PUMP HAVING RELIEF VALVE SEAT FREE OF DIRECT STRUCTURAL RESTRAINT

Abstract: A pump includes a coaxially integrated pump relief valve element (50) of high density polymer material that seats against a hard metallic sleeve (32). The sleeve (32) is pressed into a first counterbore (22) around the relief flow channel (20) with an interference fit. That axial end of the sleeve bearing the valve seat face projects, for a substantial proportion of the sleeve length, beyond the first counterbore shoulder into a second, larger diameter counterbore space (28) to provide an annular space (30) around the outside diameter surface of the sleeve to free the seat face end of the sleeve from direct structural restraint.

Description: PUMP HAVING RELIEF VALVE SEAT FREE OF DIRECT STRUCTURAL RESTRAINT BACKGROUND OF THE INVENTION The present invention relates to valve construction. More particularly, the invention relates to an improved bypass/relief valve integral with a potable liquids pump. Vane type pumps are often used by the beverage, food and health industries for quietly transferring potable liquiuϋ α iuoueiα eiy high pressures and volumetric now rates. For example, vane pumps are used to spray water into a carbon dioxide atmosphere tank at 200 to 250 psi as a step in the production of carbonated beverages. One particular design of vane pump provides a shunt flow channel between the suction and discharge conduits of the pump. Flow through this shunt is differentially controlled by coaxial valve elements. An axial bore along the relief valve plug element is flow directionally rectified by a spring biased poppet element at the discharge port end of the shunt. This, in effect, is a check valve with a spring loaded cracking bias by which fluid flow bypasses the pump rotor from the suction port directly into the discharge port when suction side pressure exceeds the pump discharge port pressure. The discharge port relief valve plug is held against a closure seat by an adjustably loaded compression spring that opposes the pump discharge pressure. Compression preload on the relief valve spring is adjusted by an axial displacement of the spring seat. The spring is seated on a screw threaded plug which is advanced or retarded by manual rotation. When the discharge pressure forces on the plug seat cross-sectional area exceed the preload force of the seating spring, the plug moves away from the valve seal face thereby permitting pump discharge fluid flow to recirculate directly back into the pump suction conduit. Pumps manufactured for sanitary applications such as in fast food restaurants, hospitals or for food processing frequently are made with brass bodies and use brass plugs in the relief valve conduit. While this design has generally performed well for many years, there is a recent demand for greater pump reliability, especially in soft drink fountain applications. It has been determined that the relief valve in this pump is a statistically substantial source of failure. The metal-to-metal valve element combination with cooperating soft metals tends to leak a minute amount but such leakage has little or no apparent effect on pump operation. Once leakage flow begins, erosion exacerbates the defect and the initial small leak develops into a catastrophic failure effectively rendering the pump unusable. A different cause of the same result arises from inaccurate or defective machine tools that turn, bore and cut imprecise or irregular shapes and surfaces. Relative to the present interest, if a relief valve seat or plug face is out- of-round the pair cannot cooperate to form a fluid-tight seal and small leaks quickly grow into large leaks. It is an objective of the present invention, therefore, to provide a relief valve design and construction for potable fluid vane pumps having greater accuracy in the shape of the valve sealing surfaces. Another object of the invention is to provide a relief valve design and construction in which one of the valve sealing elements is significantly softer than the other seal element. A further object of the invention is to disclose a valve plug material that, relative to the valve seat, is softer and tougher. SUMMARY OF THE INVENTION The foregoing objects and others to become evident from the following drawings and detailed description are accomplished by a pump having the suction and discharge ports connected together by a relief flow conduit. At the relief flow conduit juncture with the suction port, two, stair- SOBSππnτ SHEET (RUIE 26) stepped counterbores are provided to receive a thin-walled sleeve having an axial length that is preferably about 30% or more longer than the press-fit penetration of the sleeve into the deeper, smaller diameter counterbore. A valve seat is formed around the inside diameter of the sleeve at the projecting end thereof. The projecting end of the sleeve is not directly constrained by either of the counterbores, and even if the counterbores are oval or otherwise non-circular in cross-section, the projecting end of the sleeve will maintain its circular cross-sectional shape. As will become more apparent from the discussion below, the projecting end of the sleeve forms part of the valve and by remaining more precisely circular, it greatly reduces a type of leakage failure that was common in prior pumps. Confined within the sleeve bore for axial reciprocation therein is a tubular valve plug. Plug characteristics include an axial throughbore and an outside diameter shoulder near one end of the plug. A conical valve seat face is formed into the shoulder step. Below the seat face, the plug tube outside wall may be longitudinally ribbed or given a non-circular geometric section such as a square or triangle. Such outside tube wall sections provide longitudinal fluid flow channels between the valve plug outside wall and the inside wall of the sleeve bore when the plug seat face separates from the sleeve seat. A helical compression spring seated at one end thereof against the valve plug and at the other end against a threaded plug provides a selectively varied preload against the valve plug to hold the plug seat sealed against the sleeve seat in opposition to the desired magnitude of discharge pressure force. When the discharge port pressure exceeds the spring preload force, the valve plug is moved against the spring bias thereby opening the valve seat seal to allow fluid flow from the discharge port to the suction port. The internal throughbore of the tube is undirectionally closed by a tension spring biased poppet plug at the discharge port end of the plug tube. Fluid system conditions resulting in a greater pressure in the suction port than in the discharge port will permit fluid to bypass the pump vane for direct flow into the discharge port. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a sectional view of a traditional vane pump incorporating the present invention. FIG. 2 is an axially sectioned view of a bypass-relief valve plug. FIG. 3 is an end view of the bypass-relief valve plug. FIG. 4 is an axially sectioned view of the pump bypass conduit. FIG. 5 is an axially sectioned view of the bypass conduit sleeve insert. FIG. 6 is an end view of the bypass conduit sleeve insert. FIG. 7 is an axially sectioned view of the bypass valve plug without the relief poppet. FIG. 8 is an end view of the bypass valve plug. FIG. 9 is an end view of the bypass-relief valve plug having a square cross-section. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT Relative to the drawings wherein like reference characters designate like or similar elements throughout the several figures of the drawings, Figure 1 illustrates a traditional vane type pump having a pump body 10 with a rotor 12 and vanes 14 rotating within an eccentric sleeve 15. Usually, the pump body is forged or cast of brass or stainless steel although aluminum and plastic has been used. A suction port 16 channels fluid into the eccentric chamber 17 where it is transferred by the rotating vanes 14 into the SUBSTITUTE SHEET LE 26) discharge port 18. A finely meshed screen filter 19 captures particulate contaminants before reaching the pump eccentric chamber 17. Pipe or tubing connector threads are cut into the suction and discharge port entrances to receive the connectors of external fluid conduits. Between the suction and discharge ports is a cylindrical bypass conduit 20 drilled or bored along the axis 21. With respect to Figs. 4, 5 and 6, the junction of conduit 20 with the suction port 16 is double counterbored, coaxial with the axis 21. A first counterbore provides a cylindrical wall 22 which is terminated at its deep end upon a seating shoulder 24. The outer end of the cylinder wall 22 terminates at an intermediate shoulder 26 and defines the first counterbore depth A. The deep end of the second counterbore cylinder wall 28 also terminates at the intermediate shoulder 26 with a minimum wall height of B. Seated in the first counterbore with a pressfit wall engagement is a valve seat sleeve 32. The sleeve preferably is a cylindrical turning of stainless steel having an inside wall 34 diameter substantially corresponding to the bore diameter of conduit 20. The outside wall 36 has a diameter that corresponds with a pressfit engagement with the wall 22 of the first counterbore. The inner end 37 partition of the sleeve outer wall 36 has an approximately 10° tapered section 38 to controllably start the pressed insertion which terminates with abutment of the sleeve inner end 37 against the shoulder 24. The outer end 39 of the sleeve 32 carries a conical valve seat 40 having a conical face angle α of about 45.5° to 47.0°. The axial length of the sleeve 32 between outer and inner ends 37 and 39, respectively, is a distance C which is about 30% or greater than the first counterbore depth A. The radial width of intermediate shoulder 26 provides an annulus 30 of space between second counterbore wall 28 and the outside wall 36 of the sleeve which separates that portion of the sleeve projected into the annular space from any structural restraint. If the sleeve 32 wall circles are true, when fabricated, the valve seat 40 at the projected outer end of the sleeve is likely to remain a true circle even if the first counterbore wall 22 is slightly eccentric. The distance c is chosen to insure that the shape of valve seat 40 on the projected end of sleeve 32 will remain circular. While the minimum distance C will change depending on the pump size and the materials and tolerances used, a typical acceptable distance C is about 0.25 in. for a brass pump body 10 and a stainless steel sleeve 32. The circularity of the valve seat 40 is important to eliminating premature failure of the seat 40 and/or plug 50. The valve plug 50 that cooperates with the bypass conduit 20 and sleeve 32 is preferably fabricated from the General Electric proprietary high density polymer, Ultem ® . This plug features an axial throughbore 52 having a counterbore 54 at the suction port end and a poppet valve seat 55 at the discharge port end. External surfaces of the valve plug 50 include an enlarged cyclindrical shoulder 56 transitioned by a conical valve seat section 58 into a smaller, cylindrical waist section 59. The conical angle β of the valve seat is preferably about 45° or about 0.5° to 2.5° less than the conical valve seat face 40 of the sleeve 32 to assure a sharp, sealing circle. The remaining approximately half length of the plug is given a substantially circular cross-section 63 having longitudinal ribs 61. The ribs 61 contact the bypass conduit 20 walls as guides and spacers to keep the plug 50 co-axially aligned within the conduit bore. Fluid flows along the outside surfaces of the plug channels between the plug cylinder elements 63 and the conduit 20 bore walls. It will be understood that other geometric shapes for the plug ribbed section may be used such as a triangle section or square section as illustrated by Fig. 8. This square section valve plug embodiment is guided or centered within the bypass conduit bore 20 by the chamfered corners 70 of the square which provides flow channels between the channel bore 20 and the flats 72 of the square. The throughbore 52 of the plug 50 is undirectionally closed by a flow rectifying poppet valve 42 that is biased to the closed condition by a tensile spring 44. Normally, pressure will be greater in the discharge port 18 than in the suction port 16. Under such normal pressure differential conditions, the differential magnitude holds the poppet 42 against the valve seat 55 for a fluid seal. In the unusual circumstance when suction port 16 pressure exceeds discharge port 18 pressure by a differential amount dictated by the tensile force of spring 44, the poppet 42 may be lifted from the seat 55 to permit flow therethrough. Any flow through the conduit 20 passes through contaminant screen 46. The relief valve seat 58 is held against the sleeve seat face 40 by the bias of a compression spring 65 that is seated within the plug counterbore 54 adjacent the screen 46. The opposite end of the compression spring 65 is seated on a threaded plug 67 around a centering pin 69. Manual rotation of the plug 67 axially translates the spring seat to adjust the bias force exerted by the spring 65 against the plug 50. Figures 6 and 7 illustrate an embodiment of the invention without the suction-to-discharge bypass capacity of the poppet valve 42. The Figure 6 and 7 configuration of the invention provides only overpressure protection. In this case, the center bore 52 of the bypass plug 70 terminates with a solid end wall 76. Other external features of the bypass plug 70 such as the valve seat 58 and rib guides 61 remain the same. The pressure preloading spring 65 seats within the plug 70 counterbore 54 to bias the valve seat 58 into sealing engagement with the valve seat face 40. The degree of spring 65 compression against the plug 70 is determined by the degree of screw lead advancement given the threaded plug 67 toward the valve plug 70. In consequence, the pressure differential between suction port 16 and discharge port 18 at which the valve plug 70 will open is determined by the degree of spring 65 compression. Having fully disclosed the preferred embodiments of my invention, those of ordinary skill in the art may devise mechanically equivalent alternatives. As my invention, however,

Claims: I CLAIM : Claim 1. A pump having a suction port, a discharge port and a relief flow conduit between and junctured with said suction and discharge ports; first and second substantially concentric counterbores surrounding said relief flow conduit proximate of the juncture with said suction port, said first counterbore having a first axial length; a substantially cylindrical sleeve element having an outside diameter that corresponds to an inside diameter respective to said first counterbore and an axial length that is substantially greater than said first axial length whereby an assembly of said sleeve into said first counterbore projects an unrestrained axial end of said sleeve into an annular space between said sleeve outside diameter and the inside diameter corresponding to said second counterbore; a substantially circular valve seat around the projected end of said sleeve free of direct structural restraint; and, a valve plug resiliently biased against said valve seat. Claim 2. A pump as described by claim l wherein said valve plug is formed of a polymer material. Claim 3. A pump as described by claim 1 wherein said valve seat is a substantially conical area about an inside diameter of said sleeve at said projected end. Claim 4. A pump as described by claim 3 wherein said valve plug is a tubular element having an axial bore therethrough and an enlarged diameter shoulder portion about an external perimeter of said tubular element, said shoulder portion supporting a substantially conical section valve seal face for fluid sealing cooperation with said valve seat. Claim 5. A pump as described by claim 4 wherein said resilient bias is imposed on said tubular element by a first spring bearing upon said tubular element to engage said valve seal face with said valve seat. Claim 6. A pump as described by claim 5 wherein said valve plug axial bore is sealed by a poppet element to fluid flow therethrough from said discharge port to said suction port, said poppet element being secured to said valve plug to open when fluid pressure within said suction port exceeds fluid pressure within said discharge port. Claim 7. A pump as described by claim 6 wherein said valve plug is formed of polymer material. Claim 8. A pump as described by claim 4 wherein the conical angle of said valve seat conical area measured from said sleeve axis equals or exceeds the conical angle of said valve plug seal face. 10 sωsππrrc SHEET RB Claim 9. A method of fabricating an overpressure protection valve in a pump housing comprising the steps of providing a fluid flow conduit in said housing that junctures with a housing shoulder chamber; providing a first counterbore coaxially about said conduit with a first inside diameter and a first axial depth from said shoulder chamber; providing a second counterbore coaxially about said conduit with a second inside diameter less than said first inside diameter and a second axial depth measured from the depth end of said first counterbore; providing a substantially cylindrical metal sleeve element having a relatively thin annular wall between a sleeve inside diameter and a sleeve outside diameter, said sleeve having an axial length greater than said second axial depth and a sleeve outside diameter corresponding to said second counterbore inside diameter said sleeve having greater hardness and dimensional stability than said pump housing; securing said sleeve within said second counterbore to project an excess sleeve length greater than said second axial depth coaxially within said first counterbore thereby providing an unrestricted annular space between said sleeve outside diameter and said first counterbore inside diameter; and, providing a valve seating surface on the projected axial end of said sleeve. Claim 10. A method as described by claim 9 further comprising the step of providing a polymer valve plug to sealingly engage said valve seating surface. Claim 11. A method as described by claim 10 further comprising the step of resiliently biasing said valve plug against said valve seating surface.

Inventors: SINGLETERRY RON C, ZAVISA JOHN, SINGLETERRY, RON, C., ZAVISA, JOHN
Applicants: STANDEX INT CORP, STANDEX INTERNATIONAL CORPORATION
Application year: 1996
Main classification: F04C15
IPC codes: F04C14, F04C15, F04C28, F16K17