US3664759A - Self-adjusting backflow preventor for centrifugal pumps - Google Patents

Abstract

A PUMP IS DISCLOSED WHICH INCLUDES A CASING HAVING AN INLET, AN OUTLET AND A PUMPING CHAMBER DISPOSED THEREBETWEEN. AN IMPELLER IS ROTATABLY DISPOSED IN SAID PUMPING CHAMBER, AND SELF-ADJUSTING BACKFLOW PREVENTION MEANS IS DISPOSED ADJACENT SAID INLET FOR AUTOMATICALLY VARYING THE EFFECTIVE DIAMETER OF SAID INLET IN RESPONSE TO VARIATIONS IN BACKFLOW.

Description

y 3, 1972 H. J. BIHELLER 3,664,759

SELF-ADJUSTING BACKFLOW PREVENTOR FOR CENTRIFUGAL PUMPS Filed Sept. 16, 1970 HANS J BIHELLER INVENTOR.

UnitedStates Patent O 3,664,759 SELF-ADJUSTING BACKFLOW PREVENT OR FOR CENTRIFUGAL PUMPS Hans J. Biheller, River-edge, N.J., assignor to Worthington Corporation, Harrison, NJ. Filed Sept. 16, 1970, Ser. No. 72,650 Int. Cl. F04d 1/00, 15/00, 29/00 US. Cl. 415121 5 Claims ABSTRACT OF THE DISCLOSURE BACKGROUND OF THE INVENTION This invention relates to pumps, more particularly to pumps which exhibit backflow characteristics, and even more particularly to pumps which are provided with selfadjusting backflow prevention means for automatically varying the effective diameter of the pump inlets in accordance with variations in backflow.

As is well known in the art, centrifugal pumps exhibit the characteristic of partial backflow from the impeller eye into the suction or inlet end of the pump when operating at flow rates below full capacity. This problem of partial backflow is especially severe for large high specific speed impellers and ordinarily results in reduced output as well as excessive noise and vibration.

In the past, the problems incident to partial backflow have been alleviated by installing a reduced diameter throttle plate at or near the inlet end of the pump and as close as possible to the impller. Such a throttle plate, in reducing the impeller eye inlet area, prevents or minimizes backflow into the suction line and its undesirable side effects. Although this prior art technique is satisfactory when the pump is operating at low capacity, it presents distinct disadvantages when the pump is operating at higher capacities. Specifically, the reduced eye area of the impeller results in reduced pump output and also greatly increases the magnitude of pump suction pressure necessary to prevent cavitation.

It is the principal object of the invention, therefore, to provide a pump having backflow prevention means which prevent the backflow of fluid into the pump suction line when the pump is operating at less than full capacity, which backflow prevention means reduces noise and vibration as compared to the noise and vibration ordinarily experienced, and which backflow means does not reduce the output capacity of the pump.

SUMMARY OF THE INVENTION The foregoing prinicpal object as well as others not enumerated are accomplished by the pump of'the present invention, one embodiment of which may include a casing having inlet opening means, outlet discharge means, and a pumping chamber disposed therebetween; an impeller rotatably disposed in said pumping chamber; and selfadjusting backflow prevention means disposed adjacent said inlet opening means for automatically varying the effective diameter of said inlet opening means in response to variations in backflow.

In accordance with a preferred embodiment of the invention, the self-adjusting backflow prevention means comprises a plurality of flexible, wedge shaped members circumferentially disposed about the inlet opening to the pump. Each of the flexible members has one end thereof fixed with respect to the pump casing and another end thereof freely disposed with respect to the flow of fluid through the inlet opening of the pump. In this manner, the flexible members are flexed out of the flow path of fluid toward the impeller in response to increasing flow of the fluid toward the impeller. Similarly, the flexible members are free to flex into suction flow restricting position in response to an increase in backflow, thereby effectively reducing the diameter of the suction line or input to the pump up on the occurrence of reduced pump loads.

As a particularly advantageous feature of the instant invention, there is provided a fluid traversing backup means positioned in the pump suction line on the upstream side of the flexible members in the upstream direction. In one embodiment, the backup means may comprise a screen whereby at normal flow conditions, i.e. with no backflow from the impeller, the flexible members are flexed away from the screen and out of flow restricting position; whereas at reduced flow conditions, the flexible means are displaced partially or totally into contact with the backup screen and thus into flow restricting position. The fluid traversing backup means and the flexible members thus cooperate to define a variable diameter annular flow restricting means, the diameter being variable in response to the occurrence of backflow from the pump impeller to preclude introduction of backflow into the suction line.

BRIEF DESCRIPTION OF DRAWINGS A more complete understanding of the present invention may be had from the following detailed description thereof, particularly when read in the light of the accompanying drawings, wherein:

FIG. 1 is a cross sectional view of the fluid end of a pump constructed in accordance with the instant invention; and

FIG. 2 is an enlarged planar view of the self-adjusting backflow prevention means of the instant invention.

DETAILED DESCRIPTION Referring to FIG. 1, a pump structured according to the invention is designated generally by the reference numeral 10.

Pump 10 includes a casing 12 having an inlet opening 14 and an outlet opening (not shown) which is secured to a discharge line 16. Secured by suitable bolts to a flange 17 formed on the inlet end of casing 12 is a suction line 18 having a flange 19. Rigidly secured between flanges 17 and 19 such as to extend across the flow path of fluid from suction line 18 to inlet opening 14 is a backflow prevention device according to the invention, which device is designated generally by reference numeral 20 and discussed below in detail.

The interior of casing 12 defines a pumping chamber 21 within which is operably positioned an impeller 22. Impeller 22 is rigidly mounted on a shaft 24, which shaft is received for rotation within bearing 26 and driven by a suitable means such as an electric motor (not shown). Thus, the operation of the driving means imparts rotation through shaft 24 to impeller 22 thereby establishing a flow of fluid from suction line 18, through inlet opening 14, centrifugally through the impeller blades into a conventional volute 25 and thereafter out of the pump discharge opening into discharge line 16. The amount of fluid passing through discharge line 16 is often regulated externally from the pump by suitable valve means. Thus, if the flow of fluid through discharge line 16 is restricted such as to reduce the flow below the capacity of pump 10, the situation of back flow described above occurs. More specifically, although the impeller 22 of pump 10 is being driven at a speed suflicient to pump fluid at full capacity through the pump, such full capacity flow is not permitted by the restriction in discharge line 16.

As is recognized in the art, the restriction of discharge flow from centrifugal pumps such as pump 10 causes a significant backflow from the impeller eye toward suction line 18. The backflow of fluid is an annular flow around the flow of inlet fluid from suction line 18 and adjacent the inner surface 28 of inlet opening 14. In the absence of some type of backflow prevention means, the backflow would continue into suction line 18. As is discussed above, such backflow into the suction line is undesirable and thus the prior art has resorted to the use of backflow preventing devices such as throttle plates disposed adjacent the inlet of a pump for the purpose of eliminating backflow into the suction line.

The ordinary throttle plates known in the prior art are manufactured to accommodate a particular design flow condition, which flow condition is less than the full flow capacity of the pump. Their use has proven unsatisfactory, however, when the flow through the pump is at a rate other than that for which the throttle plate was designed. Specifically, the flow restricting throttle plate reduces the total capacity of the pump in addition to being a potential source of vibration, cavitation and other problems.

The present invention avoids the problems experienced in the prior art by providing a pump having a variable diameter inlet orifice, the diameter of which varies in response to variations in backflow, the amount of which backflow is a function of the amount of fluid being pumped as compared with the full flow capacity of the pump. The variable diameter inlet orifice is embodied in backflow prevention device 20 which, as noted above, is secured between the flanges 17 and 19 of pump inlet 14 and suction line 18, respectively.

Referring therefore to both FIGS. 1 and 2, the depicted embodiment of backflow prevention device 20 can be seen to comprise a plurality of flexible, generally wedge shaped members 32 which are secured on a generally circular coarse screen 36 by suitable means such as rivets 38. Wedge shaped members 32 are disposed on screen 36 such as to define a generally annular [flow restricting ring having an outside radius R and an inside radius R,.

Wedge shaped members 32 may be manufactured from any of many flexible materials such as rubber, leather, plastic and the like, limitations as to the selection of the materials being only that they be sufficiently flexible to accommodate deflection as required during operation and that they be compatible with the fluid being pumped.

As noted above, the backflow from the eye of a centrifugal pump during operation at less than capacity is an annular flow away from the impeller toward the suction line. As the fluid being discharged from the pump through discharge line 16 approaches the full capacity of the pump, the volume of backflow fluid decreases. Thus, the operation of backflow prevention device 20 is best explained in terms of operation at full flow conditions, minimum flow conditions, and intermediate flow conditions.

Considering initially the characteristics of backflow prevention device 20 during minimum flow conditions, i.e. during conditions of minimum backflow, the physical orientation of segments 32 is shown for these conditions in broken line in FIG. 1 and in solid line in FIG. 2. Specifically, during periods of minimum flow from discharge line 16, wedge shaped segments 3-2 extend radially inwardly adjacent screen 36 and cooperate to define a circular inlet opening having a radius R With the wedge shaped segments so disposed, backflowing fluid flows adjacent the surface of inlet opening '14 toward backflow prevention device 20 until, adjacent the surface of segments 32, the baokflowing fluid is caused to flow inwardly and join a fluid from suction line 18, the combined fluids thereafter being drawn toward impeller 22.

Upon the occurrence of an increased flow of discharge fluid through line 16, less fluid is caused to backflow and more fluid is drawn from suction line 18. Thus, wedge shaped segments 32 are displaced from the positions shown in broken line in FIG. 1 to the positions shown in solid line in FIG. 1, i.e. from a minimum fluid flow condition to an intermediate fluid flow condition. As is evident from FIG. 1, the displacement of wedge shaped segments 32 toward the surface of inlet opening 14 eflectively increases the size of the opening through which fluid is drawn from suction line 18. Thus, with the wedge shaped segments disposed as shown, the increased requirement for fluid from suction line 18 is accommodated through the increased opening defined by the inner edges of segments 32 without adversely effecting the capability of wedges 32 from preventing the backflow of fluid into suction line 18.

Upon the occurrence of a further increase in the amount of fluid being discharged through discharge line 16 to the point of maximum pump capacity, virtually no backflow is experienced and segments 32 are flexed fully outwardly toward the surface of inlet opening '14 so as to permit the flow of fluid from suction line 18 to proceed virtually unrestrictedly into the suction eye of the impeller 22. In this regard, segments 32 are displaced to be adjacent the surface of inlet opening 14 as shown in phantom line in FIG. 1 and thus the only restriction of the flowing fluid that occurs during maximum flow conditions is the resistance presented by coarse screen 36. The screen being coarse, however, it does not present resistance which is of significance and thus as a source of flow restriction can be disregarded.

Upon a decrease in fluid flow through pump 10 from maximum, the resiliency of the segments 32 coupled with the force exerted thereon by the occurrence of laminar backflow as discussed above, cause the segments 32 to be displaced away from the surface of inlet opening 14 thereby decreasing the size of the opening communicating suction line 18 with inlet opening 14 as well as preventing the backflow of fluid from adjacent the surface of inlet opening 14 into suction line 18. The segments 32 continue to deflect radially inwardly as the flow of fluid through discharge line 16 is decreased until the point of minimum flow is achieved, at which point the segments 32 are disposed as shown in broken line in FIG. 1. Thus, it will be appreciated that the pump 10 incorporating backflow prevention device 20 embodies a pump having thereon a backflow prevention device which automatically varies the effective diameter of the pump inlet in response to variations in the backflow of fluid. If designed properly, backflow prevention device 20 will suitably accommodate the entire range of flow rates of which the pump is capable.

It is to be recognized that although backflow prevention device 20 is shown as being disposed between the flanges 17 and 19 of pump 10 and suction pipe 18 respectively, the device could also be mounted within inlet opening 14, eg by providing an annular channel 42 (shown in broken line in FIG. 1) in the surface of inlet opening 14 and mounting the backflow prevention device by suitable means such as a spring ring or the like.

The foregoing detailed description relates to a preferred embodiment of the invention. It is to be recognized, however, that many modifications and variations to the invention can be accomplished without departing from the spirit and scope thereof.

What is claimed is:

1. In a centrifugal pump,

a casing forming a pumping chamber having a centrally disposed inlet opening and a discharge outlet,

an impeller rotatably disposed in said pumping chamher and having a suction eye communicating with the inlet opening,

backflow preventor means connected to the casing transversely of the center line of the inlet opening and disposed for operative coaction with said impeller to automatically vary the effective diameter of the inlet opening in response to variation in backflow in said pumping chamber,

said means comprising a ring of flexible members each having one end thereof fixedly connected to the casing and the end opposite from the fixed end freely movable from a predetermined minimum position to a predetermined maximum position with variations in backflow,

and back-up means coacting with each of said flexible members to maintain said predetermined minimum inlet opening at maximum baokflow conditions in said pumping chamber.

2. In a centrifugal pump as claimed in claim 1 wherein the inlet opening is of circular cross-section and the means to prevent backflow includes a plurality of flexible members connected circumferentially about said inlet opening in substantially the same transverse plain, said flexible members sized so that the planar area of said flexible members is less than the cross-sectional area of said inlet opening at the predetermined minimum inlet opening position of said flexible members.

3. In a centrifugal pump as claimed in claim 1 wherein the back-up means is disposed on the upstream side of the flexible members to prevent flexing of said flexible members in a direction opposite to the direction of fluid flow to said impeller.

4. In a centrifugal pump as claimed in claim 2 wherein each flexible member is generally wedged shaped in plan view and each wedged shaped flexible member at the outer end has a radius approximating the radius of said inlet opening and at the inner end a preselected radius to define a minimum inlet opening, said flexible members eifectively defining at predetermined minimum flow conditions a cross-sectional area less than the cross-sectional area of said inlet opening.

5. In a centrifugal pump as claimed in claim 1 wherein said back-up means comprises a screen member.

References Cited UNITED STATES PATENTS 3,483,824 12/ 1969 Sprague 415147 3,362,624 1/1968 Endress 415147 3,289,919 12/1966 Wood 415150 2,692,080 10/ 1954 Schwaiger 415147 3,174,434 3/ 1965 Schieve 415146 3,586,040 6/1971 Urback 41511 890,117 6/1908 Austin 415147 1,353,915 9/1920 Kime 41526 2,332,875 10/1943 Stratton 415147 2,908,283 10/1959 Kiifer et a1. 137-525.3 2138.5,730 9/1945 Read 415147 3,463,189 8/1969 Fritzpatrick 137----525.3

FOREIGN PATENTS 1,092,221 11/1960 Germany l37525.3 559,321 3/1957 Italy 137525.3

HENRY R. RADUAZO, Primary Examiner US. Cl. X.R.

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