US3817659A - Pitot pump with jet pump charging system - Google Patents

Abstract

A pitot pump having means built into the pump for reducing the net positive suction head otherwise required for such a pump, and increasing the pump discharge for a given such suction head.

Description

United States Patent Erickson et al.

[111 3,817,659 [451' June 18, 1974 PITOT PUMP WITH JET PUMP CHARGING SYSTEM Inventors: John W. Erickson, Huntington Beach; Barton Brown, La Crescenta; Harold L. Petrie, South Pasadena, all of Calif.

US. Cl 417/84, 417/89, 415/89 Int. Cl. F04b 25/08, F04d 1/12 Field of Search 4l7/84, 89; 415/89, 88

References Cited UNITED STATES PATENTS 10/1916 Williams ..4l5/89 2/l934 Sim ..4l5/89 2,284,362 5/1942 Birmann 415/89 2,295,024 9/1942 Boeckeler 417/84 2,690,130 9/1954 Boeckeler 417/89 2,960,202 ll/l960 Stevens et al 415/89 3,624,704 11/1971 Leonard, .lr. 415/89 FOREIGN PATENTS OR APPLICATIONS 128,170 5/1932 Austria 415/89 848,889 /1939 France 415/89 Primary ExaminerHenry F. Raduazo Attorney, Agent, or Firm-Harris, Kern, Wallen & Tinsley ABSTRACT A pitot pump having means built into the pump for reducing the net positive suction head otherwise required for such a pump, and increasing the pump discharge for a given such suction head.

4 Claims, 4 Drawing Figures I n K a5 PITOT PUMP WITH JET PUMP CHARGING SYSTEM BACKGROUND OF THE INVENTION Conventional centrifugal pumps require a minimum net positive suction head on their inlets to enable the pump to operate at design capacity and if the available suction head for a particular pump installation is less than the required suction head for such installation, cavitation in the flow results behind the pump impeller with a marked drop in efficiency of the pump, which is undesirable and sometimes unacceptable to the user of the pump.

It is well known in the centrifugal pump art to provide a jet pump ahead of a centrifugal pump to raise the pressure of the liquid delivered to the inlet of the centrifugal pump. Such pumps are described in Centrifugal and Axial Flow Pumps, by A. J. Stepanoff, published in 1948 by John Wiley & Sons, Inc., at pages 413 to 424, inclusive. In such pumps, part of the discharge of the centrifugal pump, at the discharge pressure of the centrifugal pump, is recycled back ahead of the inlet of the centrifugal pump to operate a jet pump to raise the pressure of the liquid flowing to the inlet of the centrifugal pump. A principal difficulty in such pumps is that the discharge from a centrifugal pump is normally at a substantially higher pressure than the normal required inlet pressure of the pump and to merely divert a portion of the discharge to operate such a jet pump raises the liquid pressure at the inlet of the centrifugal pump substantially above the required net positive suction head, with an attendant loss in overall efficiency of the pump system, due to cavitation or separation of the liquid in the pump inlet. Similarly, if the pressure of such diverted portion of the discharge from the centrifugal pump is merely reduced by conventional pressure reducing valves or the like, there is an attendant undesirable drop in the overal efficiency of the pump system.

THE INVENTION GENERALLY A primary object of this invention is to provide a pitot pump having jet pump means in its inlet line and supplying such jet pump means with liquid at a pressure substantially below the pressure of the main discharge of the pitot pump by secondary pitot means separate from the main pitot means delivering the discharge from the pump, with means for controlling the discharge from such secondary pitot means to insure that the pressure of the field delivered to the inlet of the pitot pump is at or only slightly above the required net positive suction head of the pitot pump, but not substantially thereabove, to insure that the pitot pump will operate at substantially maximum efficiency under a variety of installation conditions.

THE DRAWINGS FIG. 1 is a vertical sectional view through a pitot pump embodying the present invention;

FIG. 2 is a vertical sectional view of an alternative embodiment of the invention;

FIG. 3 is a cross-sectional view taken on the line 33 of FIG. 2; and

FIG. 4 is a graph illustrating the comparative advantage of the present invention over a similar but conventional pitot pump.

DETAILED DESCRIPTION OF THE INVENTION Referring to the drawings, FIG. 1 shows a pitot pump including a stationary outer housing 1 1 and a rotary inner casing 12, the outer housing including end walls 13 and 14 rigidly secured together, as by suitable bolts 15 circumferentially spaced around the end wall 14. The outer housing 11 is supported by a conventional footing structure 17 suitably secured thereto. The end wall 13 carries bearing means 18 which journals a drive shaft 19, which is connected to any suitable power source, not shown, such as an electric motor, adapted to rotate the drive shaft.

The inner casing 12 includes end walls 21 and 22 rigidly secured together as by screws 23 circumferentially spaced around the end wall 22, and the end wall 21 is rigidly connected to the drive shaft 19, as by screws 24. The end wall 22 is provided with substantially radial inlet passages 25, the rotary casing providing a pumping chamber 26.

Coaxial with the outer housing 11 and inner casing 12 is a generally tubular pitot tube assembly 27 secured at its outer end by screws 28 to a generally tubular housing extension 29 of the end wall 14. The assembly 27 being provided at its inner end with a substantially radial main pitot tube 31 having a main pitot inlet 32 facing in a direction opposite to the direction of rotation of the rotary casing 12 and communicating through a radial passage 33 with the cylindrical interior of the assembly which forms a longitudinal discharge duct 34 which in turn connects with a main outlet 35 of the pitot pump. Around the central portion of the pitot tube assembly 27 is an annular passage 37 which communicates at its inner end with the radial inlet passages 25 of the rotary casing 12 and at its outer end with an inlet chamber 38 formed in the extension 29, which in turn communicates with a main inlet 39. The right-hand end of the rotary casing 12 is rotatably supported on the pitot tube assembly 27 and in the end wall 14 of the outer housing 11 by suitable bearings 40 therebetween.

The structure described in detail thus far is conventional in pitot pumps, and the specific improvement of the present invention of FIG. 1 will now be described in detail.

The inner end of the pitot tube assembly 27 also carries a secondary pitot tube 42 extending substantially radially in the pumping chamber 26. The tube 42 has a secondary pitot inlet 43 faced in a direction opposite to the direction of rotation of the rotary casing 12, and communicating through a radial passage 44 with a secondary duct 45 which extends longitudinally in the discharge duct 34 and has a discharge end 46 communicating through a radial port 47 with a first annular groove 48 formed in the extension 29, which communicates through a cylindrical radial port 50 with a longitudinal passage 51 with an annular groove 52, which in turn communicates with an annular groove 53.

COmmunicating between the annular groove 53 and the radially inward end of the inlet chamber 38 is a jet port 54, only one of which is shown although it is to be understood that there are a plurality of such jet ports circumferentially spaced around the pitot tube assembly 27, for example, a total of six or eight. Each such jet port 54 is generally parallel to the axis of the pitot pump 10 but angled with respect thereto to provide a swirling motion to liquid flowing in the annular passage 37, such swirling motion being in the same direction as the direction of rotation of the casing 12, so as to reduce the angle of incidence of the flow passing over the inlet edges of the radial inlet passages 25 of the rotary casing 12. A manually operable needle valve 55 is provided in the extension and may be adjusted to control the amount of liquid passing through the radial port 50, as described hereinafter.

In operation, a liquid to be pumped enters the pitot pump through the main inlet 39, and passes through the inlet chamber 38 and the annular passage 37 to the inner ends of the inlet passages 25 through which it passes radially into the inner periphery of the pumping chamber 26. Rotation of the inner casing 12 by the drive shaft 19 rotates the liquid in the pumping cham ber 26 at high speed and the main pitot inlet 32 picks up such liquid, with a ram effect, and drives it inwardly through the radial passage 33 and through the discharge duct 34 to the outlet 35 of the pitot pump from which it is discharged at a pressure substantially higher than the pressure of the liquid in the main inlet 39. For a given sized pitot pump having its inner casing rotating at a predetermined speed, such discharge pressure may be 1,000 p.s.i.a.

The liquid pressure in the pumping chamber 26, while the inner casing 12 is rotating, is relatively high at the periphery of the chamber, e.g., 1,000 p.s.i.a., and is relatively lower towards the center of the chamber, e.g., 100 p.s.i.a. The secondary pitot inlet 43, being in such zone of relatively lower pressure picks up liquid at such lower pressure, e.g., 100 p.s.i.a., and delivers it through the radial passage 44 in the second pitot tube 42 to and through the secondary duct 45 and the radial port 47 to the annular groove 48, from whence it flows through the radial port 50, the longitudinal passage 51, and the annular groove 52 into the annular groove 53. Such liquid is then discharged through the jet ports 54 into the liquid flowing in the inlet chamber 38 and annular passage 37, at relatively high velocity and at a pressure substantially higher than the pressure in the main inlet 39, to effectively raise the pressure of liquid flowing to the inner ends of the radial inlet passages 25. Since such jet ports 54 are angled from the axis of the annular passage 37, liquid flowing in such passage is given a swirling motion which assists its entry into the radial inlet passages 25, and this is another object of the invention.

The embodiment illustrated in FIGS. 2 and 3 has many parts similar to corresponding parts shown in FIG. 1, and such similar parts are given the same identifying numerals in FIGS. 2 and 3 as they have in FIG. 1, but with the addition of one hundred to each, and the description of such similar parts will not be repeated.

In the FIG. 2 embodiment, as will be noted, the tubular extension 129 is substantially different from the tubular extension 29. The tubular extension 129 has a jet pump housing 160 provided with an inlet chamber 161 communicating with the main inlet 139, and has a tubular diffuser 162 provided with an axial circular passage 163, one end of which is in the inlet chamber 161 and the other end of which communicates with a generally spiral passage 164. The axial passage 163 increases in cross-sectional area to its junction with the spiral passage 164, which likewise increases in cross-sectional area to its junction with the outer end of the annular passage 137. The generally spiral form of the passage 164 gives a swirling motion to liquid delivered therefrom into the annular passage 137 and therethrough, for the same purpose as the inclination of the jet ports 54 of FIG. 1.

Provided in the bottom of the inlet chamber 161 is a jet nozzle 166 having a jet orifice 167 axially aligned with the axial passage 163 and communicating between the inlet chamber and a space 168 below the nozzle. The space 168 is connected by a passage 169 with a passage 170 which in turn communicates with the discharge end 146 of the secondary duct 145. Threaded into the housing is a manually operable needle valve 155 which may be adjusted to vary the liquid flow through the passage 170.

The embodiment of FIGS. 2 and 3 operates generally similarly to the FIG. 1 embodiment, the secondary pitot inlet 143 picking up liquid from near the axis of the pumping chamber 126 and delivering it under pressure through duct 145, passage and 169 and space 168 to the lower end or inlet of the jet orifice from which it is ejected at relatively high velocity into liquid flowing from the inlet 139 and inlet chamber 168 into the lower end of the axial passage 163 and substantially raising the presusre thereof. The diffuser 162 and jet nozzle 166 form a conventional jet pump.

Although both embodiments operate in the same general manner, for simplicity in understanding, only the operating characteristics of the embodiment of FIGS. 2 and 3 will be described in more detail, as applied to a pitot pump in which the inner diameter of the pumping chamber 126 is about sixteen inches and the rotational speed of the rotary casing 112 is about 3,550 rpm. Under such conditions the main pitot inlet 132 will deliver the liquid being pumped to the outlet 135 at a pressure of about 1,000 p.s.i.a. If liquid were delivered at such a high pressure to the jet nozzle 166 it would cause cavitation or separation in the diffuser 162 and the pump would either cease to pump liquid or its efficiency would drop far below acceptable levels. By employing the relatively short secondary pitot tube 142, liquid is delivered from the pumping chamber 126 to the inlet of the jet nozzle 166 at a much lower pressure, substantially below a pressure which would cause undesirable cavitation or separation in the diffuser 162. To merely divert and throttle a portion of the high pressure main discharge flow for delivery to the jet nozzle 166 results in serious energy losses greatly decreasing the efficiency of the pump. By providing the secondary pitot tube 142 as an independent source of liquid to be supplied to the jet nozzle at a pressure much lower than the main discharge from the main pitot tube 131, the overall efficiency of the pump can be maintained at acceptable levels.

By adjusting the needle valves 55 and 155, the fluid pressure of the liquid discharged from the jet ports 54 and 167, respectively, may be adjusted to provide a minimum jet effect required for a particular NPSH to provide a desired discharge from the pump.

For the illustrative pump referred to above, the fluid pressure in the main pitot inlet 132 will be about 1,000 p.s.i.a. and the fluid pressure in the secondary pitot inlet will be about 250 p.s.i.a. delivering liquid to the space 168 communicating with the inlet of the jet nozzle 166 at a pressure of about 200 p.s.i.a., the difference being the fluid friction loss therebetween. If the net positive suction head (i.e., NPSH) in the main inlet 139 is about eighteen feet (i.e., about 8 p.s.i.a.), the

fluid pressure in the spiral passage 164, the annular passage 137, and the inlets of the radial passages 125 will be about 45 p.s.i.a., equivalent to a NPSH of about 104 feet, and the pump will discharge about 310 g.p.m., which is substantially greater than the same pump would produce if operating with the same NPSH but without the jet pump formed by the jet nozzle 166 and diffuser 162. A specific comparison showing this advantage is discussed in the following paragraph.

FIG. 4 in curve 175 plots the performance of a conventional 16" pitot pump identical with that shown in the drawings hereof, with the exception that it had no secondary pitot tube 42 or 142 nor any jet pump supplied thereby. Curve 176 plots the performance of a 16" pump generally as illustrated in FIGS. 2 and 3 hereof. In FIG. 4, the abscissa indicates the main discharge from the pump in gallons per minute, and the ordinates indicate the NPSl-I, net positive suction head in feet, at the main inlet of the pump. In both series of tests plotted, the pump was operated at about 3,550 rpm. The point 177 on the'curve 176 indicates the condition mentioned above in which the fluid pressure at the inlet of the jet pump is about 200 p.s.i.a., the NPSH is about 18 feet, and the pump with the jet pump delivers about 310 g.p.m. To attain the same discharge for a similar pitot pump without the jet pump would require a NPSH of about 196 feet, as indicated at the point 178 on curve 175. With the same NPSH on the standard pump, indicated at point 179 on curve 175, the pump would deliver only about 120 g.p.m. Similarly, if the pump of the invention has a NPSH of only about 8.8 feet, with only 100 p.s.i.a. on the inlet to its jet pump, indicated at point 180 on curve 176, the pump will deliver about 220 g.p.m., whereas the standard pump with the same NPSH, indicated at point 181 on curve 175, will deliver only about 70 g.p.m. Similarly, if the pump of the invention has a NPSH of only about 4.1 feet, with only 50 p.s.i.a. on the inlet to its jet pump, indicated at point 182 on curve 176, the pump will deliver about 149 g.p.m., whereas the standard pump with the same NPSH, indicated at point 183 on curve 175, will deliver only about l8 g.p.m.

A primary importance of the advantages of a pitot pump employing applicants invention, over a similar but standard pump, as illustrated in the preceding paragraph, is that a prospective user of a pitot type centrifugal pump frequently can provide only a very low NPSH for a specific installation, yet requires a relatively high pump discharge, which, with the low NPSH, cannot be attained operating at a desired r.p.m. of the pump. This renders the standard pump impractical and unacceptable to the prospective user for such an installation. On the other hand, using a pump embodying applicants invention, only a relatively low NPSH is required to attain a relatively high discharge, and one that will be acceptable to the prospective user, thus substantially broadening the area in which a pitot pump can be used satisfactorily.

We have described two. preferred embodiments of our invention, but do not desire to be limited thereto, and desire to be afforded the full scope of the following claims.

We claim:

1. In a pitot pump, the combination of:

a generally cylindrical rotary casing rotatable about its central axis, including an annular pump chamher;

an outer housing surrounding said rotary casing, said outer housing having a main inlet port and a main discharge port;

drive shaft means extending into one end of said housing and rigidly connected to said casing and adapted to rotate the same;

bearing means between said drive shaft means and said housing;

generally tubular means extending longitudinally in said hosuing and upon which said casing is mounted for rotation, said tubular means being fixedly mounted on said housing and having an inlet passage therein communicating with said chamber for supplying a fluid to be pumped to said chamber, and having a discharge passage communicating with said main discharge port;

first pitot tube means mounted on said tubular means and extending radially in said chamber to a point adjacent to the inner periphery of said chamber, said first pitot tube means having adjacent its outer end a first pitot inlet facing in a direction opposite to the direction of rotation of said casing and a passage therein communicating between said first pitot inlet and said discharge duct;

second pitot tube means mounted on said tubular means and extending radially in said chamber substantially less distance than said first pitot tube means, said second pitot tube means having adjacent its outer end a second pitot inlet facing in a direction opposite to the direction of rotation of said casing and a substantially radial passage therein communicating with a longitudinally extending discharge duct in said tubular means; and

fluid jet means having a jet inlet and a jet outlet, said jet inlet being connected to said discharge duct for supplying fluid under pressure from said second pitot tube means to said jet means, said jet outlet communicating with said inlet passage for directing a jet of fluid under relatively high pressure into fluid flowing in said inlet passage at relatively lower pressure.

2. A device as defined in claim 1 in which said jet outlet of said jet means directs fluid under relatively high pressure and velocity into a stream of fluid flowing in said inlet passage at an angle thereto so as to cause said stream to flow through said inlet passage with a swirling motion.

3. A device as defined in claim 1 in which means are provided between said jet inlet and said second pitot inlet for variably controlling the flow of fluid therebetween.

4. A device as defined in claim 1 in which said jet means comprises a plurality of circumferentially spaced jet outlets each being oriented with respect to said inlet passage so as to cause fluid to flow through said inlet passage with a swirling motion.

Claims (4)

1. In a pitot pump, the combination of: a generally cylindrical rotary casing rotatable about its central axis, including an annular pump chamber; an outer housing surrounding said rotary casing, said outer housing having a main inlet port and a main discharge port; drive shaft means extending into one end of said housing and rigidly connected to said casing and adapted to rotate the same; bearing means between said drive shaft means and said housing; generally tubular means extending longitudinally in said hosuing and upon which said casing is mounted for rotation, said tubular means being fixedly mounted on said housing and having an inlet passage therein communicating with said chamber for supplying a fluid to be pumped to said chamber, and having a discharge passage communicating with said main discharge port; first pitot tube means mounted on said tubular means and extending radially in said chamber to a point adjacent to the inner periphery of said chamber, said first pitot tube means having adjacent its outer end a first pitot inlet facing in a direction opposite to the direction of rotation of said casing and a passage therein communicating between said first pitot inlet and said discharge duct; second pitot tube means mounted on said tubular means and extending radially in said chamber substantially less distance than said first pitot tube means, said second pitot tube means having adjacent its outer end a second pitot inlet facing in a direction opposite to the direction of rotation of said casing and a substantially radial passage therein communicating with a longitudinally extending discharge duct in said tubular means; and fluid jet means having a jet inlet and a jet outlet, said jet inlet being connected to said discharge duct for supplying fluid under pressure from said second pitot tube means to said jet means, said jet outlet communicating with said inlet passage for directing a jet of fluid under relatively high pressure into fluid flowing in said inLet passage at relatively lower pressure.

2. A device as defined in claim 1 in which said jet outlet of said jet means directs fluid under relatively high pressure and velocity into a stream of fluid flowing in said inlet passage at an angle thereto so as to cause said stream to flow through said inlet passage with a swirling motion.

3. A device as defined in claim 1 in which means are provided between said jet inlet and said second pitot inlet for variably controlling the flow of fluid therebetween.

4. A device as defined in claim 1 in which said jet means comprises a plurality of circumferentially spaced jet outlets each being oriented with respect to said inlet passage so as to cause fluid to flow through said inlet passage with a swirling motion.

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