Abstract:
A quick acting blast aerator comprising a spring-less actuator triggered by an exhaust valve. The actuator valve comprises a tubular body, an exhaust vent defined in the body, a dampening passageway, and a piston slidably disposed therewithin for movement between a tank filling position and a displaced, air discharge position. Preferably the piston has a projecting dampener which engages the dampening passageway. The trigger valve comprises a rigid, cylindrical housing with a hollow interior having a plurality of vent orifices radially disposed about its periphery. A pair of resilient bands surrounding the housing cover the vent orifices to form a one-way check valve. A resilient, hollow piston coaxially, slidably disposed within the trigger housing has a hollow internal chamber containing a ball valve. Mutual cooperation of the trigger piston and its internal valve govern pneumatically control the actuator.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This utility patent application is based upon previously-filed, pending U.S. Provisional Patent application Serial No. 60/350,250, which was officially filed Jan. 16, 2002, entitled Quick Release Blast Aerator Trigger Valve, and priority based upon said related prior application is hereby claimed. 
    
    
     BACKGROUND OF THE INVENTION 
     I. Field of the Invention 
     This invention relates generally to air-accumulator and discharge devices of the type generally known as air blasters, air cannons, or blast aerators. More particularly, the present invention relates to heavy duty blast aerators of the type classified in United States Patent Class 222, Subclasses 2, 3 and 195 and Class 251, Subclass 30.02. 
     II. Description of the Prior Art 
     As is well known to those with skill in the art, the passage of bulk materials through conventional handling equipment is often degraded or interrupted. Typical bulk materials comprise concrete mixtures, grains, wood chips or other granular materials disposed within large hoppers or storage bins. In conventional, conically shaped hoppers, for example, bridges or arches of bulk materials often form, preventing or minimizing the orderly flow or delivery of granular materials. Often, “rat holes” or funnels build up, and material passage is severely degraded or halted altogether. Particles of bulk material may form obstructive bonds by adhesion due to chemical or hydrostatic attraction. Particles may also interlock because of horizontal and vertical compression. Such materials usually tend to cake or congeal during bulk processing. When moisture accumulates, unwanted caking tends to block flow. It is also recognized that friction between bulk material and the walls of a typical bunker or hopper in which the material is confined decreases flow efficiency. 
     Blast aerators or air cannons have long been employed to dislodge blocked or jammed bulk material. Storage bins or hoppers, for example, are often fitted with one or more high pressure air cannons that periodically blast air into the interior to dislodge caked particles, break funnels and bridges, and destroy rat holes. Bulk flow problems can temporarily be stopped by physically vibrating the hopper or container to shake loose the jammed materials. But not all materials may be dislodged in this manner. For example, large concrete bunkers may be impossible to vibrate. Materials like soft wood chips ordinarily absorb vibratory energy and must be dislodged by other methods. 
     In many applications air blasters are preferred over vibrators because of efficiency. The forces outputted by blast aerators are applied directly to the material to be dislodged, rather than to the walls of the structure. Modern air blasters usually outperform over air slides, air wands, and various air screen devices which operate at low pressures. Live bottoms in hoppers or bins are limited in their effectiveness, since they may tend to create bridging or arching of material. Modern air cannons or blast aerators are intended for use as a flow stimulator against materials that are primarily moved by gravity. They are not intended to be the prime movers of such materials, and for safety purposes they should not be used to initiate the flow or movement of bulk materials unless a gravity feed is employed. 
     Typical blast aerators comprise a large, rigid holding tank that relatively slowly accumulates air supplied through conventional high pressure air lines provided at typical industrial facilities. A special valve assembly associated with the tank includes a high volume discharge opening directed towards or within the target application. The valve assembly periodically activates the air cannon in response to a trigger. When the blaster is detonated, the large volume of air accumulated in the holding tank is rapidly, forcibly discharged within a few milliseconds. Compressed air released by a modern blast aerator strikes the bulk material at a rate of between five hundred feet per second to eight hundred feet per second. Materials exposed to this high volume inrush are forcibly dislodged by impact. The large volume of air outputted by the aerator spreads throughout the bin or hopper, distributing forces throughout the interior that tend to homogenize and dislodge the mixture. The impacting shock wave rapidly destroys any formations of bulk material that might otherwise hinder fluid flow. 
     After an exhaust blast, the valve apparatus returns to a “fill” position, wherein an internal, displaceable piston typically blocks the aerator blast output path. The cycle repeats as air that has relatively slowly accumulated again within the blaster is subsequently discharged during the next cycle. A variety of methods have been proposed for controlling the aerator valve assemblies. Various means such as electrical solenoids have been provided for allowing or forcing the discharge piston to rapidly retreat from its normally sealed, blocking position abutting the discharge valve passageways. 
     U.S. Pat. No. 4,469,247, issued Sep. 4, 1984, and owned by Global Manufacturing Inc., discloses a blast aerator for dislodging bulk materials. The blast aerator tank has a blast discharge opening coaxially aligned with its longitudinal axis. The blast discharge assembly comprises a rigid, tubular discharge pipe comprising an internal shoulder that forms a valve seat. A resilient piston coaxially, slidably disposed within the pipe abuts the valve seat to seal the tank during the fill cycle. In the fill position the seal is maintained by a chamfered end of the piston that matingly, sealingly contacts a similarly chamfered seat portion of the valve seat assembly. A cavity at the piston rear is pressurized to close the valve by deflecting the piston. During periodic cycles, discharge occurs in response to cavity venting, whereupon the piston is rapidly displaced away from the valve seat, exposing the discharge pipe opening to the pressurized tank interior. 
     Blast aerators characterized by the foregoing generalized structure may be seen in U.S. Pat. Nos. 3,651,988; 3,915,339; 4,197,966; 4,346,822; and 5,143,256. Other relevant blast aerator technology may be seen in Great Britain Pat. Nos. 1,426,035 and 1,454,261. Also relevant are West German Patent 2,402,001 and Australian Pat. No. 175,551. 
     Global Manufacturing patent No. 4,496,076 teaches a method of employing a plurality of air cannons in a controlled array. 
     In some prior art aerator designs, the piston and valve assembly are disposed at a right angle relative to the discharge flow path. In addition, many blast aerators use a valve assembly that is mounted externally of the accumulator tank. The latter design features are seen in U.S. Pat. Nos. 3,942,684; 4,767,024; 4,826,051; 4,817,821; and 5,853,160. 
     During the hundreds of thousands of repetitive discharge cycles occurring over the normal life of a typical blast aerator, critical moving parts will inevitably wear and deform. Typical pistons encounter extremely high stresses from heat, friction, and pressure that eventually result in component failure. For example, as the piston deforms or wears, its ability to properly seal during the critical “fill cycle” is impaired. In many prior art designs that portion of the piston utilized to create a seal also functions as the working surface upon which tank pressure acts to force the piston to its rearward “blast” position, further aggravating component stress and shortening valve life. In operation, the piston must rapidly travel away from the seal during the discharge cycle. As it deforms over hundreds of thousands of blast cycles however, it may lose its symmetry, and misalignment within the valve tube can slow piston travel, enlarging the blast time period and denigrating the force of the discharge. When critical structural parts fail, injury to operating personnel may occur. At the very least, aerator component breakdown may severely limit bulk flow efficiency. Therefore some form of dynamic control over the piston that limits stress would seem desirable. Some attempts in this direction are acknowledged. 
     U.S. Pat. No. 5,441,171 discloses a protrusion on the rear of a slidably captivated piston to help slow the piston after firing. This design does not bleed air off in a controlled fashion and in fact the protrusion does not shut off the flow of air out of the valve body. 
     U.S. Pat. No. 5,517,898 discloses a pneumatic cylinder in which coaxially disposed “pistons” include dampening sleeves. In other words, ports are interconnected with internal passageways including stem portions of the cylinder to dampen piston movement by compressed air. 
     The actuator system disclosed in my prior U.S. Pat. No. 6,321,939 that was issued Nov. 27, 2001, includes a dampened, high-speed actuator. A unique, lightweight piston within the actuator is controlled through a dampening arrangement that mitigates piston shock. Special structure protruding from the piston is received within a passageway end cap when the piston is retracted during firing, and special vents govern the rate of air flow and pneumatic equilibrium. Cushioning pressures at the rear of the piston dampen piston movement. A coiled metal spring between the piston and the housing end cap provides additional cushioning. 
     During firing the spring is compressed at a very rapid rate as the piton retracts. Full compression occurs in approximately 0.01 seconds. Corresponding piston velocity for an aerator with a typical four inch O. D. actuator output pipe is approximately 200 to 250 feet per second. After repetitive cycles at such speeds, the coiled spring may fail, especially in high temperature applications. Spring problems are recognized in the aerator industry with many designs. The coils of the spring are compressed together during firing, generating heat and slowing the piston. This phenomenon degrades the output forces achievable by the air blaster. spring adds cost to the Air Blaster. 
     It is therefore proposed to provide a “spring-less” air blaster. In other words, separate mechanical springs are omitted from the new design. Instead of a mechanical spring, pneumatic forces are employed for cushioning and dampening. In this “pneumatic design” the actuator valve assembly is controlled by a special trigger. In other words, standard, electrically-operated pneumatic trigger valves have been replaced by my “quick exhaust valve” described in provisional application Serial No. 60/350,250. The actuator system disclosed in prior U.S. Pat. No. 6,321,939 has been modified as described below, and when coupled to the new quick exhaust valve, piston travel and dampening are mitigated by pneumatic forces in the trigger arrangement. 
     SUMMARY OF THE INVENTION 
     A blast aerator system with a “spring-less” actuator is triggered by a special quick exhaust valve. The rigid holding tank mounts the actuator at it&#39;s discharge end, and the exhaust valve trigger is secured to the opposite end, being coupled to the actuator through an internal pipe coaxially extending through the tank. 
     The preferred valve assembly includes an internal, slidably mounted piston that normally blocks the exhaust path (i.e., during tank filling). The piston normally contacts an internal valve seat, but when deflected away the exhaust vents are suddenly exposed and discharge occurs. In the high temperature mode, the piston is heat resistant. It is preferably made of 6061-T6 aluminum. The low temperature piston is made from resilient material such as polypropylene. A rigid valve cap closes the valve actuator assembly. The valve cap comprises an upper, dome-like portion and an integral, lower disk portion coaxially fitted to the actuator body. The piston comprises a generally cylindrical dampener that is received within a dampener passageway in the end cap. 
     The trigger at the opposite end of the tank comprises a symmetrical, ventilated housing that mounts a miniature, hollow, lightweight piston. A plurality of vent orifices radially disposed about the housing periphery, are normally covered by a pair of resilient bands that may be deflected away from the orifices in response to sufficient air pressure, thus functioning as a check valve. The captivated, generally cylindrical piston is lightweight and hollow. An air passageway extending through the trigger piston is controlled by a deflectable ball forming a valve element. The spherical check valve is captivated within a tapered chamber inside the piston for selectively blocking and exposing various air passages through the piston as it contacts or separates itself from an internal valve seat. 
     The actuator valve assembly and trigger valve assembly are in fluid flow communication. Trapped residual air within the trigger valve serves as a pneumatic spring to resist and dampen movement of the actuator valve piston. The actuator valve piston is effectively cushioned pneumatically by the trigger valve assembly, eliminating the requirement for a separate mechanical spring. Because there is no a need to machine a spring groove in the piston, piston weight and mass can be reduced; the preferred hollow actuator piston is thus capable of faster movements. 
     Thus a basic object of this invention is to provide a blast aerator with a spring-less actuator valve. 
     A related object is to provide a blast aerator with a high speed trigger mechanism that obviates the need for mechanical springs in the associated actuator valve assembly. 
     Another basic object is to provide a highly reliable blast aerator that resists high temperatures and mechanical stresses. 
     Another object is to provide a blast aerator trigger of the character described that is of minimal volume and weight. 
     A fundamental object is to provide a highly reliable blast aerator. 
     A still further object is to speed up the blast aerator charging and discharging cycle. 
     A still further basic object is to provide a blast aerator trigger of the character described that minimizes the number of required service calls. 
     A related object is to control piston deterioration by pneumatically cushioning and controlling it during blast discharges. 
     Another general object of this invention is to provide a pneumatically dampened piston and valve assembly that extends the useful life of the aerator. 
     A still further object is to further improve the aerator designs of my prior U.S. Pat. No. 6,321,939. 
     These and other objects and advantages of this invention, long with features of novelty appurtenant thereto, will appear or become apparent in the course of the following descriptive sections. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In the following drawings, which form a part of the specification and which are to be construed in conjunction therewith, and in which like reference numerals have been employed throughout wherever possible to indicate like parts in the various views: 
     FIG. 1 is a longitudinal sectional view of my new blast aerator; 
     FIG. 2 is a top plan view of the blast aerator of FIG. 1; 
     FIG. 3 is a bottom plan view of the aerator of FIG. 1; 
     FIG. 4 is an exploded isometric view of the blast aerator assembly; 
     FIG. 5 is an enlarged, fragmentary, sectional view of the spring-less actuator valve assembly, 
     FIG. 6 is a top plan view of the actuator valve assembly seen in FIG. 5; 
     FIG. 7 is an enlarged, fragmentary, longitudinal sectional view of the actuator valve assembly shown coupled to the preferred flanged coupling; 
     FIG. 8 is an isometric view of the actuator valve assembly; 
     FIG. 9 is an exploded isometric view of the actuator assembly; 
     FIG. 10 is an enlarged, partially fragmentary and isometric view of the actuator valve assembly; 
     FIG. 11 is a greatly enlarged, fragmentary isometric view of the preferred piston dampener used with the actuator valve assembly; 
     FIG. 12 is a longitudinal sectional view of the piston of FIG. 1I; 
     FIG. 13 is an exploded bottom isometric view of the actuator valve piston of FIGS. 11-12; 
     FIG. 14 is an enlarged, isometric and sectional view of the piston dampener; 
     FIG. 15 is an enlarged, longitudinal sectional view of the piston dampener; 
     FIG. 16 is a top plan view of the piston dampener of FIGS. 14-15; 
     FIG. 17 is a sectional diagrammatic view showing firing of the blaster and actuator; 
     FIG. 18 is a greatly enlarged, fragmentary longitudinal sectional view of the piston dampener; 
     FIG. 19 is an enlarged, isometric and diagrammatic view of the trigger piston and check-valve ball disposed in the aerator filling position, with portions shown in section for clarity; 
     FIG. 20 is an enlarged, sectional and diagrammatic view of the trigger piston and check-valve ball disposed in an intermediate aerator firing position, with portions shown in section for clarity; 
     FIG. 21 is an enlarged, sectional and diagrammatic view of the trigger piston and check-valve ball disposed in the aerator filling position; 
     FIG. 22 is an enlarged sectional view of the preferred trigger piston; and, 
     FIG. 23 is an exploded isometric view of the quick exhaust trigger assembly. 
    
    
     DETAILED DESCRIPTION 
     With initial reference now directed to FIGS. 1-4 of the appended drawings, an improved spring-less blast aerator constructed in accordance with the best mode of the invention has been generally designated by the reference numeral  20 . U.S. Pat. No. 6,321,939 issued Nov. 27, 2001 and entitled High Stress Blast Aerator with Dampened Piston, which is owned by Global Manufacturing Inc., the owner of this application, is hereby incorporated by reference for purposes of disclosure. 
     Aerator  20  comprises a rigid, barrel-like tank  22  of conventional construction that is mounted adjacent or upon a storage bin, hopper or the like. As explained hereinafter, the interior  24  (FIG. 1) of the blast aerator tank  22  accumulates air that is periodically discharged through a standard, twin flange coupling  26  that is coupled through standard pipes recognized by those skilled in the art that extend to the selected bulk material application (i.e., hopper, bin, bulk material storage tank etc.). Air that has accumulated within tank interior  24  is periodically discharged by the spring-less output valve assembly  28 , that is preferably coaxially secured within the aerator interior  24  by a rigid mounting flange  30  coaxially disposed at the output end  32  of tank  22 . 
     Tank  22  can be dimensioned in various sizes and shapes, as will be recognized by those skilled in the art. Preferably, tank  22  comprise a rigid tab  40  welded to its rear end  42  that facilitates mounting and handling. Optionally, a removable tank inspection plug  46  (FIG. 1) and a mating socket  48  may be included for ease of service and maintenance. A high pressure relief valve  50  is preferably threadably attached below plug  46 . An auxiliary inspection plug  52  is threadably attached to socket  53  welded to the output end  32  of the tank. As best viewed in FIG. 4, mounting flange  30  has a central aperture  31  through which the output valve assembly  28  is inserted in assembly. Flange  30  comprises a plurality of conventional, radially spaced-apart tapped orifices  33  (FIGS. 4,  7 ) for threadably receiving conventional mounting bolts. As best seen in FIG. 5, the valve output assembly body  56  has an integral, larger diameter flange portion  58  that concentrically seats within a suitable counterbore (not shown) concentrically defined in tank flange  30 . 
     The quick exhausting trigger assembly  229  sits atop the tank  22  spaced apart from the spring-less actuator assembly  28  and communicates with it via elongated, tubular fill pipe  59  (FIG. 1) that is coaxial with the longitudinal axis of the tank  22 . Pipe  59  terminates at bushing  60  that is threadably coupled to rigid socket  62  coaxially welded to the tank rear end  42  (FIG.  1 ). Trigger assembly  229  initiates operation of the spring-less actuator assembly, which is interconnected though a standard solenoid control valve communicating with a factory source of H.P. air. A suitable conventional electric timer activates the solenoid at selected intervals, typically causing aerator discharge once an hour. Examples of solenoid valve details are seen in prior U.S. Pat. Nos. 4,469,247 and 4,496,076 owned by Global Manufacturing Inc., the assignee herein, which, for disclosure purposes, are hereby incorporated by reference. 
     With primary reference now directed to FIGS. 1,  3 ,  4  and  7 , the preferred twin flange coupling  26  comprises a rigid, central pipe  66  that coaxially extends between an inner flange  68  and an outer flange  70 . Pipe  66  defines a central passageway  67  (FIG. 1) through which large volumes of air are delivered upon aerator activation. Both flanges  68 ,  70  comprise numerous conventional, radially spaced-apart mounting orifices  74  (FIG. 1) that receive conventional bolts  76  and lock washers  77  (FIG. 4) that secure coupling  26  to tank flange  30 . The valve assembly  28  concentrically seats within the counterbore defined in flange  30 . Gasket  78  is sandwiched between tank flange  30  and the inner flange  68  of coupling  26 . 
     With emphasis now directed to FIGS. 5-10, the output valve assembly  28  is generally cylindrical in appearance. The elongated, tubular valve body  56  comprises a circumferential flange  58  discussed previously that coaxially seats within tank flange  30  and thus aids in centering and alignment. The opposite, open end  80  exposes the tubular inside of the valve body  56 , which generally coaxially receives numerous valve assembly parts to be discussed later. Air accumulated in tank  22  is discharged through exhaust vents  82  (FIGS. 8,  9 ) defined in valve assembly body  56 . A preferably metallic piston  83  that is slidably mounted within valve assembly body  56  normally blocks exhaust vents  82  during the fill cycle. But when deflected away from valve seat  85  the vents  82  are exposed to rapidly vent air from the tank interior  24  to through coupling  26  discussed earlier. 
     In the best mode, the heat-resistant piston  83  is preferably machined from 6061-T6 aluminum. A low temperature aerator may employ a resilient piston made from material such as polypropylene. Metal coating or chrome plating improves piston wear resistance, and may improve sustained piston operation in very high temperature environments. Various coatings suitable for metallic parts are commercially available, as will be recognized by those with skill in the art, will work. Piston  83  is of relatively low mass, which minimizes inertia, and enables rapid piston movements. It has functioned adequately at temperatures of 400 degrees F. However, aluminum pistons suitable for blast aerator use must be adequately cushioned or dampened during at least a portion of their travel, and means are provided for that purpose as discussed hereinafter. 
     An internal ring groove  86  (FIG. 9) defined in the open end  80  of the valve body seats a snap ring  88  that secures the parts together in assembly. Preferable the annular valve seat  85  comprises an external groove  92  that receives a suitable O-ring  94 . As best seen in FIGS. 5 and 10, the lowermost portion of the valve seat  85  is urged against and retained by the internal ledge provided by valve body flange  58 . The inner end of the valve seat  85  includes an internally beveled or chamfered portion  96  that mates with the tapered end  98  (FIGS. 9,  10 ) of the piston  83 . Piston end  98  (FIG. 9) has a concentric ring groove  100  that receives an O-ring  102  that is spaced apart a from concentric ledge  103  (FIG. 10) circumscribing the piston bottom. Piston ledge  103  is disposed adjacent exhaust vents  82  when the piston is disposed in the “fill” position. 
     Piston  83  has an upper, coaxially centered ring groove  106  that seats an external O-ring  108 . As best seen in FIG. 10, a plurality of radially spaced apart air passageways  110  are defined in the tapered end  98  of the piston  83 . These passageways  110  extend between ports  111  in the terminal, interior piston surface  112  (FIG. 10) and the ring groove  100  (FIG. 9) circumscribing the bottom, tapered end  98  of the piston  83 . Resilient O-ring  102  normally occupies ring groove  100  to seal the piston against the seat. In operation, when the piston is rapidly deflected, air velocities in the immediate proximity of the piston and O-ring generate high pressures that can dislodge and deform the critical O-ring. The venting passageways  110  dynamically neutralize potentially deforming pressures, thereby preventing unwanted O-ring travel. 
     Valve cap  130  closes the valve actuator assembly. Concentric, valve cap disk portion  132  comprises an outer ring groove  140  (FIG. 9) that seats an O-ring  142  that seals the valve cap within valve assembly body  56 . Snap-ring  88  holds the cap  130  within body  56  notwithstanding pressure from internal spring  128 . Importantly, a dampener  146  is secured to the piston&#39;s central portion  127 , coaxially aligned with longitudinal axis  124  (FIG.  5 ). The integral, threaded, reduced diameter portion  148  of the plug damper is screwed directly into a suitable passageway  149  (FIG. 9) formed at the piston center. 
     Valve cap  130  comprises an upper, dome-like portion  150  that is integral with lower disk portion  132 . A peripheral, air control ring groove  152  (FIG. 9) forms a boundary between dome  150  and disk portion  132 . A resilient, air-control O-ring  154  occupies the air control groove  152 , and functions as a one-way valve. A plurality of radially spaced-apart, transverse air passageways  157  extend from the valve cap interior dampening passageway  161  through inlet ports  162  (FIG. 10) to ring groove  152 . Air control O-ring  154  is normally captivated within the air control ring groove  152  but functions as a valve, allowing one way air passage by deflecting in response to predetermined air pressure radially applied to it by passageways  157 . This facilitates tank filling, as high pressure air entering via pipe  59  (FIG. 1) traverses passageways  157  (FIG.  10 ), yieldably deflecting the air-control O-ring  154  and filling the aerator tank  22 . The dome portion  150  of the valve cap  130  comprises an internal ring groove  167  (FIGS. 7,  10 ) that seats O-ring  170  to seal inlet pipe  59  (i.e., FIGS. 1,  7 ) that delivers air to pressurize the interior of the valve assembly. 
     When piston  83  moves from the tank-fill position illustrated in FIGS. 5 and 10 to the discharge position of FIG. 17, air is compressed between piston  83  and the end cap occupying reduced volume  131  (FIG.  17 ), thereby dampening movement. As the piston moves upwardly the dampener  146  eventually enters the dampening passageway  161  (FIGS. 5,  10 ). Air entrapped within shrinking volume  129  is vented through dampening passageway  161  through the fill tube  59  (FIGS. 1,  7 ) which is controlled by the quick exhaust trigger valve  229 . Actuator piston travel is dampened by reduced venting rates caused by dampener  146  entering passageway  161 . The dampening provides a cushioning effect that decelerates the retracting piston  83  in combination with spring  128 . 
     Dampener  146  (FIGS. 14-16) comprises a lower diameter portion  148  that is integral with an upper, generally cylindrical portion  180 . As seen in FIG. 10, a suitable resilient O-ring  193  (FIG. 13) is seated within groove  194  in dampener  146 . As the dampener forcibly moves upwardly in dampening passageway  161  (FIGS. 5,  10 ) compressed air within dampening passageway  161  is vented through pipe  59 , being controlled by quick exhaust trigger assembly  229 . Velocities between adjacent surfaces generate considerable pressures that can deform or dislodge O-ring  193 . 
     To fire the aerator, fill tube  59  is depressurized or vented by the trigger assembly  229 . High pressure within the tank  22  is exposed to the actuator piston through vents  82 . Accumulated tank pressure is sufficient to initially dislodge piston  83  from the fill position when pipe  59  is depressurized or vented. Once air flows through the now-unblocked vents  82 , the piston is totally retracted to the discharge position of FIG.  17 . It&#39;s travel at this time is dampened as explained previously, in part by the dampener  146  sliding within dampening passageway  161  (FIG.  10 ). Arrows  210 ,  211  (FIG. 17) indicated airflow continues through vents  82  and pipe  66  to the target application. Once the interior tank pressure is depleted by the blast, piston  83  returns to the fill position  15 , and the cycle repeats. 
     The quick exhaust trigger valve assembly  229  is disposed upon tank  22  at the rear or filling end  34 . It is coupled to internal fill tube  36  (FIGS. 1,  3 ) that leads to actuator valve assembly  23 . A conventional source of external, high pressure air is delivered to trigger assembly  229  in the usual manner, via optional series valves and/or electric solenoid valves. Trigger assembly  229  thus allows the blat aerator tank  22  to periodically fill with air, and additionally, it periodically initiates a blast discharge by turning on the spring-less actuator assembly  28 . 
     Trigger assembly  229  (FIGS. 19-21) comprises a machined, dual diameter steel housing  240  of generally cylindrical proportions. Housing shank portion  280  (FIG. 19) extends downwardly to threaded portion  282  that screws into the aerator tank. A central discharge passageway  272  (FIG. 21) in fluid flow communication with internal volume  245  and inlet passageway  249 . 
     Housing  240  comprises a solid neck portion  246  spaced apart from a preferably circular flange portion  248 , with a reduced-diameter, central portion  250  (FIG. 21) existing  26  therebetween. Portion  250  comprises a plurality of radially spaced apart passageways  251  that are normally blocked by a pair of overlapping, resilient, preferably rubber, circumscribing bands  254  (FIGS. 21,  23 ). These deflectable bands forms a one-way check valve, as they can be deflected outwardly (i.e. in a displacement direction perpendicular to the longitudinal axis of the trigger housing region  250 ) to vent air, but they do not allow air to enter the trigger interior. The passageways  251  oriented perpendicular to the longitudinal axis of the housing, and they communicate with trigger housing interior  245  depending upon the position of piston  260 . 
     The trigger housing rear end comprises a circular flange  248  that receives an annular cap  252  via fasteners  253  with O-ring  258  (FIG. 21) sandwiched therebetween. An integral hub  247  coaxially aligned at the center of plate  252  defines a passageway  249 , which is connected to a remote controlling electric solenoid. The trigger assembly  229  is preferably screwed unto the aerator tank  22  as in FIG.  1 . The aligned pipes and bushings provide a fluid flow passageway that connects the tank interior  24  (FIG. 1) with the trigger assembly interior  244  and  245  (FIG.  21 ). 
     The trigger piston  260  is slidably disposed within the housing interior  245  between end cap  252  and body  246 . The cylindrical housing interior  245  forms a “cylinder” in which annular piston body  290  is dynamically and coaxially disposed for reciprocal motion. Piston  260  is displaceable between the “fill” position of FIGS. 11,  12 , nesting against and within passageway  44 , and a retracted actuating position (i.e., FIGS. 16,  17 ). Piston  60  comprises a generally cylindrical, annular body  90  that is integral with a downwardly-projecting, conical bottom  292 . In the fill position the piston conical bottom  92  (FIG. 22) bears against valve seat  322  (FIG.  19 ), and annular body blocks passageways  251 . When disposed in the actuating position, the piston top  260  (FIG. 21) approaches the underside of cap  252 . 
     A plurality of vertical air passageways  293  (FIG. 22) are defined in piston bottom  292 , radially spaced-apart about the longitudinal, axis of the piston. Passageways  293  are in fluid flow communication with the interior piston passageway  298  and the piston chamber  300 . As best seen in FIG. 22, the upper portion of the generally trapezoidal chamber  300  forms a valve seat  299 . A valve element, preferably a resilient ball  302  (FIG.  23 ), is trapped within chamber  300 , normally free to rest on surface  306 A (FIG.  20 ). Seat  299  forms a boundary with the lower, coaxial chamber  300 ) that gradually increases in diameter towards the bottom of the piston. Airflow through passageway  298  is blocked when ball  302  is deflected into contact with seat  299 . Groove  294  defined in piston body  290  seats a resilient, deflectable O-ring  296  (FIG.  23 ). The elongated through-passageway  298  is coaxial with the center of the piston. 
     Operation: 
     Referring now to FIGS. 19 and 20, air enters passageway  249  via the solenoid as indicated by arrow  320 . This pushes piston  260  downwardly into contact with internal valve seat  322  defined within the housing  240 . At this time ball  302  is also displaced, and it is deflected downwardly (i.e., as viewed in FIG. 19) out of contact with its seat  299  formed at the top of the chamber  300 . Air now passes through the interior of piston  260 , exiting vents  229  and entering pipe  59  as indicated by arrows  329  to reach actuator assembly  28 . The actuator fills the interior of the blast aerator until the tank  22  reaches a sufficient line pressure. The piston  260  stays sealed because of the piston O-rings and the seat-to-surface seals. Since the area exposed to air pressure is larger on the solenoid side than at the tank side, the piston is held firmly against the seat  322 . 
     When the solenoid depressurizes passageway  249  at the piston rear, check ball  302  pops upwardly into contact with seat  299  and closes. Tank pressure now progressively blows the piston  260  back against housing cap  52  as indicated by arrows  330 A and  330  (FIG.  20 ). Backpressure is vented to atmosphere through radially spaced apart, housing orifices  251  (FIG. 20) as the resilient, surrounding bands  254  deflect. Now pipe  59  (FIG. 1) is depressurized, and the blast aerator valve assembly  23  activates and fires the aerator. Backward movement of its piston is dampened by the combination of trigger piston  260  and its internal check valve formed by ball  302 . After detonation, the pressures equalize, and subsequent overpressure applied by the solenoid to passageway  49  again closes the piston for recharging. The cycle continues in the fashion, as governed by the electrical programming of the control solenoid. 
     It will be understood that certain features and subcombinations are of utility and may be employed without reference to other features and subcombinations. This is contemplated by and is within the scope of the claims. 
     As many possible embodiments may be made of the invention without departing from the scope thereof, it is to be understood that all matter herein set forth or shown in the accompanying drawings is to be interpreted as illustrative and not in a limiting sense.