor a brush compatible with such a pneumatic propulsion system.  
         [0016]     U.S. Pat. No. 4,011,100 issued on Mar. 8, 1977 to Louis A. R. Ross, titled “Pipe Cleaning Method And Apparatus,” describes two embodiments of a device utilizing a pneumatically driven motor to rotate a cleaning element, or to rotate blower jets for blowing dust from the interior walls of a duct. The pneumatic motor may also provide linear propulsion for the device, but the device requires a mechanical restraining cable to be connected thereto and a separate line to serve as the pneumatic supply. No means of providing a high volume of low pressure air for propelling a brush through a tube, is disclosed by Ross.  
         [0017]     U.S. Pat. No. 4,822,430 issued on Apr. 18, 1989 to Victor V. Carberry, titled “Method And Apparatus For Cleaning Boiler Burners,” describes a pneumatically powered tube cleanout tool. However, rather than using low pressure air to propel a series of brushes through a tube, Carberry uses a pneumatically powered rotary motor which he passes through the tube. The motor is supplied with pressurized air by a long hose which is extended through the tube as the tool passes through the tube. The motor rotates cutting blades on the front thereof, which dislodge scale and deposits from the inner surface of the tube. The present system does not utilize any form of rotary cutting blades, but rather uses a series of discs having different abrasive grades to remove deposits and polish the interior of the tube.  
         [0018]     U.S. Pat. No. 4,872,834 issued on Oct. 10, 1989 to John W. Williams, Jr., titled “Recovery Boiler Port Cleaner,” describes a device which is permanently affixed to the outer wall of a recovery boiler, to periodically clean the air port of the boiler for optimum air flow therethrough. The device is pneumatically operated, but does nothing more than reciprocate inwardly and outwardly to thrust a cleaning blade into the air port. No means of providing a large volume of air under low pressure to drive a free brush completely through an elongate boiler tube, is disclosed by Williams, Jr. Moreover, Williams, Jr. requires a source of electrical power to operate an automatic timer for his device. While the present system may be electrically operated, it may also be operated strictly by means of pneumatic pressure with no requirement for electrical power.  
         [0019]     U.S. Pat. No. 6,467,121 issued on Oct. 22, 2002 to Joseph J. Franzino et al., titled “Rotary Tube Scrubber,” describes a rotary brush configuration having a series of radially extending, flexible arms each having a longitudinal cutting edge thereon, with each of the arms having a circumferential discontinuity therebetween. The Franzino et al. brush must be mechanically driven by a rotary shaft, in order to clean the interior walls of the boiler tube. Franzino et al. do not disclose any pneumatic means of propelling a free brush through a boiler tube, and their brush, with its longitudinally disposed cutting edges, cannot provide any real degree of cleaning action unless it is rotated within the tube.  
         [0020]     Japanese Patent Publication No. 2002-277,192 published on Sep. 25, 2002 to Kurita Engineering Co. Ltd., titled “Method For Cleaning Boiler,” describes (according to the drawing and English abstract) a tube cleanout system utilizing a cleaning fluid mixed with water. The boiler is emptied and the water and cleaning fluid mixture is pumped through the boiler to clean the interiors of the boiler tubes. Neither mechanical brushing nor means of pneumatically propelling such free brushes through the tubes, is apparent in the &#39;192 Japanese Patent Publication.  
         [0021]     The website for Scaleaway Tools &amp; Equipment Ltd., accessed on May 2, 2003, describes an electric motor which drives a flexible rotary shaft to power a rotary tool at the shaft end opposite the motor. A series of different cleaning tools and brushes is also disclosed, but for those brushes with flexible bristle elements, no pneumatic seal is apparent.  
         [0022]     Finally, the website for Goodway Technologies, accessed on May 6, 2003, describes a pneumatic gun for use in pneumatically propelling a cleaning element through the tube of a boiler. The Goodway website specifically states that the gun requires a minimum of 90 psi, with up to 120 psi being allowable. This is more than an order of magnitude higher than the air pressure provided with the present system. Goodway makes no disclosure of any large volume air supply, as provided with the present invention. The use of relatively low air volumes, results in a need for relatively high pressures in order to provide sufficient pneumatic propulsive energy to propel the cleanout element through the tube of the boiler. However, the use of such high air pressures can be hazardous, and results in the cleanout element becoming a projectile (the word used by Goodway in describing their cleanout element). The difference between the Goodway system and the present invention is somewhat analogous to the difference between the air pressure developed by an air rifle to fire a BB or pellet, versus the air pressure stored in a small balloon. The total propulsive energy available for release is comparable, but the high pressure developed by the air rifle is considerably more dangerous. It is also noted that the Goodway projectiles are formed of a soft and dense foam, which while possibly reducing the potential hazard of their high velocity passage through the boiler tube due to the high pressure air used, cannot provide the cleaning and polishing action of the multiple grades of abrasive materials used in each of the scrubbing elements of the present invention.  
         [0023]     None of the above inventions and patents, taken either singly or in combination, is seen to describe the instant invention as claimed. Thus a boiler tube cleanout system solving the aforementioned problems is desired.  
       SUMMARY OF THE INVENTION  
       [0024]     The present boiler tube cleanout system propels a tube brush pneumatically through a boiler tube by means of a relatively large air volume delivered under relatively low pressure. This is accomplished by limiting the input pressure of a conventional source of pneumatic pressure, e.g. “shop air,” which is normally supplied at between 90 and 120 pounds per square inch (psi), depending upon the setting of the compressor regulator. The present system includes an air tank with an input valve which shuts off incoming airflow when the tank pressure reaches a relatively low value, e.g. on the order of seven to eight psi. An air supply hose extends from an output valve on the tank, with a trigger operated pneumatic nozzle at the distal end thereof.  
         [0025]     Signal and return lines extend along the hose. Once the tank is pressurized, airflow passes through a signal line to the trigger. Pulling the trigger actuates a switch at the nozzle end of the signal line to allow airflow to return to the output valve through the return line, signaling the output valve to open and provide a large volume of air from the previously filled tank. This propels a tube cleanout brush through the tube, which scrubs away any soot and/or other foreign matter which has been relatively loosely deposited on the inner surface of the tube.  
         [0026]     The tube brush is free, i.e. not attached in any way to any of the apparatus of the present invention. The brush preferably includes a series of abrasive discs thereon, arranged sequentially along a central rod or tube. A non-porous backing is applied to the trailing end of the assembly, to preclude airflow through the porous discs of the tube brush assembly. The abrasive discs are preferably formed of a loosely matted plastic strand material, which may or may not be impregnated with harder abrasive material as desired. Such material is available under the trade name of Scotchbrite®, and is available in a number of different densities and abrasive grades to provide different degrees of abrasion as desired.  
         [0027]     The operating system for the present boiler tube cleanout system is preferably entirely pneumatic, in order to avoid the need for electric power in addition to the conventional “shop air” pneumatic source needed for the operation of the present invention. However, the various switches and valves associated with the operation of the present invention may alternatively be of a type providing for electric actuation, if so desired. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0028]      FIG. 1  is an environmental, perspective view of a boiler tube cleanout system according to the present invention, showing its operation and use.  
         [0029]      FIG. 2  is a detailed perspective view of the boiler tube cleanout apparatus of  FIG. 1 , showing further details thereof.  
         [0030]      FIG. 3  is a detailed perspective view of the pneumatic outlet nozzle used with the apparatus of  FIG. 1 .  
         [0031]      FIG. 4  is a schematic diagram of the pneumatic operating system of the present tube cleanout apparatus.  
         [0032]      FIG. 5  is a schematic diagram of an alternative electrically controlled pneumatic system for use with the present invention.  
         [0033]      FIG. 6  is an exploded perspective view of an exemplary tube cleanout brush which may be used with the present invention. 
     
    
       [0034]     Similar reference characters denote corresponding features consistently throughout the attached drawings.  
       DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0035]     The present invention comprises various embodiments of a boiler tube cleanout system, for cleaning soot and combustion byproducts from the interiors of the fire tubes in a fire tube type boiler. The present system provides numerous advantages over previously developed boiler tube cleaning systems, in that the present system utilizes a relatively large volume of relatively low pressure air to propel a brush pneumatically through each of the tubes of the boiler. The present invention is preferably operated and controlled by a purely pneumatic system, but may alternatively use an electric control system to control and operate the pneumatics of the device, if so desired. The brushes which are pneumatically propelled through the boiler tubes are also specialized, with each brush preferably including a series of brush elements thereon, with each element being of a different abrasive grade for optimum cleaning.  
         [0036]      FIGS. 1 and 2  provide perspective views of the air delivery tank and apparatus of the present invention, with  FIG. 1  being an environmental view showing additional components and operation of the system. In  FIG. 1 , the system  10  is shown being used to clean out a series of tubes T in a boiler B, after the ends of the tubes have been accessed by opening or removing the access panel conventionally installed therewith. The system  10  includes a low pressure air tank  12  which receives air from a conventional source of relatively high pressure air (e.g., “shop air,” or perhaps a portable compressor) which is delivered to the air tank  12  by a conventional high pressure air hose H. A high volume, low pressure delivery hose  14  extends from the low pressure air tank  12  to an outlet nozzle  16  at the distal end thereof, to supply a large volume of air under low pressure from the tank  12  to propel a cleanout brush  18  through the boiler tube T.  
         [0037]     A series of brushes  18  may be placed in the inlets of a number of the boiler tubes T, generally as shown in  FIG. 1 , with the operator of the present system  10  merely shifting the outlet nozzle  16  from tube to tube to propel each brush  18  through its respective tube T. The brushes  18  are retrieved at the opposite, downstream ends of the tubes T for reuse. The opposite ends of the tubes T may be covered with a temporary cover (tarp, etc.) to collect the brushes  18  and the soot and other combustion byproducts brushed from the interiors of the tubes T during the cleaning operation. A slight vacuum may be applied to the downstream ends of the tubes T in order to avoid blowback of the soot through the tubes; this is conventional in such operations.  
         [0038]     The air tank  12  is a low pressure device, as noted further above. While the tank  12  is preferably rated for relatively high pressure, the components of the present system  10  render the tank  12  incapable of accepting or storing air at pressure significantly over the nominal operating pressure of seven to eight pounds per square inch (psi) for the system  10 . Air pressure within the tank  12  is controlled by a pneumatic inlet valve  20  between the high pressure inlet hose H and the tank  12 . The inlet valve  20  receives a signal (preferably pneumatic, but alternately by electrical means) from a pneumatic (or electric) switch  22 , to close the inlet valve  20  to the incoming higher pressure shop air delivered by the inlet hose H when the internal volume  24  of the tank  12  reaches a predetermined pressure.  
         [0039]     Additional insurance that the tank  12  cannot exceed the desired low pressure is provided by a relief valve  26  extending from the tank  12 , and set to release the tank pressure if it exceeds the nominal operating pressure by some predetermined amount, e.g. twelve psi. A pressure gauge  28  is also provided for monitoring the internal pressure of the tank  12 , with a dump valve  30  also provided so the operator may relieve the internal pressure within the tank  12  when the system  10  is not in use.  
         [0040]     A high volume pneumatic outlet valve  32  is also provided on the tank  12 , communicating with the internal volume  24  of the tank  12 . The delivery hose  14  extends from its outlet valve connection end  34  to its opposite nozzle end  36 , from which the delivery nozzle  16  extends. The outlet valve  32  is actuated by a trigger on the delivery nozzle  16 , as explained below.  
         [0041]      FIG. 3  provides a detailed illustration of the outlet nozzle  16  of the present system. The nozzle  16  may include a rigid, or semi-rigid, body portion  38  to which the nozzle end  36  of the delivery hose  14  is connected. A handle  40  may be provided, extending from the body portion  38 . The opposite end of the body  38  has an outlet port  42  extending therefrom. The outlet port  42  is preferably formed of a pliable, resilient material in order to provide a good seal against the end of a boiler tube, and may be provided in any of a number of different sizes or diameters in order to fit different diameter boiler tubes. The nozzle body  38  and outlet port  42  are preferably configured to provide easy interchange of different size or diameter ports  42 , as required.  
         [0042]     A trigger  44  (which may alternatively comprise a pushbutton, rocker switch, etc., rather than the toggle depicted in  FIG. 3 ) serves to actuate a switch  46  at the nozzle body  38 , with the switch  46  triggering the outlet valve  32  at the tank  12 . The switch  46  is preferably a pneumatic device, with operation of the trigger  44  opening the pneumatic valve comprising the pneumatic switch  46 . Alternatively, the switch  46  may be electrically actuated, with operation of the trigger  44  closing the electrical contacts of the switch to close the electrical circuit. A signal line  48  (pneumatic or electric, depending upon the operating system used) extends from the air pressure switch  22  on the tank  12  to the trigger operated switch  46  at the outlet nozzle  16 . A return line  50  (pneumatic or electric) extends from the switch  46 , back to the outlet valve  32 . The signal and return lines are preferably enclosed within the hose  14 , for damage protection.  
         [0043]     Completing the circuit by operating the switch  46 , allows a pneumatic or electric signal to pass from the air pressure switch  22  to the outlet valve  32 , opening the outlet valve  32  to release the air pressure within the tank  12  to expel a large volume of low pressure air from the nozzle  38 . This serves to propel a tube cleanout brush  18  through a boiler tube T, when the outlet port  42  of the nozzle assembly  16  is placed against the end of a boiler tube T in which a brush  18  has been placed.  
         [0044]      FIG. 4  provides a schematic diagram of the pneumatic operating system of the present invention, less the distal end of the low pressure delivery hose  14  and its outlet nozzle. The internal volume  24  of the tank  12  is supplied with air from the inlet valve  20 , which communicates pneumatically with the tank  12  by means of an inlet line  52 . The inlet valve  20  is supplied with air from a relatively high pressure source via a conventional high pressure air hose H connected to a shop air supply or other suitable source of air pressure. A conventional quick disconnect coupling C may be used to connect the air pressure supply hose H to the tank  12  apparatus. The inlet valve  20  opens in accordance with signals provided by the pressure switch  22 , which signals the valve  20  to close to incoming air when the tank  12  pressure reaches a predetermined point. Thus, the tank  12  is filled quite rapidly due to the high pressure of the incoming air from the hose H and through the valve  20 , but the incoming airflow is shut off as soon as the tank  12  pressure reaches the predetermined desired limit, e.g. seven to eight psi.  
         [0045]     The pressure switch  22  may be considered as a double pole, double toggle type switch, but operating by means of pneumatic principles and systems in the schematic system illustrated in  FIG. 4  of the drawings. The common port  54  of the switch  22  receives airflow under pressure from the incoming air delivered by the high pressure supply hose H, with flow being divided between the inlet valve  20  and the switch  22  at a tee fitting  56 . An air pressure regulator  58  may be installed in the switch supply line  60  between the tee  54  and the pressure switch  22 , as required. While many types of pneumatic switches may be capable of functioning when supplied with relatively high pressure shop air, it is possible to use less costly switches by reducing the incoming pressure to the switch  22  to around twenty five psi or less by means of the regulator  58 .  
         [0046]     The sense port  62  of the pneumatic switch  22  receives a pressure signal by means of a tank pressure connection line  64 , extending from the tank  12  to the switch  22 . Tank pressure to either side of a predetermined cutoff or switch point, will cause the switch  22  to open or close pneumatic valves or ports therein, thereby delivering or cutting off pneumatic flow to the inlet valve  20  and to the air pressure trigger switch  46  at the nozzle  16  shown in  FIG. 3 . When air pressure in the tank  12  is below the predetermined set point, e.g. seven to eight psi, the inlet valve port  66  of the switch  22  is normally open, allowing air to flow from the common supply line  60 , through the switch  22 , to the inlet valve  20  via the line  68 , providing pneumatic pressure to hold the inlet valve  20  open to allow the tank  12  to fill.  
         [0047]     The pneumatic switch  22  includes another pneumatic switch port  70  which is normally closed when the tank pressure is below the predetermined switch point for the pneumatic switch  22 . This port  70  is connected to the trigger switch  46  at the nozzle  16  (shown in  FIG. 3 ) by the signal line  48 , which extends from the normally closed port  70  to the trigger switch  46  via the low pressure delivery hose  14 . So long as this port  70  is closed, air cannot flow from the pneumatic switch  22  to the trigger switch  46 . Thus, operation of the trigger switch  46  will not result in air flow back to the outlet valve  32  via the return line  50 , which results in the outlet valve  32  remaining closed to prevent release of air and operation of the system.  
         [0048]     However, once the air pressure in the tank  12  reaches the predetermined switch point, this pressure is sensed by the pneumatic switch  22  via the tank pressure connection line  64  to the sense port  62  of the switch  22 . This cutoff pressure causes the switch  22  to close the normally open port  66 , thus cutting off air flow to the inlet valve  20  to cause the inlet valve  20  to close, thereby stopping any further pressure buildup in the tank  12  beyond the preset cutoff point. Simultaneously, the switch  22  opens the normally closed port  70 , allowing air to flow to the trigger switch  46  via the signal line  48 . Actuation of the trigger  44  opens the valve at the pneumatic trigger switch  46  to allow air to flow from the open port  70 , along the signal line  48 , through the trigger switch  46 , and back along the return line  50  to actuate the outlet valve  32 , thereby allowing the large volume of low pressure air within the tank  12  to be released.  
         [0049]     The above described sudden release of the volume of air within the tank  12  results in a pressure drop, as well. When the pressure drops below the predetermined set point for the switch  22 , the previously opened port  70  to the trigger switch  46  reverts to its normally closed condition, thereby ceasing operation of the trigger switch  46 . Simultaneously, the previously closed port  66  reverts to its normally open condition, thereby allowing air to flow from the common supply line  60  through the switch  22  to the inlet valve  20 , thereby signaling the inlet valve  20  to open in order to refill the tank  12  with another volume of air for further operation of the present system. The capacity of the inlet and outlet valves  20  and  32  is preferably relatively large, in order to allow rapid cycling of the device and rapid discharge of the air volume within the tank  12  when the trigger  48  of the nozzle  16  is actuated.  
         [0050]      FIG. 5  of the drawings provides a schematic view of an exemplary electrical system for the present invention, including the delivery hose with an electrically actuated trigger switch at the nozzle thereof. The tank  12  is essentially identical to the tank  12  of other embodiments discussed further above, and receives air pressure from a relatively high pressure supply line or hose H. However, the inlet valve  20   a  (the housing of which is shown in broken lines in  FIG. 5 ) is an electrically actuated device, having a solenoid valve  20   b  therein actuated by a solenoid  20   c  to control the flow of air into the tank  12 . The outlet valve  32   a  (in broken lines) is also electrically controlled, by a solenoid valve  32   b  actuated by a solenoid  32   c.    
         [0051]     The operation of the two valves  20   a  and  32   a  is controlled by a switch  22   a , with the housing shown in broken lines in  FIG. 5 . The switch  22   a  is a double pole, double toggle type switch, just as in the pneumatic switch  22  of the pneumatically operated system discussed further above. However, the switch  22   a  of the system of  FIG. 5  is electrically operated. The switch  22   a  receives an air pressure signal from a pressure transducer  62   a , which may be considered somewhat analogous to the sense port  62  of the pneumatic system of  FIG. 4 . The transducer  62   a  actuates a normally open, double throw switch  70   a , depending upon the preset tank pressure required to operate the switch  70   a . When the pressure in the tank  12  reaches the predetermined set point, e.g. seven to eight psi, the transducer  62   a  closes the switch  70   a , with the closed position shown in broken lines in  FIG. 5 .  
         [0052]     This allows electrical power to flow across a closed contact  70   b , thereby sending electrical power to a solenoid  68   a  to actuate a double throw switch  68   b  somewhat analogous to the normally open pneumatic port  68  of the system of  FIG. 5 . The switch  68   b  is normally closed (as shown in solid lines in  FIG. 5 ) which allows electrical power to flow through the switch  68   b  to the solenoid  20   c  of the inlet valve  20   a , thereby holding the valve  20   b  open to allow air to flow into the tank  12  from the supply line or hose H. However, when the internal pressure in the tank  12  reaches the predetermined set point, the transducer  62   a  closes the normally open switch  70   a  to actuate the solenoid  68   a , thereby switching the switch  68   b  from its normal position to its alternate position  68   c  as shown in broken lines in  FIG. 5 .  
         [0053]     The now open switch position  68   b  cuts off electrical power through the line  68   d  to the inlet valve control solenoid  20   c , thereby releasing the valve  20   b  to close off incoming air flow from the hose or line H to stabilize the internal pressure in the tank  12  at the desired level. Simultaneously, the alternate switch position  68   c  allows electrical power to flow through the switch  68   c  to the signal line  48   a , to the trigger switch  46   a  at the nozzle  16 . When the trigger switch  46   a  is closed to the position  46   b  shown in broken lines, the circuit from the switch position  68   c , through the signal line  48   a , across the trigger switch at  46   c , and back along the return line  50   a  to the outlet valve solenoid  32   c  is completed. This actuates the solenoid  32   c  to open the valve  32   b , thereby releasing the previously built up pressure within the tank  12 .  
         [0054]     When the pressure within the tank  12  drops below the set point for the pressure transducer  62   a  and switch  70   a , the switch  70   a  reverts to its normally open position as shown in solid lines, thereby opening the circuit to the solenoid  68   a . This causes the switch position  68   c  to revert to its normally closed position  68   b , shown in solid lines in  FIG. 5 . This closes the circuit to the inlet valve solenoid  20   c  via the line  68   d , causing the valve  20   b  to open to allow air flow to replenish the pressure within the tank  12 . Simultaneously, the circuit to the trigger switch  46   a  is opened, thereby disabling the trigger switch to prevent further operation until the tank pressure builds up sufficiently to close the pressure switch  70   a  to its position  70   b  shown in broken lines in  FIG. 5 .  
         [0055]      FIG. 6  provides an exploded perspective view of an exemplary boiler tube cleanout brush  18  for use with the present system. The brush or cleaning element  18  is preferably relatively light weight, in order to avoid potential injury to persons or damage to property as it leaves the downstream end of a boiler tube. The relatively low pressure used in the present system, along with the conventional tarps or covers used to close off the downstream end of the boiler during the cleaning operation, will generally preclude such injury or damage in any event. However, the light weight of the cleanout brushes  18  of the present system, provides an even greater margin of safety.  
         [0056]     The brush  18  has a hollow central core  72  which may be formed of light cardboard stock, plastic, or other suitable light weight material as desired. A series of toroidal brush elements or pads, e.g. pads  74   a ,  74   b ,  74   c , and  74   d , is assembled sequentially along the core  72 , with a tubular spacer  76  placed along the core  72  between each brush pad  74   a  through  74   d  to space the pads  74   a  through  74   d  apart from one another and at each end of the core  72  to retain the leading and trailing brush pads on the core  72 . As the boiler tube brush  18  of the present system is propelled through a boiler tube by pneumatic pressure, some means must be provided to prevent the propelling air pressure from passing through the brush  18 . This may be accomplished by installing a plug  78  (or tape, etc.) in the leading end  72   a  (or trailing end  72   b ) of the core  72 , and providing a non-porous disc  80  at the trailing end  72   b  of the core  72  to block any significant air flow through the porous pads. Alternatively, the tube may remain open or only partially blocked, in order to allow air flow therethrough to blow soot and other loose material from the tube in advance of the passage of the brush  18 , if so desired. Also, each of the pads  74   a  through  74   d  may have a non-porous disc provided therewith, with the discs serving to stiffen and reinforce the pads  74   a  through  74   d  to provide better contact with the interior walls of the tube.  
         [0057]     The brush pads  74   a  through  74   d  are formed of a flexible, porous, loosely matted abrasive material, suited for scrubbing and polishing soot and other combustion byproducts from the interior wall of a boiler tube as the pads  74   a  through  74   d  are pushed through the tube by the air pressure expelled from the tank  12  of the present boiler tube cleanout system. Scotchbrite® material manufactured by the 3M Company has been found to be well suited for such a task.  
         [0058]     Scotchbrite® material is provided in a wide variety of different abrasive grades, and it is preferred that the cleanout brush  18  of the present invention utilize a series of different pads, e.g. pads  74   a  through  74   d , each of a different abrasive grade from one another, or at least comprising two different abrasive grades. As an example, the leading pad  74   a  positioned adjacent the leading end  72   a  of the core  72  may be formed of relatively coarse material, in order to scrub away any heavy deposits of material on the interior walls of the tubes. The next pad  74   b , or pads  74   b  and  74   c , may have intermediate abrasive properties, while the last pad  74   d  at the trailing end  72   d  of the core  72  may be of a relatively fine abrasive grade, in order to perform a final polish of the interior of the tube as the brush element  18  is propelled therethrough. It will be seen that a greater or lesser number of such pads  74   a  through  74   d , with varying degrees of abrasive harshness, may be installed upon a core  72  to customize the brush element  18  as desired, depending upon the type(s) and amount(s) of combustion byproduct(s) which may be built up within the boiler tubes.  
         [0059]     In conclusion, the present boiler tube cleanout system greatly facilitates the periodic cleaning of fire tube boiler tubes, which is required for optimum efficiency of such devices. The relatively low pneumatic pressure used by the present system also greatly enhances safety during such operations. After accessing the boiler tubes for cleaning, a person using the present invention need only ready the system for operation by confirming that the tank dump valve is closed, and perhaps actuating any electrical system where an electrically controlled embodiment is used. The user may then connect a conventional source of pneumatic pressure (e.g., “shop air,” or perhaps a portable compressor transported to the job site) using a conventional high pressure air hose or the like, and install one or more brush elements (preferably a series of such elements, for greater efficiency) in the exposed ends of the boiler tubes.  
         [0060]     The user then need only apply the air outlet nozzle to the end of each boiler tube in which a cleanout brush has been installed, and actuate the trigger at the nozzle to release the entire volume of low pressure air stored in the tank to push the brush through the tube, thereby scrubbing and removing any deposits within the tube. The operation is repeated for each tube, with the recycle time being very low due to the relatively large capacity of the valves used and the relatively high pressure (e.g., perhaps up to 150 psi) provided by conventional pneumatic sources. The result is a significant savings of time in the boiler cleaning operation, as well as a significantly safer system for cleaning the tubes in a fire tube boiler.  
         [0061]     It is to be understood that the present invention is not limited to the embodiments described above, but encompasses any and all embodiments within the scope of the following claims.