Patent Publication Number: US-6901960-B2

Title: Double diaphragm pump including spool valve air motor

Description:
FIELD OF THE INVENTION 
   The present invention relates to air operated double diaphragm pumps, and more particularly to double diaphragm pumps incorporating a spool valve as an air motor. 
   BACKGROUND OF THE INVENTION 
   Air operated double diaphragm pumps are known for pumping a wide variety of substances. In some applications, double diaphragm pumps are utilized to pump caustic chemicals, in other applications, comestible substances such as flowable foods and beverages can be pumped. In such applications, the pumps are often constructed primarily of materials that resist corrosion and that are chemically compatibable with the substances being pumped. In this regard, polymeric materials are often used for various pump components. 
   To operate the double diaphragm pump, air motors are having flow control spool valves are often provided to regulate the flow of compressed air through the pump and oscillatingly drive the pump diaphragms. The spool valves generally include a valve housing that defines a valve chamber, and a spool that is received by the valve chamber. The spool includes a plurality of seals that delimit the chamber into two or more subchambers. The spool is slidably movable within the valve chamber such that the seals, and therefore the subchambers, move within the chamber to regulate the flow of pressurized air to the pump diaphragms. 
   SUMMARY OF THE INVENTION 
   The present invention provides a spool valve including a valve housing, a first insert surrounded by the housing, and a second insert surrounded by the housing. The inserts each include an inner surface that cooperates with the valve housing to at least partially define a valve chamber. A spool is slidably positioned within the valve chamber and includes a first seal engaging the inner surface of the first insert, and a second seal engaging the inner surface of the second insert. The first and second seals delimit the valve chamber into valve subchambers. 
   The present invention also provides a double diaphragm pump that includes a pump housing, first and second pump diaphragms, an inlet manifold, an outlet manifold, and an air motor. The pump housing defines first and second pumping chambers, and the diaphragms are housed in respective ones of the pumping chambers. Each diaphragm divides its respective pumping chamber into a first subchamber and a second subchamber, and the diaphragms are coupled to one another other for reciprocating movement within the pumping chambers. 
   The inlet manifold and the outlet manifold are coupled to the pump housing and communicate with at least one of the first subchambers. The air motor is also coupled to the pump housing and fluidly communicates with the second subchambers to reciprocatingly drive the diaphragms. The air motor includes a spool valve having a valve housing, an insert surrounded by the valve housing, and a spool. The valve housing and the insert cooperate to at least partially define a valve chamber, and the spool is slidably positioned within the valve chamber. The spool includes a seal engaging an inner surface of the insert and delimiting the valve chamber into valve subchambers. Movement of the spool within the valve chamber selectively communicates pressurized fluid to one of the second subchambers to move the associated diaphragm, thereby pumping fluid through the pump. 
   The present invention further provides a method for making an air motor for a double diaphragm pump. A tubular insert is formed that has a generally cylindrical inner surface, and the insert is positioned within a cavity of a forming die. A polymer is molded around the insert to form a valve body. The valve body cooperates with the inner surface of the tubular insert to define at least a portion of a valve chamber. A valve spool including a seal is inserted into the valve chamber, and the seal is aligned for engagement with the inner surface of the insert such that the valve chamber is delimited into valve subchambers. 
   Other features of the invention will become apparent to those skilled in the art upon review of the following detailed description and drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a front view of an air operated double diaphragm pump assembly embodying the invention. 
       FIG. 2  is an end view of the air operated double diaphragm pump assembly of FIG.  1 . 
       FIG. 3  is a section view taken along line  3 — 3  of FIG.  2 . 
       FIG. 4  is a section view taken along line  4 — 4  of FIG.  2 . 
       FIG. 5  is a section view similar to  FIG. 4  illustrating an alternative embodiment of the invention. 
   

   Before one embodiment of the invention is explained in detail, it is to be understood that the invention is not limited in its application to the details of construction and the arrangements of the components set forth in the following description or illustrated in the drawings. The invention is capable of other embodiments and of being practiced or being carried out in various ways. Also, it is understood that the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting. The use of “including” and “comprising” and variations thereof herein is meant to encompass the items listed thereafter and equivalents thereof as well as additional items. 
   DETAILED DESCRIPTION 
     FIGS. 1-3  illustrate an air operated double diaphragm pump  10  embodying the invention. The pump  10  includes a main pump housing assembly  14  that includes a centerbody  18 , a pair of air caps  22  coupled to opposite sides of the centerbody  18 , and a pair of fluid caps  26  coupled to the air caps  22  and cooperating therewith to define a pair of pumping chambers  30   a ,  30   b  (see FIG.  3 ). Each fluid cap  26  includes an inlet flange  34  and an outlet flange  38 . The inlet flanges  34  are coupleable, independently or in combination, to an inlet manifold  42 . Similarly, the outlet flanges  38  are coupleable, independently or in combination, to an outlet manifold  46 . The flanges  34 ,  38  and manifolds  42 ,  46  can be configured such that the pumping chambers  30   a ,  30   b  operate in parallel to pump a single fluid (as illustrated), pump two fluids independently of each other, or mix two pumped fluids together in the outlet manifold  46 . An air motor  48  in the form of a spool valve assembly is secured to the centerbody  18  and is configured to drive the pump  10 , as will be described further below. 
   With reference to  FIG. 3 , flexible diaphragms  50   a ,  50   b  are secured within respective pumping chambers  30   a ,  30   b  between the associated air caps  22  and fluid caps  26 . The diaphragm  50   a  delimits the pumping chamber  30   a  into a first subchamber  54   a  and a second subchamber  58   a . Similarly, the diaphragm  50   b  delimits the pumping chamber  30   b  into a first subchamber  54   b  and a second subchamber  58   b . The first subchambers  54   a ,  54   b  communicate with the inlet manifold  42  and the outlet manifold  46 , and the second subchambers  58   a ,  58   b  communicate with the air motor  48  via the centerbody  18 . The diaphragms  50   a ,  50   b  are coupled to each other by a diaphragm rod  62  that is slidingly coupled to the centerbody  18 . During pump operation, the diaphragm rod  62  reciprocates within the centerbody  18  and the diaphragms  50   a ,  50   b  deflect within the pumping chambers  30   a ,  30   b  to increase and decrease the volume of the first subchambers  54   a ,  54   b , and the second subchambers  58   a ,  58   b.    
   To regulate fluid flow through the pump  10 , the outlet manifold  46  and the inlet flanges  34  include check valves  66 . The illustrated check valves  66  are ball check valves and include a valve ball  70 , a valve seat  74 , and a valve spring  76 . The valve springs  76  urge the valve balls  70  into sealing engagement with the valve seat  74 . In some embodiments, the valve springs  76  can be eliminated and the valve balls  70  are urged into engagement with the valve seats  74  due to pressure pulses that are inherent in pump operation. The check valves  66  operate in a known manner to allow fluid to flow substantially in a single direction from the inlet manifold  42  toward the outlet manifold  46 . Other types of check valves, such as flapper valves can be used as well. In some embodiments, the check valves  66  can be formed integrally with the inlet and outlet manifolds,  42 ,  46 , or integrally with the fluid caps  26 . Other embodiments can incorporate check valves  66  that are completely separate assemblies that are positioned and secured between the manifolds  42 ,  46  and the fluid caps  26  upon assembly of the pump  10 . 
   Referring now to  FIG. 4 , the spool valve air motor  48  includes a valve housing comprising a valve block  78  and a valve cap  82  that are coupled to one another and cooperate to at least partially define a generally cylindrical valve chamber  86 . The valve cap  82  includes a portion  89  that is received by the valve block  78 , and the valve cap  82  is secured to the valve block  78  by fasteners  88 , although other techniques for securing the valve cap  82  to the valve block  78  such as clamps, adhesives and the like can be used as well. The valve block  78  defines an inlet opening  90  in a central portion thereof that communicates with the valve chamber  86 . The inlet opening  90  can include a threaded insert  92  such that a source of pressurized fluid, such as air, can be coupled to the inlet opening  90 , thereby increasing the pressure within the valve chamber  86 . The inlet opening  90  can also be coupled to the pressurized air source using other known connections, such as air nipples and the like. The valve block  78  also defines an outlet opening  94  that provides fluid communication between the valve chamber  86  and the centerbody  18 , as well as other pump components. 
   A valve spool  98  is received by the valve chamber  86  and is slidingly movable therein for reciprocation along a valve axis  100 . The valve spool  98  is movable between a first position (illustrated in  FIG. 4 ) where the valve spool  98  is shifted toward the valve cap  82 , and a second position (not shown), where the valve spool  98  is shifted away from the valve cap  82 . The illustrated valve spool  98  includes a large end  102  and a small end  106 , and a generally resilient annular seal  110  surrounds each end  102 ,  106 . The seals  110  engage the valve block  78  and the valve cap  82  to delimit the valve chamber  86  into valve subchambers  86   a ,  86   b ,  86   c . The valve spool  98  also includes two radially extending collars  114  positioned between the ends  102 ,  106 . During operation of the illustrated pump  10 , subchamber  86   a  is substantially always vented to the atmosphere, subchamber  86   b  is substantially always at an elevated pressure, and subchamber  86   c  alternates between the elevated pressure and atmospheric pressure. The changes in pressure within the subchamber  86   c  reciprocatingly drive the valve spool  98  between the first and second positions. Specifically, an end surface  115  of the valve spool  98  faces the subchamber  86   c , and an annular surface  116  of the valve spool  98  faces the subchamber  86   b . The surface area of the annular surface  116  is less than the surface area of the end surface  115  such that, when an equal pressure is applied to both surfaces (as is the case when the subchamber  86   c  is at the elevated pressure), the total force acting upon the end surface  115  is greater than the total force acting on the annular surface  116 . The valve spool  98  is therefore urged toward the first position (illustrated in FIG.  4 ), which is referred to as the “piloted position”. When the subchamber  86   c  is vented to the atmosphere, the total force on the end surface  115  is reduced, and the pressure applied to the annular surface  116  moves the valve spool  98  toward the second position. 
   Positioned in the outlet opening  94  of the valve block  78  is a valve plate  118 . The valve plate  118  defines a pair of fill orifices  122   a ,  122   b , and an exhaust orifice  126  between the fill orifices  122   a ,  122   b . The valve plate  118  substantially overlies the outlet opening  94  such that air flowing out of the valve chamber  86   b  flows through at least one of the fill orifices  122   a ,  122   b . A valve insert  130  slidingly engages the valve plate  118  and is carried between the radially extending collars  114  of the valve spool  98  for reciprocating movement therewith. The valve insert  130  includes a concave recess  134  that is configured to provide fluid communication between one of the fill orifices  122   a ,  122   b  and the exhaust orifice  126 , depending upon the position of the valve spool  98  in the valve chamber  86 . In the illustrated embodiment, the valve insert  130  and the valve plate  118  are fabricated from ceramic materials, however other types of materials can be used as well. An adapter plate  135  is positioned between the spool valve  48  and the centerbody  18  and provides communication channels  136  that afford communication between the fill and exhaust orifices  122   a ,  122   b ,  126 , and the centerbody  18 . Differently configured adapter plates  135  can be provided such that the spool valve air motor  48  can be used with a variety of pump centerbodies  18 . The adapter plate  135  and the centerbody  18  cooperate to afford communication between the fill orifices  122   a ,  122   b  and the second subchambers  58   a ,  58   b  respectively. 
   With reference to  FIGS. 3 and 4 , the fill orifice  122   a  is open to the valve chamber  86   b , and the fill orifice  122   b  is in communication with the exhaust orifice  126  by way of the concave recess  134 . As such, pressurized air flows from the valve chamber  86   b , through the fill orifice  122   a , and into the second subchamber  58   a . The increased pressure in the second subchamber  58   a  causes the diaphragm  50   a  to deflect such that the volume of the second subchamber  58   a  increases, and the volume of the first subchamber  54   a  decreases. As a result of the volume changes, pumped fluid is expelled from the first subchamber  54   a  into the outlet manifold  46 . Simultaneously, due to the connection provided by the diaphragm rod  62 , the opposite diaphragm  50   b  deflects such that the first subchamber  54   b  increases in volume and the second subchamber  58   b  decreases in volume. The increase in volume of the first subchamber  54   b  draws fluid past the associated check valve  66  and into the first subchamber  54   b  from the inlet manifold  42 . As the second subchamber  58   b  decreases in volume, the air therein is vented to the atmosphere. In some embodiments, the air in the second subchamber  58   b  is vented to the atmosphere via the fill orifice  122   b , the concave recess  134 , and the exhaust orifice  126 . In other embodiments, air in the second subchamber  58   b  is vented directly to the atmosphere via a dump valve (not shown) that is in fluid communication with the second subchamber  58   b  and the atmosphere. 
   When the diaphragms  50   a ,  50   b  and the diaphragm rod  62  reach the end of their travel, a pilot valve (not shown) is operated and the pressure within the valve chamber  86   c  is changed such that the valve spool  98  moves within the valve chamber  86 , thereby moving the valve insert  130 . Movement of the valve insert changes the flow configuration of the fill orifices  122   a ,  122   b  such that the fill orifice  122   b  is in communication with the pressurized valve chamber  86   b , and the fill orifice  122   a  is in communication with the exhaust orifice  126  by way of the concave recess  134 . As a result, the diaphragms  50   a ,  50   b  move in an opposite direction, further changing the volumes of the first subchambers  54   a ,  54   b  and the second subchambers  58   a ,  58   b  to pump additional fluid from the inlet manifold  42  toward the outlet manifold  46 . The valve spool  98  and the diaphragms  50   a ,  50   b  continue moving in a reciprocating manner throughout pump operation. 
   To facilitate sealing within the valve chamber  86 , the valve block  78  is provided with a first sealing insert  138 , and the valve cap  82  is provided with a second sealing insert  142 . The valve block  78  at least partially surrounds the first insert  138  and cooperates therewith to define a first portion of the valve chamber  86 . Similarly, the valve block  78  at least partially surrounds the second insert  142  and cooperates therewith to define a second portion of the valve chamber  86 . When the valve cap  82  is secured to the valve block  78 , the chamber is substantially completely defined. Each insert  138 ,  142  is positioned in the valve chamber  86  to surround one of the ends  102 ,  106  of the valve spool  98 . Each insert  138 ,  142  includes a generally cylindrical inner surface  146  that sealingly engages the associated annular seal  110 . The cylindrical inner surfaces  146  are preferably fabricated to provide sealing surfaces having a reduced surface roughness with respect to the surfaces of the valve block  78  and valve cap  82 . For example, in the illustrated embodiment, the valve block  78  and the valve cap  82  can be fabricated of a reinforced polymer including glass fiber fillers. Glass filled polymers of this type are utilized in diaphragm pump applications for various reasons, some of which may include chemical compatibility, corrosion resistance, and strength. One drawback to the use of glass filled polymers however is an increased surface abrasiveness due to the reinforcing glass fibers. This surface abrasiveness can lead to accelerated seal wear and leaking. By providing the sealing inserts  138 ,  142 , the surfaces upon which the seals  110  slide can be manufactured to have improved surface characteristics, thereby extending the life of the seals  110  and reducing the likelihood of leakage between the valve chambers  86   a ,  86   b ,  86   c . In addition, the inserts  138 ,  142  can be fabricated in such a way that dimensional stability (e.g. the roundness and diameter of the cylindrical inner surfaces  146 ) is improved when compared to traditional injection molding techniques. 
   In some embodiments, including the embodiment illustrated in  FIG. 4 , the inserts  138 ,  142  can be formed from a generally tubular fiber-matrix composite material. One method for forming the inserts  138 ,  142  includes winding glass fibers around a mandrel, binding the fibers together with an epoxy matrix, and cutting the resulting section of composite tubing to appropriate lengths. Once the individual inserts  138 ,  142  are formed, the inserts can be positioned within injection molding dies and the valve block  78  and the valve cap  82  can be injection molded around the inserts  138 ,  142 . It should be appreciated of course that other materials, such as metals, other composites, and polymers can be used in the fabrication of the inserts  138 ,  142 . The valve block  78  and the valve cap  82  can be formed using other materials and manufacturing techniques as well, and the inserts  138 ,  142  can be inserted within the valve block and the valve cap  82  by other methods, such as press fitting, for example. 
   During pump operation, the seals  110  engage the inner surfaces  146  of the inserts  138 ,  142 . The length and positioning of the inserts  138 ,  142  is such that the seals  110  and the inserts  138 ,  142  are in substantially continues sealing contact throughout movement of the valve spool  98  between the first and second positions. 
     FIG. 5  illustrates an alternative embodiment of the invention. Elements of the air motor illustrated in  FIG. 5  have been given the same reference numerals as the corresponding elements from  FIG. 4 , increased by two hundred. The air motor  248  includes a valve block  278 , and a valve cap  282 . The valve block  278  is generally tubular, and the valve cap  282  is secured to and overlies one end of the valve block  278 , and cooperates therewith to partially define the valve chamber  286 . The opposite end of the valve block  278  includes an opening that receives a secondary valve cap  150 . The secondary valve cap  150  overlies the opening and closes the valve chamber  286 . The secondary valve cap  150  and the valve cap  282  are secured to the valve block  278  using elongated fasteners  154  and nuts  158 , however other fastening methods are possible as well. 
   The valve chamber  286  receives the valve spool  298  and the annular seals  310  sealingly and slidingly engage the inner surfaces  346  of the valve cap  282  and the secondary valve cap  150 . The valve insert  330  and the valve plate  318  operate in substantially the same manner as the valve insert  130  and valve plate  118  of FIG.  4 . The valve cap  282  and the secondary valve cap  150  are preferably fabricated from a material having improved surface characteristics with respect to the fabrication material of the valve block  278 . For example, the valve block  278  (like the valve block  78 ) can be fabricated using a glass filled polymer. To reduce seal wear and improve pump life, the valve cap  282  and the secondary valve cap  150  can be fabricated using a non-filled polymer, or from other materials such as metals, or composites. By utilizing the above-described construction, the valve block  278  is provided with suitable strength and stiffness to withstand the internal pressure forces developed during pump operations, while the valve cap  282  and secondary valve cap  150  improve the surface characteristics of the sealing surfaces to reduce seal wear. 
   Various features of the invention are set forth in the following claims.