Abstract:
A valve assembly for a pump includes a pump chamber and a pump head having complementary recesses formed therein which cooperate to define a valve compartment including a pocket and an opposed seat. A flexible valve element is disposed between the recesses and adapted to move between a closed position against the seat which prevents fluid flow and an open position away from the valve seat which permits fluid flow. The dimensions of the valve compartment are selected to limit the movement of the valve element in the open position, which increases the pump efficiency and prevents damage to the valve element and/or valve overlap.

Description:
BACKGROUND OF THE INVENTION 
   This invention relates generally to pumps and more particularly to a check valve for a pump. Many types of pumps use check valves; however for the purpose of describing the present invention diaphragm pumps in particular are considered herein. Typical diaphragm pumps use an elastomeric component as a passive check valve to facilitate the pumping action of the pump. A pump will typically contain two valves, one identified as the inlet valve and the other identified as the outlet valve. During the down-stroke or intake stroke of the pump, the suction action of the diaphragm will pull the inlet valve into an open position and the outlet valve into a closed position thus pulling the media into the pump on the inlet side only. During the up-stroke or exhaust stroke of the pump, the compression action of the diaphragm will push the inlet valve into a closed position and the outlet valve into an open position thus expelling the media on the outlet side only. 
   The valves will perform this action once during each cycle of the pump. For a diaphragm pump, this equates to once per full revolution. Therefore, a diaphragm pump that runs at 4000 RPM will cycle the valves 67 times per second. The speed of the pump, multiplied by the volume the pump displaces with each stroke determines how much force is applied to actuate the valve, thus directly impacting how far the valve will displace if not physically limited. If this valve travel distance is not controlled correctly, the valve can easily travel further than required or could also be over-restricted and not allowed to travel as far as needed. Either condition results in a pump that runs inefficiently and/or produces higher than desired noise levels. 
   Accordingly, there is a need for a pump valve having a controlled stroke. 
   BRIEF SUMMARY OF THE INVENTION 
   Therefore, it is an object of the invention to provide a valve assembly in which the stroke of a flexible valve is limited to prevent inefficiency and excess noise. 
   It is another object of the invention to provide a valve assembly which prevents overlap of intake and exhaust valves. 
   It is another object of the invention to provide a valve assembly having good sealing characteristics without excess travel of the valve elements. 
   These and other objectives are met by the present invention, which in one preferred embodiment includes a valve assembly for a pump, including a pump chamber having a first recess formed therein; a pump head having a second recess formed therein, the second recess cooperating with the first recess to define a first valve compartment including a first valve pocket and an opposed first valve seat; and a flexible first valve element disposed between the first and second recesses and adapted to move between a closed position against the first valve seat which prevents fluid flow and an open position away from the first valve seat which permits fluid flow in a first direction. The dimensions of the first valve compartment are selected to limit the movement of the first valve element in the open position. 
   According to another preferred embodiment of the invention, a valve assembly further includes a third recess formed in the pump chamber; a fourth recess formed in the pump head, the fourth recess cooperating with the third recess to define a second valve compartment including a second valve pocket and an opposed second valve seat; and a flexible second valve element disposed between the third and fourth recesses and adapted to move between a closed position against the second valve seat which prevents fluid flow and an open position away from the second valve seat which permits fluid flow in a second direction. The dimensions of the second valve compartment are selected to limit the movement of the second valve element in the open position. 
   According to another preferred embodiment of the invention, one of the valve elements is an intake valve for permitting flow from an intake port to a pump, and the other of the valve elements is an outlet valve for permitting flow from the pump to an outlet port. The dimensions of the first and second valve compartments are selected to limit the movement of the first and second valve elements when the pump is moving a fluid flow from the inlet port through the pump to the outlet port, such that at least one of the valve elements is always in the closed position. 
   According to another preferred embodiment of the invention, wherein the first and second valve elements include an elastomeric material. 
   According to another preferred embodiment of the invention, the first and second valve elements include ethylene propylene diene terpolymer. 
   According to another preferred embodiment of the invention, the first and second valve elements comprise a fluoroelastomer. 
   According to another preferred embodiment of the invention, the first and second valve elements comprise a perfluoroelastomer. 
   According to another preferred embodiment of the invention, the first and second valve elements comprise silicone. 
   According to another preferred embodiment of the invention, the first and second valve elements have a hardness from about 40 Durometer to about 90 Durometer. 
   According to another preferred embodiment of the invention, a pump assembly includes a pump chamber having a first recess formed therein; a pump head having housing having a second recess formed therein, the second recess cooperating with the first recess to define a first valve compartment including a first valve pocket and an opposed first valve seat; and a flexible first valve element having a selected first thickness disposed between the first and second recesses and adapted to move through a stroke length between a closed position against the first valve seat which prevents fluid flow and an open position away from the first valve seat which permits fluid flow. The dimensions of the first valve compartment are selected to limit the stroke length of the first valve element to less than about 1.6 times the first thickness. 
   According to another preferred embodiment of the invention, the valve assembly further includes a third recess formed in the pump chamber; a fourth recess formed in the pump head, the fourth recess cooperating with the third recess to define a second valve compartment including a second valve pocket and an opposed second valve seat; and a flexible second valve element having a selected second thickness disposed between the third and fourth recesses, and adapted to move between a closed position against the second valve seat which prevents fluid flow and an open position away from the second valve seat which permits fluid flow in a second direction. The dimensions of the second valve compartment are selected to limit the stroke length of the second valve element to less than about 1.6 times the second thickness. 
   According to another preferred embodiment of the invention, the dimensions of the first and second valve compartments are selected such that the stroke lengths of the first and second valve elements are from about 0.19 times the thickness of the respective valve element to about 0.93 times the thickness of the respective valve element. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The subject matter that is regarded as the invention may be best understood by reference to the following description taken in conjunction with the accompanying drawing figures in which: 
       FIG. 1  is an exploded perspective view of a pump head constructed in accordance with the present invention. 
       FIG. 2  is a perspective view of a valve for use with the present invention. 
       FIG. 3  is a top view of the valve of  FIG. 2 . 
       FIG. 4  is a side view of the valve of  FIG. 2 . 
       FIG. 5  is a side cross-sectional view of a prior art valve in an at-rest or closed position. 
       FIG. 6  is a side cross-sectional view of a prior art valve in a fully extended or open condition. 
       FIG. 7  is a side cross-sectional view of a valve compartment constructed in accordance with the present invention, with the valve in a fully extended or open position. 
       FIG. 8  is a side cross-sectional view of a pump head constructed in accordance with the present invention. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1  illustrates a portion of a prior art diaphragm pump assembly. A head  10  is attached to a chamber  12 . The head  10  and the chamber  12  are referred to collectively as a pump head  14 . Inlet and outlet connections  16  and  18  extend from the head  10 . Each of these connections communicates with a fluid flow path through the pump head  14  and into a diaphragm pump body of a known type (not shown) which is attached to a lower end  20  of the pump head  14 . The head  10  and the chamber  12  each have complementary recesses  22  therein. When the head  10  is assembled to the chamber  12 , these recesses  22  cooperate to define an inlet valve compartment  24  and an outlet valve compartment  26 . Inlet and outlet diaphragm valves  28  and  30  are received in these compartments and are trapped between the head  10  and the chamber  12 . The upper part of the inlet valve compartment  24  is defined by an annular, radiused inlet valve seat  32  formed in the head  10 . The inlet valve  28  seals against the inlet valve seat  32  in the closed position. The lower part of the inlet valve compartment  24  is defined by an inlet valve pocket  34  in the chamber  12  opposite the inlet valve seat  32 . 
   The outlet valve compartment  26  is substantially identical to the inlet valve compartment  24 , except for the direction of flow. The upper part of the outlet valve compartment  26  is defined by an outlet valve pocket  36  formed in the head  10 . The lower part of the outlet valve compartment  26  is defined by annular, radiused outlet valve seat  38  in the chamber  12 , opposite the outlet valve pocket  36 . The outlet valve  30  seals against the outlet valve seat  38  in the closed position. 
     FIGS. 2 ,  3 , and  4  illustrate an exemplary valve  40 , which is representative of both the inlet valve  28  and the outlet valve  30  as used in the diaphragm pump described herein. The valve  40  is a flat, elongated member of an elastomeric material having a central portion  42  connected to a pair of end tabs  44  by a pair of necked-down portions  46 . In the illustrated example the valve  40  has an overall length “L” of about 13.5 mm (0.530 in.), a width “W” of about 5.2 mm (0.205 in.), and a thickness “T” of about 0.69 mm (0.027 in.) These dimensions may be varied to suit a particular application. 
   Each of the inlet and outlet valves  28  and  30  has a “stroke” defined as the deflection of its center portion from the fully open position to the fully closed position.  FIGS. 5 and 6  show partial cross-sections through the inlet valve compartment  24  of the pump head  14  of  FIG. 1 . For a typical application the depth “D” of the prior art inlet valve pocket  34  is such that the inlet valve stroke may be about 1.14 mm (0.050 in.) Similarly, the outlet valve (not shown in  FIGS. 5 and 6 ) has a stroke of about 1.27 mm (0.050 in.) The depth D of the prior art valve pockets allow an essentially uncontrolled stroke, with resulting over-travel, of the valves. 
   When the outlet valve  30  has over-traveled during the up-stroke, on the subsequent down-stroke, media will be pulled in through the inlet side and, for an unknown duration, the outlet side. This reduces the overall throughput (free flow) of the pump and the ability to achieve the maximum load points (pressure or vacuum). During the next up-stroke of the pump, the same effect will occur with the inlet valve  28 . Because the inlet valve  28  was allowed to over-travel during the previous down-stroke, media will be will be expelled on the inlet side for an unknown duration in addition to the outlet side. Both of these conditions may be described as valve “overlap” which is undesirable in this type of pump. 
     FIG. 7  is a partial cross-sectional view through the inlet valve compartment of an exemplary pump head  114  constructed in accordance with the present invention.  FIG. 8  is an orientation view which shows the portion “A” of the pump head  114  that is illustrated in  FIG. 7 . It is noted that  FIGS. 5 and 6  depict the details of the same area of the prior art pump head  14 . The pump head  114  is substantially similar to the prior art pump head  14  described above and includes a chamber  112 , a head  110 , and an inlet valve  128 . The chamber  112  has an inlet valve pocket with a reduced depth “d”, relative to the prior art. In this example, the depth “d” of the inlet valve pocket  134  is set such that the inlet valve travel is only about 0.64 mm (0.025 in.), instead of the 1.14 mm (0.050 in.) allowed for the prior art inlet valve  28  in the same application. This prevents over-travel of the inlet valve  128 . The travel of the outlet valve (not shown) is limited in a similar fashion, by modifying the depth of the outlet valve pocket in the head  110 . 
   The inverse of over-travel is under-travel. If the valve is limited from traveling far enough, the flow of media through the port is restricted and the pump efficiency is again compromised. To overcome this condition, the pump speed would need to be increased to make up for the built-in restriction, thus consuming more energy and operating at higher noise levels. It is therefore important to note that the valve travel is not simply reduced. The valve travel must be matched to the performance requirements of the pump and the characteristics of the valve material. Elastomer durometer, for example, will affect how the valve travel should be controlled. A lower durometer material, 40 durometer for example, will have a much greater uninhibited travel than say a 90 durometer material and will require a tighter control on valve travel distance. Under-travel may be controlled by the selection of elastomeric material used for the valve. A higher durometer elastomer, 90 durometer for example, will not be as likely to succumb to an over-extension during its open time, but will also not seal as well against the valve seat when it is in a closed position, and may be subject to under-travel. 
   A benefit of using a softer durometer material is a more efficient sealing condition between the elastomeric valve and the valve seat. A softer durometer elastomer, 40 durometer for example, will seal more effectively being more able to conform to minor irregularities in the sealing surface. The more flexible material will, however, be more apt to over-extend during the actuation of the valve thus staying open longer than required. The limitation of the valve stroke in the present invention allows the use of a relatively soft durometer elastomer for the valve by the limiting of the pocket depth. 
   It has been found that by controlling the valve travel as described above, the pump will become more efficient and, all other conditions being equal, the overall pump performance will improve. It is noted that just by regulating the valve stroke to a more efficient point, the sound level of the pump has a tendency to be reduced slightly. Furthermore, because the overall pump performance increases, the speed of the pump can be reduced to return the performance to the desired level. As pump speed is one of the largest contributing factors for elevated sound levels, this has an even more dramatic effect on reducing the noise levels. 
   The optimum valve stroke will differ depending on the style of pump, the type of valve material, and the media being pumped. A mid range air pump using a 70 durometer ethylene propylene diene terpolymer (EPDM) valve, for example, may run most efficiently with a valve stroke of 0.64 mm (0.025 in.) A lower performance pump using an 80 durometer VITON valve material, for example, may benefit from a valve stroke as low as 0.13 mm (0.005 in.) Overall pump head size will also contribute in defining the correct stroke length. A larger pump for example will have a larger valve with a greater length and sealing surface area and may operate more efficiently with a higher valve stroke. The inlet valve and outlet valve may obtain optimum performance using different stroke distances. The important considerations are to choose the valve material and the valve pocket depth so that the valve stroke will be large enough to provide unrestricted flow for the fluid media, without being so large as to risk breaking the valve, causing excessive noise or creating valve overlap as noted above. Other materials which meet these requirements, such as silicone, may be used. This technique may be applied to pumps for both air and liquid with the same benefits being seen accordingly. 
   There are other benefits to limiting the valve stroke. For example, some types of working media, such as corrosive gaseous or liquid chemicals, may attack the valve material and cause deterioration. Therefore, special materials such as perflouroelastomers, which are resistant to harsh chemicals, are used to construct the valve. These materials have a relatively low flexural strength and will not withstand extreme bending. If these materials are displaced beyond their limit, they can actually crack and/or break, and may fail if subjected to standard valve deflection. By controlling the displacement of the valve, exotic materials that have a lower flexural strength can be utilized without the risk of a pump failure because of a compromised valve. 
   The foregoing has described a valve for use with a diaphragm pump. While specific embodiments of the present invention have been described, it will be apparent to those skilled in the art that various modifications thereto can be made without departing from the spirit and scope of the invention. It will also be apparent that pumps other than diaphragm pumps that use similar valve technology will see the same benefits from this invention. Accordingly, the foregoing description of the preferred embodiment of the invention and the best mode for practicing the invention are provided for the purpose of illustration only, and not for the purpose of limitation.