Abstract:
An air driven diaphragm pump having two, opposed pumping cavities. A center section assembly between the pumping cavities includes a cylinder and a power amplifier piston. The power amplifier piston as well as the diaphragms are coupled with a common control shaft. A valve assembly is arranged with a manifold to receive pressurized air and distribute that air in alternating fashion to the sides of the power amplifier piston as well as to each of the diaphragms. By directing pressure to a side of the power amplifier piston facing the same direction as the diaphragm receiving pressure, an amplified pressure on a pump chamber is experienced. With the power amplifier piston being approximately twice as large as the diaphragm assembly, an amplification of three times the pressure on the pump chamber is experienced. Both pump chambers are able to operate to pump material. A relief valve includes an actuator and a valve element which cooperate through a compression spring and stops to provide a force profile for valve actuation and energy for positive actuation. Both the compression spring and a return spring are configured for longevity through a great number of cycles. Blocks of elastomeric material are disclosed.

Description:
This is a divisional application of U.S. patent application Ser. No. 08/842,377, filed Apr. 23, 1997 now U.S. Pat. No. 5,927,954; which, as to subject matter which is common, is a continuing application of U.S. patent application Ser. No. 08/649,543, filed May 17, 1996, now converted to a U.S. Provisional Application Ser. No. 60/058,208 filed May 17, 1996, now expired. 
    
    
     BACKGROUND OF THE INVENTION 
     The field of the present invention is pneumatic mechanisms including reciprocating air driven devices such as air driven diaphragm pumps and valving for such devices. 
     Pumps having double diaphragms driven by compressed air directed through an actuator valve are well known. Reference is made to U.S. Pat. Nos. 5,213,485; 5,169,296; and 4,247,264; and to U.S. Pat. Nos. Des. 294,946; 294,947; and 275,858. An actuator valve using a feedback control system is disclosed in U.S. Pat. No. 4,549,467. The disclosures of the foregoing patents are incorporated herein by reference. 
     Common to the aforementioned patents on air driven diaphragm pumps is the presence of two opposed pumping cavities. The pumping cavities each include a pump chamber housing, an air chamber housing and a diaphragm extending fully across the pumping cavity defined by these two housings. Each pump chamber housing includes an inlet check valve and an outlet check valve. A common shaft typically extends into each air chamber housing to attach to the diaphragms therein. An actuator valve receives a supply of pressurized air and operates through a feedback control system to alternately pressurize and vent the air chamber side of each pumping cavity. Feedback to a valve piston is typically provided by the shaft position. 
     The aforementioned pumps are limited by the magnitude of the inlet air pressure. Even so, such pumps have found great utility in the pumping of many and varied liquids and even powders. Conveniently, shop air is frequently the source of pressure, typically running in the 80 psi to 90 psi range. Naturally, some applications would be advantaged or even made possible by increased pumping pressure. Such applications include long process piping, extremely viscous product pumping, such as automotive paints and paint base compounds, and high compaction filter press operations. Such filter press operations are becoming more and more common with the imposition of stricter environmental regulations requiring the solids in liquid waste to be filtered to a solid waste for safe handling, transportation and disposal. Higher pressures aid in these operations. 
     A number of enhanced pressure air driven diaphragm pumps are available. These pumps typically rearrange the passages of a conventional air driven diaphragm pump such as described above in a manner that allows one of the two pumping chambers to continue to function in that capacity while the other is used as a further air chamber for magnifying the pumping pressure. To this end, the valves in one of the pump chamber housings are blanked off with a blind seat, plugs or specially constructed chamber. Pressurized air is then introduced to the pump chamber side of the diaphragm in the specially prepared pumping cavity. This pressure is provided at the same time that air pressure is provided to the air chamber side of the unmodified pumping cavity. In this way, a single pumping chamber is provided which is subject to twice the compressive pressure as would otherwise be supplied in a conventional air driven diaphragm pump. However, the ability to pump on each stroke is lost and flow rate is reduced. Such pumps create pressure imbalances with possible components failure. 
     Pumps employing a single pumping cavity have also been modified with amplified air pressure through the provision of an adjacent cylinder with air pressure alternately provided to opposing sides of an included piston. Air pressure is again provided to the air chamber side of the pumping diaphragm. 
     Pressure relief valves are also known. Such devices include valve bodies with actuator pins extending therefrom to lift a valve element off of a seat. A flow path through the valve body extends across the valve seat such that flow may be controlled by the valve element which is in turn controlled by the force on the actuator pin. Return springs are used to seat the valve when not lifted from the seat by the actuator pin. 
     SUMMARY OF THE INVENTION 
     The present invention is directed to relief valves useful with reciprocating air driven devices which can withstand a great number of cycles and operate to provide positive opening characteristics. 
     In a first separate aspect of the present invention, the relief valve includes a compression spring between the valve element and the actuator. The compression spring accumulates energy to insure a positive opening of the valve with movement of the actuator. 
     In a second separate aspect of the present invention, the relief valve includes a return spring having the characteristic of an advantageous displacement/force relationship and the ability to withstand a great number of cycles in operation. Installed, the return spring assumes a dome shape and elastomeric material may be employed. 
     In a third separate aspect of the present invention, the relief valve employs the energy storage capacity of a compression spring with the force transmission characteristics of a solid link in opposition to pressure to provide a positive opening characteristic to a valve element. 
     In a fourth separate aspect of the present invention, a compression spring between a valve element and an actuator in a relief valve is configured for extended longevity. A block of resilient material is located within a rigid seat to provide the ability to withstand a great number of cycles of the valve without disabling component wear and fatigue failure. 
     In a fifth separate aspect of the present invention, one or more of the foregoing separate aspects may be combined to positive advantage. 
     Accordingly, it is an object of the present invention to provide improved pneumatic equipment. Other and further objects and advantages will appear hereinafter. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is an end view of a amplified pressure air driven diaphragm pump. 
     FIG. 2 is a top view of the pump of FIG.  1 . 
     FIG. 3 is a cross-sectional side view of the pump of FIG.  1 . 
     FIG. 4 is a front view of the interior of the cylindrical housing of the center section. 
     FIG. 5 is a cross-sectional view taken along line  5 — 5  of FIG.  4 . 
     FIG. 6 is a plan view of a pump diaphragm. 
     FIG. 7 is a cross-sectional view of the diaphragm of FIG. 6 taken along line  7 — 7  of FIG.  6 . 
     FIG. 8 is a plan view of a valve cylinder. 
     FIG. 9 is a cross-sectional view of the valve cylinder taken along line  9 — 9  of FIG.  8 . 
     FIG. 10 is a cross-sectional side view of the valve cylinder taken along line  10 — 10  of FIG.  9 . 
     FIG. 11 is a portion of an air cylinder shown in cross section with the additional detail of a lubricating port. 
     FIG. 12 is a plan view of a valve piston. 
     FIG. 13 is an end view of the valve piston. 
     FIG. 14 is a cross-sectional view of the valve piston taken along line  14 — 14  of FIG.  12 . 
     FIG. 15 is a cross-sectional view of a pressure relief valve. 
     FIG. 16 is a plan view of a manifold. 
     FIG. 17 is a side view of the manifold. 
     FIG. 18 is an end view of the manifold. 
     FIG. 19 is a bottom view of the manifold. 
     FIG. 20 is a cross-sectional view of the manifold taken along line  20 — 20  of FIG.  16 . 
     FIG. 21 is a cross-sectional view of a second pressure relief valve. 
     FIG. 22 is a plan view of an unstressed return spring employed in the valve of FIG.  22 . 
     FIG. 23 is a cross-sectional view of the spring taken along line  23 - 23  of FIG.  22 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Turning in detail to the drawings, FIGS. 1-3 illustrate an amplified pressure double diaphragm pump. Two opposed pumping cavities are arranged to either side of the pump. Each cavity is partially defined by a pump chamber housing  20 . Each pump chamber housing  20  includes a dome shaped cavity  26  intersected by a substantially cylindrical passage  28 . Strengthening ribs  29  are found on the outside of each housing  20 . An inlet check valve, generally designated  30 , includes a ball  32  constrained by retainers  34  and cooperating with a valve seat  36 . The retainers  34  are structurally located within the cylindrical passage  28  of the pump chamber housings  20 . The valve seat  36  on the inlet check valve  30  is conveniently arranged within an adjacent cylindrical cavity  38 . The seat  36  includes an annular notch to receive an O-ring  40  which is softer than the valve seat  36  to prevent pressurized flow around the seat. 
     An inlet manifold  42  provides the adjacent cylindrical cavity  38  of the inlet check valve  30  associated with each pump chamber housings  20 . The manifold  42  includes an inlet  44  with an attachment flange  46 . A passageway  48  extends to each opposed cavity  26 . Support feet  50  are conveniently formed with the inlet manifold  42  to allow stable positioning of the pump. The inlet manifold  42  and the pump chamber housings  20  each include mounting flanges  52  and  54 , respectively. Fasteners  56  associated with the flanges  52  and  54  provide a high pressure joint to resist leakage. The O-rings  40  are also positioned to compress under pressure against the part line between the flanges  52  and  54  to further avoid leakage. 
     An outlet manifold  58  is positioned at the upper end of the pump chamber housings  20  in alignment with the cylindrical passage  28 . Mating flanges  60  and  62  are associated with the outlet manifold  58  and the pump chamber housings  20 , respectively. Fasteners  64  retain the components in position. The manifold includes an outlet  66  having an attachment flange  68 . 
     Outlet check valves, generally designated  70 , associated with the pump chamber housings  20  are constructed in a manner similar to that of inlet check valves  30 . Balls  72  are retained by retainers  74  located within the outlet manifold  58 . Valve seats  76  are positioned in cylindrical cavities  78  located in the upper portion of each pump chamber housing  20 . The valve seats  76  include O-rings  80  as in the case of the inlet check valves  30 . 
     Two air chamber housings  82  are positioned inwardly of the opposed pump chamber housings  20 . The air chamber housings  82  each provide a concave air chamber cavity  83  to closely receive the pumping mechanism located within the opposed pumping cavities when at one end of the stroke so as to minimize air usage. An inlet to each air chamber cavity  83  is provided through a stainless tube  84 . Strengthening and cooling ribs  85  are located on the outer surface of the air chamber housing  82 . 
     Bisecting the opposed pumping cavities are two diaphragms, generally designated  86 , in association with a control shaft assembly including two diaphragm pistons, generally designated  88 . Each of the pump chamber housings  20  and the air chamber housings  82  includes an annular groove for receipt of a diaphragm  86 . The grooves are located on mating surfaces between corresponding pump chamber housings  20  and air chamber housings  82  such that fasteners  90  may compress the components together to securely retain an outer, annular bead  92  on each diaphragm  86 . Inner beads  94  are similarly retained by the diaphragm pistons  88 . Between the beads  92  and  94 , a thin walled annular diaphragm body  96  accommodates flexure and the pressure of both the operating air and the pumped material. 
     The diaphragm pistons  88  each include an inner piston element  98  and an outer piston element  100 . These elements  98  and  100  are securely drawn together by fasteners  102  to ensure clamping of the inner bead  94  of each diaphragm  86 . 
     Located between the opposed pumping cavities and fastened to the air chamber housings  82  is a center section assembly, generally designated  104 . The center section assembly is attached to each air chamber housing  82  by fasteners  106 . The center section assembly  104  is shown to include a cylindrical housing  108  and an end plate  110 . The end plate  110  is retained on the cylindrical housing  108  by fasteners  112 . An O-ring  114  provides sealing at the part line between the cylindrical housing  108  and the end plate  110 . Defined within the center section assembly is a cylinder. 
     In addition to the diaphragm pistons  88 , the control shaft assembly includes a control shaft  116 . The control shaft  116  is shown to be fabricated in two parts with a threaded stud linking the two. Each end of the shaft  116  is threaded so as to be received and fixed to the diaphragm pistons  88 . This arrangement causes the diaphragm pistons  88  and the diaphragms  86  to move together. The shaft extends through seals  118  which are associated with both the center section assembly  104  and the air chamber housings  82  as can best be seen in FIG.  3 . O-rings  120  provide sliding seals while an O-ring  122  provides a static seal on each of the seals  118 . 
     Located within the cylindrical interior of the center section assembly  104  and fixed to the control shaft  116  is a power amplifier piston  124 . This piston is captured between shoulders on each shaft portion. The power amplifier piston  124  is shown to include a center bushing  126 , a piston body  128  and peripheral piston rings  130  for sealing the piston against the inner wall of the cylindrical housing  108 . The control shaft  116 , the power amplifier piston  124 , and the cylindrical housing  108  are most conveniently concentrically arranged about a center axis. 
     To provide power to the pump, a valve assembly is associated with the pump. The valve assembly includes a valve body  132 . Leading to the valve body  132  is a filter  134  to receive and filter a source of pressurized air. The valve body  132  includes an inlet passage  136  into a valve cylinder  138 . The inlet passage  136  includes a partially circumferential channel  140  to aid in the flow of air into the valve cylinder  138 . The valve cylinder  138  is closed by endcaps  142 , one of which is illustrated in FIG.  2 . 
     A valve piston  144 , illustrated in FIGS. 12,  13  and  14 , is sized to fit within the valve cylinder  138  of FIGS. 9 and 10. The fit of the piston  144  within the cylinder  138  is preferably loose enough so that full inlet pressure may build up at the ends of the piston between strokes. The valve piston  144  includes an annular inlet passage  146 . Axial passages  148  and  150  are positioned to either side of the annular inlet passage  146 . Indexing holes  152  accommodate a mating pin (not shown) associated with one of the endcaps  142  to keep the piston appropriately indexed within the valve cylinder  138 . 
     The valve body  132  includes ports  154 ,  156 ,  158  and  160 . These ports  154 - 160  cooperate with the inlet passage  146  and the axial passages  148  and  150  of the valve piston  144 . When the valve piston  144  is in one extreme position at the end of the cylinder  138  nearest the port  154 , the annular inlet passage  146  is in communication with the port  156 . At the same time, the axial passage  150  is in communication with the ports  158  and  160 . With the valve piston  144  in the other extreme position at the end of the cylinder  138  nearest the port  160 , the annular inlet passage  146  is then associated with the port  158  and the axial passage  148  is associated with the ports  154  and  156 . 
     To distribute pressurized air to and vent air from the air cavities associated with both the diaphragms  86  and the power amplifier piston  124 , a manifold, generally designated  162 , is positioned between the valve cylinder  138  and the center section assembly  104 . The manifold  162  includes ports  164 ,  166 , 168  and  170  on the top surface thereof. These ports match up with ports  154  through  160 , respectively, on the valve cylinder  138 . An exhaust passage  172  extends partly through the body of the manifold  162 . The ports  164  and  170  extend to this exhaust passage  172  which exhausts to atmosphere. Ports  166  and  168  extend to distribution passages  174  and  176 , respectively. These distribution passages  174  and  176  each extend to near opposite ends of the manifold  162 . Passage  174  exits to the underside of the manifold  162  through ports  178  and  180 . Similarly, distribution passage  176  extends to ports  182  and  184 . The ports  178  and  182  couple with tubes  84  leading to the air chamber housings  82 . Ports  180  and  184  are coupled with tubes  186  which extend to the center section assembly  104  on either side of the power amplifier piston  124 . A port  187  in the cylindrical housing  108  accommodates a fitting  188  associated with one of the tubes  186 . 
     Two pressure relief valves, generally designated  189 , are engaged with each side of the center section assembly  104  in threaded holes  190 . Actuators  191  extend from the pressure relief valves  189  from either side toward the power amplifier piston  124 . The extent to which the actuators  191  extend into the path of travel of the power amplifier piston  124  provides preselected limits on the piston stroke. Adjustments may be made by rotating the pressure relief valves  189  within the holes  190  provided in the center section assembly  104 . 
     One of the pressure relief valves  189  is illustrated in FIG.  15 . The valve  189  includes a first valve body portion  192  and a second valve body portion  194 . The first valve body portion  192  includes a threaded stud  196  for threaded association with the center section assembly  104 . The first valve body portion  192  also includes a valve seat  198  having a central cavity  200  to receive the actuator  191 . The central cavity  200  extends through both the valve seat  198  and the threaded stud  196  to allow the actuator  191  to extend from the end of this threaded stud  196  for engagement with the power amplifier piston  124 . Vent passages  202  are arranged in the valve seat  198  to vent toward atmosphere. An attachment flange  204  extends outwardly from the valve seat  198 . Through the attachment flange  204 , the first valve body portion  192  may be fastened to the second valve body portion  194 . The second valve body portion  194  provides a chamber  206  within which the actuator  191  may move. Displaced from the actuator  191  through the second valve body portion  194  is a threaded hole  208  through which pressure may be supplied to the chamber  206 . A coil spring  210  biases the actuator  191  such that the protruding portion extends outwardly of the threaded stud  196  and a sealing flange  212  extends over the vent passages  202 . The first valve body portion  192  provides a channel for an O-ring  214  with which the outer periphery of the sealing flange  212  of the actuator  191  cooperates. 
     A second pressure relief valve, generally designated  230 , is illustrated in FIGS. 21 through 23. The same reference numerals as applied to the relief valve illustrated in FIG. 15 are applied where appropriate. Two of the relief valves  230  would be appropriately employed with each side of the center section assembly  104  in the threaded holes  190 . 
     The relief valve  230  includes a valve body  232  assembled from a valve guide  234  and a valve chamber  236 . The valve guide  234  includes a radially extending flange  238  to meet with the periphery of the valve chamber  236  for attachment using machine screws  240 . The valve guide  234  is threaded about the periphery of the body  242  for assembly with the threaded holes  190 . The valve guide  234  includes a guideway  244  which is conveniently cylindrical. The guideway  244  is restricted at one end and includes an access port  246  through that restricted end. The valve chamber  236  defines a cavity  248  which may also be conveniently cylindrical and which is diametrically larger than the guideway  244 . The guideway  244  extends to the cavity  248 . The valve chamber  236  includes a threaded hole  208  through which pressure may be supplied from the valve cylinder  132 . 
     An annular cavity  250  is defined between the valve guide  234  and the valve chamber  236 . The cavity  250  receives an O-ring  252  which may protrude from the surface of the valve guide  234  which faces on the cavity  248 . This surface along with the O-ring  252  define a valve seat outwardly of the guideway. Vent passages  202  also extend through the wall facing on the cavity  248  to provide exhaust. The vent passages  202  are inwardly of the O-ring  252 . A flow path is defined in the relief valve from the hole  208 , through the cavity  248 , across the O-ring  252  defining the valve seat and from the vent passages  202 . 
     An actuator  254  is positioned within the guideway  244  against the restricted end. The actuator  254  is mounted within the guideway  244  such that it may slide within the guideway. An actuator pin  256  extends through the access port  246 . An O-ring seal  258  retained by a snap ring  260  provides a seal about the actuator pin  256 . The actuator pin  256  as employed in the present embodiment is intended to extend into the path of travel of the piston body  128 . To insure longevity of the pump, the actuator is adjusted to interfere with the path of travel of the piston body  128  to a greater degree than is required for marginal operation. This accommodates wear and anomalies. 
     A valve element, generally designated  262 , is also located within the valve body  232 . The valve element  262  faces the guideway  244  and includes a cylindrical body  264  extending slidably into the guideway  244 . A disk  266  extends radially from the cylindrical body  264  and has a first surface facing the cavity  248  and a second surface facing the valve seat so as to seal against the O-ring  252 . The disk  266  is within the cavity  248  to receive pressure upon the first surface. The disk  266  is shown to be displaced from the inner wall of the cavity  248 . This reduces wear and interference and allows air to pass freely about the outer periphery of the disk. 
     Both the actuator  254  and the valve element  262  include cylindrical spring seats  268  and  270 , respectively. These seats  268  and  270  are open cavities facing one another to receive a compression spring  272 . The rims  274  and  276  located about the spring seats  268  and  270 , respectively, act as stops to define a rigid compression link  5  between the actuator  254  and the valve element  262  upon compression of the compression spring  272 . 
     The compression spring  272  is shown to be a cylindrical block of material which is hollow and closed at one end. It has been found that an elastomeric material marketed under the trademark HYTREL® by DuPont performs well in this application. The block  272  may be selected from a wide variety of configurations. The configuration as illustrated offers some sealing ability to the chamber defined between spring seats  268  and  270 . 
     A return spring, generally designated  278 , is located within the cavity  248  between the valve body  232  and the disk  266  of the valve element  262 . This return spring  278  is shown in its relaxed state in FIGS. 22 and 23. A pin  280  located on the valve element  262  cooperates with a hole  282  in the center of the return spring  278  to insure placement. The spring  278  is also preferably of an elastomeric material such as HYTREL® and is arranged within the cavity  248  in a dome shape. The return spring  278  includes a central body  284  about the hole  282  and legs  286  which extend both radially and, when within the cavity  248 , are curved axially. Spaces between the legs  286  allow flow from the threaded hole  208  to the valve seat. Because of the flattened dome shape, the spring constant is relatively small through the anticipated movement of the valve element  262 . This provides for a relatively predictable return force in spite of manufacturing tolerances and the like. The spring constant then increases substantially beyond this range of movement. The return spring  278  is also preloaded to establish a bias of the valve element  262  toward seating against the O-ring  252 . 
     At rest, the relief valve  230  has the valve element  262  seated against the O-ring  252  of the valve seat because of the preload compression on the return spring  278 . The compression spring  272  may or may not include a preload. However, any preload is appropriately substantially smaller than the preload on the return spring  278  such that the compression force of the return spring  278  dominates. The actuator  254  also extends toward the restricted end of the guideway  244  to its travel limit. 
     In operation, pressure is contained within the cavity  248  from the hole  208 . As the disk  266  is against the O-ring  252 , pressure cannot be vented from the device. As the actuator pin  256  is depressed into the valve body  232 , this motion is resisted by the pressure within the cavity  248  exerted against the disk  266  on the side facing the cavity. It is also resisted by the return spring  278 . A typical pump application would employ shop air having a force exerted across the disk  266  of about 100 lbs. The return spring  278  preferably has a precompression of about 35 lbs. of force. 
     The force associated with depression of the actuator pin  256  is transmitted to the valve body  262  through the compression spring  272 . The compression spring is preferably designed to reach a maximum of about 80 lbs. of force when the rims  274  and  276  engage. The 80 lbs. of force remains as no match to the combined pressure force of about 100 lbs. and return spring force of about 35 lbs. However, once a rigid link is established between the actuator  254  and the valve element  262 , force increases substantially instantaneously to in excess of the combined pressure and return spring forces. The disk  266  then moves from the O-ring  252  of the valve seat. 
     As pressure drops within the cavity  248  and increases on the second side of the disk  266 , the compression force of the compression spring  272  becomes dominant. The energy stored within that spring can, therefore, drive the valve element  262  further open. As the compression force of the compression spring  272  reduces with expansion of the spring, it comes into equilibrium with the return spring  278  and remains there until the actuator pin  256  is allowed to extend from the valve body  232 . The bias force of the return spring  278  then becomes dominant as the force from the compression spring  272  drops toward zero. The valve element  262  can then return to a seated position. The ranges of compression force thus operating provide for the return spring  278  to have a greater minimum compression force than the compression spring  272  and the compression spring  272  to have a greater maximum force than the return spring  278 . 
     Extending from each of the holes  208  of the pressure relief valves  189  or  230  are elbows  216 . The elbows are coupled with flexible tubes  218  which extend to the manifold  162 . Elbows  220  are threaded into the manifold  162  at two passages  222 . The passages  222  turn  90  degrees to meet the valve cylinder  138  of the valve assembly. Ports  224  extend through the wall of the cylinder to annular grooves  226 . Thus, valve control passageways including the tubes  218 , the passages  222  and the ports  224  cooperate with the pressure relief valves  189  or  230  to vent the ends of the valve cylinder  138  when the actuator  191  is forced by the power amplifier piston  124  away from the valve seat  198 . 
     Turning to the operation of the double diaphragm pump, it shall be described from rest. With no pressure to the pump, the valve piston  144  will fall to the lower end of the valve cylinder  132  which is preferably arranged with the axis of the valve cylinder  132  in vertical orientation. Pressure will be introduced through the filter  134  and into the inlet passage  136 . The annular inlet passage  146  on the valve piston  144  will convey the pressurized air to the port  158 . It will then pass into the manifold  162  through the port  168  to the distribution passage  176 . From the port  182 , the pressure will be conveyed by a tube  84  into one of the air chamber housings  82 . The pressurized air presented to the air chamber cavity  83  will put force on the diaphragm  86 . Pressure is also conveyed by the port  184  through the tube  186  to one side of the power amplifier piston  124 . The pressurized working surfaces of both the diaphragm  86  and the power amplifier piston  124  are facing in the same direction. With the pressure accumulating in one of the air chambers and on a corresponding side of the power amplifier piston, the diaphragms  86 , the diaphragm pistons  88  and the control shaft  116  move to compress one of the pump chambers  24  and expand the other. The appropriate check valves open to alternately expel material from and draw material into the pump chambers  26 . 
     During the stroke of the control shaft  116 , the pressure relief valves  189  or  230  are closed. The valve piston  144  loosely fits within the valve cylinder  138 . Consequently, the pressurized air entering through the inlet passage  136  fully pressurizes the ends of the valve piston  144 . The differential pressure diametrically cross the valve piston  144  from the inlet passage  136  to the port  158  draws the valve piston  144  against the ports  154 ,  156 ,  158  and  160 . Additionally, the exhaust passage  172  is open to the ports  154  and  160  which further draws the valve piston  144  against these ports. The axial passage  148  couples the ports  154  and  156  so that, as one side of the power amplifier piston  124  is being pressurized, the other is being vented. At the same time, as one air chamber is being pressurized, the other is being vented. 
     Once the power amplifier piston  124  reaches one of the actuators  191  or actuator pins  256 , the upper end of the valve cylinder  138  is vented through a valve control passageway. As this occurs, a transitory unequal distribution of forces exists axially on the valve piston  144 . Because the valve piston  144  has spacers  228  at either end, a small volume of air is present even with the valve piston  144  hard against one end of the valve cylinder  138 . This causes the piston to shift to the upper end of the valve cylinder  138 , reversing the pressurizing and venting. At this time, the control shaft  116 , through the reversal of pressure and vent, moves in the opposite direction. In this way, each cycle continues to create an oscillation of the control shaft  116  and all components associated therewith to alternately pump from each pump cavity  26 . 
     The diaphragm pistons  88 , the diaphragms  86  and the power amplifier piston  124  thus cooperate to provide an amplified pressure to each pump cavity  26 . With the surface area of the power amplifier piston at approximately twice the active area of each diaphragm piston  88  and diaphragm  86  together, the resulting amplification may be three times that experienced with pressure on the diaphragm  86  and diaphragm piston  88  alone. At the same time, both pump cavities  26  of the double diaphragm pump are able to be used in pumping with each reversal of the control shaft  116  resulting in both a suction stroke on one side and a power stroke on the other. Through the design of the manifold  162 , no increased complication is experienced with the control and pressure valving. 
     Accordingly, an improved amplified pressure air driven diaphragm pump with double working diaphragms is disclosed. While embodiments and applications of this invention have been shown and described, it would be apparent to those skilled in the art that many more modifications are possible without departing from the inventive concepts herein. The invention, therefore, is not to be restricted except in the spirit of the appended claims.