DIAPHRAGM PUMP

Abstract: A diaphragm pump is provided having a plurality of piston inlets connecting a hydraulic fluid source with the piston chamber and a plurality of check valves each having a ball and valve seat disposed within the inlets. The valve seat includes a conical section sloped such that the tangential contact point between the ball and valve seat is located at a position outward from the inner edge of the valve seat. The distance the ball is permitted to move between the open and closed positions is such that the check valve closes substantially in conjunction with the piston beginning its power stroke and the ball is not able to generate a high closure velocity. A diaphragm plunger includes a spherical surface portion designed to impact a diaphragm stop at a position away from the edges of the stop and plunger. An isolation reservoir is connected to a piston reciprocating chamber such that hydraulic fluid completely fills the piston reciprocating chamber and further flows into the isolation reservoir. A sliding valve includes a housing which has at least one elongated slot to permit the flow of hydraulic fluid into the piston chamber.

Description: DIAPHRAGM PUMP Background of the Invention Field ofthe nvention The present invention relates generally to an improved diaphragm pump and more specifically to an improved diaphragm pump for use under pressure feed conditions. Description ofthe Art Diaphragm pumps which presently exist in the prior art include a diaphragm, a pumping chamber on one side ofthe diaphragm containing an inlet passage and discharge passage, a piston chamber filled with hydraulic fluid and separated from the pumping chamber by the diaphragm and a piston assembly defining one end ofthe piston chamber and adapted for reciprocating movement between a first position and a second position to define a power stroke and return stroke. Such a pump is disclosed in U.S. Patent No. 3,884,598. During operation, the piston moves toward (power stroke) and away (return stroke) from the diaphragm, or into and out of the piston chamber thereby causing such reciprocating movement to be transferred, by the hydraulic fluid which fills the piston chamber, to the diaphragm. As the piston moves away from the diaphragm, the diaphragm flexes away from the pumping chamber, allowing the pumping fluid to be drawn into the pumping chamber through the inlet passage. As the piston moves toward the diaphragm, the diaphragm flexes toward the pumping chamber, causing the fluid in the pumping chamber to be discharged through the discharge passage. Prior diaphragm pumps include some type of mechanism to cause the reciprocation ofthe piston. It is known to utilize a cam or wobble plate which is canted with respect to its center shaft so that the rotation ofthe center shaft causes reciprocation ofthe wobble plate which transfers such motion to the piston. The wobble plate mechanism is typically located adjacent the piston assembly in an enclosed compartment filled with hydraulic fluid. In this way, the hydraulic fluid lubricates the wobble plate mechanism while also serving as a hydraulic fluid source for the piston assembly. The prior diaphragm pumps also include an inlet from the hydraulic fluid source into the piston chamber. Typically, some type of reload check valve is disposed within the inlet to permit the flow of hydraulic fluid into the piston chamber when the pressure in the piston chamber is less than the pressure in the hydraulic fluid source and to prevent the flow of hydraulic fluid into the piston chamber when the pressure in the piston chamber is greater than the pressure in the hydraulic fluid source. In this way, the reload check valve is closed during the power stroke and is open during at least a portion ofthe return stroke to allow replenishing of any hydraulic fluid in the piston chamber lost between the piston and piston housing during the power stroke. Typically, a sliding valve is also utilized in these prior diaphragm pumps to regulate the flow of hydraulic fluid from the hydraulic fluid source into the piston chamber based on the relative positions ofthe piston and diaphragm. The sliding valve includes a cylinder connected to the diaphragm which is disposed in a corresponding cylinder housing ofthe piston where it is biased toward the cylinder housing. The piston cylinder housing includes a circular port or hole positioned between the hydraulic fluid inlet and the cylinder. Based on the relative movement between the piston and diaphragm due to the varying amount of hydraulic fluid in the piston chamber, the sliding valve is variable between an open position in which the cylinder housing port is open to allow hydraulic fluid into the piston chamber and a closed position in which the cylinder connected to the diaphragm blocks the port to prevent the flow of hydraulic fluid into the piston chamber. The piston assembly in these prior diaphragm pumps includes a diaphragm stop disposed adjacent the diaphragm within the piston chamber. The diaphragm stop is positioned to limit the return movement ofthe diaphragm toward the piston which allows the piston chamber to be replenished with hydraulic fluid lost during the power stroke when the pump is operating under pressure feed conditions. The diaphragm includes a diaphragm plunger connected to the diaphragm such that the diaphragm plunger contacts the diaphragm stop when the pump is operating under pressure feed conditions. In this way, during the return stroke under pressure feed, the diaphragm plunger contacts the diaphragm stop to stop the movement ofthe diaphragm toward the piston while the piston continues to move an additional distance to complete the return stroke. This allows the pressure in the piston chamber to drop below the pressure in the pumping chamber as well below the pressure in the hydraulic fluid source. At this point, the reload check valve opens to allow replenishing of hydraulic fluid in the piston chamber, if necessary, before the piston begins its power stroke. It should be noted that the position ofthe piston upon completing the return stroke is referred to as bottom dead center. These prior diaphragm pumps described above were originally designed for vacuum feed conditions where the pumping fluid is not under pressure. In operation, these prior diaphragm pumps performed sufficiently under vacuum feed conditions. These prior pumps were also utilized for pressure feed applications where the pumping fluid is supplied under pressure. In actual operation under pressure feed conditions, however, these prior diaphragm pumps experience numerous problems. These problems have led to drastically reduced pump life and performance under pressure feed conditions to the point where these prior diaphragm pumps have experienced pump failure after only approximately 5% ofthe expected life ofthe pump under normal (vacuum feed) conditions. First, as described above, the diaphragm impacts the diaphragm stop during each return stroke under pressure feed conditions. The diaphragm plunger in these prior diaphragm pumps was designed so that the linear impact surface ofthe plunger was parallel with the linear impact surface ofthe diaphragm stop. This allowed the force ofthe impact to be evenly distributed along the entire impact surface ofthe plunger and diaphragm stop. However, during actual operation, the plunger often impacts the diaphragm stop at varying angles other than precisely parallel to the diaphragm stop due to the flexible nature ofthe diaphragm. Additionally, manufacturing tolerances preclude having parts match perfectly. As a practical matter, it is not feasible to manufacture the impact surfaces of the plunger and diaphragm stop so close to parallel to assure uniform contact along the entire length of these surfaces. Rather, the manufacture of these surfaces will vary so that the slope ofthe plunger impact surface is often steeper or shallower than the corresponding slope ofthe diaphragm stop. The result ofthe plunger impacting the diaphragm stop off center or the impact surfaces ofthe plunger or diaphragm stop being manufactured off parallel is that the plunger impacts the diaphragm stop at varying positions other than parallel. In particular, the plunger and diaphragm stop impact, and thus concentrate the impact forces, at the extreme limits of possible contact, the inner edge ofthe diaphragm stop and the outer edge ofthe plunger. Over time, repeated contacts between the plunger and diaphragm stop concentrated at these extreme edges can lend to chipping ofthe inner edge ofthe diaphragm stop or the outer edge ofthe plunger. Since the piston chamber is entirely enclosed, these chips from the inner edge ofthe diaphragm stop or the outer edge ofthe plunger have no means of escaping from the piston chamber and thus move around within the piston chamber, contacting the various components ofthe piston assembly, such as the piston and piston housing. This results in significant deterioration ofthe piston assembly reducing the usefiil life ofthe pump. This can even lead to complete pump failure if these chips become lodged between the piston and the piston housing to lock up the piston all together. It should be noted that this problem with chipping ofthe diaphragm stop and plunger is not present under vacuum feed conditions since the diaphragm plunger does not normally contact the diaphragm stop during the return stroke as shown in FIG. 3. Another problem with these prior diaphragm pumps under pressure feed conditions concerns the build up of excessive pressure within the piston chamber during the power stroke. The graph shown in FIG. 19 illustrates the build up of pressure (line A) in the piston chamber in relation to the movement ofthe piston during the power stroke under pressure feed conditions for a prior diaphragm pump. The velocity ofthe piston during the power stroke is also shown on the graph (line B). For the particular pump shown in the graph, the expected pressure is approximately 1,000 psi during the power stroke. As the graph illustrates (line A), the actual pressures experienced within the piston chamber include pressure peaks up to approximately 3,000 psi, or three times the expected pressure. During pump operation under pressure feed, these extreme pressure oscillations tend to cause significant deterioration ofthe piston assembly components at a much faster rate than under vacuum feed conditions. There are several explanations concerning the cause of this excessive pressure build up in the piston chamber under pressure feed conditions. First, the closure time for the reload check valve noticeably effects the pressure build up during the start ofthe power stroke. As explained above, the piston chamber is only able to replenish its hydraulic fluid under pressure feed conditions after the diaphragm plunger impacts the diaphragm stop and the piston moves the additional limited distance to complete the return stroke. This allows the piston chamber to depressurize to a level below diat in the hydraulic fluid source (which is at atmospheric pressure). During this limited time period, the reload check valve, which had been closed during the power stroke and most ofthe return stroke, is now opened with the hydraulic fluid from the hydraulic fluid source driving the ball to its open position. The hydraulic fluid flows around the ball and down the hydraulic fluid inlet and into the piston chamber to replenish any hydraulic fluid lost during the power stroke. Once the piston assembly reaches the end of he return stroke, the piston begins to move forward again and the hydraulic fluid in the piston chamber attempts to escape through the hydraulic fluid inlet and forces the ball ofthe reload check valve back against the valve seat to close the hydraulic fluid inlet. Until the ball moves from the open to the closed position, the pressure in the piston chamber cannot begin its buildup as the piston begins its power stroke. It should be noted that the distance the ball moves from the open to the closed positions is referred to as ball lift, see FIG. 8. Since the time that the reload check valve is open is relatively short under pressure feed conditions, the reload check valve in these prior diaphragm pumps was designed with a ball lift that was large enough to ensure sufficient flow of hydraulic fluid into the piston chamber to completely replenish the hydraulic fluid lost during the power stroke (see FIG. 8). However, by designing a sufficient ball lift to ensure complete reload ofthe piston chamber, the closure time for the reload check valve is such that the piston begins accelerating to achieve a noticeable portion of its maximum velocity during the power stroke before the reload check valve closes. As shown in the graph in FIG. 19, the reload check valve does not close and allow pressure build up to begin in the piston chamber until the input shaft ofthe wobble plate has already rotated through approximately 1/1 Oth ofthe power stroke (18°) with the piston reaching approximately 30% ofits maximum velocity (line B). In other words, the piston velocity is rapidly increasing before the reload check valve closes and the pressure build up can begin. Until the reload check valve closes, the hydraulic fluid in the piston chamber is not experiencing any pressure build up and has substantially zero velocity. Once the reload check valve closes, the already accelerating piston "slams" against the body of hydraulic fluid in the piston chamber to begin pressure build up. Due to the increasing velocity ofthe piston at the beginning of pressure build up, the piston chamber experiences severe oscillations in pressure. The severe pressure oscillations or "pressure rings" reach peak pressures of more than three times the expected pressure in the piston chamber during the power stroke, as shown in the graph in FIG. 19. Another factor that serves to accentuate the severity of these pressure rings stems from the introduction of air into the piston chamber. Ifthe hydraulic fluid in the hydraulic fluid source is intermixed within any air when it flows into the piston chamber to reload the hydraulic fluid lost in the piston chamber, this will also affect the pressure build up during the power stroke. After the piston begins its power stroke and the reload check valve closes, the piston can begin pressure build up in the piston chamber. However, if there is air intermixed with the hydraulic fluid in the piston chamber, the movement ofthe piston during the power stroke will first compress the air, a highly compressible substance, before it can begin pressure build up ofthe hydraulic fluid, a substantially incompressible substance. Thus, the time it takes to compress any air contained in the piston chamber increases the delay from the time the piston starts its power stroke to when pressure build up begins. This added delay allows the piston velocity to increase even further before the beginning of pressure build-up which increases the severity ofthe pressure rings experienced in the piston chamber during the power stroke. The problem of hydraulic fluid intermixed with air results from the location ofthe hydraulic fluid source. As previously discussed, the hydraulic fluid is stored in the chamber adjacent the piston assembly, which also houses the reciprocating mechanism or wobble plate. Typically, this chamber is filled with hydraulic fluid such that the entire wobble plate mechanism is covered. However, a certain amount of free air exists between the top surface ofthe hydraulic fluid and the top ofthe wobble plate chamber (see FIG. 17). This is necessary so that as the hydraulic fluid heats up upon operation ofthe wobble plate mechanism, the hydraulic fluid has room to expand within the wobble plate chamber without overflowing out the vent in the hydraulic fluid fill tube. During operation ofthe pump, the rotation ofthe wobble plate mechanism vigorously stirs up the hydraulic fluid in the wobble plate chamber such that it mixes with any free air present in the chamber. The result is a frothy mixture of hydraulic fluid and air within the wobble plate chamber. When the hydraulic fluid from the wobble plate chamber enters the inlet to reload the piston chamber, this compressible hydraulic fluid-air mixture flows into the piston causing air entrapment in the piston chamber with the resulting effects described above. Another significant problem with the pnor diaphragm pumps under pressure feed conditions concerns the impact ofthe ball with the valve seat in the reload check valve. As discussed above, under pressure feed conditions, the reload check valve is closed during the power stroke and during most ofthe return stroke until the diaphragm impacts the diaphragm stop and the piston moves an additional short distance to complete the return stroke. During this short period, the reload check valve opens to allow hydraulic fluid into the piston chamber and then quickly closes as the piston begins its power stroke. The ball ofthe reload check valve is driven to the open position and then forced right back to its closed position against the inner edge of the valve seat. (See FIGS. 8, 91). A typical time for refill in these prior diaphragm pumps is approximately 0.005 seconds. Due to the short time period for refill, the ball ofthe reload check valve develops high velocities in both opening and closing ofthe valve. In particular, the closure velocity for the ball under pressure feed conditions is high enough that it leads to damage ofthe valve seat and ball. The ball is able to achieve these high velocities due in part to the ball lift distance which is large enough to allow sufficient flow of hydraulic fluid for a complete reload as discussed above (see FIGS. 8, 9). The high closure velocity ofthe ball results in high impact forces between the ball and the inner edge ofthe valve seat (see FIG 8). This causes chipping ofthe inner edge ofthe valve seat and damage to the ball as well. Similar to the diaphragm stop chipping, these chips from the inner edge ofthe valve seat are transported by the hydraulic fluid into the piston chamber where there are no effective means for the chips to escape. Thus, these chips from the valve seat reside in the piston chamber for an extended period and cause damage to various piston components. As shown in FIG. 8, the reload check valve of these prior diaphragm pumps is designed such that the ball impacts the inner edge ofthe valve seat to close the valve. The valve seat is sloped slightly toward its inner edge to direct the ball toward the inner edge ofthe valve seat while still permitting sufficient flow around the ball for hydraulic fluid reload as shown in FIG. 9. Due to the relatively large ball lift, the ball is also able to move around within the reload check valve as it is driven between the open and closed position such that it may impact the inner edge ofthe valve seat at varying angles resulting in increased chipping ofthe valve seat. An additional problem with these prior diaphragm pumps concerns partial reload of hydraulic fluid under pressure feed conditions. As discussed above, the reload check valve is designed with sufficient ball lift to provide adequate flow of hydraulic fluid into the piston chamber during the short time period for reload. However, in actual operation, these pumps tend to run rough under pressure feed conditions indicating that only partial reload is occurring. This is believed to be due to the circular port or opening ofthe cylinder housing ofthe piston which connects the hydraulic fluid inlet with the piston chamber (see FIG. 15). This circular shape ofthe port does not allow sufficient flow into the piston chamber to ensure that complete reload is achieved under pressure feed conditions. Partial reload results in a loss of flow delivery for the pump since the piston is not transferring maximum displacement to the pumping chamber. It should be noted that partial reload is not a problem under vacuum feed conditions since the piston assembly is able to reload hydraulic fluid throughout the entire length ofthe return stroke. Another problem involves pump flow under intermediate pressure flow conditions. In actual operation, these prior diaphragm pumps experience a fall off in pump flow at intermediate pressure feed. This is believed to be caused by the closure time ofthe reload check valve. Due to the relatively large ball lift required to ensure adequate hydraulic fluid flow for reload, the closure time is such that a noticeable portion of hydraulic fluid escapes from the piston chamber back up the inlet into the hydraulic fluid source before the reload check valve can close. This reduces the amount of hydraulic fluid in the piston chamber during the power stroke thus reducing the displacement ofthe pumping chamber by the diaphragm. This results in reduced flow ofthe pump under intermediate pressure feed conditions. What is needed is an improved diaphragm pump for use under pressure feed conditions that minimizes the severe pressure oscillations within the piston chamber as the pressure builds up during the power stroke and further eliminates reload check valve damage and diaphragm stop or plunger damage to minimize the amount of debris within the piston chamber while still ensuring complete reload of hydraulic fluid to the piston chamber to maintain maximum efficiency ofthe pump. Summary pf the Invention The present invention provides an improved diaphragm pump for use under pressure feed conditions having a piston adapted for reciprocal movement, a flexible diaphragm, a pumping chamber on one side ofthe diaphragm, a piston chamber on the other side ofthe diaphragm, a source of hydraulic fluid connected with the piston chamber to allow hydraulic fluid into the piston chamber, hydraulic fluid in the piston chamber serving to transfer motion ofthe piston to the diaphragm, and a piston reciprocating mechanism. According to one aspect ofthe present invention, the piston assembly includes a plurality of piston inlets connecting the hydraulic fluid source with the piston chamber and a plurality of check valves disposed within the inlets. The check valves are preferably ball valves having a ball and valve seat with the ball valve moveable between a closed position and open position such that the ball is disposed in contacting relationship against the valve seat when the ball valve is in the closed position. The valve seat includes a conical section sloped inward toward the hydraulic fluid inlet and has an inner edge adjacent to the inlet. The slope ofthe conical section is such that the tangential contact point between the ball and valve seat when the ball valve is in the closed position is located at a position on the conical section outward from the inner edge ofthe valve seat. Further, the distance the ball is permitted to move between the open and closed positions is such that the ball valve closes substantially in conjunction with the piston beginning its power stroke and the ball is not able to generate a high closure velocity when moving from the open to the closed position. According to another aspect ofthe present invention, the piston assembly includes a diaphragm stop for limiting movement ofthe diaphragm away from the pumping chamber with the diaphragm stop having an inner edge portion. A diaphragm plunger is preferably provided which contacts the diaphragm stop during the return stroke ofthe piston under a pressure feed condition. The plunger includes a spherical surface portion such that the spherical surface portion impacts the diaphragm stop at a position outward from the inner edge ofthe diaphragm stop and inward from the outer edge ofthe plunger to prevent contact at the fragile edges and eliminate a source of wear debris. The diaphragm pump preferably includes a piston reciprocating chamber adjacent the piston with the hydraulic fluid source located within the piston reciprocating chamber. The pump preferably includes an isolation reservoir adjacent and connected to the piston reciprocating chamber such that the hydraulic fluid completely fills the piston reciprocating chamber and further flows into the isolation reservoir to form an upper surface of a hydraulic fluid within the isolation reservoir. According to another aspect ofthe present invention, the piston assembly includes a sliding valve responsive to the relative movement between the diaphragm and the piston for controlling the flow of hydraulic fluid from the hydraulic fluid source into the piston chamber. The sliding valve includes a cylinder valve connected to the diaphragm and a cylinder valve housing connected to the piston and adapted to receive the cylinder valve therein. The cylinder valve housing includes at least one elongated slot disposed adjacent the cylinder valve to permit the flow of hydraulic fluid into the piston chamber. The above-described features and advantages, along with various other advantages and features of novelty, are pointed out with particularity in the claims of the present application which form a part hereof. However, for a better understanding ofthe invention, its advantages, and objects obtained by its use, reference should be made to the drawings which form a further part ofthe present application and to the accompanying descriptive manner in which there is illustrated and described prefeπed embodiments ofthe invention. Brief Description ofthe Drawings FIG. 1 is a cross sectional view of a piston assembly in accordance with the principles ofthe present invention with the piston and diaphragm in a first position at the completion ofthe return stroke under pressure feed conditions and just prior to the power stroke (bottom dead center); FIG. 2 is a cross sectional view ofthe piston assembly shown in FIG. 1 with the piston and diaphragm in a second position at the completion ofthe power stroke under pressure feed conditions and just prior to the return stroke; FIG. 3 is a cross sectional view ofthe piston assembly shown in FIG. 1 with the piston and diaphragm in the first position at the completion ofthe return stroke under vacuum feed conditions and just prior to the power stroke; FIG. 4 is a cross sectional view ofthe piston assembly shown in FIG. 1 with the piston and diaphragm in a second position at the completion ofthe power stroke under vacuum feed conditions and just prior to the return stroke; FIG. 5 is a cross sectional view ofthe piston assembly according to the principles ofthe present invention with the ball valves shown in the closed position; FIG. 5 A is an enlarged cross sectional view ofthe ball and valve seat shown in FIG. 5; FIG. 6 is a cross sectional view ofthe piston assembly shown in FIG. 5 with the ball valves shown in the open position; FIG. 7 is a top view ofthe piston assembly shown in FIG. 5 showing the location ofthe ball valves; FIG. 8 is a cross sectional view of a partial piston assembly of a prior diaphragm pump showing the ball valve in the closed position; FIG. 9 is a cross sectional view ofthe partial piston assembly shown in FIG. 8 showing the ball valve in the open position; FIG. 10 is a cross sectional view of a diaphragm plunger according to the principles ofthe present invention; FIG. 11 is a cross sectional view of a diaphragm plunger of a prior diaphragm pump; FIG. 12 is a cross sectional view of a portion ofthe piston assembly of FIG. 1 showing the diaphragm plunger in contact with the diaphragm stop; FIG. 13 is an enlarged cross sectional view of a portion ofthe diaphragm plunger and diaphragm stop of FIG. 12; FIG. 14 is a cross sectional view of a cylinder valve housing according to the principles ofthe present invention; FIG. 15 is a cross sectional view of a cylinder valve housing of a prior diaphragm pump; FIG. 16 is a cross sectional view of a diaphragm pump according to the principles ofthe present invention: FIG. 17 is a cross sectional view of a prior diaphragm pump; FIG. 18 is a graph ofthe pressure (line A) in the piston chamber of a diaphragm pump according to the principles ofthe present invention and the piston velocity (line B) as a function ofthe rotation ofthe input shaft ofthe wobble plate through the power stroke under pressure feed conditions; FIG. 19 is a graph ofthe pressure (line A) in the piston chamber of a prior diaphragm pump and the piston velocity (line B) as a function ofthe rotation of the input shaft ofthe wobble plate through the power stroke under pressure feed conditions; FIG. 20 is a graph ofthe pressure in the piston chamber of a prior diaphragm pump as a function ofthe rotation ofthe input shaft ofthe wobble plate through several piston cycles under pressure feed conditions; FIG. 21 is a graph ofthe pressure in the piston chamber of a diaphragm pump modified with four piston inlets and reduced ball lift in the ball valves as a function ofthe rotation ofthe input shaft ofthe wobble plate through several piston cycles under pressure feed conditions; FIG. 22 is a graph of the pressure in the piston chamber of a diaphragm pump modified to include all the prefeπed embodiments ofthe present invention as a function ofthe rotation ofthe input shaft ofthe wobble plate through several piston cycles under pressure feed conditions; and FIG. 23 is a graph ofthe piston position away from bottom dead center and piston velocity of a diaphragm pump according to the principles ofthe present invention as a function ofthe rotation ofthe input shaft ofthe wobble plate through the power stroke. Detailed Description of the Invention Referring now to the drawings in which similar elements are numbered identically throughout, a description of prefeπed embodiments is provided. In FIG. 16, a cross sectional view of a diaphragm pump according to the principles of the present invention is generally illustrated at 10. Referring to FIG. 1, the diaphragm pump ofthe present invention includes a piston assembly which is adapted for use in a high pressure, hydraulically balanced, multi-pistoned diaphragm pump ofthe type described in U.S. Patent No. 3,884,598. The apparatus ofthe present invention includes a piston assembly movable between a first and second position, a diaphragm assembly movable between a first and second position in response to the movement ofthe piston assembly, and a pumping assembly in which pumping fluid is drawn into a pumping chamber through an inlet passage and forced out through a discharge passage in response to the movement ofthe diaphragm. More specifically, the piston assembly includes a relatively cylindrical piston 20 comprising an end section 22 and a piston sleeve section 24 integrally formed with the end section 22 and extending downward from the outer edge ofthe end section 22 (see FIG. 1). A base section 26 is connected with the interior surface ofthe piston sleeve 24 in a sealing relationship by the seal 30 so that the base section 26 is movable with the end and sleeve sections 22, 24. The piston 20 is adapted to slidably fit within a piston cylinder 16 which is integrally formed with the pump casting 12 and whose inner cylindrical surface approximates the outer cylindrical surface ofthe piston sleeve section 24 to substantially prevent the flow of hydraulic fluid from the piston chamber 34, defined in part by the interior ofthe piston 20, between the outer surface ofthe sleeve section 24 and the inner surface ofthe piston cylinder 16 during a reciprocation ofthe piston 20 (see FIG. 1). It should be noted that although the close fitting relationship between the sleeve section 24 and the cylinder 16 is sufficiently tight so that reciprocating movement ofthe piston 20 causes coπesponding reciprocal movement ofthe diaphragm assembly 80 as will be discussed below, the fitting between such surfaces is loose enough to allow a limited amount of hydraulic fluids to leak from the piston chamber 34 during the downward movement or power stroke ofthe piston 20. This controlled leakage serves to lubricate the sliding surfaces ofthe sleeve section 24 and the cylinder 16 and to aid in cooling the piston chamber fluid when such fluid is replenished. Referring to FIG. 16, a reciprocating mechanism 50 is provided to reciprocate the piston 20 between a first position and a second position. A cam or wobble plate 52 is provided which is canted with respect to the center line of shaft 53. A hemispherical foot 56 is disposed in a coπesponding recess 23 in the upper surface ofthe piston end section 22 with the hemispherical foot 56 adapted to slidably engage the lower surface ofthe cam or wobble plate 52 to transfer the reciprocating motion of the wobble plate 52 to the piston 20. During operation ofthe pump, the wobble plate 52 reciprocates to cause a coπesponding reciprocation ofthe piston 20. FIGS. 1 and 2 illustrate the upper and lower position ofthe piston 20 as it moves between the power stroke and return stroke. After the piston's downward movement from the position in FIG. 1 to that in FIG. 2 (power stroke), the piston 20 is retumed to the position of FIG. 1 (return stroke) by a coil spring 32 which has one end supported by the base section 26 ofthe piston 20 and the other end supported by a portion ofthe piston cylinder 16. The wobble plate mechanism 50 is disposed in a wobble plate chamber 58 ofthe pump. The wobble plate chamber is filled with hydraulic fluid which serves to lubricate the wobble plate mechanism 50 as well as to provide a hydraulic fluid source adjacent the end section 22 ofthe piston 20 (see FIG. 16). The piston 20 includes a hydraulic fluid inlet 36 to connect the wobble plate chamber 58 with the piston chamber 34. A reload check valve 70 is disposed within the inlet 36 to permit the flow of hydraulic fluid into the piston chamber 34 when the pressure in the piston chamber is less than the pressure in the wobble plate chamber 58 and to prevent the flow of hydraulic fluid into the piston chamber 34 when the pressure in the piston chamber 34 is greater than the pressure in the wobble plate chamber 58. In this way, the reload check valve is closed during the power stroke and is open during at least a portion ofthe return stroke to allow replenishing of any hydraulic fluid lost from the piston chamber between the piston sleeve section 24 and the piston cylinder 16 during the power stroke. As shown in FIG. 5, the hydraulic fluid inlet 36 includes an upper section 38 formed in the end section 22 ofthe piston 20. The reload check valve 70 which includes a ball 72 and valve seat 74 is disposed adjacent the upper section 38 of the hydraulic fluid inlet 36 (see FIGS. 5, 6). A ball stop member 27 is disposed adjacent the reload check valve 70 between the end section 22 and base section 26 of the piston 20. This ball stop member 27 forms the base ofthe reload check valve 70 against which the ball 72 ofthe reload check valve 70 rests when the check valve is in the open position. The base section 26 ofthe piston 20 is adapted to receive a cylinder valve housing 28 within the interior ofthe base section 26. The outer surface ofthe cylinder valve housing 28 is dimensioned such that there exists a small gap between the cylinder valve housing 28 and the base section 26 which forms a hollow cylindrical sleeve 39 (see FIGS. 5, 6). The outer wall ofthe cylinder valve housing 28 includes an opening 29 adjacent the cylindrical hollow sleeve. The cylindrical hollow sleeve is disposed adjacent to the reload check valve 70 and forms a lower section 39 of the hydraulic fluid inlet 36 such that hydraulic fluid retained in the wobble plate chamber 58 can flow through the inlet upper section 38, around the reload check valve 70, down the lower section 39 ofthe inlet 36 and through the cylindrical valve housing opening 29 to reach the piston chamber 34. A lower seal 31 is provided to seal the bottom portion ofthe base section 26 and cylindrical valve housing 28. As shown in FIGS. 1, 12, a diaphragm assembly 80 is disposed at and defines one end ofthe piston chamber 34 and includes a flexible diaphragm 82 disposed in a sealed relationship between the pump castings 12, 14, a base plate 84 secured to the bottom or pumping side ofthe diaphragm 82, a diaphragm plunger 86 disposed immediately above the diaphragm 82, and a diaphragm stem 90 extending upwardly from the diaphragm plunger 86 into the piston chamber 34. The diaphragm stem 90 includes an inner bore 93 with the lower end 94 having internal threads such that a screw 98 is inserted through the base plate 84 and diaphragm 82 for engagement with the lower end 94 ofthe diaphragm stem 90 to securely connect the diaphragm assembly 80. Referring to FIG. 12, a diaphragm stop 100 is disposed adjacent the diaphragm assembly 80 within the piston chamber 34. The diaphragm stop 100 extends inward from the piston cylinder 16 and is positioned to engage a portion ofthe diaphragm 82 as the piston 20 approaches the end of its return stroke under pressure feed conditions. In particular, the diaphragm stop 100 includes an impact surface 102 disposed adjacent the diaphragm plunger 86. As will be discussed in more detail below, the diaphragm stop 100 is positioned to limit the movement ofthe diaphragm 82 toward the piston 20 which allows the piston chamber 34 to be replenished with hydraulic fluid lost during the power stroke when the pump is operating under pressure feed conditions. The diaphragm stem 90 includes a cylinder head 92 formed at the upper portion ofthe diaphragm stem 90 which is disposed within the cylinder valve housing 28 ofthe piston 20. A spring 99 is disposed between the cylinder head 92 and the bottom ofthe cylinder valve housing 28 to bias the diaphragm assembly 80 toward the piston chamber 34 (see FIG. 12). The cylinder head 92 ofthe diaphragm stem 90 and the cylinder valve housing 28 ofthe piston 20 cooperate to form a sliding valve assembly 106 for controlling the flow fluid between the hydraulic fluid inlet 36 and the piston chamber 34 (see FIG. 2). The sliding valve assembly 106 is in the open position when the cylinder head 92 is disposed above the opening 29 in the cylinder valve housing 28, so that hydraulic fluid in the lower section 39 ofthe hydraulic fluid inlet 36 can enter into the piston chamber 34 through a plurality of apertures 96 connected to the inner bore ofthe diaphragm stem 90 (see FIG. 12). The sliding valve assembly is closed when the cylinder head 92 is disposed against and blocks the opening 29 in the cylinder valve housing 28 to prevent hydraulic fluid from entering the piston chamber 34 (see FIGS. 3, 4). Disposed immediately below the diaphragm assembly 80 is a pumping chamber 40 and a pumping valve assembly. The pumping valve assembly includes an inlet valve 42 and discharge valve 46 which are oriented to allow fluid to flow from the supply conduit 44 in through the inlet valve 42 into the pumping chamber 40 and from the pumping chamber 40 out through the discharge valve 46 to the discharge conduit 48 (see FIGS. 1, 2). The basic cycle ofthe pump consists ofthe piston 20 moving through its return stroke in which pumping fluid is drawn from the supply conduit 44 into the pumping chamber 40 through the inlet valve 42 and the piston then moves through its power stroke with the hydraulic fluid in the piston chamber forcing the diaphragm 82 forward towards the pumping chamber 40 to displace the pumping fluid in the pumping chamber 40 and discharge the pumping fluid out the discharge valve 46 to the discharge conduit 48. The above description of the general apparatus ofthe diaphragm pump ofthe present invention provides a pump well-suited for normal pump conditions i.e., vacuum feed conditions where the fluid to be pumped is not under pressure (see FIGS. 3, 4). The following description concerns particular prefeπed embodiments ofthe diaphragm pump ofthe present invention which are designed to improve reliability, performance and long-term wear ofthe diaphragm pump under pressure feed conditions, where the fluid to be pumped is supplied under pressure. It is appreciated that the diaphragm pump with these particular embodiments not only show significantly improved performance under pressure feed conditions but also is well suited for vacuum feed conditions. It is helpful to first outline the performance characteristics ofthe diaphragm pump ofthe present invention under pressure feed conditions and then proceed with a description ofthe prefeπed embodiments. Under pressure feed conditions, the piston 20 and diaphragm assembly 80 reciprocate between the positions shown in FIGS. 1 and 2. During the power stroke, the reload check valve 70 is closed due to the force ofthe hydraulic fluid in the piston chamber 34 and lower section 39 of the hydraulic fluid inlet 36 against the ball 72 ofthe reload check valve 70 (FIG. 2). Even as the piston 20 reciprocates back on its return stroke, the reload check valve 70 remains closed as the pressure in the pumping chamber 40 (under pressure feed), and the coπesponding pressure in the piston chamber 34. is still above atmospheric pressure, which is the pressure ofthe hydraulic fluid in the wobble plate chamber 58. As the piston 20 nears the end ofthe return stroke, the diaphragm assembly 80 impacts the diaphragm stop 100 to prevent further movement ofthe diaphragm 82 toward the piston 20 while the piston 20 continues back a short additional distance to complete the return stroke (FIG. 1). This allows the piston chamber 34 to depressurize below the pressure in the pumping chamber 40 and below the pressure ofthe hydraulic fluid in the wobble plate chamber 58 as well. The reload check valve 70 is then driven open by the force ofthe hydraulic fluid entering through the upper section 38 of the hydraulic fluid inlet 36 to reload any lost hydraulic fluid in the piston chamber 34. During this reload or replenishing period, the sliding valve assembly 106 is open with the diaphragm cylinder head 92 positioned above the opening 29 of the cylinder valve housing 28 to allow hydraulic fluid into the piston chamber 34 (see FIG. 1). It should be noted that under pressure feed conditions, the sliding valve assembly 106 generally remains in the open position and the reload check valve 70 remains closed for most of the entire reciprocation cycle. After the piston 20 returns the short additional distance after the diaphragm assembly 80 contacts the diaphragm stop 100, the piston 20 begins its power stroke and the hydraulic fluid in the piston chamber 34 seeks to escape out the hydraulic fluid inlet 36 and consequently closes the reload check valve 70 so the piston chamber 34 can begin the pressure build up associated with d e power stroke ofthe piston. Pursuant to a prefeπed embodiment, the reload check valve 70 ofthe present invention is designed to facilitate quick closure ofthe reload check valve 70 while minimizing any potential damage to the ball 72 or valve seat 74. Referring to FIG. 5, the reload check valve 70 has a reduced ball lift 73 compared to prior diaphragm pumps (see FIG. 8). This reduces the time required for closure ofthe reload check valve 70 when the piston 20 begins its power stroke. By reducing the closure time ofthe reload check valve 70, the hydraulic fluid in the piston chamber 34 is able to begin pressure build up substantially in conjunction with the piston 20 beginning its power stroke. At this position, the piston velocity is still relatively low as the piston 20 is just beginning its acceleration through the power stroke (see FIGS. 18, 23). Consequently, the pressure peaks or pressure rings associated with the pressure build up in the piston chamber 34 are greatly reduced in the present invention as compared to prior diaphragm pumps with a larger ball lift. (See FIG 19). The graph in FIG. 18 shows that pressure build up begins in the present invention substantially in conjunction with the piston 20 beginning its power stroke (within approximately 2 degrees of rotation ofthe input shaft 53 from bottom dead center). This is significantly quicker pressure build up as compared to the prior diaphragm pumps where the pressure build up would not begin until the input shaft 53 ofthe wobble plate mechanism 50 had already rotated through approximately 1/10th (or 18 degrees) ofthe power stroke (see graph in FIG. 19). This reduced closure time also helps eliminate the problem of pump flow fall off under intermediate pressure conditions described previously. The reduced closure time means that less hydraulic fluid in the piston chamber 34 is able to escape out the inlet 36 before the reload check valve 70 closes at the start ofthe power stroke. The loss of less hydraulic fluid translates into better pump performance without noticeable flow fall off under intermediate pressure conditions. Furthermore, the reduced ball lift provides a better metering pump. By reducing the loss of hydraulic fluid back out the inlet 36, the volume of hydraulic fluid in the piston chamber 34 is maintained so that the displacement ofthe pumping chamber 40 per revolution is more consistent. This provides for better metering when it is necessary to know precisely how much pumping fluid has been delivered through the pump. Another consequence ofthe reduced ball lift 73 in the reload check valve 70 is lower ball closure velocity. Since the ball 72 has a shorter distance to travel from the open to the closed position against the valve seat 74, the ball 72 is not able to achieve as high a closure velocity as in prior diaphragm pumps with larger ball lifts (see FIG. 8). This reduced closure velocity ofthe ball 72 results in lower impact forces when the ball 72 contacts the valve seat 74 to close the reload check valve 70. This lower closure velocity is not high enough to cause valve seat and ball damage as found in the prior diaphragm pumps having higher closure velocities discussed previously. While the shorter ball lift in the reload check valve reduces the ball valve closure time and ball closure velocity with the significant benefits described above, the flow of hydraulic fluid through the reload check valve 70 is noticeably reduced due to d is smaller ball lift 73 as shown in FIG. 5. Adequate hydraulic fluid flow through the hydraulic fluid inlet 36 is necessary to ensure complete reload ofthe piston chamber 34 on each reciprocation ofthe piston 20. Hydraulic fluid flow during reload is particularly important under pressure feed conditions given the relatively short time period for reload. To meet this flow demand, the reload check valve 70 of the present invention includes a plurality of hydraulic fluid inlets 36 and a coπesponding plurality of ball valves 71 having a reduced ball lift 73 disposed within the inlets 36. As shown in FIGS. 5, 6, the upper inlets 38 and ball valves 71 are positioned within the end portion 22 ofthe piston 20 so that each ball valve is adjacent the hollow sleeve or lower section 39 ofthe hydraulic fluid inlet 36. With this aπangement, the ball valves 71 experience short closure time and low ball closure velocities and yet the flow of hydraulic fluid through the plurality of inlets 36 is sufficient for complete reload ofthe piston chamber 34 during the reload period under pressure feed conditions. In a prefeπed embodiment, four inlets are disposed about the end section 22 ofthe piston 20 with four ball valves 71 having a reduced ball lift 73 (see FIG. 7). In this prefeπed embodiment, the ball lift 73 is designed to be less than or equal to 0.08 ofthe ball diameter. It is appreciated that a variety of other multiple inlet-ball valve combinations may be utilized in accordance with the principles ofthe present invention. The ball lift 73 may be varied so long as the ball valve 71 maintains minimal closure time to control the pressure rings associated with pressure build up and low closure velocity ofthe ball which is not high enough to damage the valve seat or ball. The number of inlets may be varied as well based on the chosen ball lift 73 to ensure adequate hydraulic fluid flow for complete reload of the piston chamber 34 under pressure feed conditions. It is also appreciated that an appropriate ball lift is variable depending on the operating conditions ofthe pump such as the viscosity ofthe hydraulic fluid. A more viscous hydraulic fluid will close the ball valve more quickly and is thus more tolerant of a larger ball lift 73. In accordance with another aspect of a prefeπed embodiment, the ball valves 71 include an improved valve seat configuration. Referring to FIGS. 5. 5 A and 6, the valve seat 74 for the ball valve 71 is designed to eliminate damage due to ball impact against the valve seat 74. The ball seat 74 includes a conical section 75 which is sloped inward toward the upper section 38 of the hydraulic fluid inlet 36 and terminates at an inner edge 76 (see FIG. 6). This sloped conical section 75 helps direct the ball 72 toward die central axis 79 ofthe valve seat 74 to facilitate efficient closure ofthe ball valve 71. As shown in FIGS. 5-6, the slope (or angle) 77 ofthe conical section 75 is designed so d at the tangential contact point 78 between me ball 72 and valve seat 74 is located at a position on die conical section 75 outward from the inner edge 76 ofthe valve seat 74 (see FIG. 5). In this way, as a ball 72 is slammed against me valve seat 74 as the piston 20 begins its power stroke, the ball 72 does not impact the inner edge 76 ofthe valve seat 74 (see FIG. 5 A), which is prone to chipping upon repeated impacts. This minimizes the potential damage to the valve seat or ball and significantly improves me long-term performance ofthe diaphragm pump under pressure feed conditions as compared to prior diaphragm pumps with a valve seat configuration in which the ball impacts the inner edge ofthe valve seat (see FIGS. 8- 9). It should be noted that die slope angle 77 (FIG. 6) may be varied within a certain range in accordance with the principles ofthe present invention. The slope angle 77 must provide for tangential contact ofthe ball 72 against the conical section 75 at a sufficient distance away from the inner edge 76 to prevent chipping. However, me slope angle 77 must not be too steep or this will result in significantly reduced flow dirough the ball valve 71 and may effect me ability to provide sufficient hydraulic fluid flow for complete reload ofthe piston chamber under pressure feed conditions. In one embodiment, me slope angle 77 is chosen to provide a tangential contact point at least 0.015 inches from the inner edge 76 of me valve seat 74. In a prefeπed embodiment, the slope angle 77 is chosen to provide a tangential contact point at approximately 0.020 inches from the inner edge 76 ofthe valve seat 74 (see FIG. 5A). This dimension is chosen to force the tangential contact point far enough way from the inner edge 76 ofthe valve seat 74 to insure no contact with the inner edge 76. When the ball 72 contacts the valve seat 74, there is a certain amount of elastic deformation between the ball 72 and the valve seat 74 to form an area of contact suπounding the circular tangential contact point. This area or zone of contact is estimated to be approximately 0.005 to 0.010 inches wide. Therefore, by designing the slope 77 ofthe valve seat 74 to direct the tangential contact point to at least 0.015 inches from the inner edge 74 ofthe valve seat 74. this insures that the 0.005 to 0.010 inch area or zone of contact between me ball 72 and valve seat 74 never propagates over to the inner edge 76 ofthe valve seat 74. This eliminates the possibility of valve seat chipping due to ball impact. In accordance with anomer prefeπed aspect of die present invention, a prefeπed diaphragm plunger 86 is provided as illustrated in FIG. 10. As discussed above, the diaphragm plunger 86 contacts the diaphragm stop 100 on the return stroke ofthe piston 20 under pressure feed conditions. The diaphragm plunger 86 includes a spherical impact surface 88 which is designed to impact the coπesponding lower surface 102 ofthe diaphragm stop 100 at a position outward from the inner edge 104 ofthe diaphragm stop 100 and inward from the outer edge 89 ofthe plunger 86 (see FIG. 12). These edges 89, 104 are prone to chipping upon repeated impact under pressure feed conditions. As shown in FIG. 13, d e spherical impact surface 88 ofthe diaphragm plunger 86 contacts the lower surface 102 ofthe diaphragm stop 100 at a position away from the inner edge 104 the diaphragm stop 100 and the outer edge 89 of me plunger 86. In ϋhis way, the spherical surface 88 distributes impact forces along a portion ofthe diaphragm stop 100 so that the impact forces are not localized at a single point on the diaphragm stop 100. It is appreciated that such a design ofthe plunger impact surface 88 prevents the diaphragm plunger 86 from contacting the inner edge 104 ofthe diaphragm stop 100 or the outer edge 89 ofthe plunger 86 which greatly reduces the possibility of chipping ofthe fragile edges 104, 89 ofthe diaphragm stop 100 and plunger 86 as compared to prior diaphragm pumps in which die impact surface ofthe diaphragm plunger is a linear surface permitting impact at the inner edge ofthe diaphragm stop or outer edge 89 ofthe plunger 86 (see FIG. 11). It is further appreciated that this spherical impact surface 88 is also more tolerant of variances in manufacturing tolerances ofthe stop 100 and plunger 86 or off-center plunger impacts as the spherical surface 88 assures contact between the plunger 86 and diaphragm stop 100 away from the edges of d e stop 100 and plunger 86 even if me angle ofthe plunger impact varies (see FIG. 13). In a prefeπed embodiment, me radius ofthe spherical surface 88 is chosen so that the plunger 86 impacts the diaphragm stop 100 at the midway point between die inner edge 104 of me stop 100 and die outer edge 89 of me plunger 86. (See FIGS. 12, 13). This provides die maximum tolerance of eπor in bom directions from the edges ofthe plunger 86 and stop 100 in the case of off-center plunger impact or manufacturing variances from designed plunger 86 and stop 100 dimensions. This minimizes the possibility of contact at eidier edge of die plunger 86 or stop 100 under pressure feed conditions to significantly reduce the possibility of chipping at diese extreme edges 89, 104. Pursuant to additional aspects of a prefeπed embodiment, the graphs in FIGS. 20-22 illustrate the pressure in the piston chamber over the course of several piston cycles for various diaphragm pumps. FIG. 20 is for a prior art diaphragm pump described in die background ofthe invention and FIG. 21 is for a pump modified to have four inlets into the piston chamber and a reduced ball lift in each ball valve as described above. In comparing these two graphs, it is noted mat me modified pump has significantly reduced pressure peaks during the start ofthe power stroke as compared to the prior diaphragm pump. However, the pressure rings are still noticeably present and me pressure fluctuates throughout the entire piston cycle (see FIG. 21). To further reduce die pressure rings and pressure fluctuations, it is necessary to make additional modifications to me pump which will be described below to obtain the more consistent and moderate pressures illustrated in the graph in FIG. 22. According to one aspect of a prefeπed embodiment, d e diaphragm pump 10 preferably includes an hydraulic fluid isolation reservoir 64 to reduce die possibility of air entrapment within die piston chamber 34 during pump operation. Referring to FIG. 16, the hydraulic fluid isolation reservoir 64 is disposed adjacent to and at a position above me wobble plate chamber 58. A hydraulic fluid fill tube 60 is provided which extends dirough the hydraulic fluid isolation reservoir 64 into the wobble plate chamber 58 to permit filling ofthe pump with hydraulic fluid as needed. The hydraulic fluid isolation reservoir 64 is connected to d e wobble plate chamber 58 dirough at least one passageway 62. In a prefeπed embodiment, the passageway 62 extends around the hydraulic fill tube 60 so diat hydraulic fluid can freely flow between die wobble plate chamber 58 and hydraulic fluid isolation reservoir 64 (see FIG. 16). In this way, the diaphragm pump 10 is filled wid hydraulic fluid prior to use such diat the entire wobble plate chamber 58 is filled with hydraulic fluid and hydraulic fluid further flows into a portion of me hydraulic fluid isolation reservoir 60 to form an upper surface 66 of hydraulic fluid within die hydraulic fluid isolation reservoir 64. This upper surface 66 of hydraulic fluid is adjacent a certain amount of free air widiin me hydraulic fluid isolation reservoir 64. During operation, the motion ofthe wobble plate mechanism 50 within the wobble plate chamber 58 does not serve to mix the hydraulic fluid wim any air since no free air exists in the wobble plate chamber 58. Rather, hydraulic fluid in the hydraulic fluid isolation reservoir 64 which is adjacent a certain amount of free air is not disturbed by d e motion of me wobble plate mechanism and dius die hydraulic fluid does not intermix wim the free air to form a compressible mixture. It should also be noted the passageway 62 allows the hydraulic fluid in the wobble plate chamber 58 to expand as it heats up during pump operation and flow into the isolation reservoir 64 without overflowing out d e fill tube 60. This isolation reservoir 64 greatly reduces the possibility of air entrapment in die piston chamber 34 as compared to prior diaphragm pumps without the isolation reservoir as shown in FIG. 17. The hydraulic fluid isolation reservoir 64 of d e present invention leads to improved pump performance and reduces the possibility and severity of any pressure peaks or rings within d e piston chamber 34 during the initial build up of pressure in the piston chamber during the power stroke of the piston (See FIG. 22). It is noted that during operation, the diaphragm pump 10 needs to maintain a minimum level of hydraulic fluid widiin the hydraulic fluid isolation reservoir 64 to ensure mat no free air is able to enter the wobble plate chamber 58. Filling of hydraulic fluid dirough the fill tube 60 accomplishes this in view ofthe passageway 62 connecting die hydraulic fluid isolation reservoir 64 and d e wobble plate chamber 58. It is appreciated mat one may vary the location and connection of d e hydraulic fluid isolation reservoir 64 with respect to the wobble plate chamber 58 while still maintaining a complete fill of hydraulic fluid widiin the wobble plate chamber 58 in accordance wid the principles of d e present invention. Pursuant to another aspect of a prefeπed embodiment, the sliding valve assembly 106 includes a prefeπed opening 26 in the cylinder valve housing 28. As shown in FIG. 14, the cylinder valve housing 28 includes an elongated slot opening 29 which connects the hydraulic fluid inlet 36 widi die piston chamber 34. As described above, d e time period for hydraulic fluid reload under pressure feed conditions is relatively short and die elongated slot opening 29 in die cylinder valve housing 28 facilitates efficient flow of hydraulic fluid from the hydraulic fluid inlet 36 into the piston chamber 34. In a prefeπed embodiment, diree slots 29 are disposed symmetrically about the cylinder valve housing 28 for enhanced flow. As noted above, die sliding valve assembly 106 is generally open during the entire refill period under pressure feed conditions (see FIGS. 1, 2). The elongated slot opening 29 provides for quicker reload of hydraulic fluid as compared to die circular port in the sliding valve assembly of prior diaphragm pumps as shown in FIG. 15. This improved slot opening 29 reduces the likelihood of partial reload under pressure feed conditions and improves the overall reliability and performance of the diaphragm pump. It is appreciated that a variety of elongated shapes may be utilized for the slot opening including a rectangular or oval shape while still providing a suitable opening in accordance wim the principles ofthe present invention. It is noted d at the combination of diese prefeπed embodiments of die diaphragm pump described above results in a vastly improved diaphragm pump for use under pressure feed conditions. Referring to line A in the graph in FIG. 18. a diaphragm pump ofthe present invention shows drastically reduced pressure peaks or rings within the piston chamber during the power stroke with the pressure build up beginning substantially in conjunction with die piston beginning die power stroke in contrast to a similar graph for a prior diaphragm pump (see line A in FIG. 19). This results in a diaphragm pump with more consistent flow and pressures in all phases of the pumping cycle and greater long-term performance under pressure feed conditions. As illustrated in FIGS. 21-22, die combination of a diaphragm pump incorporating all modifications (FIG. 22) provides additional improvement in reducing the pressure peaks during the power stroke as compared to a pump modified wim only additional piston inlets and reduced ball lift in d e ball valves (FIG. 21). Pressure fluctuations are also reduced throughout the entire piston cycle when incoφorating all modifications in a diaphragm pump of me present invention (FIGS. 21-22). Wim respect to piston component deterioration due to plunger-stop impact and ball-valve seat impact, tests conducted with the present invention have demonstrated significant improvement in pump reliability and performance under extended use. Inspection ofthe piston components after use under pressure feed conditions indicates substantially no damage or chipping ofthe plunger or stop edges or the valve seat which significantly reduces the pump failure rate as compared to prior diaphragm pumps described above. It is to be understood that even ough numerous characteristics and advantages of various embodiments ofthe present invention have been set forth in the foregoing description, togedier widi d e details of die structure and function of various embodiments ofthe invention, d is disclosure is illustrative only and changes may be made in d e detail, especially in matters of shape, size, and arrangement of parts within the principles of die present invention, to me full extent indicated by die broad general meaning ofthe terms in which the appended claims are expressed. Odier modifications of die invention will be apparent to those skilled in me art in view ofthe foregoing descriptions. These descriptions are intended to provide specific examples of embodiments which clearly disclose the prevent invention. Accordingly, the invention is not limited to the described embodiments or to use of specific elements, dimensions, materials or configurations contained merein. All altemative modifications and variations of die present invention which fall within the spirit and broad scope of me appended claims are covered.

Claims: WHAT IS CLAIMED IS: 1. A diaphragm pump having a piston adapted for reciprocal movement from a first to a second position defining a power stroke and from the second to die first position defining a return stroke, a diaphragm moveable between first and second positions, a pumping chamber on one side of d e diaphragm, a piston chamber on die odier side of d e diaphragm having a volume defined, in part, by die relative positions ofthe piston and diaphragm, a source of hydraulic fluid connected widi die piston chamber to allow hydraulic fluid into die piston chamber, the hydraulic fluid in the piston chamber serving to transfer motion ofthe piston to the diaphragm, and means for reciprocating the piston, said diaphragm pump comprising: a plurality of piston inlets connecting the hydraulic fluid source with the piston chamber; and check valve means for permitting the flow of hydraulic fluid from the hydraulic fluid source to the piston chamber when the pressure in die piston chamber is less than the pressure in the hydraulic fluid source and for preventing the flow of hydraulic fluid when d e pressure in the piston chamber is greater than d e pressure in die hydraulic fluid source, said check valve means including a plurality of ball valves, each having a ball and valve seat, which are disposed widiin the plurality of inlets from the hydraulic fluid source to the piston chamber, said ball valves movable between a closed position and an open position such diat die ball is disposed in contacting relationship against die valve seat when die ball valve is in d e closed position, said valve seat including a conical section sloped inward toward die hydraulic fluid inlet and having an inner edge adjacent die inlet, wherein the slope of d e conical section is such that die tangential contact point between the ball and valve seat when the ball valve is in the closed position is located at a position on the conical section outward from the inner edge of die valve seat, and wherein the distance the ball is permitted to move between die open and closed positions is such diat the ball valve closes substantially in conjunction with the piston beginning its power stroke and the ball is not able to generate a high closure velocity when moving from the open to the closed position. 2. The diaphragm pump of claim 1 wherein the distance d e check valve ball is permitted to move between the open and closed positions is less than or equal to 0.08 ofthe diameter ofthe ball. 3. The diaphragm pump of claim 1 wherein the slope ofthe conical section of die valve seat is such d at the tangential contact point between the ball and valve seat when the ball valve is in the closed position is equal to or greater d an 0.015 inches from me inner edge of die valve seat. 4. The diaphragm pump of claim 1 wherein die slope of die conical section ofthe valve seat is such diat the tangential contact point between die ball and valve seat when d e ball valve is in die closed position is equal to or greater than 0.020 inches from the inner edge of die valve seat. 5. The diaphragm pump of claim 1 wherein said check valve means includes four ball valves disposed within four inlets from the hydraulic fluid source to the piston chamber. 6. The diaphragm pump of claim 1 further comprising a diaphragm stop for limiting movement ofthe diaphragm away from the pumping chamber, said diaphragm stop having an inner edge; and a diaphragm plunger connected to the diaphragm which contacts the diaphragm stop during die return stroke of die piston under a pressure feed condition, said plunger having an outer edge and including a spherical surface portion wherein the spherical surface portion contacts the diaphragm stop at a position outward from the inner edge of die diaphragm stop and inward from the outer edge of tiie plunger when the plunger contacts the diaphragm stop. 7. The diaphragm pump of claim 6 wherein the spherical surface portion ofthe plunger contacts the diaphragm stop at a point midway between the inner edge of d e diaphragm stop and the outer edge ofthe plunger. 8. The diaphragm pump of claim 1 further comprising a piston reciprocating chamber adjacent die piston such that the hydraulic fluid source is located widiin the piston reciprocating chamber; and an isolation reservoir adjacent and connected to said piston reciprocating chamber such that the hydraulic fluid completely fills the piston reciprocating chamber and further flows into the isolation reservoir to form an upper surface of hydraulic fluid widiin die isolation reservoir. 9. The diaphragm pump of claim 1 further comprising sliding valve means responsive to the relative movement between the diaphragm and piston for controlling the flow of hydraulic fluid from the hydraulic fluid source into the piston chamber, wherein the sliding valve means includes a cylinder valve connected to d e diaphragm and a cylinder valve housing connected to d e piston and adapted to receive the cylinder valve therein, said cylinder valve housing including at least one elongated slot disposed adjacent said cylinder valve to permit the flow of hydraulic fluid into the piston chamber. 10. A diaphragm pump having a piston adapted for reciprocal movement from a first to a second position defining a power stroke and from the second to die first position defining a return stroke, a diaphragm moveable between first and second positions, a pumping chamber on one side of die diaphragm, a piston chamber on the omer side ofthe diaphragm having a volume defmed, in part, by the relative positions ofthe piston and diaphragm, a source of hydraulic fluid connected with die piston chamber to allow hydraulic fluid into the piston chamber, the hydraulic fluid in the piston chamber serving to transfer motion ofthe piston to the diaphragm, and means for reciprocating the piston, said diaphragm pump comprising: a plurality of piston inlets connecting the hydraulic fluid source with the piston chamber; check valve means for permitting the flow of hydraulic fluid from the hydraulic fluid source to d e piston chamber when the pressure in the piston chamber is less than the pressure in the hydraulic fluid source and for preventing die flow of hydraulic fluid when the pressure in the piston chamber is greater than the pressure in the hydraulic fluid source, said check valve means including a plurality of ball valves, each having a ball and valve seat, which are disposed widiin die plurality of inlets connecting die hydraulic fluid source wid die piston chamber, said ball valves movable between a closed position and an open position such diat die ball is disposed in contacting relationship against the valve seat when the ball valve is in the closed position, said valve seat including a conical section sloped inward toward die hydraulic fluid inlet and having an inner edge adjacent die inlet, wherein the slope ofthe conical section is such diat d e tangential contact point between the ball and valve seat when the ball valve is in the closed position is located at a position on die conical section outward from the inner edge ofthe valve seat, and wherein the distance die ball is permitted to move between the open and closed positions is such tiiat die ball valve closes substantially in conjunction with the piston beginning its power stroke and die ball is not able to generate a high closure velocity when moving from the open to the closed position; a diaphragm stop for limiting movement ofthe diaphragm away from the pumping chamber, said diaphragm stop having an inner edge; a diaphragm plunger connected to the diaphragm which contacts the diaphragm stop during the return stroke ofthe piston under a pressure feed condition, said plunger having an outer edge and including a spherical surface portion wherein the spherical surface portion contacts the diaphragm stop at a position outward from the inner edge of die diaphragm stop and inward from the outer edge ofthe plunger when the plunger contacts the diaphragm stop; a piston reciprocating chamber adjacent d e piston such that die hydraulic fluid source is located widiin d e piston reciprocating chamber; an isolation reservoir adjacent and connected to said piston reciprocating chamber such that hydraulic fluid completely fills tiie piston reciprocating chamber and further flows into the isolation reservoir to form an upper surface of hydraulic fluid widiin d e isolation reservoir: and sliding valve means responsive to the relative movement between the diaphragm and piston for controlling the flow of hydraulic fluid from the hydraulic fluid source into die piston chamber, wherein the sliding valve means includes a cylinder valve connected to die diaphragm and a cylinder valve housing connected to the piston and adapted to receive the cylinder valve therein, said cylinder valve housing including at least one elongated slot disposed adjacent said cylinder valve to permit the flow of hydraulic fluid into the piston chamber. 1 1. The diaphragm pump of claim 10 wherein the distance the check valve ball is permitted to move between the open and closed positions is less than or equal to 0.08 ofthe diameter of die ball and the slope of die conical section of the valve seat is such diat the tangential contact point between the ball and valve seat when d e ball valve is in the closed position is equal to or greater than 0.015 inches from the inner edge of d e valve seat. 12. The diaphragm pump of claim 10 wherein the spherical surface portion ofthe plunger contacts the diaphragm stop at a point midway between the inner edge ofthe diaphragm stop and the outer edge of the plunger.

Inventors: POWERS FREDERICK ALLAN, POWERS, FREDERICK, ALLAN
Applicants: WANNER ENGINEERING, WANNER ENGINEERING, INC.
Application year: 1996
Main classification: F04B43
IPC codes: F04B43