GB2332242A

GB2332242A - A pitot tube pump

Info

Publication number: GB2332242A
Application number: GB9813420A
Authority: GB
Inventors: Rudy Struylaart
Original assignee: STERLING FLUID SYS BV
Current assignee: STERLING FLUID SYS BV
Priority date: 1997-08-27
Filing date: 1998-06-23
Publication date: 1999-06-16
Also published as: GB2332242A9; NL1009952A1; GB9813420D0; NL1009952C2; CA2241508A1

Abstract

A pump has a static pitot tube 18 within an internal volume of a rotor 14. Fluid is drawn through radial passages (17, fig 2) in the rotor 18 as it rotates and forced into the pitot tube 18. The radial passages have a smooth transition surface with the internal volume, the inside diameter of the internal volume may be larger at a point (38, fig 2) spaced away from a cover 16 of the rotor 14. The cover 16 and the rotor 14 may each be an investment casting, and have a seal (37, fig 5) between them having a serpentine shape. Fluid is conducted away from the pitot tube 18 by transfer tube 24. The pitot tube 18 may be an investment casting to give a smooth internal passage, welded to the transfer tube (fig 9). Modifications taught include transfer tube 24 mounting and sealing(figs 4 and 7); a drive shaft cooling fan (57, fig 6); and a lubrication feed system (fig 8).

Description

2332242 PITOT TUBE PUMP

FIELD AND BACKGROUND OF THE INVENTION

The present invention relates in general to pumps, and in particular, a Aw and useful pitot type, high pressure, centrifugal pumping apparatus.

This type of equipment provides high pressure and operates on a principle illustrated in Fig. 1. Fig. 1 is a.sectional view of a typical pitot pump unit generally designated 10, which, as will be explained, also incorporates the present invention. Liquid enters the pump via a suction line or connection 12 and is directed to a rotor cover 16, where the liquid is centrifuged outwardly and enters a closed rotor 14. The rotor cover 16 is. a specially designated distribution manifold to impart maximum kinetic energy to the liquid and is rotated with rotor 14 by a motor or otherwise driven shaft 11. The liquid, with this high kinetic energy enters the rotor casing and rotates with the casing in accordance with thebasic laws of centrifugal force and liquid motion.

1 -5 A stationary pitot tube 18 is placed inside the rotor and has an opening 19 located as near to the maximum inside rotor diameter as possible. Pitot tubes are named after the French engineer H. Pitot.

Liquid under centrifugal pressure and high velocity enters pitot tube 18 and is directed toward the center of the machine identified by central axis 20. The internal passage of the tube 18 is shaped similar to a diffusion nozzle to convert some of the kinetic energy to pressure energy.

The liquid is then directed a discharge 22 of the pumping unit 10 via a central transfer tube 24 and manifold 26. Due to high velocities experienced at the rotor periphery, the close proximity of the pitot tube to the rotor internal surfaces and the pitot tubes physical size, considerable shock waves can arise with resultant loadings being transferred to the pitot tube construction and mounting arrangement.

SUMMARY OF THE INVENTION

An object of the present invention is to improve the construction of the pitot tube, including its mounting and securing arrangements, for a pitot tube pump.

Another object is to reduce internal turbulence by flow path improvements, thus having the overall result of improving efficiency (by about 3%), reducing vibration and reducing noise transmission (25dbA max).

Other improvements concerning the cooling of the bearing housing, lubrication control of the bearings, and control of seal flush liquid are also achieved by the invention.

2 The invention also achieves Further characteristics and safer operation. advantages will become apparent from the description of some of the preferred but not exclusive embodiments of the invention.

The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of this disclosure. For a better understanding of the invention, its operating advantages and specific objects attained by its uses, reference is made to the accompanying drawiLngs and descriptive matter in which embodiments of the invention are illustrated.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings:

Fig. 1 is a sectional view of a complete pumping unit having features of the invention; Fig. 2 is an enlarged sectional view of the interface between the rotor cover and the rotor, showing improved liquid flow passage and increased sealina area; Fig. 3 is a sectional view of the pitot tube and rotor; Fig. 3A is a sectional view taken on line 3A-3A of Fig. 3; Fig. 3B is an end view taken in elevation, of the inlet end of pitot tube 18; Fig. 4 is a partial, enlarged sectional view of an area of the pump showing securing of the pitot tube transfer tube to the pump case; Fig. 5 is an enl.arged sectional view of the joining area between the rotor cover and the rotor; 3 Fig. 6 is a sectional view showing an exterior, shaft-mounted bearing housing cooling fan of the invention; Fig. 7 is a sectional view of a seal flush flow control bush of the invention; Fig. 8 is a sectional view of a positive shaft mounted bearing lubrication feed control of the invention; and Fig. 9 is a sectional view, partly in elevation, of the pitot tube and transfer tube.

DESCRIPTION OF THE PREFERRED EMBODIMENT

The liquid to be pumped by the pump of the present invention enters the rotor cover 16, shown in Fig. 2, via the inlet of the pumpind equipment and through internal passages 17, is centrifuged outwardly and directed into the periphery of the rotor 14 at high velocity and considerable kinetic energy. Turbulence at the joining area 15 of the rotor cover 16 to the rotor 14, is co nsiderably reduced by the invention, by usina a one piece investment casting technique for both the cover 16 and the rotor 14. This has allowed the smooth transition of the liquid with no discontinuity of the casting jointing faces 35 and 36, increased sealing area 37 and reduction in turbulence to the liquid with reduced erosion of material as shown in Fig. 5.

Referring to Fig. 5, the outer joining face 36 of the internal passages 17 smoothly transition into the outer joining face 35 of the internal volume of rotor 14 without corners and without steps. To achieve this 4 n smooth transition, the inner joining face 35 of rotor 14 has an inside diameter which is smaller than the maximum inside diameter shown at 38 in Fig. 2, which is axially spaced into the body of rotor 14, from the seal or joining separation 37 between the cover 16 and the rotor 14. The inside diameter of rotor 14, after maximum inside diameter location 38, smoothly reduces and eventually extends radially inwardly toward the central axis 20 of the pump. Seal area or margin 37 between cover 16 and rotor 14 is also S-shaped or serpentine in cross-section as shown in Fig. 2A, to increase the length of the seal between cover 16 and rotor 14. The seal material at serpentine seal 37 and between these parts may be any appropriate sealing material such as PTFE (for example, PTFE sold under the trademark TEFLON).

The pitot tube 18 6s shown in Fic. 3, is placed inside the rotor 14 and rotor cover (not shown in Fig. 3) and extends from the center of the unit at 20 to the maximum ID periphery 38 of the rotor 14 and, hence, is subjected to variable surface velocities as the radius increases. To minimize surface turbulence and resultant drag and losses, the pitot tube 18 is externally shaped like an aerofoil section shown at 27 in Fig. 3A. The liquid is collected by the pitot tube at high velocity and pressure into inlet opening 19, and is conveyed radially to the center of the machine by an internal passage 21 within the pitot tube 18. This internal passage has a very accurate, varying section to enable diffusion to take place, converting the kinetic energy imparted to the liqqid, to potential energy. Due to the complexity of the Internal and external shape of the pitot tube 18 and the high variable loads that are imparted to the pitot tube, the construction is difficult and normally consisted of several sections joined by welding. The present invention uses investment casting techniques to enable the pitot tube 18 to be constructed as a one piece item, giving improvements in strength and internal flow design by mutual blending of all internal passageways, improving the external aerofoil shape to minimize external flow discontinuity and improving strength.

Referring to Figs. 3A and 3B, the one piece pitot tube 18 has an outer airfoil shape 27 which has pointed uostream and downstream ends with respect to the rotational direction of rotor 14, and smoothly curved and symmetrical outer surfaces between the pointed ends. The internal passage 21 is sinilarly shaped and also smoothly increases in both circumfrencial and axial dimensions, radially inwardly along the pitot tube 18, from the circumfrencially extending inlet opening 19, to the central axis 20, where pitot tube 18 meets the central tr'ansfer tube 24, by a smooth curving of passage 21 from the radial direction in pitot tube 18, to the axial direction in transfer tube 24. This smoothly curved section of passage 21 is also cast into the one piece pitot tube 18.

The interior pitot tube flow as shown in Fig. 4, is directed along the center axis 20 of the pump to the Discharge 22 via the flow transfer tube 24 which is welded directly to the pitot tube 18 as shown at weld 29 in Fig. 9.

6 This transfer tube 24 is secured to the pump casing 40 and is required to absorb all the shock lcSads, rotational forces and pressure loads applied to the pitot tube 18. To achieve accurate location relative to all other parts, the transfer tube 24 is recessed into the pump casing 40. The present invention improves the securing and location of the pitot tube assembly 18 by extending the location length into the pump case 40. The increased location length depends upon the output pressure, flow, rpm, and dimensional details of the pump and is varied to suit these conditions. Typical lengths of location engagement vary between 10 to 30% of the total transfer pitot tube length but may be greater than this dependent upon the operating conditions. The increased location length also allows increased length of pitat tube securing faseners or screws 41. To reduce fatigue loading there is an un-engaged part of the thread length 42 along the fasteners 41, creating fastener flexibility and, hence, increasing fatigue resistance.

The fatigue resistance of the adjacent faces to fasteners 41 has also been improved by the use of a hardened protection ring 43 shown in Figs. 5, under the heads of the fasteners 41. Ring 43 increases the load face area of the fixing force to the pump case 40. The pump of the invention can be used to pump extremely corrosive liquid requiring, in some cases, the use of special corrosion resistance material for the pump case 40 which may not have sufficient strength at the intersection point of the fastener heads.

7 is The velocity of the liquid within the tube 24, although diffused within the pitot tube 18, still retains considerable kinetic energy. At the intersection of the flow transfer tube 24 with the pump case 40 as shown in Fig. 4, the flow must turn through 900 from the pump axis 20 to the pump discharge 22,26. To minimize turbulence, a manifold plug 44 has a cast passage 28 therein to give flow continuity.

A gasket sealing or seal 45 is inserted between the hardened protection rina 43 and manifold plug 44 to prevent corrosive liquid contact with the pitot transfer tube fastener heads, thereby preventing corrosion of the fasteners 41 and relaxation of the fastening loads.

When pumping high temperature liquids, heat transfer from the high temperatur e liquid to the bearing system can result in unacceptabe lubricating oil temperatures. To provide cooling of a bearing housing 56 in Fic. 6, an external shaft mounted fan 57 passes air from the drive end of shaft 11 over the exterior of the bearing housing 56 by an externally mounted guide closure 58 forming a cowl around fan 57.

The sealing system between the rotating elements and stationary casing on this type of pitot pump occurs on the suction side of the pump and is generally effected by the use of a mechanical shaft seal to prevent leakage into the rotor casing. Many sealing systems are used depending on the liquid being pumped and can result in a multitude of different seal chambers 70. To minimize these variations, a double seal chamber 70 is used under conditions where a single seal system 69 in Fig. 7 is acceptable with flu:.hing of the seal chamber to provide 8 seal cooling and positive leakage inward to the pump liquid. A flow reduction bush 71 of a material that is inert to most chemicals such as PTFE, is used to minimize the flushing liquid quantity.

When used at high speed, lubrication supply to the bearings 82, show in Fig. 8, is critical and the flow of lubricant must be controlled accurately to ensure minimum or maximum flow conditions are not exceeded. To avoid the use of external lubrication systems, a small screw type pump 83 is fitted integrally with the drive shaft 11. Lubrication to the screw pump 83 is from a sump in the bearing housing 40, using conventional oil thrower rinas 84. The lubrication supply is transferred to a collection f eed cup 85. The orifice 86 of this CUD and/or the size of the scroll 87 in the screw pump is used to regulate the quAntity of lubrication supplied.

By using the various aspects of the present invention, an improved pitot tube centrifugal pump is achieved. The various metallic parts of the present invention can be stainless steel or other appropriate metal or synthetic materials. The various seals may be TEFLON (a trademark) or other appropriate seal materials. Lubricants to be used with the present application are of known types.

while specific embodiments of the invention have been shown and described in detail to illustrate the application of the principles of the invention, it will be understood that the invention may be embodied otherwise without departing from such principles.

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Claims

WHAT IS CLAIMED IS

1 a pitat tube pump for pumping a fluid, comprising: a pump casing having a suction connection for receiving a fluid, a discharge connection for discharging the fluid, and a central axis; a rotor assembly mounted for rotation around said axis and in said casing, said rotor assembly having a rotor defining an internal volume, and a rotor cover connected to said rotor for closing said internal volume; said rotor cover containing a plurality of radially extending rotor cover passages for communicating said suction connection with said internal volume for passing fluid from said suction connection to said internal volume by centrifugal force due to rotation of said rotor assembly, each rotor cover passage having in inlet end near said axis and an outiet end at a joining area between said rotor and said cover and near an outer perimeter of said internal volume, said passages having surfaces which without corners and without steps, sa id internal volume for reducing moving in the joining area; said outlet ends of smoothly transition to the perimeter of turbulence of fluid a fluid seal between said rotor and said rotor cover in the joining area; and a pitot tube fixed to said casing and extending in said internal volume of said rotor, said pitot tube having an inlet opening near the outer perimeter of said internal volume for receiving fluid in said volume, and an outlet end communicating with said discharge connection, for discharging fluid to said discharge connection.

2. A pitot tube pump according to claim 1 wherein the perimeter of the internal volume has an inside diameter adjacent said cover which is smaller than a maximum inside diameter of said volume which is spaced away from said cover.

3. A pitot tube pump according to claim 2 wherein said fluid seal between said rotor and said rotor cover has a serpentine cross-sectional shape.

4. A pitot tube pump according to claim 1 wherein said fluid seal between said rotor and said rotor cover has a serpentine cross-sectional shape.

5. A pitot tube pump according to claim 1 wherein said pitot tube is made of on investment casted piece, said pitot tube having an outer aerofoil shape and an inner passage which smoothly expands from the inlet opening toward the central axis.

6. A pitot tube pump according to claim 5 including a transfer tube connected to the outlet of said pitot tube and extending parallel to said central axis, said transfer tube being welded to said pitot tube.

7. A pitot tube pump according to claim 6 wherein said transfer tube includes an attachment end connected to said casing, said attachment end being in contact with said casing for at least about 10% of the length of said transfer tube.

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8. A pitot tube pump according to claim 1 including a transfer tube extending parallel to said central axis and being connected between said outlet of said pitot tube and said discharge connection, said transfer tube having a length in contact with said casing for fixing said transfer tube and pitot tube to said casing, a plurality of fasteners for fastening said transfer tube to said casing, and a hard protection ring between said casing and said transfer tube, through which said fasteners extend.

9. A pitot tube pump according to claim 8 wherein said transfer tube has a length which is in contact with said casing which is about 10-25% of the total lenath of said transfer tube for increa sing the length of connection between said transfer tue and said casing.

10. A pitot tube pump according to claim 8 including an axial opening in said casing which communicates an interior of said transfer tube to said discharge connection, and a manifold pump in said axial opening containing a curved passage for communicating the interior of said transfer tube to said discharge opening, smoothly and through approximately 900.

11. A pitot tube pump according to claim 1 including a drive shaft connected to said rotor assembly for rotating said rotor assembly, a bearing connected between said casing and said drive shaft for rotatably mounting said drive shaft to said casing, said pump casing including a bearing housing around said bearing, and a fan connected to said shaft and adjacent said bearing housing for blowing air over said bearing housing to cool said bearing.

12 12. A pitot tube pump according to claim 11 including a cowl around said fan for directing air toward said bearing housing.

13. A pitot tube pump according to claim 1 including a transfer tube connected between said pitot tube and said pump casing for fixing said pitot tube to said pump casing and for communicating said pitot tube outlet to said discharge connection, said pump casino defining a seal chamber around said transfer tube, a flow reduction bush in said seal chamber and a single seal system in said seal chamber for sealing said seal chamber around said transfer tube.

14. A pitot tube pump according to claim 1 including a drive shaft rotatably Munted to said pump casing and connected to said rotor assembly for rotating said rotor assembly, a bearing connected between said pump casing and said drive shaft for rotatably mounting said drive shaft, said pump casing including a lubrication sump for containing lubrication and means for propelling lubrication above said shaft, and a screw pump connected to said shaft and rotatable in said bearing housing for supplying lubrication to said bearing.

15. A pitot tube pump according to claim 14 including a lub-rication cup in said casing above said screw pump and an orifice in said cup for supplying lubrication to said screw pump.

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16. A pitot tube pump according to claim 15 including a throw ring connected to said drive shaf t and moveable through said sump for propelling lubricant up into said cup.

17. A pitot tube pump substantial.ly as herein described with reference to the accompanying drawings.

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