Abstract:
A pump comprising a valve housing and a spool slidably positioned within the valve housing. The spool has a supply face, a first end face, and a second end face, and is slidable between a first position wherein pressurized supply air is supplied to the supply face and the first end face, the first end face having a greater surface area than the supply face, a second position wherein the supply air is supplied to the supply face and is blocked from both the first and second end faces, and a third position wherein the supply air is supplied to the supply face and the second end face.

Description:
BACKGROUND  
         [0001]    The present invention relates to double-diaphragm pumps and particularly to valves that direct the flow of pressurized air to air chambers of double-diaphragm pumps. Conventional double-diaphragm pumps include two diaphragms, one coupled to each end of a connecting rod. Pressurized air is alternately pumped into and evacuated from air chambers created between each of the diaphragms and an air cap associated with each diaphragm. As pressurized air is being pumped into the air chamber associated with one diaphragm, the air chamber associated with the other diaphragm is evacuated so that the diaphragms work together in a reciprocating motion to pump a fluid through the pump.  
           [0002]    In conventional double-diaphragm pumps, a main valve (typically a spool valve) controls the filling and emptying of the air chambers. The spool valve typically moves back and forth along its axis, connecting and blocking various channels through the pump to control the flow of pressurized air. Typically, a pilot valve associated with the main valve is used to start the main valve moving in one direction or another. The pilot valve is used to help “kick” the main valve back and forth.  
         SUMMARY OF THE INVENTION  
         [0003]    According to the present invention, a pump includes a spool valve that acts as its own pilot valve. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0004]    [0004]FIG. 1 is a schematic view of a pump according to the present invention including a spool valve having a spool positioned in a left-most position, thereby routing pressurized supply air to a right air chamber;  
         [0005]    [0005]FIG. 2 is a schematic illustration of the pump of FIG. 1 with the spool in a center or intermediate position blocking the supply of pressurized air to the right air chamber and to a left air chamber; and  
         [0006]    [0006]FIG. 3 is a schematic illustration of the pump of FIG. 1 with the spool in a right-most position, thereby routing pressurized supply air to the left air chamber.  
     
    
     DETAILED DESCRIPTION  
       [0007]    Referring to FIG. 1, a pump  100  according to the present invention includes a spool valve or main valve  102  having a spool  104 . The spool  104  has an exterior surface  105  and includes a left channel  106  and a right channel  108  formed through the spool  104 . As the spool  104  slides within a valve housing  116 , the channels  106  and  108  alternatingly direct supply air from a supply channel  110  to either of a left air chamber  112  or right air chamber  114 . The spool  104  is housed within the valve housing  116  so that the exterior surface  105  of the spool is spaced from an interior surface  117  of the housing  116 . The left air chamber  112  and the right air chamber  114  are associated with left and right diaphragms, respectively, (not shown) in a double-diaphragm pump arrangement, as will be readily known to those of ordinary skill in the art. As will also be readily known to those of ordinary skill in the art, the supply of air to one of the left and right air chambers  112 ,  114  causes the diaphragm associated with that air chamber to move to an extended or outward position pumping fluid out of an associated fluid chamber (not shown) on the opposite side of the diaphragm. At the same time, the opposite diaphragm moves to a withdrawn or inward position, drawing fluid into a fluid chamber (not shown) associated with it.  
         [0008]    Referring to FIG. 1, the spool  104  is moved to a left-most position within the valve housing  116 . The spool  104  is moved to the left-most position as the result of supply air from the supply channel  110  filling a supply chamber  118 , thereby applying force to a supply face  120 . As can be seen with reference to FIGS. 1-3, and as will become more apparent below, the volume of the supply chamber  118  changes depending on the position of the spool  104 . However, in all cases, the supply chamber  118  is being supplied pressurized air from the supply channel  110  and, therefore, the supply face  120  always has a force on it which makes the spool  104  tend to move to the left.  
         [0009]    With the spool  104  moved to its left-most position as shown in FIG. 1, a right spool port  122  of the spool  104  is in fluid communication with the supply chamber  118 . This allows pressurized air to flow from the supply chamber  118  through the right spool port  122  and into the right channel  108 . In this way, air flows along a pathway  124  expanding the right air chamber  114  and driving its associated diaphragm outward. Additionally, the pressurized air flowing into the right air chamber  114  provides a force, indicated by arrows  125 , on a right end face  123  that, along with the force on the supply face  120 , pushes the spool  104  to the left. (It should be noted that in FIG. 1, as well as FIGS. 2 and 3, the pressurized supply air is indicated by a dotted texture. Although it is pointed out above that the supply air flows along pathway  124  when the spool  104  is in its left-most position, the dotted texture indicates the spaces that are filled with pressurized supply air. Additionally, exhaust air (discussed below) is indicated by a diagonal line texture in FIGS. 1-3.)  
         [0010]    At the same time, with the spool  104  in its left-most position, a left spool port  126  is in fluid communication with a left exhaust chamber  128  that is connected through a left exhaust port  130  to a left exhaust channel  132 . In this way, air is exhausted from the left air chamber  112  along a pathway  134  causing a left diaphragm associated with the left air chamber  112  to collapse inwardly. Additionally, as will be readily apparent to one of ordinary skill in the art, the right diaphragm and left diaphragm may be interconnected by a connecting rod (not shown). Therefore, the supply of pressurized air to the right air chamber  114  causing it to expand and drive its associated right diaphragm outwardly will, through the connecting rod, pull the left diaphragm inwardly.  
         [0011]    When the left diaphragm moves to a certain extent inwardly, it begins pushing on the spool  104 . The left diaphragm may push on the spool  104  through direct contact, or through some mechanical connection such as a pin, arm, tab, etc., as will be readily apparent to one of ordinary skill in the art. Eventually, the left diaphragm will move the spool  104  to an intermediate or center position, as shown in FIG. 2. Referring to FIG. 2, in the intermediate position, the right spool port  122  is blocked by a right seal  136 , thereby cutting off the flow of pressurized supply air from the supply chamber  118  to the right air chamber  114 . At the same time, a left seal  138  blocks the left spool port  126  so that it is no longer connected to the left exhaust chamber  128  and air is no longer exhausted from the left air chamber  112 . With the spool  104  in its intermediate position, air is neither supplied to nor exhausted from either the left air chamber  112  or the right air chamber  114 . However, the movement of the left diaphragm, discussed above, which moved the spool  104  to the intermediate position shown in FIG. 2, is sufficient to move the left spool port  126  just beyond the left seal  138 , so that the left spool port  126  is in fluid communication with the supply chamber  118 .  
         [0012]    Referring to FIG. 3, with the left spool port  126  in fluid communication with the supply chamber  118 , pressurized supply air from the supply channel  110  flows through a supply port  140  along a pathway  142  and into the left air chamber  112 . The flow of supply air into the left air chamber  112  creates a force, indicated by arrows  143 , on a left-end face  144  of the spool  104 . Even though the supply air continues to provide a force on the supply face  120  that tends to move the spool  104  to the left as discussed above, the spool  104  nevertheless moves to the right because the force  143  applied to the left-end face  144  is greater than the force on the supply face  120 . This is because the total surface area of the surfaces that comprise the left-end face  144  is greater than the total surface area of the supply face  120 . As shown in FIG. 3, the surface area of the left-end face  144  is approximately twice the surface area of the supply face  120 . However, other configurations where the surface area of the left-end face  144  is greater than the surface area of the supply face  120  may be used. Because of the differential in surface areas between the left-end face  144  and the supply face  120 , the spool  104  moves from a position wherein the left spool port  126  is just right of the left seal  138  to its right-most position.  
         [0013]    With the spool  104  positioned as shown in FIG. 3, pressurized supply air is supplied to the left air chamber  112  pushing outwardly the left diaphragm. At the same time, the right spool port  122  is in fluid communication with a right exhaust chamber  146  that is connected to a right exhaust channel  148 . In this way, air from the right air chamber  114  flows along a pathway  150  exhausting the right air chamber  114 . In a manner similar to that discussed above with regard to the left diaphragm, this causes the right diaphragm to collapse inwardly. Eventually, the right diaphragm contacts, either directly or indirectly, the right end of the spool  104  urging it to the left. The collapsing movement of the right diaphragm causes the spool  104  to move left and again assume the intermediate position shown in FIG. 2. In the position shown in FIG. 2, the supply of pressurized air through the left spool port  126  and the left channel  106  is cut off, thus removing the force on the left-end face  144 . The force on the supply face  120  created by the pressurized air in the supply chamber  118  takes over in the absence of the force  143  on the left-end face  144 . Therefore, the spool  104  tends to again move to the left once the collapsing right diaphragm has moved the spool  104  far enough over (to its trip point) so that the left seal  138  cuts off the flow of supply air through the left spool port  126 . The force of the pressurized supply air on the supply face  120  moves the spool  104  to its left-most position as shown in FIG. 1, and the cycle discussed above starts over.  
         [0014]    Although the invention has been described in detail with reference to certain described constructions, variations and modifications exist within the scope and spirit of the invention as described and defined in the following claims.