WO1992015787A1

WO1992015787A1 - Pitot pump with improved rotor cover

Info

Publication number: WO1992015787A1
Application number: PCT/US1992/001778
Authority: WO
Inventors: James G. Shaw; Sheldon M. Childs
Original assignee: Baker Hughes Incorporated
Priority date: 1991-03-08
Filing date: 1992-03-05
Publication date: 1992-09-17
Also published as: AU1571192A

Abstract

An improved rotor cover design for a pitot pump is disclosed. The design features a plurality of vanes (14, 16, 18, 20) emanating from the eye of the rotor cover exiting from the eye at a preferred angle of not more than 15-20 degrees from a tangent drawn to the eye. The path (36, 38, 40, 42) taken by the vanes is gradually sloping so that the vanes have at least one change in direction as they extend outwardly from the eye of the rotor cover to the periphery. The preferred embodiment comprises 4 vanes (14, 16, 18, 20) extending from the eye to the periphery, with intermediate partially extending vanes (22, 24, 26, 28) extending from the rotor cover periphery toward the eye and terminating approximately midway between.

Description

TITLE: PITOT PUMP WITH IMPROVED ROTOR COVER

FIELD OF THE INVENTION The field of this invention relates to pitot-type cen¬ trifugal pumps.

BACKGROUND OF THE INVENTION

A pitot pump includes an outer stationary housing secured to one end of the housing of an electric motor. Within the outer housing, a rotatable inner casing is fixed to the motor shaft. A fluid intake pipe extends axially through one side wall of both the outer housing and inner casing and into the main pump chamber of the inner casing, terminating within such chamber adjacent a central inner opening in the opposite side wall of such casing. Radial passages extend within the oppo¬ site side wall from such central opening and terminate adja¬ cent the outer periphery thereof. Fluid injection ports connect the outer ends of the radial passages with the outer portions of the main chamber.

A stationary pick-up tube within the main chamber in¬ cludes a streamlined radial arm portion mounted on the intake pipe and a streamlined circumferential head portion having an intake opening at approximately the same distance from the rotational axis of the casing as the injection ports. The radially inner end of the hollow pick-up arm communicates with the discharge pipe which passes from the main chamber through the interior of the larger intake pipe.

As the casing is rotated on the motor shaft, water or other fluid is drawn into the radial passages through the intake pipe from an external source. Centrifugal force urges the fluid to the outer ends of the radial passages where it is injected into the main chamber through the injection ports. Fluid at the periphery of the main chamber passes into the head of the pick-up t'be under high pressure and, thence, into the discharge pipe and to an outlet.

The above-described pitot pump is illustrated in detail in U.S. Patent 3,384,024. Subsequent to the disclosure in this patent, there have been other patents that deal with variations of the basic design. U.S. Patent 3,999,881 deals with modification to the pitot tube. Past designs have empha¬ sized rotor covers (impellers) with a multiplicity of radial passages of uniform cross-section, such as shown in U.S. Patent 3,795,459. This patent claims that use of diverging wall spaces in the radial vanes cause fluid turbulence and decrease the efficiency of pitot pumps. Some of the improve¬ ments in the area of pitot pumps have dealt with efforts at reducing the required net positive suction head (NPSH) of such pumps. This concept is illustrated in U.S. Patent 4,280,790. This patent teaches the interruption of a leak path existing between the outlet tube connected to the pitot tube and the inlet to the rotor cover. It is claimed that the addition of the ring in the leak path renders the fluid flow considerably less energetic and facilitates the dissipation of velocity head, thereby attenuating the adverse effects of net positive suction head.

Still other patents deal with further improvements to the profile of the pitot tube, such as U.S. Patent 4,264,269. Others employ pitot tubes with inlets at various radial dis¬ tances from the entry into the rotor cover to accommodate different output flows and/or pressures. Each of the pitot tubes has its own separate outlet tube, and the desired per- for ance is selected by allowing flow to exit from the rotor cover from the preselected pitot tube. This design is illus¬ trated in U.S. Patents 3,994,618 and 3,977,810. The pitot pumps can be multi-stage and can be designed to accommodate gasses as well as liquids. This design is illustrated in U.S. Patent 4,059,364. Specific attention is directed to Figure 3, illustrating the design of the rotor cover, which features eight generally radial constant cross- sectional paths, with fairly small outlets at the outer per¬ iphery of the rotor cover, having a generally rectangular shape. This design, in order to deal with the possibility of entrained liquids in the gas, further features a baffle system within the radial vanes to knock out liquid prior to its emergence from the radial vanes.

One of the disadvantages of the rotor cover designs illustrated in the patents above is the vibration problem. Pitot pumps by design are built to rotate at high speeds, sometimes in excess of 5000 revolutions per minute (rpm). The prior use of eight or more radial vanes, each with small discrete outlets at the periphery of the rotor cover, broke the wake created behind the pitot tube, increasing the vibra¬ tion experienced by the pump. The use of a multiplicity of vanes, with some designs having the vanes exiting nearly perpendicularly from the eye of the rotor cover, created turbulence at the inlet which raised the NPSH requirements.

The preferred embodiment of the apparatus of the present invention, by minimizing the number of vanes emanating from the eye of the impeller, has permitted a greater percentage of the eye area to be allotted toward exit paths to the pe¬ riphery of the rotor cover, minimizing turbulence and, accord¬ ingly, NPSH requirements. The preferred design incorporates an exit angle in the 15-20 degree range from the eye of the impeller, which is also directed at minimization of the NPSH requirements. The use of intermediate partially extending vanes to divide the flowpaths emanating from the eye of the impeller at approximately their midpoint further helps to reduce turbulence and improve the overall performance effi¬ ciency. The use of broad outlets at the outer periphery of the rotor cover, which extend for a greater percentage of the peripheral dimension of the rotor cover, minimize the previ- ously encountered vibration problems with pitot pump designs, as well as improve the efficiency of the pump, permitting a decrease in applied horsepower for a given performance charac¬ teristic as compared to prior designs or permitting higher flows and/or pressures with the applied horsepower of a previ- ous design.

SUMMARY OF THE INVENTION

An improved rotor cover design for a pitot pump is dis¬ closed. The design features a plurality of vanes emanating from the eye of the rotor cover exiting from the eye at a preferred angle of not more than 15-20 degrees from a tangent drawn to the eye. The path taken by the vanes is gradually sloping so that the vanes have at least one change in direc¬ tion as they extend outwardly from the eye of the rotor cover to the periphery. The preferred embodiment comprises 4 vanes extending from the eye to the periphery, with intermediate partially extending vanes extending from the rotor cover periphery toward the eye and terminating approximately midway between.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 is an elevational view, showing the rotor cover and the vanes and highlighting the short vane layout.

Figure 2 is an elevational view of the rotor cover, showing the embodiment shown in Figure 1 and highlighting the long vane layout.

Figure 3 is a table showing the locus of points, angles and radii referred to in Figures 1 and 2. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The apparatus of the present invention is illustrated in Figures 1 and 2. The apparatus A comprises of a rotor cover usable in pitot-type centrifugal pumps. The detailed discus- sion of the construction and method of operation of pitot- type pumps will not be reviewed in great detail. However, the background of the invention describes the operation of such pumps, and the disclosures of U.S. Patents 3,384,024; 3,977,810; 3,994,618; 4,264,269; 4,280,790; 3,795,459; and 3,999,881 are incorporated by reference herein as if fully set forth.

The apparatus A is diagrammatically illustrated in Fig¬ ures 1 and 2. While certain specific dimensions are recited, those skilled in the art will appreciate that larger or smaller dimensions can be used with the caveat that the pro¬ portionality between the dimensions is retained. Accordingly, while the specific embodiment shown in Figures 1 and 2 is referred to, it will be understood in this application when reference is made to the drawings of Figures 1 and 2, that different sizes are within the spirit of the invention, while the proportionality of the dimensions is retained. The appa¬ ratus A will be referred to interchangeably as a rotor cover and/or impeller, with the understanding that the implications are that those two words are interchangeable in a pitot pump. The impeller is generally shown in the figures by the reference numeral 10. It is circular in shape and has an eye area 12. The eye 12 is circular in shape to permit rotation of the impeller at the required speed for the pump, which can exceed 5000 rpms. The pitot tube which is within the rotor (not shown) terminates in a tube that extends through the eye 12 to provide for discharge from the pump. As such the pitot tube (not shown) is stationary while the complete rotor assem¬ bly, of which impeller 10 is a component, rotates about the outlet tube from the pitot tube which extends through the impeller eye 12.

In the preferred embodiment, there are four vanes 14, 16, 18, and 20. The preferred spacing of these vanes 14-20 is approximately equally spaced at about 90 degrees. In between vanes 14-20 are divider vanes 22, 24, 26, and 28. All of the recited vanes raise up from a base surface 30 of the impeller 10. Thus, each pair of vanes such as 14 and 16 create a flowpath from the eye 12 to the outer periphery generally referred to as 32.

As shown in Figures 1 and 2, the liquid enters the im¬ peller 10 around the periphery of the outlet tube from the pitot tube and is flung radially outwardly from the eye 12 due to the rotation of impeller 10. The fluid is forced through four discrete flowpaths as shown in the preferred embodiment and labeled 36, 38, 40, and 42. By examination of Figures 1 and 2, it can readily be seen that the flowpaths 36-42 are of varying cross-section. The height of the vanes 14-20 is preferably equal so that the depths of all flowpaths are the same from the eye 12 to the periphery 32. However, the flow¬ paths differ in cross-section by the diverging nature of the vanes 14-20 as they extend from the eye 12 to the outer pe¬ riphery 32.

Referring specifically to the construction of the vanes 14-20, it is seen that they form an exit angle with a tangent to the impeller eye 12. In the preferred embodiment, the exit angle is in the order of approximately 15-20 degrees. How¬ ever, other angles may be employed, with varying results on the NPSH requirement as well as the efficiency and output pressure of the pump. It has been learned through experimen¬ tation that the NPSH requirement is reduced with the exit angle from the eye 12 of the vanes 14-20 being in the order of about 20 degrees or less. Further, by employing fewer vanes than the prior known designs, a greater percentage of the impeller eye 12 exit area is available for fluid flow. This tends to decrease fluid churning or frothing which ad¬ versely impacts the NPSH requirements of the particular pump employing the impeller 10 of the present invention.

Again comparing the design of the impeller 10 to known designs at the outer periphery 32, it is seen that a signifi¬ cant portion of the outer periphery is open for exiting fluid flow from the base surface 30 of the impeller. As compared to prior designs that used many discrete flowpaths of fairly narrow cross-section, vibration became a serious concern due to the flow exiting from each path creating turbulence in the wake from the pitot tube. As a way to decrease the impact on the wake caused from the pitot tube, the impeller 10 of the present invention provides for large outlets from the impeller 10 at its outer periphery 32, which represent a more continu¬ ous flow out of the impeller 10 and less frequent bombardment into the wake caused by the pitot tube, thereby minimizing the vibration felt by the pump rotor of which impeller 10 is an integral part. Those skilled in the art will appreciate that the flow within the impeller as it reaches the outer periph¬ ery 32 is forced to make approximately a 90 degree angle turn so that the exit flow from the impeller is directed in a plane approximately perpendicular to the plane of rotation of impel- ler 10. With greater than a majority of the available periph¬ eral area employed for exiting fluid as compared to prior designs, the output flow from the impeller 10 is seen to be more evenly balanced and applied over a substantial portion of the entire rotor housing to minimize vibrational tendencies found in prior designs using significantly more flowpaths of narrow and constant cross-section which provided exit ports of only a minor portion of the outer periphery. The general shape of vanes 14-20 is also significant. As can be seen in Figures 1 and 2, there is a reversal slope of these vanes at a point indicated generally as 44. The reversal slope 44 allows for a fairly small exit angle from the eye 12, followed by a diverging cross-sectional area as the flowpath created by two vanes is followed from the eye 12 to the outer periphery 32. The divider vanes 22-28 commence in a direction generally parallel to the vanes 14-20 at a point approximating the point of the reversal slope 44 on vanes 14-20. Specifically, as illustrated in Figure 2, the point is at about 7.6520 inches, as indicated by dashed circle 46. The divider vanes 22-28 are preferably located so that they bisect the flowpaths 36-42 at a point radially outward from dashed circle 46. Divider vanes 22-28 terminate adjacent the outer periphery 32, using an approach angle closely ap¬ proximating that of vanes 14-20. Referring now to Figure 3, the coordinates, angles, and radii given indicate directly the configurations for the short vane development as illustrated in Figure 1 and for the long vane development illustrated in Figure 2. Those skilled in the art will appreciate that these rotor covers can be made larger or smaller, retaining the same proportions and still be within the spirit of the invention. Slight modifications to the angles can also be made within the purview of the invention. The reverse slope allows for im- proved performance as far as reduced NPSH requirement and higher output presure. If the diverging vanes are used with¬ out the reverse slope, the advantage of reduced NPSH will be obtained, but the output pressure will not be as great.

The foregoing disclosure and description of the invention are illustrative and explanatory thereof, and various changes in the size, shape and materials, as well as in the details of the illustrated construction, may be made without departing from the spirit of the invention.

Claims

1. An impeller for a pitot pump, compising: an eye area located about its center to allow fluid to pass therethrough; a plurality of vanes extending from said eye area to adjacent the outer periphery of said impeller, said vanes defining a flowpath of varying cross-sectional area there¬ between.

2. The impeller of claim 1, wherein said vanes extend¬ ing from said eye area toward said periphery have at least one slope reversal.

3. The impeller of claim 2, wherein said eye area is circular and each of said vanes exits from said eye area at an angle in the range of up to about 20 degrees from a tangent drawn from the eye area periphery at the point of exit of each of said vanes.

4. The impeller of claim 3, wherein said flowpaths at a point adjacent the periphery of said impeller extend over a majority of said peripheral length.

5. The apparatus of claim 4, further comprising at least one divider vane extending from adjacent the periphery of said impeller to part way toward said eye and disposed between a pair of said vanes.

6. The impeller of claim 5, wherein said divider vane follows generally the shape of said vanes as it extends in¬ wardly from the periphery toward said eye of said impeller, said diver vane terminating at a radial distance from said eye approximating the radial distance of said slope reversal of said vanes.

7. The apparatus of claim 6, wherein said flowpaths turn adjacent the periphery of the impeller to expel fluid from the impeller in a direction approximately perpendicular to the plane of flow in said impeller.

8. The impeller of claim 7, wherein said impeller fur- ther comprises four nested divider vanes at about 90 degree spacing.

9. The impeller of claim 8 and constructed with dimen¬ sions, angles, and radii as indicated and proportional to what is shown in Figures 1-3.

10. The impeller of claim 2, wherein said flowpaths at a point adjacent the periphery of said impeller extend over a majority of said peripheral length.

11. The apparatus of claim 3, further comprising at least one divider vane extending from adjacent the periphery of said impeller part way toward said eye and disposed between a pair of said vanes.

12. The apparatus of claim 1, further comprising at least one divider vane extending from adjacent the periphery of said impeller part way toward said eye and disposed between a pair of said vanes.

13. The impeller of claim 12, wherein said divider vane follows generally the shape of said vanes as it extends in¬ wardly from the periphery toward said eye of said impeller, said diver vane terminating at a radial distance from said eye approximating the radial distance of said slope reversal of said vanes.

14. The apparatus of claim 13, wherein said flowpaths turn adjacent the periphery of the impeller to expel fluid from the impeller in a direction approximately perpendicular to the plane of flow in said impeller.

15. The impeller of claim 14, wherein said impeller fur¬ ther comprises four nested divider vanes at about 90 degree spacing.

16. The impeller of claim 15 and constructed with di en- sions, angles, and radii as indicated and proportional to what is shown in Figures 1-3.

17. The impeller of claim 1, wherein said eye area is circular and each of said vanes exits from said eye area at an angle in the range of up to about 20 degrees from a tangent drawn from the eye area periphery at the point of exit of each of said vanes.

18. The apparatus of claim 17, further comprising at least one divider vane extending from adjacent the periphery of said impeller part way toward said eye and disposed between a pair of said vanes.

19. The impeller of claim 18, wherein said divider vane follows generally the shape of said vanes as it extends in¬ wardly from the periphery toward said eye of said impeller, said diver vane terminating at a radial distance from said eye approximating the radial distance of said slope reversal of said vanes.

20. The impeller of claim 19, wherein said impeller fur- ther comprises four nested divider vanes at about 90 degree spacing.