BACKPACK SPRAYER WITH SELECTABLE INTERNAL PUMP

Abstract

An internal pump backpack sprayer system includes a first tank, a second tank and a pump unit. The first tank includes a tank housing for holding a fluid. The second tank is received within the first tank and receives a pressurized fluid. The pump unit has a cylinder housing with first and second inlets and first and second outlets, a piston within a cylinder and a pressure discharge assembly. When the piston moves in an up-stroke, fluid is drawn from the first tank through the first inlet while all or some pressurized fluid is discharged through the pressure discharge assembly with a remainder being discharged to the second tank through the second outlet. When the piston moves in a down-stroke, fluid is drawn from the first tank through the second inlet while pressurized fluid is discharged to the second tank through the first outlet.

Claims

1. An internal pump backpack sprayer system comprising: a) a first tank including a tank housing defining an open internal volume configured to hold a fluid therein; b) a second tank dimensioned to be received within said internal volume of said first tank and configured to receive a pressurized fluid therein; and c) a selectably adjustable pump unit comprising a cylinder and piston assembly having a cylinder housing with first and second inlets and first and second outlets, a piston located and moveable within a cylinder and a pressure discharge assembly in fluid communication with said cylinder, wherein when said piston moves in an up-stroke, a first portion of said fluid is drawn from said first tank through said first inlet while all or some of a first portion of said pressurized fluid is discharged through said pressure discharge assembly with a remainder, if any, of said first portion of said pressurized fluid being discharged to said second tank through said second outlet, and wherein when said piston moves in a down-stroke, a second portion of said fluid is drawn from said first tank through said second inlet while a second portion of said pressurized fluid is discharged to said second tank through said first outlet.

2. The backpack sprayer system of claim 1 wherein said pump unit is received within said internal volume of said first tank, said pump unit being fluidly coupled to said first tank and said second tank, wherein said pump unit further includes a piston rod coupled to said piston at a first end of said piston rod.

3. The backpack sprayer system of claim 1 wherein said cylinder and piston assembly comprises: a) said cylinder housing having an inlet tube wall defining an inlet tube, an outlet tube wall defining an outlet tube, an inner cylinder wall defining said cylinder, and a bottom wall including an inlet tube orifice coinciding with said inlet tube, an outlet tube orifice coinciding with said outlet tube and a cylinder inlet orifice and cylinder outlet orifice coinciding with said cylinder, said cylinder housing having a top end located opposite said bottom wall; b) a first pressure chamber defined within said inner cylinder wall between said bottom wall of said cylinder housing and said piston; c) a cylinder head located at said top end of said cylinder housing, wherein a second pressure chamber is defined within said inlet tube, said outlet tube and said inner cylinder wall between said piston and said cylinder head, and wherein said cylinder head includes said pressure discharge assembly thereon with said pressure discharge assembly in fluid communication with said cylinder; d) a pump manifold secured to said bottom wall of said cylinder housing, said pump manifold including an inlet well fluidly separated from an outlet well, wherein said inlet well includes an inlet orifice in fluid communication with said first tank and said outlet well includes an outlet orifice in fluid communication with said second tank; e) an inlet check valve assembly located in said inlet well and including an inlet check valve housing defining said first and second inlets, an inlet tube check valve and a cylinder inlet check valve; and f) an outlet check valve assembly located in said outlet well and including an outlet check valve housing defining said first and second outlets, an outlet tube check valve and a cylinder outlet check valve; and wherein during said up-stroke of said piston within said cylinder, said inlet tube check valve and said cylinder outlet check valve are closed and said cylinder inlet check valve and said outlet tube check valve are open, and wherein during said down-stroke of said piston within said cylinder, said inlet tube check valve and said cylinder outlet check valve are open and said cylinder inlet check valve and said outlet tube check valve are closed.

4. The backpack sprayer system of claim 2 wherein said pump unit further includes a fluid agitator mounted on said piston rod.

5. The backpack sprayer system of claim 4 wherein said fluid agitator comprises one or more paddles and configured to reciprocally travel within said internal volume as said piston rod translates during said up-stroke and said down-stroke.

6. The backpack sprayer system of claim 2 wherein a translating rod is pivotally coupled to said piston rod, whereby translation of said translating rod in a first direction causes said piston to move in either said up-stroke or said down-stroke and whereby translation of said translating rod in an opposing second direction causes said piston to move in the other of said up-stroke or said down-stroke.

7. The backpack sprayer system of claim 6 wherein said translating rod is positioned external said first tank and is configured to translate within a recess defined within a back wall of said first tank.

8. The backpack sprayer system of claim 1 wherein said pressure discharge assembly includes a discharge sidewall and a discharge regulator unit mounted thereto.

9. The backpack sprayer system of claim 8 wherein said discharge sidewall defines male threads and wherein said discharge regulator unit includes a cap having a cap sidewall defining a set of female threads configured to threadably receive said male threads therein to removably secure said cap to said discharge sidewall.

10. The backpack sprayer system of claim 8 wherein said discharge sidewall defines female threads and wherein said discharge regulator unit includes a plug having a plug sidewall defining a set of male threads configured to be threadably received within said female threads to removably secure said plug in said discharge sidewall.

11. The backpack sprayer system of claim 8 wherein said pressure discharge assembly includes a discharge sidewall defining a discharge cavity encircling a discharge aperture defined within said cylinder housing, and wherein said discharge regulator unit includes a cap adjustably mounted onto said discharge sidewall and a valve received within said discharge port, wherein said valve is biased against said cap to occlude said discharge aperture.

12. The backpack sprayer system of claim 11 wherein said valve includes: a) a shaft extending through said discharge aperture and having a first end within said cylinder housing and a second end within said discharge cavity; b) a seat on said shaft and located within said discharge cavity an intermediate distance between said shaft first end and said shaft second end; and c) a valve spring between a top surface of said seat and an inner surface of said cap whereby said seat is biased to occlude said discharge aperture.

13. The backpack sprayer system of claim 12 wherein said cap is selectively positionable on said discharge sidewall to adjust a biasing force of said valve spring.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0016] FIG. 1 is a front perspective view of a sprayer system in accordance with an aspect of the present invention;

[0017] FIG. 2 is a rear perspective view of the sprayer system shown in FIG. 1;

[0018] FIG. 3 is a side cross section view of the sprayer system shown in FIGS. 1 and 2;

[0019] FIG. 4 is a perspective view of the sprayer system shown in FIGS. 1 and 2 with the spray tank and backpack frame removed;

[0020] FIG. 5 is an expanded view of a double action pump unit used within the sprayer system shown in FIGS. 1 and 2;

[0021] FIG. 6 is an exploded view of the double action pump unit shown in FIG. 5;

[0022] FIG. 7 is a cross section view of the double action pump unit shown in FIG. 5 following a piston up-stroke and immediately prior to a piston down-stroke;

[0023] FIG. 8 is a cross section view of the double action pump unit shown in FIG. 5 following a piston down-stroke and immediately prior to a piston up-stroke;

[0024] FIG. 9 is a perspective view of an alternative embodiment of a pump unit suitable for use within the sprayer system shown in FIGS. 1 and 2;

[0025] FIG. 10 is an expanded view of an exemplary pressure discharge assembly included on the pump unit shown in FIG. 9; and

[0026] FIG. 11 is an expanded cross section view of the pressure discharge assembly portion of the pump unit shown in FIG. 9.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0027] Referring now to the drawings, and with particular reference to FIGS. 1-3, in accordance with an aspect of the present invention, a backpack sprayer system 10 may generally comprise a first tank 12 and a second tank 14 mounted onto a modular backpack frame 16. Modular backpack frame 16 may comprise a frame plate 18 and support member 20, such as that shown and described within commonly owned U.S. patent application Ser. No. 16/351,882 filed on Mar. 13, 2019, the entirety of which is hereby incorporated by reference. Rear wall 12a of first tank 12 and rear surface 18a for frame plate 18 may each have a curved profile so as to more ergonomically rest against a user's back during use. First tank 12 includes a first tank housing 22 which defines an open internal volume 24 which receives a spray fluid, such as water or dilute chemical solution, therein. Second tank 14 is dimensioned to be received within open internal volume 24. Second tank 14 includes a second tank housing 26 defining a pressurized fluid chamber 28 which is configured to receive a pressurized fluid therein, as will be described in greater detail below.

[0028] With reference to FIGS. 3 and 4, first tank 12 and second tank 14 are each individually fluidly coupled to an internal pump unit 30 resident within open internal volume 24 of first tank housing 22. With additional reference to FIGS. 5-8, and in accordance with an aspect of the present invention, pump unit 30 is configured as a double action piston pump generally comprising a cylinder and piston assembly 32 and piston rod 34. By way of example and without limitation thereto, cylinder and piston assembly 32 may include a cylinder housing 36 having an inlet tube wall 38 defining an inlet tube 40, an outlet tube wall 42 defining an outlet tube 44, an inner cylinder wall 46 defining a cylinder 48, and a bottom wall 50 including an inlet tube orifice 52 coinciding with the inlet tube 40, an outlet tube orifice 54 coinciding with the outlet tube 44 and a cylinder inlet orifice 56 and cylinder outlet orifice 58 coinciding with the cylinder 48. Cylinder housing 36 also has a top end 60 located opposite bottom wall 50.

[0029] A piston 62 is located and moveable within cylinder 48 such that a first pressure chamber 64 is defined within inner cylinder wall 46 between bottom wall 50 of cylinder housing 36 and piston 62. Piston rod 34 is coupled to piston 62 at a first end 66 of piston rod 34. Cylinder head 68 is located at top end 60 of cylinder housing 36 and includes an aperture 70 so as to allow passage of piston rod 34 therethrough. A second pressure chamber 72 is defined within inlet tube 40, outlet tube 44 and inner cylinder wall 46 between piston 62 and cylinder head 68. A cylinder collar and seal 74 is coupled to cylinder head 68 and forms a fluid-tight seal about piston rod 34 to prevent fluid leaking from second pressure chamber 72 about piston rod 34.

[0030] Pump manifold 76 is secured to bottom wall 50 of cylinder housing 36 and includes an inlet well 78 fluidly separated from an outlet well 80. Inlet well 78 includes an inlet orifice 82 in fluid communication with first tank 12 and outlet well 80 includes an outlet orifice 84 in fluid communication with second tank 14 (FIGS. 5 and 6). An inlet check valve assembly 86 is located within inlet well 78 and includes an inlet check valve housing 88 having a bottom wall 90 which includes an inlet tube well orifice 92 and cylinder inlet well orifice 94. An inlet tube check valve 96 is configured to interact with inlet tube orifice 52 and inlet tube well orifice 92 while a cylinder inlet check valve 98 is configured to interact with cylinder inlet orifice 56 and cylinder inlet well orifice 94. Similarly, an outlet check valve assembly 100 is located within outlet well 80 and includes an outlet check valve housing 102 having a bottom wall 104 which includes a cylinder outlet well orifice 106 and an outlet tube well orifice 108. A cylinder outlet check valve 110 is configured to interact with cylinder outlet orifice 58 and cylinder outlet well orifice 106 while an outlet tube check valve 112 is configured to interact with outlet tube orifice 54 and outlet tube well orifice 108. In accordance with an aspect of the invention, check valves 96, 98, 110 and 112 are ball valves. Each check valve may include a valve spring 96a, 98a, 110a, 112a coupled with a respective ball valve 96, 98, 110, 112. Valve springs 96a, 98a are configured to bias ball valves 96, 98 toward check valve housing bottom wall 90 while valve springs 110a, 112a are configured to bias ball valves 110, 112 toward cylinder housing 36.

[0031] As shown most clearly in FIG. 7, during an up-stroke of piston 62 within cylinder 48, as shown generally by arrow 114, fluid from first tank 12 is directed into first pressure chamber 64 while pressurized fluid within second pressure chamber 72 is discharged to second tank 14. To that end, upward travel of piston 62 creates a vacuum within cylinder 48 whereby cylinder outlet check valve 110 is drawn upwardly (with additional urging to the spring bias of valve spring 110a) to seat against cylinder outlet orifice 58 so as to close the check valve. Conversely, cylinder inlet check valve 98 is opened due to the vacuum overcoming the spring bias of valve spring 98a whereby fluid from first tank 12 is drawn under vacuum through inlet orifice 82 within pump manifold 76, cylinder inlet well orifice 94 and cylinder inlet orifice 56 as generally indicated by arrow 116. Simultaneously, upward travel of piston 62 (arrow 114) compresses fluid within second pressure chamber 72 such that the pressurized fluid travels downwardly within inlet tube 40 and outlet tube 44. The flow of pressurized fluid drives inlet tube check valve 96 downwardly (with additional urging to the spring bias of valve spring 96a) to seat against inlet tube well orifice 92 so as to close the check valve. Conversely, outlet tube check valve 112 is opened due to the downward pressure of the fluid overcoming the spring bias of valve spring 112a whereby the pressurized fluid within second pressure chamber 72 is discharged through outlet tube orifice 54, outlet tube well orifice 108 and outlet orifice 84 in pump manifold 76 to second tank 14 as generally indicated by arrow 118.

[0032] With reference to FIG. 8, during a down-stroke of piston 62 within cylinder 48, as shown generally by arrow 120, fluid from first tank 12 is directed into second pressure chamber 72 while pressurized fluid within first pressure chamber 64 is discharged to second tank 14. To that end, downward travel of piston 62 creates a vacuum within second pressure chamber 72 such that outlet tube check valve 112 is drawn upwardly (with additional urging to the spring bias of valve spring 112a) to seat against outlet tube orifice 54 so as to close the check valve. Conversely, inlet tube check valve 96 is opened due to the vacuum overcoming the spring bias of valve spring 96a whereby fluid from first tank 12 is drawn under vacuum through inlet orifice 82 in pump manifold 76, inlet tube well orifice 92 and inlet tube orifice 52 as generally indicated by arrow 122. Simultaneously, downward travel of piston 62 (arrow 120) compresses fluid within cylinder 48. The flow of pressurized fluid drives cylinder inlet check valve 98 downwardly (with additional urging to the spring bias of valve spring 98a) to seat against cylinder inlet well orifice 94 so as to close the check valve. Conversely, cylinder outlet check valve 110 is opened due to the downward pressure of the fluid overcoming the spring bias of valve spring 110a whereby the pressurized fluid within first pressure chamber 64 is discharged through cylinder outlet orifice 58, cylinder outlet well orifice 94 and outlet orifice 84 in pump manifold 76 to second tank 14 as generally indicated by arrow 124.

[0033] In accordance with an aspect of the present invention, pump unit 30 may be a manually actuated pump with piston rod 34 pivotally coupled to a first end 126 of a translating rod 128 at piston rod second end 130. Second end 132 of translating rod 128 is coupled to a pump actuator, such as actuating rod 134. Actuating rod 134 may be selectively coupled to a handle 136 whereby movement of handle 136 in a first direction causes actuating rod 134 to rotate which translates translating rod 128 either upwardly or downwardly, which in turn drives piston rod in an opposing upward or downward movement whereby piston 62 engages in either a down-stroke (arrow 120) or an up-stroke (arrow 114). Movement of handle 136 in an opposing second direction reverses direction of movement of actuating rod 134, translating rod 128, piston rod 34 and piston 62 in the other of the down-stroke or up-stroke. Handle 136 may be mounted to either end 138, 140 of actuating rod 134 so as to enable left-handed or right-handed operation of pump unit 30.

[0034] In accordance with a further aspect of the present invention, translating rod 128 and actuating rod 134 may be located externally of first tank 12. Rear wall 12a of first tank 12 may also include a recess 12b wherein translating rod 128 may be positioned such that movement of translating rod 128 is not impeded by a user's body when backpack sprayer system 10 is worn against the back of the user. Additionally, while shown as described as a manually actuated pump, it should be noted by those skilled in the art that an electrically driven pump, such as but not limited to a battery powered pump, may also be employed, and that such pumps are to be considered within the teachings of the instant disclosure.

[0035] In accordance with a further aspect of the present invention, backpack sprayer system 10 may include an agitator within open internal volume 24 of first tank housing 22. As shown most clearly in FIGS. 3 and 4, one exemplary agitator may be a paddle 142, and more particularly a pair of paddles 142 mounted on respective arms 144 connected to a common yoke 146. Yoke 146 may be affixed to piston rod 34 such that upward and downward travel of piston rod 34, as described above, causes upward and downward travel of paddles 142. In this manner, paddles 142 may agitate fluid within first tank housing 22. Paddles 142 may be flat, continuous members, or may be a flat member including one or more apertures therethrough. Apertures may promote agitation by increasing fluid flow paths around and through the paddle, while also reducing compressive forces within the fluid as the paddles move through the fluid.

[0036] From the above description of pump unit 30, particularly in view of FIGS. 7 and 8, it should be noted that second tank 12 is filled with pressurized fluid upon each up-stroke and down-stroke of piston 62. Such operation is in contrast to pump systems generally used in the art of backpack sprayers. Typically, backpack sprayers employ pumps that charge the second tank only on one stroke, i.e., either the up-stroke or down-stroke, but not both. As a result, pump system 10 including a double action pump unit 30 can utilize a pump unit having a smaller footprint. That is, typical backpack sprayers may use pump units having cylinder diameters of approximately 2 inches. In accordance with an aspect of the present invention, cylinder 48 has a diameter of approximately 1.5 inches. Assuming 2 inches of piston travel per stroke, double action pump system 10 may still output approximately 25% more volume per stroke cycle (one up-stroke and one down-stroke) than a single action pump system using a larger cylinder. Moreover, the force required to drive a piston is proportional to the piston diameter. Thus, a piston with a larger diameter requires greater pumping force to drive the piston. Thus, in accordance with an aspect of the present invention, a 25% reduction in piston diameter (1.5 inches as opposed to 2 inches) leads to a greater than 50% reduction in required pumping force. As a result, less energy is required to drive pump system 10 as compared to generally available backpack spray systems. This reduction in required pumping force enables additional advantages. For example, when the pump unit is manually actuated, requiring less pumping force leads to less user fatigue. Further, the pressure volume may be charged with pressurized fluid having a higher pressure. That is, a lower pumping force allows the pump unit to discharge a greater volume of fluid into the fixed volume of the pressure vessel (more fluid within a fixed space yields higher fluid pressures).

[0037] While pump system 10 provides numerous advantages, as described above, there remain certain instances when reduced pumping force is desired, particularly during the up-stroke portion of the pumping cycle. By way of example, reduced up-stroke pressure may be desired when spraying a viscous liquid or when the user lacks the strength needed to drive the pump in the up-stroke direction. Thus, in accordance with the present invention, an alternative pump unit 200 allowing for selective adjustment of the up-stroke pressure is shown with reference to FIGS. 9-11. Alternative pump unit 200 may be identical to internal pump unit 30 with the exception of a modified cylinder head 268 and pressure discharge assembly. Accordingly, pump unit 200 includes cylinder housing 36 with inlet tube wall 38, outlet tube wall 42 and respective cylinder 48, inlet tube 40 and outlet tube 44, along with pump manifold 76 (including check valves 96, 98, 110 and 112 and valve springs 96a, 98a, 110a, 112a, not shown), as described above.

[0038] As shown in FIGS. 5-8, internal pump unit 30 includes a cylinder head 68 which creates a closed second pumping chamber 72. That is, during an up-stroke, fluid within second pressure chamber 72 can only exit pump unit 30 through outlet tube orifice 54 so as to pressurize second tank 14 as described previously. As a result, the up-stroke portion of the pumping cycle when using pump unit 30 and handle 136, actuating rod 134, and translating rod 128 imposes a pumping force upon the user that requires different muscles than are used during the pump down-stroke. A user may, therefore, wish to reduce or remove this up-stroke pumping force with an understanding that such reduction/removal would decrease the pumping efficiency of the pump unit. However, cylinder head 68 creates a closed system with no provision for a reduction of the up-stroke pumping force.

[0039] Turning now to FIGS. 10 and 11, cylinder head 268 of pump unit 200 is configured to provide for user-selected reduction of the up-stroke pumping force. In one aspect of the invention, cylinder head 268 includes a pressure discharge assembly 210. With reference to FIG. 11, pressure discharge assembly 210 is in fluid communication with second pressure chamber 272. Pressure discharge assembly 210 may generally include a discharge sidewall 212 and a discharge regulator unit 214 mounted thereon. In one aspect of the present invention, discharge sidewall 212 may define male threads while discharge regulator unit 214 includes a cap 218 having a cap sidewall 220 defining a set of female threads. The female threads may be configured to threadably receive the male threads therein so as to removably secure cap 218 to discharge sidewall 212. Alternatively, discharge sidewall 212 may define female threads and discharge regulator unit 214 may include a plug having a plug sidewall defining a set of male threads which are configured to be threadably received within the female threads of discharge sidewall 212 so as to removably secure the plug in discharge sidewall 212.

[0040] In either of the above embodiments wherein discharge side wall 212 and discharge regulator unit 214 include corresponding threaded features, when the corresponding features are fully thread to one another, a closed system is created such that pump unit 200 operates as a dual action pump similar to pump unit 30 described above. However, when the threaded features are fully unthreaded (i.e., cap 218 or the plug is removed), a fully open system is created such that pump unit 200 operates as a single stroke pump with no pressurization of second tank 14 during the up-stroke portion of the pumping cycle. As a result, a user may selectively configure pump unit with full up-stroke force (closed system) or no up-stroke force (open system).

[0041] In another aspect of the present invention, pressure discharge assembly 210 may include discharge sidewall 212 which defines a discharge cavity 222 encircling a discharge aperture 224 defined within cylinder head 268. Discharge regulator unit 214 of pressure discharge assembly 210 includes a cap 226 securely, yet adjustably mounted onto discharge sidewall 212. By way of example, cap 226 may be mounted to discharge sidewall 212 through a snap connection such that cap 226 may rotate about discharge sidewall 212 without becoming freed from discharge sidewall 212. Discharge regulator unit 214 may further include a valve assembly 228 received within the discharge cavity 222. Valve assembly 228 may be biased against cap 226 so as to occlude discharge aperture 224.

[0042] By way of example, valve assembly 228 may include a shaft 230 having a first end 232 which is received in and extends through discharge aperture 224 to reside within the cylinder housing 32 and/or second pressure chamber 272 and/or inlet tube 40. Shaft 230 may include an opposing second end 234 configured to reside within discharge cavity 222. Shaft 230 may further include a seat 236 and optional seal 237 (such as a O-ring) located an intermediate distance between the shaft first end 232 and shaft second end 234 on the shaft. Seat 236 is positioned within the discharge cavity 222 whereby a valve spring 238 mounted between a top surface 240 of seat 236 and an inner surface 242 of cap 226 biases seat 236 (and seal 237) so as to occlude discharge aperture 224. Cap 226 may be selectively positionable on discharge sidewall 212 so as to controllably adjust a biasing force of valve spring 238, as will be described in greater detail below. Cap 226 and discharge sidewall 212 may include respective indicia 244, 246 to visually signal to the user the cap 226 position and resultant biasing force of valve spring 238.

[0043] With reference to FIG. 11 (in conjunction with FIG. 7), during an up-stroke of piston 62 within cylinder 48, as shown generally by arrow 114, fluid from first tank 12 is directed into first pressure chamber 64 while fluid within second pressure chamber 272 is discharged to first tank 12 via pressure discharge assembly 210 and/or to second tank 14 via outlet tube orifice 54. To that end, upward travel of piston 62 creates a vacuum within cylinder 48 whereby cylinder outlet check valve 110 is drawn upwardly (with additional urging due to the spring bias of valve spring 110a) to seat against cylinder outlet orifice 58 so as to close the check valve. Conversely, cylinder inlet check valve 98 is opened due to the vacuum overcoming the spring bias of valve spring 98a whereby fluid from first tank 12 is drawn under vacuum through inlet orifice 82 within pump manifold 76, cylinder inlet well orifice 94 and cylinder inlet orifice 56 as generally indicated by arrow 116.

[0044] Simultaneously, upward travel of piston 62 (arrow 114) compresses fluid within second pressure chamber 272. Should this compression pressurize the fluid to a degree which overcomes the biasing force of valve spring 238, seat 236 disengages discharge aperture 224 whereby at least a portion of the fluid may exit pump unit 200 through pressure discharge assembly 210. By way of example and without limitation thereto, cap 226 may include one or more through-holes 248 defined therethrough such that fluid may pass from second pressure chamber 272 to first tank 12. A remaining portion of the pressurized fluid within second pressure chamber 272 may also travel downwardly within outlet tube 44 whereby outlet tube check valve 112 is opened due to the downward pressure of the fluid overcoming the spring bias of valve spring 112a such that the pressurized fluid is discharged through outlet tube orifice 54, outlet tube well orifice 108 and outlet orifice 84 in pump manifold 76 to second tank 14 as generally indicated by arrow 118.

[0045] Therefore, as described above, incremental rotation of cap 226 incrementally adjusts the spring bias of valve spring 238, wherein a higher spring bias causes less fluid to discharge though pressure discharge assembly 210 and more fluid to pressurize second tank 14, which also increases the pumping force during the up-stroke. Thus, to reduce the pumping force, cap 226 may be positioned so as to minimize the spring bias of valve spring 238. As a result, most, if not all, of the fluid in second pressure chamber 272 may freely discharge through pressure discharge assembly 210 without pressurizing the fluid and increasing the pumping force needed during the up-stroke.

[0046] With continued reference to FIG. 11 (along with reference to FIG. 8), during a down-stroke of piston 62 within cylinder 48, as shown generally by arrow 120, fluid from first tank 12 is directed into second pressure chamber 272 while pressurized fluid within first pressure chamber 64 is discharged to second tank 14. To that end, downward travel of piston 62 creates a vacuum within second pressure chamber 272 such that outlet tube check valve 112 is drawn upwardly (with additional urging due to the spring bias of valve spring 112a) to seat against outlet tube orifice 54 so as to close the check valve, along with drawing seat 236 (and seal 237) against discharge aperture 224 (with additional urging due to the spring bias of valve spring 238) so as to occlude discharge aperture 224 and prevent intake of fluid from first tank 12 into second pressure chamber 272 through pressure discharge assembly 210. Conversely, inlet tube check valve 96 is opened due to the vacuum overcoming the spring bias of valve spring 96a whereby fluid from first tank 12 is drawn under vacuum through inlet orifice 82 in pump manifold 76, inlet tube well orifice 92 and inlet tube orifice 52 as generally indicated by arrow 122.

[0047] Simultaneously, downward travel of piston 62 (arrow 120) compresses fluid within cylinder 48. The flow of pressurized fluid drives cylinder inlet check valve 98 downwardly (with additional urging to the spring bias of valve spring 98a) to seat against cylinder inlet well orifice 94 so as to close the check valve. Conversely, cylinder outlet check valve 110 is opened due to the downward pressure of the fluid overcoming the spring bias of valve spring 110a whereby the pressurized fluid within first pressure chamber 64 is discharged through cylinder outlet orifice 58, cylinder outlet well orifice 94 and outlet orifice 84 in pump manifold 76 to second tank 14 as generally indicated by arrow 124.

[0048] The foregoing description of the preferred embodiment of the invention has been presented for the purpose of illustration and description. It is not intended to be exhaustive nor is it intended to limit the invention to the precise form disclosed. It will be apparent to those skilled in the art that the disclosed embodiments may be modified in light of the above teachings. The embodiments described are chosen to provide an illustration of principles of the invention and its practical application to enable thereby one of ordinary skill in the art to utilize the invention in various embodiments and with various modifications as are suited to the particular use contemplated. Therefore, the foregoing description is to be considered exemplary, rather than limiting, and the true scope of the invention is that described in the following claims.