Abstract:
Quick acting blast aerators having rigid accumulation tanks with internal valve assemblies comprising a tubular body, an end cap teat receives air through an inlet controlled by solenoids, and an internal piston that contacts a valve seat during filling, and retracts to expose exhaust vents upon firing. The valve calp comprises a ring groove and an O-ring check valve. An internal dampening passageway vertically extends through the cap. Internal air passageways extend form the passageway to the air-control groove, admitting air into the tank by dislodging the O-ring. The high temperature piston slides between a tank-fill position bearing against the valve seat and a retracted position exposing the exhaust vents. An internal return spring extends between a deep, annular recess in the piston, and a groove formed in the bottom of the end cap. A dampener projecting from the piston is received within the passageway traversing the end cap.

Description:
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 know 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 cohesive bonds either by adhesion due to chemical or hydrostatic attraction, or particles may 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 tends to interfere with proper flow. 
     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. 
     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 are also preferred 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 prine 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 accumulate air supplied through the H.P. air lines available 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 structure periodically activates the air cannon, and the large volume of air that was slowly accumulated in the holding tank is rapidly, forcibly discharged within a few milliseconds. The volume of compressed air released by a typical quick opening valve in 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. 
     Thus, the blast of the 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 matlingly, 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 highly 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 the 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. 
     I have found that it is desirable to not only dampen piston travel and movements, but to control the flow of air from the valve body. To dampen piston movement, it is proposed to bleed off pressure in a controlled fashion. I have found it desirable to pressurize the entire rear area of the piston to prevent damaging internal impacts. 
     SUMMARY OF THE INVENTION 
     A quick acting blast aerator system according to my invention comprises a rigid, cylindrical tank adapted to be secured upon a container or hopper. A preferred embodiment is ideal for high temperature applications. The aerator comprises a special valve assembly preferably mounted within the tank. The high temperature variation includes a metallic, heat-resistant piston, and a special dampening system for preventing piston damage. 
     The preferred valve assembly comprises a rigid, tubular- body having a pair of opposed ends, and a plurality of exhaust vents. The body is secured with suitable flanges to the tank discharge end. An elongated, fill pipe extends through the tank interior to the actuator valve assembly for delivering air. The inlet pipe is controlled by suitable, conventional external solenoid valves that alternately pressurize it (i.e., by connection with factory H.P. air) and depressurizes it (i.e., for aerator firing). A piston is slidably mounted within the valve assembly body and normally blocks the exhaust vents during tank filling. Preferably the piston contacts an internal valve seat coaxially secured to the valve assembly body at one end. When the piston is deflected away from valve seat the exhaust vents are unobstructed and discharge of the aerator 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 is sealed and fitted at the top of the valve assembly body and closes the valve actuator assembly. A snap-ring seated within a suitable ring groove holds the cap coaxially within the actuator valve body. Preferably the valve cap comprises an upper, domelike portion and an integral, lower disk portion coaxially fitted to the actuator body. Importantly, an air control ring groove defined in the cap forms a boundary between the dome and disk portions. Further, an internal dampening passageway extends through both the disk and dome portions. A resilient, air-control O-ring seated within the air control groove functions as a one-way valve. Numerous internal, radially spaced-apart, air passageways extend from the interior dampening passageway to the air-control groove, and these conduct air into the aerator to fill the tank by dislodging the air-control O-ring. 
     The piston moves from a tank-fill position bearing against the valve seat, to a retracted position exposing the exhaust vents. An internal return spring extends between a deep, annular recess formed in the piston, and a glove formed in the bottom of the end cap. Importantly, in the high temperature embodiment, the piston comprises a generally cylindrical dampener that is received within the dampener passageway longitudinally traversing the end cap. The preferred dampener comprises a lower diameter portion screwed to a threaded recess in the piston top, and an upper, generally cylindrical portion that enters the dome passageway. A central bore extends concentrically through the dampener interior. An upper ring, groove in the dampener seats an O-ring. Accidental dislodging of the O-ring is prevented by venting passageways extending between the dampener interior bore and the dampener O-ring groove. Further passageways beneath the dampener O-ring establish fluid flow communication between the dampener exterior and its bore for dampening control. 
     Thus a basic object is to provide a highly reliable blast aerator or air cannon whose piston is conditioned for the high stresses encountered in response to both high pressure and high temperatures. 
     Another object is to provide a blast aerator of the character described in which the internal quick dump valve subassembly is operationally disposed completely within the holding tank. 
     A fundamental option is to provide a high capacity blast aerator of the character described with an improved valve assembly. It is a feature of my invention that a special piston design provides controlled dampening of the piston during its rearward stroke to minimize mechanical shock. 
     A related object is to control piston wear and minimize piston deformation by pneumatically cushioning and controlling the piston during blast discharges. 
     Another general object of this invention is to provide a dampened piston and valve assembly that extends the useful life of the apparatus. 
     A still further basic object is to provide a blast aerator of the character described that minimizes the frequency of service calls required in the field. 
     A further object is to provide an improved valve assembly that can be retrofitted to existing blast aerators and air canionis. 
     Another object of this invention is to provide a blast aerator of the character described characterized by a high volume blast Output valve assembly. 
     Another important object is to maximize the efficiency and life of the valve assembly piston by dynamically cushioning it during critical movements. 
     A still further object is to provide a blast pipe assembly of the character described which can easily and efficiently be employed with existing aerator tank designs. 
     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 fragmentary sectional view of my new high temperature blast aerator with my new dampened actuator, with portions thereof shown in section or broken away for clarity, 
     FIG. 2 is a top plan view of the high temperature blast aerator taken generally from a position above FIG. 1 
     FIG. 3 is a bottom plan view of the high temperature blast aerator taken generally from a position beneath FIG. 1; 
     FIG. 4 is an exploded isometric view of the preferred high temperature blast aerator; 
     FIG. 5 is an enlarged, fragmentary, sectional view of the high temperature actuator valve assembly; 
     FIG. 6 is a top plan view of the high temperature actuator valve assembly of FIG. 5; 
     FIG. 7 is an enlarged, fragmentary, longitudinal sectional view of a preferred actuator valve assembly shown coupled to the preferred flanged coupling; 
     FIG. 8 is an isometric view of the high temperature actuator valve assembly; 
     FIG. 9 is an exploded isometric view of the preferred high temperature actuator; 
     FIG. 10 is an enlarged, fragmentary isometric view of the preferred high temperature actuator valve assembly with portions thereof shown in section for clarity, 
     FIG. 11 is a greatly enlarged fragmentary isometric view of the preferred high temperature piston dampener; 
     FIG. 12 is a longitudinal sectional view of the preferred high temperature piston dampener; 
     FIG. 13 is a top plan view of the preferred high temperature dampener, taken from a position generally above FIG. 12; 
     FIG. 14 is an enlarged, fragmentary, and sectional diagrammatic view of the high temperature valve assembly, with portions thereof shown in section for clarity or omitted for brevity, illustrating component position when in a discharging position; 
     FIG. 15 is a reduced scale diagrammatic view similar to FIG. 14 showing the high temperature valve assembly disposed in a tank filling position; 
     FIG. 16 is a fragmentary diagrammatic view similar to FIGS. 14 and 15 but showing valve assembly piston movement as it retracts from the closed, fill position of FIG. 15 to the discharge position of FIG. 14; 
     FIG. 17 is a fragmentary sectional view of an alternative low-temperate embodiment, with portions thereof shown in section or broken away for clarity; 
     FIG. 18 is an enlarged, fragmentary, sectional view of the low temperature actuator valve assembly; 
     FIG. 19 is a top plan view of the low temperature actuator valve assembly of FIG. 18; 
     FIG. 20 is an exploded, isometric view of the preferred low temperature actuator; and, 
     FIG. 21 is an isometric view of the low temperature actuator valve assembly. 
    
    
     DETAILED DESCRIPTION 
     With initial reference now directed to FIG. 1-6 of the appended drawings, a high temperature blast aerator constructed in accordance with the best mode of the invention has been generally designated by the reference numeral  20 . As described hereinafter, a preferred low temperature aerator is designated by the reference numeral  21  (FIG.  17 ). 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. Aerator  20  is ideally adapted for attachment to high temperature applications such as ovens or kilns, and includes a special valve assembly described later that employs a metallic, heat-resistant piston. 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 (FIGS. 7,  14 ) 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 new valve assembly  28 , that is coaxially secured within the aerator interior  24  by a rigid, front 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 valve assembly  28  is inserted for mounting. 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 assembly body  56  has an integral, larger diameter flange portion  58  that concentrically seats within a suitable counterbore (not shown) concentrically defined in flange  30  (i.e., FIGS. 1,  7 ). An elongated, tubular fill pipe  59  (FIG. 1) that is coaxial with the longitudinal axis of the tank  22  extends within tank interior  24  between actuator valve assembly  28  and a bushing  60 . This pipe comprises an air inlet means for filling, the tank. The bushing,  60  is threadably coupled to a rigid socket  62  coaxially welded to the tank real end  42  (FIG.  1 ). Suitable external pneumatic solenoid control valves (not shown) coupled to busling,  60  (FIG. 1) in the usual manner control the aerator  20  by actuating valve assembly  28 , as will hereafter be described. In general, a one inch, three-way, normally-open electric solenoid valve is preferred. The solenoid control valve interconnects the valve assembly with a factory source of H.P. air for filling, and/or switches to ambient air pressure for firing. A suitable conventional electric timer activates the timer 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, foor 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,  7 ) 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. 4) that receive conventional bolts  76  (and lock washers  77 ) 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 improved actuator 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 (FIG. 9) to be discussed later. Air accumulated in tank  22  is discharged through exhaust vents  82  (FIG. 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  (i.e., as illustrated in FIGS. 14 and 16) 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. (The low temperature aerator  21  (FIG. 17) to be discussed later employs a resilient piston made from material such as polypropylene.) It appears from recent experiments that a metal coating or chrome plating improves 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, but experimental results are not definitive at this time. However, it appears that heat resistant, self lubricating coatings are preferred. The high temperature aluminium piston  83  is of relatively low mass, which minimizes inertia, and enables rapid piston movements. It has functioned adequately at tent 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. High pressure air within the filled tank exerts pressure on the piston  83  via ledge  103  which is sufficient to dislodge piston  83  when dampener passageway  161  is vented to atmosphere. The fill pipe  59  vents tile dampener passageway when it is depressurized by external solenoid valves to fire the aerator. 
     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 operations 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. 
     As best seen in FIGS. 5 and 10, a relatively deep, annular recess  120  is formed in the top  122  of aluminum piston  83 . Recess  120  is concentric with the longitudinal axis  124  (FIG. 5) of the piston  83 , and with the integral, reduced diameter center portion  122 . A return spring  128  concentrically seated within recess  120  atop piston  83  surrounds piston center portion  127  and extends upwardly into mechanical contact with a valve cap  130 . The upper portion of springy  128  is seated within an annular groove  135  cut into the underside of the lower disk portion  132  of valve cap  130 . After the aerator  20  discharges, spring  128  rapidly pushes the piston back into sealing contact with the valve seat  85 . Importantly, the deep recess  120  is sized to adequately seat and house the compressed spring  128 , which compresses during piston travel when the aerator is activated. In this manner, unwanted, potentially injurious mechanical contact of the Spring with the valve cap  130  is prevented, as adequate spring clearance is provided by the captivating recess  120 . 
     Noting FIGS. 5,  7  and  8  collectively, the 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 . As mentioned earlier, 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. 14, the volume  129  (FIGS. 5,  15 ) between the piston  83  and the end cap disk portion  132  shrinks; air trapped therewithin acts as a cushion as it compresses, and a dampening effect upon the piston is provided. Volume  129  (i.e., FIG. 15) contracts during piston displacement to the much smaller volume  131  (FIG.  16 ). During this piston movement the return spring  128  is shielded within piston recess  120 . 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  (FIG. 1,  7 ). 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 . 
     Turning to FIGS. 11-13, dampener  146  comprises a lower diameter portion  148  previously described that is integral with an upper, generally cylindrical portion  180 . Portion  180  comprises a central bore  182  that extends concentrically downwardly into the dampener interior from annular top  186 . Transverse passageways  187 ,  188  establish fluid flow communication between the dampener exterior and bore  182 . Air is controllably vented through passageways  187 ,  188  (FIG. 11) as the piston and dampener move upwardly and volume  129  (FIG. 5) contracts. A pair of similar transverse passageways  190 ,  191  (FIG. 11) establish fluid flow communication between concentric groove  194  (FIGS. 11,  12 ) and internal bore  182 . As seen in FIG. 10, a suitable resilient O-ring  193  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 . Velocities between adjacent surfaces generate considerable pressures that can deform or dislodge O-ring  193 . Vents  190 ,  191  (FIG. 11) equalize pressure on opposite sides of dampener O-ring  193  (FIG. 10) to prevent deformation and removal. 
     The valve actuator filling cycle is best-illustrated in FIG.  14 . High-pressure air travelling through the fill pipe  59  is designated by the arrow  200 . The overpressure dislodges O-ring  154  from its seat, allowing air to enter the blast tank, as indicated by arrows  202 ,  203 . 
     To fire the aerator, fill tube  59  is depressurized or vented by the external solenoid apparatus, as indicated by arrow  206  (FIG.  15 ). At this time it should be noted that O-ring  154  remains seated. High pressure within the tank is exposed to the piston through vents  82 . Pressure accumulated about ledge  103  (FIG. 10) is sufficient to initially dislodge piston  83  from the fill position (FIG. 15) once pipe  59  is depressurized or vented. Once air flows through the now-unblocked vents  82 , as indicated by arrows  207 ,  208 , the piston is totally retracted to the discharge position of FIG.  16 . 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 ). Airflow  210 ,  211  continues through vents  82  and pipe  66  to the intended application. Once the interior tank pressure is depleted by the blast, piston  83  returns to the fill position of FIG. 15, and the cycle repeats. 
     The low temperature blast aerator  21  (FIG. 17) is very similar to aerator  20  discussed above. However, it employs a low temperature valve assembly  28 B with a resilient, polypropylene piston  83 B instead or aluminum piston  83 . The valve assembly body  56  is the same as previously described. As before, valve assembly  28 B is mechanically secured to mounting flance  30 . As before, a tubular fill pipe  59  (FIG. 17) extending through tank interior  24  pressurizes the valve assembly. Suitaible external pneumatic solenoid control valves are employed. 
     With primary emphasis now on FIG. 18-21, tile low pressure actuator assembly  28 B is generally cylindrical, employing the same tubular valve body  56  discussed earlier. Air accumulated in aerator  21  is discharged through vents  82  defined in the valve assembly body  56 , as discussed earlier. The preferably polypropylene piston  83 B is suitable for low temperature applications. It is slidably mounted within valve assembly body  56 , and normally blocks vents  82  during the fill cycle. Other parts like cap  130  are assembled as before. 
     Piston  83 B has a beveled end  98 B (FIG. 18) that mates with the valve seat  85  discussed previously. Piston end  98 B has a concentric ledge  103 B (FIG. 18) circumscribing the piston bottom. Piston ledge  103 B blocks vents  82  when in the “fill” position. High pressure air within the filled tank pressurizes piston  83 B via ledge  103 B 
     Piston  831 B has an upper, coaxially centered ring groove  106 B (FIG. 20) that seats O-ring  108 B. The annular recess  120 B formed in the top  122 B of piston  83 B is concentric with the longitudinal axis of the piston  83 B. The return spring  128  concentrically seated within recess  120 B atop piston  83 B Surrounding piston center portion  127 B extends upwardly into mechanical contact with valve cap  130  and annular groove  135  explained earlier. 
     The valve actuator filling cycles illustrated in FIGS. 14 and 15 apply in this case as well. High-pressure air is delivered through the fill pipe  59 , and O-ring  154  is dislodged, filling the blast aerator tank. When the till tube  59  is depressurized or vented, piston retraction exposes to vents  82 , and a blast occurs as aforedescribed. 
     From the foregoing, it will be seen that this invention is one well adapted to obtain all the ends and objects herein set forth together with other advantages which are inherent to the structure. 
     It will be understood that certain features and subcombiniations 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.