Abstract:
A double diaphragm pump for moving large volumes of water that may be laden with debris includes a pair of fourteen-inch diameter elastomeric diaphragms, driven by reciprocating push rods pivotally coupled to opposed eccentrics. An engine drives a gearbox having two outputs. One eccentric is attached to each output. A pair of weighted flap valves control flow to and from each diaphragm chamber. A vacuum pressure gauge monitors inlet pressure. A relief valve relieves vacuum pressure in the event of a blockage or other flow impediment.

Description:
FIELD OF THE INVENTION 
     This invention relates generally to pumps, and, more particularly, to a high volume pump with 180 degree offset diaphragms, and an inlet with a vacuum relief valve. 
     BACKGROUND 
     Diaphragm pumps are useful for transferring large volumes of water for agricultural, construction and marine industries among others. Such pumps may efficiently transfer even mud-laden water. Typically, such pumps comprise an elastomeric diaphragm driven by a pushrod or fluctuating pressure. 
     Heretofore, diaphragm pumps for construction have been limited in size to avoid excessive pressure. A large diameter pump may collapse and irreparably damage a hose if debris impedes flow through the hose. After the hose collapses, the elastomeric diaphragm experiences a pressure spike with considerable attendant stresses and strains, which may compromise the integrity or useful life of the diaphragm. Affected components may warp. Seals around the pump may fail under the increased pressures experienced during a collapse. 
     To avoid such problems, most prior art pumps limit diaphragm size to below 12 inches in diameter. Such size limitations avoid the pressures that can harm hoses, the diaphragms and seals. However, such pumps achieve limited volumetric flow rates. 
     What is needed is a large diameter diaphragm pump, that is capable of transferring large volumes of water, including water laden with mud and debris, and is responsive to flow blockages. The pump should include diaphragms having a radius greater than 6 inches and means to prevent excessive pressure differentials that could damage diaphragms, hoses and seals. 
     The invention is directed to overcoming one or more of the problems and solving one or more of the needs as set forth above. 
     SUMMARY OF THE INVENTION 
     To solve one or more of the problems set forth above, in an exemplary implementation of the invention, a double diaphragm pump for moving large volumes of water that may be laden with debris is provided. The pump includes a pair of 12 to 16-inch (preferably 14 to 14.5 inch) diameter elastomeric diaphragms, driven by reciprocating push rods pivotally coupled to opposed eccentrics. An engine drives a gearbox having two outputs. One eccentric is attached to each output. A pair of weighted flap valves controls flow to and from each diaphragm chamber. A vacuum pressure gauge monitors inlet suction pressure. A vacuum relief valve relieves pressure in the event of a blockage or other flow impediment. 
     In one embodiment, an exemplary double diaphragm pump according to principles of the invention includes a pair of diaphragm chambers; a pair of elastomeric diaphragms, including one elastomeric diaphragm attached to each diaphragm chamber, each elastomeric diaphragm having a radius of at least 6 inches, and each diaphragm chamber having a width of at least 11.00 inches. A pair of inlet valves, including an inlet valve for each diaphragm chamber, control the flow of fluid into the diaphragm chamber. A pair of outlet valves, including an outlet valve for each diaphragm chamber, control the flow of fluid from each diaphragm chamber. An inlet fluidly is coupled to the inlet valve and fluidly coupled to the diaphragm chamber. Each inlet valve is disposed between its corresponding diaphragm chamber and the inlet. 
     To prevent pressure spikes, a vacuum relief valve is fluidly coupled to the inlet. The vacuum relief valve includes a valve mechanism opening at a set pressure condition (e.g., a reduced pressure in the inlet indicative of a flow impediment relative to ambient pressure), and an auxiliary port through which ambient air may flow into the inlet when the valve mechanism opens. In one embodiment, the valve, may, optionally, include a manual actuator to manually open the valve mechanism. Spring tension or compression in the valve mechanism may be adjusted using an adjuster, such as a threaded adjuster (e.g., screw), thereby adjusting or regulating the set pressure. 
     An inlet manifold, which may comprise a plurality of interconnected channels and flow paths, leads from the inlet to each diaphragm chamber. Thus, each diaphragm chamber is fluidly coupled to the inlet manifold and each inlet valve is disposed in the inlet manifold (e.g., at the interface between the inlet manifold and the chambers). 
     Being a high volume pump, each elastomeric diaphragm has a radius of 6.0 to 8.00 inches, preferably about 7.0 to 7.25 inches, for a diameter of about 14.0 to 14.50 inches. 
     Optionally, a vacuum pressure gauge is fluidly coupled to the inlet. In one embodiment, the gauge is directly coupled to the inlet. In another embodiment, the gauge is fluidly coupled to the vacuum relief valve, in fluid communication with the inlet. The vacuum pressure gauge may have a readable display indicating pressure within the inlet. 
     The exemplary pump is powered by an engine via a gearbox. The engine includes an output. The gearbox includes one input, two outputs and a gear train coupling the one input of the gearbox to the two outputs of the gearbox. The output of the engine is coupled to the input of the gearbox and rotates at 1,800 to 2,200 rpm during operation. Each output of the gearbox rotates (through reduction) at 60 to 80 rpm during operation. 
     An eccentric is attached to each output of the gear box. A pair of pushrods is provided. Each pushrod has a first end and a second end. The first end of each pushrod is coupled to one of the eccentrics. The second end of each pushrod is coupled to one of the diaphragms. The pushrods are driven in reciprocating motion by rotation of eccentrics. The reciprocating motion is between a first position closest to the diaphragm to which the pushrod is coupled, and a second position furthest from the diaphragm to which the pushrod is coupled. Reciprocating motion of the pushrods causes compression and suction motion of the diaphragms. Each eccentric is 180° apart, such that one pushrod is in a first position when the other pushrod is in a second position. 
     Each of the pair of inlet valves and outlet valves may be a one-way flap check valve including a resilient elastomeric flap covering an opening in an inlet or outlet horizontal wall when closed and exposing the opening when opened. A weight may be provided on each resilient flap to facilitate closure. 
     The pump may include various access and clean-out panels and ports. For example, a removable access panel may be provided over each of the pair of outlet valves. Each such access panel is removable secured with a plurality of bolts (e.g., 4 or more bolts) to prevent leakage under high outlet pressure. A gasket is provided for a fluid impervious seal. 
     The double diaphragm pump according to principles of the invention may be mounted on a trailer for transportation. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The foregoing and other aspects, objects, features and advantages of the invention will become better understood with reference to the following description, appended claims, and accompanying drawings, where: 
         FIG. 1  is a perspective view of an exemplary diaphragm pumping system according to principles of the invention; and 
         FIG. 2  is a front view of an exemplary diaphragm pumping system according to principles of the invention; and 
         FIG. 3  is a plan view of an exemplary diaphragm pumping system according to principles of the invention; and 
         FIG. 4  is a side view of an exemplary diaphragm pumping system according to principles of the invention; and 
         FIG. 5  is a first perspective view of an exemplary diaphragm pumping system according to principles of the invention; and 
         FIG. 6  is a second perspective view of an exemplary diaphragm pumping system according to principles of the invention; and; and 
         FIG. 7  is a first perspective view of an exemplary diaphragm pumping mechanism according to principles of the invention; and 
         FIG. 8  is a second perspective view of an exemplary diaphragm pumping mechanism according to principles of the invention; and 
         FIG. 9  is a back view of an exemplary diaphragm pumping mechanism according to principles of the invention; and 
         FIG. 10  is a side view of an exemplary diaphragm pumping mechanism according to principles of the invention; and 
         FIG. 11  is a plan view of an exemplary diaphragm pumping mechanism according to principles of the invention; and 
         FIG. 12  is a front view of an exemplary diaphragm pumping mechanism according to principles of the invention; and 
         FIG. 13  is a first perspective view of an exemplary diaphragm pumping mechanism according to principles of the invention; and 
         FIG. 14  is a second perspective view of an exemplary diaphragm pumping mechanism according to principles of the invention; and 
         FIG. 15  is a perspective view of chambers of an exemplary diaphragm pumping mechanism according to principles of the invention; and 
         FIG. 16  is a plan view of chambers of an exemplary diaphragm pumping mechanism according to principles of the invention; and 
         FIG. 17  is a perspective cutaway view of an outlet chamber of an exemplary diaphragm pumping mechanism according to principles of the invention; and 
         FIG. 18  is a perspective cutaway view of an inlet chamber of an exemplary diaphragm pumping mechanism according to principles of the invention; and 
         FIG. 19  is a side view of an inlet port of an exemplary diaphragm pumping mechanism according to principles of the invention; and 
         FIG. 20  is a perspective view of an inlet port of an exemplary diaphragm pumping mechanism according to principles of the invention; and 
         FIG. 21  is a schematic view of a pressure relief valve for an exemplary diaphragm pumping mechanism according to principles of the invention; and 
         FIG. 22  is a schematic of a flapper valve for an exemplary diaphragm pumping mechanism according to principles of the invention; and 
         FIG. 23  is a profile view of an exemplary diaphragm, in an un-deformed state, for an exemplary diaphragm pumping mechanism according to principles of the invention; and 
         FIG. 24  is a perspective view of an exemplary diaphragm, in an un-deformed state, for an exemplary diaphragm pumping mechanism according to principles of the invention; and 
         FIG. 25  is a profile view of an exemplary diaphragm, in a flexed downwardly state for expelling fluid, for an exemplary diaphragm pumping mechanism according to principles of the invention; and 
         FIG. 26  is a perspective view of an exemplary diaphragm, in a flexed downwardly state for expelling fluid, for an exemplary diaphragm pumping mechanism according to principles of the invention; and 
         FIG. 27  is a profile view of an exemplary diaphragm, in a flexed upwardly state for drawing in fluid, for an exemplary diaphragm pumping mechanism according to principles of the invention; and 
         FIG. 28  is a perspective view of an exemplary diaphragm, in a flexed upwardly state for drawing in fluid, for an exemplary diaphragm pumping mechanism according to principles of the invention; and 
         FIG. 29  is a profile view of an exemplary adjustable vacuum relief valve for an exemplary diaphragm pumping mechanism according to principles of the invention; and 
         FIG. 30  is a plan view of an exemplary adjustable vacuum relief valve for an exemplary diaphragm pumping mechanism according to principles of the invention; and 
         FIG. 31  is a cutaway view of an exemplary adjustable vacuum relief valve for an exemplary diaphragm pumping mechanism according to principles of the invention; and 
         FIG. 32  is a perspective view of an exemplary adjustable vacuum relief valve for an exemplary diaphragm pumping mechanism according to principles of the invention. 
     
    
    
     Those skilled in the art will appreciate that the figures are not intended to be drawn to any particular scale; nor are the figures intended to illustrate every embodiment of the invention. The invention is not limited to the exemplary embodiments depicted in the figures or the specific components, configurations, shapes, relative sizes, ornamental aspects or proportions as shown in the figures. 
     DETAILED DESCRIPTION 
     Referring to  FIGS. 1 through 6 , various views of an exemplary diaphragm pumping system  100  according to principles of the invention is conceptually illustrated. The system comprises a pumping mechanism  120  on a trailer  105 . A motor or engine, such as a diesel engine  110  (e.g., a 5.7 hp Hatz diesel engine at about 2000 rpm), drives an input of a transmission (e.g., gearbox  115 ) having two rotating outputs with eccentrics  135 ,  140 . A push rod  125 ,  130  couples each eccentric  135 ,  140  to a diaphragm  190 ,  195 . Each push rod  125 ,  130  may have a fixed length or a variable length to adjust the stroke. The pumping mechanism  120  includes an inlet  160  and an outlet chamber  145  with a pair of opposed outlet ports  150 ,  155 , one of the outlet ports  150  being shown capped (i.e., closed) and the other being shown open  155 . A user may select which outlet port to use. Various access ports  170 ,  175 ,  180 ,  185  enable access for cleaning chambers and maintaining valves. While the exemplary embodiment includes a trailer  105 , the invention is not limited to trailer-mounted pumping mechanisms. 
     Various chambers, manifolds, inlets and outlets are shown in  FIGS. 7-14 . The exemplary pumping mechanism  120  comprises a positive displacement diaphragm pump that uses a combination of the reciprocating action of a pair of elastomeric diaphragms  190 ,  195  and suitable valves (e.g., check valve, butterfly valves, flap valves, or any other form of shut-off valves) to pump a fluid. The diaphragms  190 ,  195  flex, causing the volume of each pump chamber  129 ,  134  ( FIG. 7 ) to increase and decrease. When a diaphragm flexes (upwardly) to increase the volume of a pump chamber  129 ,  134 , pressure decreases and fluid is drawn into the pump chamber through the inlet  160 , an inlet chamber  146  and a manifold  148  coupling the inlet  160  to each pump chamber  129 ,  134 . When a diaphragm flexes (downwardly) to decrease the volume of a pump chamber  129 ,  134 , pressure increases and fluid is expelled from the pump chamber through an outlet manifold  147  to an outlet chamber  145  and through whichever outlet  150 ,  155  is open. The pumping mechanism  120  is configured with the eccentrics  135 ,  140  180° apart. Thus, one diaphragm flexes upwardly while the other diaphragm flexes downwardly, and vice versa. This pumping action repeats cyclically, similar to that of the cylinders in an internal combustion engine. 
     Each eccentric  135 ,  140  is a disk (eccentric sheave) attached to a rotating output axle of the gear box  115 . Each push rod  125 ,  130  terminates with a bearing  127 ,  132 . Each bearing  127 ,  132  pivotally attaches to the eccentric sheave  135 ,  140 , off-center. The push rods  125 ,  130  impart reciprocating motion to the diaphragms  190 ,  195 . Thus, the eccentrics  135 ,  140  and push rods  125 ,  130  convert rotary into linear reciprocating motion in order to drive the diaphragms  190 ,  195 . 
     Referring now to  FIGS. 23 through 28 , various views of an exemplary diaphragm, in an un-deformed state ( FIGS. 23 ,  24 ), a flexed downwardly state for expelling fluid ( FIGS. 25 ,  26 ), and a flexed upwardly state for drawing in fluid ( FIGS. 27 ,  28 ), for an exemplary diaphragm pumping mechanism according to principles of the invention, are provided. The diameter, d, of the diaphragm  190  is from 12 to 16 inches, preferably about 14 to 15 inches, and more preferably about 14 to 14.5 inches. The pushrods  125 ,  130  driven by the rotating eccentrics  135 ,  140  provide a stroke effective for pumping. The stroke length cannot exceed the depth of the diaphragm chamber or the maximum tensile stress of the diaphragm. In an exemplary embodiment, the stroke length is about 7-inches, including 3.5 inches downwardly from the at-rest position for the expelling portion of the stroke, h 1  in  FIGS. 25 , and 3.5 inches upwardly from the at-rest position for the drawing-in portion of the stroke, h 2  in  FIG. 27 . The diaphragm  190  includes a flanged outer periphery  191  for securing the diaphragm over a diaphragm chamber using an annular bolt-on clamp. A flanged inner periphery  193  is secured to a disk-shaped flange coupled to the pushrods  125 ,  130 . The portion  192  of the diaphragm  190  between the outer  191  and inner  193  flanges is a portion that stretches during pumping action. 
     To maintain a tight seal even under high pressure, in a preferred embodiment the access ports  180 ,  185  on the outlet chamber  145  include panels secured with four or more attachments (e.g., bolts). These ports  180 ,  185  are exposed to high positive pressure pushing outwardly on the panel, while ports  170 ,  175  on the inlet side experience a negative pressure drawing the panel inwardly. A gasket may be provided between the panel and each corresponding port  170 ,  175 ,  180 ,  185  to ensure a hermetic seal. 
     As shown in  FIGS. 15 through 18 , check valves (e.g., flap valves) control flow into and from the pump chambers  129 ,  134 . In the particular non-limiting embodiment shown, a pair of non-return check valves  191 ,  196  yield to inward flow from the inlet  160  into the pump chambers  129 ,  134 , while preventing reverse flow of the pumped fluid from the pump chambers  129 ,  134  to the inlet  160 . Likewise, a pair of non-return check valves  181 ,  186  yield to outward flow from the pump chambers  129 ,  134 , while preventing reverse flow of the pumped fluid from the outlet chamber  145  into the pump chambers  129 ,  134 . 
     The gear box  115  serves as a transmission. It includes an input (e.g., a shaft) rotated by an output (e.g., flywheel or shaft) of the engine  110 . A speed and torque-converting gear train in the gear box reduces rotations from the input (i.e., at about 1,800 to 2,200 rpm) to about 60 to 80 rpm at output shafts, to which the eccentrics  135 ,  140  are attached. In the exemplary embodiment depicted in the figures, the output shafts of the gearbox  115  are orthogonal to the input shaft of the gearbox  115 . A non-limiting example of a suitable gear box is a Wormaster series gear box by Renold plc of Manchester, England. 
     In an exemplary embodiment, a vacuum pressure gauge  165  and vacuum relief valve  166  are fluidly coupled to the inlet  160 . The vacuum pressure gauge  165  and vacuum relief valve  166  may be separate components, each of which is separately coupled to the inlet, as shown in  FIG. 14 , or coupled together as in  FIGS. 19 and 20 . The vacuum relief valve  166  may be used without the pressure gauge  165  or with the vacuum pressure gauge  165 . The vacuum pressure gauge  165  and/or vacuum relief valve  166  may be fluidly coupled to the inlet  160 , or to a chamber or manifold that is in fluid communication with the inlet  160 . 
     The vacuum relief valve  166  (i.e., check valve), fluidly coupled to the inlet  160 , controls or limits the vacuum pressure in the system. A schematic of a non-limiting example of a vacuum relief valve  166  is provided in  FIG. 21 . Vacuum pressure is relieved by allowing ambient air  220  to flow into the inlet from an auxiliary passage  225  of the flow housing  230  of the valve  166 . The exemplary relief valve  166  is designed or set with a spring  235  that holds a shank and a valve seat  210  against port  200 , preventing fluid flow  205  therethrough. In the exemplary embodiment illustrated, the spring  235  is a tension spring that draws the valve seat  210  against the port  200 . However a biasing mechanism other than a tension spring may be utilized without departing from the scope of the invention. The spring  235  allows the valve seat to open at a predetermined set pressure (i.e., negative pressure at the port  200 ). When the set pressure is exceeded, i.e., when the negative pressure is sufficient to unseat the valve seat, the relief valve becomes a “path of least resistance” as the valve seat  210  is forced open and fluid  220  is sucked in through the auxiliary route  225 . The drawn-in fluid  220  (i.e., air) flows into the pump chamber. As the fluid  220  enters, the negative pressure inside the inlet  160  and pumping system  120  will be relieved. Once it reaches the valve&#39;s reseating vacuum pressure, the valve seat  210  will close. 
     The vacuum pressure gauge  165  measures the vacuum pressure (i.e., negative pressure or vacuum) at the inlet  160  through which fluid is sucked into the pumping mechanism  120 . By way of example and not limitation, the gauge may comprise an aneroid gauge, such as a bourdon, diaphragm or bellows pressure gauge, or an electronic pressure sensor such as a piezoresistive, capacitive, inductance, piezoelectric, optical or potentiometric sensor. The purpose of the gauge is to indicate operating vacuum pressure and excessive pressure. Operating pressure evidences normal operation. A vacuum pressure spike indicates a blockage. An upstream blockage causes a high negative pressure. 
     A shaft  240  and handle  245  allow a user to manually open the valve seat  210  to relieve vacuum pressure. Manual release is particularly beneficial if a valve is malfunctioning and does not open when a blockage causing a vacuum pressure spike is experienced, and/or if the valve set pressure is excessive for the system, and/or to test responsiveness of the valve or pressure gauge, and/or to relieve pressure to facilitate clearing of a partial blockage that is insufficient to open the valve. 
     In FIGS.  2  and  7 - 9 , the offset relationship of the push rods  125 ,  130  is apparent. One push rod  125  is in a raised (suction) position, while the other push rod  130  is in the lowered (compression) position. The raised push rod  125  and its corresponding diaphragm  190  draw fluid into the corresponding diaphragm chamber, while the lowered push rod  130  and corresponding diaphragm  195  expel fluid from the corresponding diaphragm chamber. As the eccentrics rotate 180°, the raised push rod  125  moves to a lowered position and the lowered pushrod  130  moves to a raised position. In each case, the raised pushrod causes its diaphragm to draw fluid into the corresponding diaphragm chamber, while the lowered pushrod causes its diaphragm to expel fluid from its diaphragm. 
       FIGS. 16 and 17  illustrate valve locations. Outlet valves  181 ,  186  are located at the bottom surface of the outlet manifold  145 . Each outlet valve is in fluid communication with a diaphragm chamber  129 ,  134 . Each outlet valve opens  181 ,  186  when fluid is expelled from the outlet chamber  129 ,  134 . Each outlet valve  181 ,  186  is urged closed by negative pressure in the corresponding diaphragm chamber  129 ,  134  when the pushrod  125 ,  130  for the corresponding diaphragm  190 ,  195  is in the raised position. Each outlet valve  181 ,  186  is drawn open from pressure in the corresponding diaphragm chamber  129 ,  134  when the pushrod  125 ,  130  for the corresponding diaphragm  190 ,  195  is in the lowered position. When the outlet valve opens, fluid flows from the corresponding diaphragm chamber  129 ,  134  through a corresponding outlet passage  147 ,  149 , through the corresponding outlet valve  181 ,  186 , into the outlet manifold  145 , where it may exit through whichever outlet  150 ,  155  is open. The outlet passages  147 ,  149 , that connect each diaphragm chambers  129 ,  134  to the outlet manifold  145  are clearly shown in  FIGS. 10 and 13 . Each passage connects one diaphragm chamber to the outlet manifold  145 . During normal operation, only one outlet valve  181 ,  186  is open at a time. The open valve  181 ,  186  allows fluid flow from the corresponding passage  147 ,  149  into the manifold  145 . The closed valve  181 ,  186  prevents fluid flow from the manifold  145  into the passage  147 ,  149  served by the closed valve  181 ,  186 . 
     Inlet valves  191 ,  196  are located at the bottom surface of each diaphragm chamber. Each inlet valve is in fluid communication with a diaphragm chamber  129 ,  134 . An inlet valve  191 ,  196  opens when fluid is drawn into the corresponding diaphragm chamber  129 ,  134 . Each inlet valve  191 ,  196  is urged closed by pressure in the corresponding diaphragm chamber  129 ,  134  when the pushrod  125 ,  130  for the corresponding diaphragm  190 ,  195  is in the lowered position. Each inlet valve  191 ,  196  is drawn open by negative pressure in the corresponding diaphragm chamber  129 ,  134  when the pushrod  125 ,  130  for the corresponding diaphragm  190 ,  195  is in the raised position. When the inlet valve opens, fluid flows from the inlet  160  through inlet passage  146 , into the inlet manifold  148 , which is below each diaphragm chamber  129 ,  134 , through whichever valve  191 ,  196  is open, and into the corresponding diaphragm chamber  129 ,  134 . The inlet passages  146 , that connects the inlet  160  to the inlet manifold  148  is clearly shown in  FIGS. 10 and 13 . During normal operation, only one inlet valve  191 ,  196  is open at a time. The open valve  191 ,  196  allows fluid flow from the inlet manifold  148  into the diaphragm chamber  129 ,  134  served by the open valve  191 ,  196 . The closed valve  191 ,  196  prevents fluid flow from the inlet manifold  148  into the diaphragm chamber  129 ,  134  served by the open valve  191 ,  196 . 
     The valves operate 180° apart in a 360° cycle. An inlet valve  191 ,  196  for a diaphragm chamber  129 ,  134  is never opened, during normal operation, when the outlet valve  181 ,  186  corresponding to the diaphragm chamber  129 ,  134  is opened. An inlet valve  191 ,  196  for a diaphragm chamber  129 ,  134  is never opened, during normal operation, when the other inlet valve  191 ,  196  is opened. Concomitantly, an outlet valve  181 ,  186  for a diaphragm chamber  129 ,  134  is never opened, during normal operation, when the other outlet valve  181 ,  186  is opened. Likewise, an outlet valve  181 ,  186  for a diaphragm chamber  129 ,  134  is never opened, during normal operation, when the inlet valve  191 ,  196  corresponding to the diaphragm chamber  129 ,  134  is opened. In sum, during normal operation, only one inlet valve is opened at a time, and only one outlet valve is opened at a time, and when an outlet valve for one diaphragm chamber is open, the inlet valve for the other diaphragm chamber is open, and an inlet valve only opens when the pushrod for the diaphragm for a chamber is in the raised position, and an outlet valve only opens when the pushrod for the diaphragm for a chamber is in the lowered position. 
     While the invention is not limited to a particular valve design and various one way valves may be utilized, in a preferred embodiment, flap valves are used, as schematically illustrated in  FIG. 22 . Each flap valve is oriented over an opening  315  (i.e., port through which fluid may flow) in a horizontal wall of a flow path. The valve includes a resilient elastomeric valve body  300  attached at or near one edge to a horizontal base  316  through which the port  315  is formed. All other edges of the valve body  300  are not attached to the base  316 . The valve body  300  covers the entire port  315  when the valve body is in the closed position  305 . To assist closure without appreciably impairing opening, a weight  310  may be attached to the valve body  300 . The weight may be from 4-16 ounces, depending upon the size of the port  315 , mass of the valve body  300  and fluid pressures. The valve body  300  bends and its unattached edges deflect away from the port  315  when in an open position  306 . In the open position  306 , fluid may flow through the port  315 . In the closed position  305 , the resilient properties of the valve body  300  and gravity cause the valve body to return to the closed position  305 , thereby preventing flow through the port  315 . 
       FIGS. 29-32  conceptually illustrate another exemplary adjustable vacuum relief valve  400  for an exemplary diaphragm pumping mechanism according to principles of the invention. The valve  400  is threaded into the inlet  160 . The valve  400  includes a threaded neck  420 , e.g., a neck with NPT tapered threads, that threads into a threaded female port in the inlet  160 . A hollow housing  415  with a hexagonal periphery contains a spring  430 , valve body  435  and valve seat  440 . The spring  430  urges the valve body  435  against the valve seat  440 . A vacuum in the inlet  160  draws the valve body  435  away from the valve seat  440 . Fins  425  guide movement of the valve body  435 . A knurled threaded sleeve  405  defines the valve seat  440  and amount of spring  430  compression. Threading the sleeve  405  into the housing  430  increases compression of the spring  430 , which increases the force exerted by the spring against the valve body  435 , which increases the force by which the valve body  435  is held against the valve seat  440  in the closed (i.e. sealed) position. Conversely, threading the sleeve  405  in the opposite direction (i.e., out of the housing  430 ) decreases compression of the spring  430 , which decreases the force exerted by the spring against the valve body  435 , which decreases the force by which the valve body  435  is held against the valve seat  440  in the closed (i.e. sealed) position. If the pressure difference between ambient pressure and the pressure (vacuum) in the inlet  160  is sufficient to exert a force on the valve body  435  towards the threaded neck  420 , then the valve body  435  will move away from the valve seat  440 , breaking the seal and allowing ambient air to enter through the sleeve  405 , which defines an auxiliary port for admitting air into the inlet when the valve is opened. Thus, the vacuum relief valve includes an opening through which ambient air may enter the inlet if pressure in the inlet  160  appreciably drops. Such a pressure drop may occur when a blockage impedes flow through a hose to the inlet  160 . By admitting air through the valve  400 , the risk of hose collapse and other potential damage is reduced. 
     While an exemplary embodiment of the invention has been described, it should be apparent that modifications and variations thereto are possible, all of which fall within the true spirit and scope of the invention. With respect to the above description then, it is to be realized that the optimum relationships for the components and steps of the invention, including variations in order, form, content, function and manner of operation, are deemed readily apparent and obvious to one skilled in the art, and all equivalent relationships to those illustrated in the drawings and described in the specification are intended to be encompassed by the present invention. The above description and drawings are illustrative of modifications that can be made without departing from the present invention, the scope of which is to be limited only by the following claims. Therefore, the foregoing is considered as illustrative only of the principles of the invention. Further, since numerous modifications and changes will readily occur to those skilled in the art, it is not desired to limit the invention to the exact construction and operation shown and described, and accordingly, all suitable modifications and equivalents are intended to fall within the scope of the invention as claimed.