US2268358A - Centrifugal pump - Google Patents

Description

Dec. 30, 1941.

E. 1f. TURNER GENTRIFUGAL PUMP V Filed March 1.3, 1939 2 Sheets-Sheet 2 MWA/FU UMA/fa 'fai Patented Dec. 30, 1941 UNITED STATES PATENT ortica CENTRIFUGAL PUMP Edward T. Turner, Dayton, Ohio Application March 13, 1939, Serial No. 261,567

2 Claims. (Cl. 10S-103) This invention relates to a centrifugal pump and is a continuation in part of my pending application Serial No. 722,446, filed April 26, 1934, which has matured into Patent No. 2,151,948, of March 28, 1939.

One object of the invention is to provide a simple and inexpensive pump which will operate with high efficiency to pump a liquid or an elastic uid.

A further object of the invention is to provide such a pump which will operate at a high efciency when built in small sizes.

A further object of the invention is to provide a simple and inexpensive structure which will operate efficiently either as a pump or as a motor.

A further object of the invention is to provide a multi-stage pump mechanism comprising a plurality of pump units which require a relatively small amount of power for their operation.

A further object of the invention is to provide a simple inexpensive and efficient system for effecting the compression of Iiuids.

A further object of the invention is to provide a structure of such a character that it may be operated as a pump to effect adiabatic compresinjector; Fig. 2 is a section taken axially of the ff pump on a line 2-2 on Fig. l; Fig. 3 is a front elevation of a compressing apparatus of which the pump forms a part; Fig. 4 is a sectional view similar to Fig. 1 showing a slight modification; Fig. 5 is a sectional view of a modified form of the pump taken transversely to its axis; and Fig. 6 is a sectional view, partly i'n elevation, of a multi-stage pumping apparatus embodying a plurality of pump units.

In these drawings I have illustrated certainI embodiments of my invention, each of which is adapted for use either as a pump for pumping or compressing a uid, either a liquid or an elastic iiuid, or as a motor operated byv such a fluid, and

in which the construction is such as to provide 'f high eciency in all sizes and to provide an efficiency in small sizes which is much higher than is possible with an ordinary centrifugal pump or rotary fluid motor of similar capacity. These embodiments have been chosen for the purpose f of illustration and it will be understood that the construction may take various forms and may be utilized for various purposes where a centrifugal pump or motor of high eiiiciency is desired.

The construction and operation Will be described primarily as embodied in the pump but it must be borne in mind that a pump and a motor are of the same general design. The pump may be used as a motor and vice versa, the only difference being that they are operated in reverse directions. Further, the principle and general design of elastic fluid pumps and motors are the same as for liquids, the only difference being in dimensions.

The ordinary centrifugal pump, and uid motor, when built in a small size, is very inefficient, this being partially due to the large disk, or impeller, friction losses, and partially due to the fact that it is not possible to construct small units according to the formulas which have proven most eliicient in the design of large centrifugal pumps. The diameter and velocity of the impeller of a centrifugal pump are determined by the total head against which fluid is to be pumped and are` the same irrespective of the capacity of the motor or pump. Therefore the disk friction loss in a pump of small capacity is substantially the same as in a pump of large capacity and in the ordinary pump such losses may equal a substantial part of the applied power. The loss of this power may not be serious in a large capacity pump but in a small capacity pump this loss may be several times the energy required to pump the fluid against the required head in a theoretically perfect pump, and therefore in small pumps it is important that means be provided for greatly reducing the disk friction losses.

'Well known formulas and designs have been developed for the construction of the volute type of centrifugal pumps. However, when these formulas are applied to smaller pumps, say fractional horse power pumps, the spacing between the crown plates of the impeller becomes so small that it is not practical to cast or otherwise construct the impellers. To avoid the narrow space between the' crown plates the radial velocity of the fluid from the impeller, in small sizes, must be very low, much lower than is obtainable in the ordinary designs. In the ordinary volute type of pump the absolute tangential velocity of the iiuid in the volute is considerably less than the rim velocity of the impeller, there being very little velocity energy in the fluid in the volute and substantially all the energy in the volute being in the form of pressure energy.

Higher absolute tangential velocities in the volute contribute to lower impeller velocities and the higher the tangential velocity the lower is the required impeller velocity. When the tangential velocity of the fluid equals the rim velocity of the impeller the required rim velocity of the impeller will be much less than the required rim velocity in ordinary designs. When it is remembered that disk friction losses are proportional to the square of the diameter of the impeller land to the cube of its rim velocity it will be apparent that the disk friction energy losses in the pump here illustrated will be very much less than the disk losses in the ordinary pump having an impeller of the same diameter. In the present pump the rim velocity of the impeller may be approximately seventy percent of the required rim velocity of an ordinary pump and the friction disk losses may be as low as thirty-five percent of the disk losses in the ordinary pump, thus effecting a reduction of approximately sixty-five in the friction losses.

Further savings may be effected by using an impeller of relatively small diameter and operating the same at a high speed and, in the present pump, the impeller may be operated at a high angular velocity, in special cases as high as ten thousand to forty thousand R. P. M. The smaller the diameter of the impeller the greater may be the width or space between the crown plates for a predetermined fluid rim radial velocity. Also as the tangential velocity of the fluid in the volute tends to approach the rim velocity of the impeller the less is the required radial velocity of the fluid at the rim of the impeller. Thus by designing a pump for tangential velocities that tend to approach the rim velocity of the impeller and by the use of relatively small diameter impellers it is possible to provide impellers for small capacity pumps with large spacings between the impeller crown plates.

As is well known, in standard volute pumps the spacing between the crown plates must be carefully calculated at all points. With a pump of the present design the exact spacing is not important, it being only necessary to make sure that the width between the crown plates is such as to provide an ample outlet for the fluid. However, the spacing at the rim of the impeller should not be so large as to result in a lack of uniformity in the` radial flow of the fluid from the impeller, which might permit too large a portion of the fluid to be discharged from the impeller near the discharge end of the volute. To insure high tangential velocities the vanes of the impeller should be substantially radial at the rim of the impeller. However, it is preferable that they should be curved at the point of fluid entrance in order to avoid eddy current losses.

The fluid may be discharged from the volute either at a high pressure or at a high velocity, as desired, and in the present pump the volute fluid pressure energy may be converted into velocity energy, thus discharging the fluid at a velocity considerably in excess of the volute velocity, or the volute fluid velocity energy may be converted into pressure energy, thus discharging the fluid at a pressure substantially ln excess of the pressure energy in the volute.

The characteristics of the several parts of any given pump must be determined by mathematical computation in accordance with the work which that pump is to perform. However, in each such pump the cross sectional area of the outlet 20 should be equal to the volume of liquid per unit of time to be discharged divided by approximately ninety-five percent of the rim velocity of the impeller. The constant ninety-five is subject to minor variations in accordance with conditions under which the pump is to operate. The cross sectional area of the volute channel where it merges into the outlet orifice 20 should be equal to the cross sectional area of that orifice. The width of the volute channel 53 at its open side or inlet should be equal to the diameter of the outlet 20, and the width of the discharge port or outlet of the impeller should be only slightly less than the inlet to the volute channel.

The pumps illustrated in the drawings are designed to overcome the objectionable features of ordinary centrifugal pumps and to provide a pump of this type which will have a high eiliciency in small sizes, as outlined above. In the construction shown in Figs. 1 and 2 the pump comprises a two part casing, the rear part of which is shaped to provide the rear wall 35 and the circumferential wall 36 of the casing. The other part of the casing forms the front wall 31, and the two parts are rigidly connected one to the other, as by means of screws 38. The rear part of the casing has a rearwardly extending boss 39 which is rigidly mounted on a supporting bracket 40 and has a longitudinal bore forming a bearing for the impeller shaft 4|, a stuffing box 42 being arranged about this shaft to prevent leakage. The front part of the casing has a forwardly extending boss 43 and the front wall 31 and the inner portion of this boss are provided with a relatively large cavity 44, while the outer portion of the boss is provided with an inlet passageway 45, with which is connected an inlet conduit I6. The impeller is rotatably mounted in the space between the front and rear walls of the casing and comprises front and rear crown plates 46 and 41 which preferably converge toward the periphery of the impeller and which are connected one to the other by integral blades or vanes 48, which extend inwardly from the periphery or rim of the impeller but terminate at a considerable distance from the axis of the impeller. The rear crown plate 41 has a boss 49 in which the shaft 4| is rigidly mounted, this boss preferably extending into a recess in the boss 39 of the casing. The front crown plate has a boss 50 extending into the cavity 44 and provided with a passageway 5| which communicates with and forms a continuation of the inlet passageway 45 and is flared lnwardly so that its inner end has a diameter approximately equal to the distance between the inner ends of opposite blades. In the present arrangement a ring of anti-friction material 52 is mounted about the passageway 45 in the boss 43 and the outer end of the boss 50 of the impeller bears againstI this ring, thus providing a substantially` leak-tight connection that offers no substantial frictional resistance to the rotation of the impeller. The shaft 4| may be driven from any suitable source of power, such as the belt pulley 4|a. 'I'he pulley preferably overhangs the bearing so as to avoid bending strains on and vibration of the shaft.

The circumferential wall of the casing is shaped to provide a volute channel 53, sometimes referred to as the volute, which may be of any suitable length, and when the casing has a single outlet, as shown in Figs. 1 and 2, the volute channel preferably extends about vthe major portion of the impeller. This volute channel gradually increases in cross sectional area, toward the outlet 20, from a point just beyond the outlet. The rate of increase is comparatively small so that the volute has a relatively small capacity and the liquid will move through the same at relatively high velocity. The cross sectional area of this volute is directly proportional to the volume of liquid being pumped and its cross sectional area is such that the velocity of the flow of the liquid therein will at all points be substantially constant and substantially equal to the tangential component of the absolute velocity of the liquid discharged from the impeller into the volute. When the surface of the volute channel is smooth, as when the casing is formed of die castings, the irictional resistance to the flow of the liquid is reduced so that the velocity of flow may to advantage be substantially equal to the peripheral velocity of the rim of the impeller. The volute maybe of any suitable cross sectional shape and, in the present instance, it is U-shaped in cross section so that the inner side of the volute is open and form-s the inlet port for the same. This inlet is of a width equal to the greatest width of the volute and the cross sectional area of the volute is proportional to its depth, which increases slowly toward the pump outlet.

The width of the outlet from the impeller, which in the present instance is determined by the distance between the crown plates, is slightly less than the width oi the inlet port for the volute but is of substantial width. The capacity of the impeller outlet results in the liquid being discharged from the impeller at negligible radial velocity. The blades 48 may be arranged in any suitable manner but I prefer that they should be approximately radial, instead of being backwardly curved as in the old type of pump. In the present instance, they are substantially radial at the rim of the impeller but the inner portions thereof have a slight forward curvature to avoid eddy currents and the like. The absolute radial velocity of the liquid discharged from the impeller being negligible the absolute tangential velocity, which is in the direction of the iiow of the liquid in the volute, will represent substantially the total velocity of the liquid discharged from the impeller, and this liquid is discharged into a body of liquid in the volute which is moving at a high velocity. Consequently the velocity of the liquid discharged from the impeller will not be dissipated in the volute but will tend to equal the velocity of the liquid therein. This construction permits the use of an impeller of smaller diameter than is necessary in the ordinary centrifugal pump and this results in a very small loss due to irictional contact between the impeller and the liquid, and the power required to operate the pump is relatively small.

In Fig. 3 I have shown the pump as a part of an apparatus for compressing uids, in which the pump circulates a liquid propellant through a closed circuit, a compressible uid being mixed with and compressed by the liquidA from the pump and the mixture of liquid propellant and' fluid being then separated one from the other and the liquid propellant being returned from the separator to the inlet of the pump. In the arrangement shown in Fig. 3 the pump as a whole is indicated by the reference numeral I3 and the outlet thereof is connected with an injector I2 to which a compressible iiuid. is supplied by a conduit II, the injector being in turn connected by a conduit I4 with a separator I5, the lower portion of which is connected by a conduit I6 with the inlet of the pump, and the upper portion of which is provided with an outlet I1 for the compressed iiuid. In the arrangement shown, the injector is connected directly with the outlet of the pump and is of such a character that the pressure energy of the liquid discharged from the pump will be converted into velocity energy, thereby increasing the velocity of the flow of the liquid through the injector, and after the compressible fluid has been intermingled with the liquid propellant the flow of the latter is decelerated and its velocity energy is converted into pressure energy, thereby causing the iiuid to be compressed in the liquid propellant. The liquid propellant may be of any suitable character, such as an oil or mercury, and the iluid may be any compressible fluid which is immiscible with the propellant. The injector, as shown in Fig. l, is provided with a passageway, the inlet portion 2| of which has its inlet end, which is connected with the outlet 20 of the pump casing, of a diameter approximately equal to the diameter of the pump outlet and this outlet portion of the passageway is then gradually reduced in diameter so that the inner part thereof is of a diameter considerably less than the diameter of the pump outlet. The diameter of this portion of the passageway is thus so proportioned that the pressure energy oi the liquid is converted into velocity energy. The liquid passing through the inlet portion of the passageway is delivered to an intermediate portion of the passageway which, as shown at 22, is of a diameter somewhat greater than the diameter of the inner part of the inlet portion 2|, and the fluid supply pipe II communicates with this intermediate portion 22 of the passageway, the pipe II being provided with a check valve Ila. The outlet portion 23 of the passageway has its inner end of a diameter approximately equal to the diameter of the intermediate portion 22 and is then reduced to a somewhat smaller diameter and then gradually enlarged to a diameter which is approximately equal to the diameter of the pipe I4, as shown at 24. This shape of the outlet portion of the passageway results in a constant rate of deceleration of the flow of the liquid and the conversion of the velocity energy thereof into pressure energy. This in turn causes the fluid which has been intimately mixed with the liquid to be compressed thereby between pressure limits determined by the shape of the injector, and the increased pressure at the discharge end of the injector will prevent the expansion of the fluid after it leaves the injector. Preferably the inner end of the inlet portion 2I of the passageway is slightly ared, as shown at 25, to cause the liquid to spread as it leaves the same and to be so agitated in the intermediate portion 22 of the passageway that the incoming fluid will be thoroughly mixed therewith. The separator may be of any suitable character but, as here shown, it comprises a closed receptacle having in its upper portion a baiiie 2S, and the pipe I4 enters the upper end of the receptacle and discharges against the baffle, thus releasing the fluid and permitting it to separate from the liquid, which moves by gravity and pressure to the bottom of the receptacle and is discharged under pressure through the conduit I6 to the pump. The outlet I1 leads from the upper end of the separator and may be connected with a storage receptacle or any suitable point of use for the compressed iiuid. The heat of compression is absorbed vby the liquid and should be extracted therefrom to prevent excessive rise of temperature due to repeated passages of liquid through the injector, as the lower` the temperature of compression the greater will be the compressor eiciency. The mass of propellant is large in relation to the uid which is mixed therewith and the rise in temperature due to compression is small but if permitted to continue it would cause a constant rise in temperature which would constantly increase the power required to effect compression. It is therefore preferable that some external means be provided to extract the heat of compression from the liquid, subsequent to compression, and thus maintain the same substantially at a constant predetermined pressure. As shown in Fig. 3, the return pipe I6 is provided with a radiator 21 about which a cooling medium may be circulated. In the present instance air is circulated about the radiator by a fan 28.

It will be understood that while the pump here shown is especially useful in a compression system, it is capable of use for various purposes and any suitable discharge nozzle may be substituted for the injector l2. In Fig. 4 I have shown a pump as provided with a discharge nozzle 54 adapted to convert velocity energy into pressure energy for use when it is desirable to have such pressure energy, and by means of this nozzle I am able to prevent dissipation of the velocity energy within the volute channel.

In Figs. and 6 I have shown a multi-stage pumping mechanism which comprises a plurality of pump units, in the present instance two, mounted in a well casing 55 and driven by a shaft 56 which extends beyond the upper end of the well casing and may be connected with any suitable source of power, such as an electric motor 51. Each pump unit comprises a housing having a bottom wall 58 provided with an inlet 59, and an upper portion 6B which forms the side and top walls of the housing, this upper portion converging upwardly to provide a relatively small outlet, the outlet of the lower housing communicating with the inlet of the upper housing and the outlet of the upper housing communicating through a conduit 6l with a discharge chamber 62 with which is connected a discharge pipe 63. If desired, the bottom wall of the upper housing may be rigidly secured to or formed integral with the upper portion of the lower housing, as shown in Fig. 6.

Mounted Within each of said housings is a pump casing similar to that above described but, in the present instance, the bottom wall 58 of the housing also forms the bottom wall of the pump casing. The upper portion 64 of the pump casing is secured to the bottom wall 58 and, as here shown, is provided with a circumferential flange 65 clamped between the top and bottom walls of the housing. The impeller 66 is similar to the impeller above described and is supported in the pump casing by the shaft 56 and is provided in its lower side with a tubular extension or boss 61 arranged axially thereof and journaled in a bushing 58 mounted in the bottom wall 58 of the housing in line with the inlet 59, this tubular boss 61 thus constituting both a journal for the impeller and an inlet to the impeller.

The upper part of the body of the pump casing 64 is spaced from the walls 60 of the housing and is preferably provided with a plurality of outlets 69, in the present instance four. The interior of the pump casing is so shaped as to form a plurality of arcuate channels 10 which extend about the periphery of the impeller a distance determined by the number of outlets 69. Each channel is connected with one of the outlets 69 and the cross sectional area thereof gradually increases toward that outlet. Each channel 10 is provided at its inner side with a continuous inlet opening communicating with the peripheral outlet opening of the impeller. The relative dimensions of the impeller outlet and the channels are substantially the same as above described and the outlet opening of the impeller is of such width with relation to the cross sectional area of each channel and to the inlet to the channel that the radial velocity of the fluid discharged from the impeller will be low and the tangential component of the absolute velocity of that fluid will approximate the peripheral velocity of the rim of the impeller, and the velocity of flow of fluid in each channel will at all points be substantially constant and substantially equal to the tangential component of the absolute velocity of the liquid discharged from the impeller to the channel. Each outlet 69 is so shaped as to convert the velocity energy of the discharged liquid into pressure energy, so that the liquid is discharged from the several outlets into the housing at a relatively high pressure and low velocity and passes at'this pressure from each lower housing to the pump of the next higher housing where the pressure energy is further increased and the liquid delivered into the discharge chamber 62 at a high pressure.

The use of a plurality of channels in the casing is not limited to pumps forming parts of a multi-stage mechanism but may be employed in single pumps or motors, where their use results in increased eiiiciency. The fluid friction loss in a short volute is relatively less than in a long volute, and therefore the total fluid friction loss in the several short volutes is substantially less than it is in a single volute of a length equal to the combined lengths of the short volutes.

A pump of either character above described may be operated as a motor by reversing the direction of flow of the fluid through the same and delivering the fluid thereto under pressure. A pump provided with a discharge nozzle, or nozzles, of the type shown in Fig. 4 is particularly well adapted for use as a motor. When so used the impeller becomes a rotor and the impeller outlet becomes an inlet to the rotor. The peripheral outlet 20 becomes the inlet to the motor and the axial inlet of the pump becomes the outlet of the motor. Fluid under pressure is delivered to the nozzle in which a portion of the pressure energy thereof is converted into velocity energy and the fluid at high velocity and at a reduced pressure is discharged into the volute channel of the motor casing. As it travels through the channel successive portions of the fluid pass through the inlet to the rotor at low radial velocity and the pressure and tangential velocity energies are converted into mechanical energy as the fluid passes through the rotor to the axial outlet thereof, the velocity and pressure energies of the fluid discharged through the outlet being negligible. It is desirable that such a por tion of the pressure energy of the fluid in the nozzle 54 shall be converted into velocity energy, that the velocityY of flow of the uid in the channel will approximately equal the rim velocity of the rotor, and that the pressure of the fluid in the volute shall approximately equal the velocity energy therein. Likewise the pump shown in Figs. and 6 will operate at high eiliciency as a motor, the several pump outlets being connected with a source of supply of iluid under pressure, and thus converted into motor inlets in each of which a portion of the pressure energy of the working iluid will be converted into velocity energy, as above described. Thus the organization shown in Fig. 6 may be utilized as a multistage motor.

While I have shown and described certain embodiments of my invention I wish it to be understood that I do not desire to be limited to the details thereof as various modifications may occur to a person skilled in the art.

Having now fully described my invention, what I claim as new and desire to secure by Letters Patent, is:

1. In a centrifugal pump, a casing having a substantially circular work chamber, an axial inlet, a peripheral outlet tangential to said chamber, and an arcuate channel in the peripheral wall of said chamber having a transversely curved outer wall and substantially parallel side Walls spaced apart at the inner side of the channel to provide the same with a continuous inlet, said channel gradually increasing in cross sectional area from one end thereof to the other end thereof and the larger end of said channel merging into the tangential outlet of said casing and being of substantially the same cross sectional area as the bore of said outlet, and an impeller rotatably mounted in said Work chamber and comprising side members spaced one from the other and converging toward their peripheral edges to form a substantially continuous outlet communicating with said channel and of a width slightly less than the Width of the inlet of said channel, one of said side members having an axial inlet communicating with the inlet of said casing, and substantially radial blades arranged between the peripheral portions of said side members with their inner ends spaced from the axis of the impeller.

2. In a centrigugal pump, a casing having a substantially circular work chamber, an axial inlet, a peripheral outlet tangential to said chamber and an arcuate channel in the peripheral wall of said chamber having substantially parallel side walls spaced apart at the inner side of the channel to provide the same with a continuous inlet, said channel gradually increasing in cross sectional area from one end thereof to the other end thereof and the larger end of said channel merging into the tangential outlet of said casing and being of substantially the same cross sectional area as the bore of said outlet, an irnpeller rotatably mounted in said work chamber and comprising side members spaced one from the other and having their peripheral portions spaced to form a substantially continuous outlet communicating with said channel and of a width slightly less than the width of the inlet of said channel, one of said side members having an axial inlet communicating with the inlet of said casing, and substantially radial blades arranged between the peripheral portions of said side members with their inner ends spaced from the axis of said impeller.

EDWARD T. TURNER.

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