US3168048A

US3168048A - Full range operable high specific speed pumps

Info

Publication number: US3168048A
Application number: US310567A
Authority: US
Inventors: Toyokura Tonitaro; Kida Kazuo
Original assignee: Dengyosha Machine Works Ltd
Current assignee: Dengyosha Machine Works Ltd
Priority date: 1962-11-14
Filing date: 1963-09-23
Publication date: 1965-02-02
Anticipated expiration: 1982-02-02

Description

1965 TOMITARO TOYOKURA ETAL 3,

FULL RANGE OPERABLE HIGH SPECIFIC SPEED PUMPS Filed Sept. 23. 1963 3 Sheets-Sheet 1 Feb. 2, 1965 TOMITARO TOYOKURA ETAL I 3,163,048

FULL RANGE OPERABLE HIGH SPECIFIC SPEED PUMPS 3 Sheets-Sheet 6 Filed Sept. 23, 1963 V] c u H 4% H u E m I Wm Q. a w W .m n P "u d L t e (T: w m ow W ,H I IS I" c 5 //I IMLD I D xufiwmo wwm Lu Gr 0 $2 5m V l m 0 m fiiinb Z L. .h w M oi zm 7 J J H I 5 2 5 ll AU W N 2 0 United States Patent Ofiiice aisaais Patented Feb. 2, 1965 3,168,043 FULL RANGE (WERABLE lglGH SPECTFIC SPEED PUlviP Tonlitaro Toyoknra, isogo kn, Yokohama, and Karma) Kida, Kaya-machi, Mishima, lapan, assignors to Dengyosha Machine Works, Ltd, Tokyo, .lapan, a corporation of Japan Filed Sept. 23, 1963, Ser. No. 310,567 Claims priority, application Japan, Nov. 14, W62, 3'7 51,230 1 Claim. (Cl. 103 85 The present invention relates to full range operable high specific speed pumps.

An axial flow pump of a large capacity and to be used for comparatively low head considerably increases its driving power at the shut-off point (zero discharge). At present, with a fixed blades pump of specific speed higher than about 1,200 (r.p.m., m., m. /min.), it has been considered almost impossible to design and manufacture such a pump which is operable up to the shut-off point by a prime mover selected by driving power of pump at the maximum efficiency point without lowering the pump efficiency and the cavitation characteristics and moreover having stable head-capacity curve. Generally, high specific speed pump considerably increases the head at low flow rates and accordingly, if the pump can be driven for the all discharge range including zero point by reducing shut-off horse power, it becomes possible to lift water even when the head changes for a Wide range by the level change of water tank on the delivery side or suction side and moreover, such pump is very easy to be handled.

The object of the invention is to provide a special type full range operable high specific speed pump which has fixed blades and sufliciently satisfies the above requests allowing the shut-oft operation and enabling to make the shut-off power ratio (ratio of shaft horse powers at the shut-otf point and at the best efficiency point) less than 1.2 without lowering pump quality.

In order that the invention may be more readily carried ried into effect, it will now be described more fully with reference to the accompanying drawing, in which- FIG. 1 illustrates diagrammatically condition of flow nearabout the impeller of a conventional type high specific speed pump,

FIG. 2 illustrates curves analysing the shaft horse power of a conventional type high specific speed pump,

FIG. 3 is a partial spectional view illustrating a conventional type high specific speed pump for explaining reference characters described in the specification,

FIG. 4 is a curve diagram for illustrating the velocity distribution at low flow rate on the suction side of impeller of a conventional type high specific speed pump,

FIG. 5 is a vertical sectional view or" a full range operable high specific speed pump embodying the invention.

FIG. 6 is a partial sectional view illustrating the easing wall having contracted passage embodying the invention taken for comparison with a conventional casing wall,

FiG. 7 shows curve diagrams illustrating the experi mental results which shows the degree of improvements in characteristics of the pumps shown in FIGS. 5 and 8 of the invention,

FIG. 8 is a partial sectional view of the pump used for the experiments in P16. 7,

FIG. 9 is a sectional view of an embodiment of a full range operable high specific speed pump of the invention and FIG. 10 are characteristic curves of the full range operable high specific speed pump of the invention and that of a conventional type taken for comparison.

After Various investigations the inventors have ascertained that the water flow in the impeller of a high specific speed pump having a wide water passage nearabout the impeller has a large radial velocity component in partial discharge and the flow of water on the meridian section at the shut-out point is as shown in FIG. 1 and consists of circulating flows at the front and rear of the impeller. The result of analysis of the brake horse power for the all discharge range of a conventional high specific speed pump is shown in FIG. 2. The three kinds of work done by the impeller as shown for determining the brake horse power at low flow rates may be determined as follows:

(a) The work done given to the discharge of water from the pump;

(b) The work done given to the circulating flow on the delivery side of the impeller;

82 (becam Isa- 0mm) wherein 7 represents specific gravity of water, g is an acceleration of gravity, w an angular velocity of impeller, r the radius, Cu a velocity component of Water in the circumferential direction, 11 a velocity com onent in the meridian direction, the suffices d and s illustrate the value on the delivery or suction side of impeller respectively. D, D D and 5, s s illustrating the range of integration are shown in FIG. 3.

In order to reduce the shaft horse power at low flow rates, it is necessary to reduce the work done by the impeller represented by each of the above equations. To this end the practicable ones are as follows:

(A) The velocity component Cu in the circumferential direction of the fluid flowing into the impeller should be made large.

(B) The velocity component in the meridian direction 11 of the fluid flowing in or out of the impeller should be reduced.

The process (A) increases the second term on the right side of the Formulae l, 2 and 3, while, the process (B) decreases each term of these formulae, and both of them are effective to reduce the Work done by the impeller.

Now considering about the process (A), in order to increase the velocity component Cu in the circumferential direction of fluid flowing into the impeller 1 from its suction side 5, it is necessary to utilize a large velocity component in the circumferential direction of the fluid reverse flowing into the suction side 5 of the impeller blades, that is, as apparent from the distribution of the velocity component 11S in the meridian direction and the velocity component Cu in the circumferential direction on the suction side of the impeller as shown in FIG. 4, the contra-flow has a larger velocity component in the circumferential direction so that the impeller may be so constructed that the contra-flow at the suction side 5 of the impeller might induce a large velocity component in the circumferential direction (pre-rotation) for the positive flow nearabout the boss. This is accomplished by placing the impeller l in a divergent pipe 2 and providing a contracted passage 3 of a suflicient length L on the suction side 5 of the impeller 1. Then the positive flow nearabout the boss having a large pre-rotation flows into the impeller 1 and moves to the radial direction and fiows out to the delivery side 4 and suction side 5 and the circumferential velocity component Ca of the fluid on the delivery side 4 does not substantially vary by the prerotation and also the change of the circumferential velocity component Cu of the fluid reverse-flowing into the suction side is comparatively small as ascertained by the experiments, so that the Work done by the impeller obtained by the Formulae l and 3 respectively is reduced. In order to increase the circumferential velocity component Cu of the fluid flowing into (reverse flow) the impeller on the delivery side, it is preferable to increase the distance between the impeller blades and the guide vanes 7.

Concerning the process (B), the outward flow caused in the impeller blades 1 at low flow rates impinges on the casing wall 6 and is reversed partly to the suction side 5. The reverse flow occurs due to the fact that the fluid particles impinged on the casing wall 6 outside of impeller blades 1 is more easily to reverse flow towards the suction side than to flowing out to the delivery side 4. In a conventional high specific speed pump the power loss due to the reverse flow to the suction side 5 nearabout the shut-01f point is specially large so that it is necessary to reduce the reverse flow. To this end, it is necessary to increase the resistance to the reverse flow to the suction side and to prevent the reverse flow. If the casing wall 6 surrounding the impeller is formed as a divergent pipe 2 as shown in FIG. 5, the resistance to the reverse flow is increased and the quantity of reverse flow to the suction side 5 is naturally reduced. According to the results of experiments it was found that even using the casing 6 formed with such divergent pipe 2 the velocity component r in the meridian direction on the delivery side 4 of the impeller is substantially unchanged and the quantity of flow into the impeller from suction side 5 reduces so much as the quantity of reverse flow to the suction side 5 is reduced. By providing an extended contracted passage 3 on the suction side of the impeller the reverse flow is prevented severely so that the meridian velocity component of the positive flow nearabout the boss is also reduced. On the section of the suction side 5 of impeller blades, the flow will have a large velocity gradient at nearabout the shut-off point (refer to FIG. 4) so that the above effect is more remarkable.

The average value H of the theoretical head of the delivery flow is given by the formula by assuming the discharge of water from the impeller as q (excluding the circulating flow on the delivery side) in Formula 1 thus, H is reduced by the increase of the pre-whirl as explained by (A). The circulating flow on the delivery side 4 of the impeller is controlled by H so that the decrease of H means the reduction in the quantity of circulating flow on the delivery side 4 and the work done by the impeller represented by the Formula 2 decreases.

The provision of an extended contracted passage 3 directly before the impeller (refer to FIG. 5) might be considered at one glance to result in the reduction of pump efliciency and cavitation characteristics so that it has never been imagined before in high specific speed pumps. However in mixed flow pumps of a conventional type even at the best elficiency point the flow of fluid at the entrance of the impeller 1 can not provide uniform velocity distribution by the effect of the curved passage and the uniform flowing condition can not be expected over the all width of the entrance passage and also the cavitation characteristics do not seem to be sufficient. Also in axial flow pumps, since the peripheral speed of the impeller is large the relative velocity of fluid to the impeller at the entrance in case of normal quantity of flow becomes large, and the rate of retardation of relative velocity in the impeller becomes large to increase the loss. In the high specific speed pump operable for the full range of quantity of flow of the invention the velocity distribution of fluid flowing into the impeller is uniform at nearabout the normal quantity of flow, and the rate of retardation of flow on the suction side 5 of the impeller is small so that the pump characteristic is improved. As the power loss due to the circulating flow before and after the impeller is reduced conspicuously, the efliciency of pump in the range of partial flow is improved remarkably.

Furthermore, by providing a narrow passage on the suction side of the impeller, the unstable range of rightward rising of the head-capacity curve is prevented as explained below. Namely, as shown in FIG. 6 the stream lines for the points having comparatively large radii become like the curve (a)(a) (corresponds to a new type, showing the casing wall by (A)(A)) and the curve (b)( b) (corresponds to a conventional type, the casing wall being shown by (A)-(B)) so that the radial velocity component v of the fluid for this invention at the entrance of the impeller becomes larger than 1 for the conventional pump. Accordingly the radial velocity component in the impeller becomes larger so that the reverse flow on the suction side of the impeller is caused at a comparatively large quantity. When the reverse flow occurs at the suction side of the impeller, the attach angle of the blades in the zone of positive flow of comparatively small radius is reduced and the stall of the blades does not occur so that the characteristics is stabilized to considerably reduce the vibration and noise at partial flow rates.

The experimental results showing the remarkable improvement of the performance by providing a contracted passage on the suction side of the impeller of high specific speed pump is shown in FIG. 7. The test was carried out with a vertical pump of inlet diameter of 250 mm. having the construction as shown in FIG. 5 (the result is shown by the full line in FIG. 7) and FIG. 8 (the result is shown by the broken line). The delivery pressure was measured after the bend on the delivery side. As to L L D and D refer to FIGS. 5 and 9. As apparent from these drawings, by providing narrow passage of a suitable length on the suction side of the impeller the effects as shown in the following items can be recognized.

(a) Shut-01f shaft power ratio u decreases considerabl ir) The unstability e of the characteristic curve (in the drawing, H1; max shows the pump head at the best efliciency point) is considerably improved.

' (c) The value of the best efliciency somewhat increases.

(d) Cavitation factor of Thoma (61;,5H correspond to the efiiciency lowering point and the head lowering point respectively at the best efficiency point) is invariable.

(e) The shut-01f head ratio (ratio of heads at the shut-01f point and best efiiciency point) is substantially unchanged.

(f) Specificspeed is substantially constant.

Further, tests were carried out for a pump of more 'high specific speed (Ns=2,300 (r.p.m., m /min. m.))

and a larger horizontal pump (800 mm. bore) respectively and similarly good results were obtained.

An example of the characteristic curve of high specific speed pump which is operable for full range designed by the principle of the invention as fully explained in the foregoing having such a construction as shown in FIG. 5 and having specific speed of 1,500 (r.p.m., m min. in.) is shown by the full line in FIG. 10, wherein the characteristic curve of a conventional pump is shown by broken lines for the sake of reference. In the full range operable high specific speed pump according to the invention the shaft horse power at low flow rates is considerably reduced if compared with conventional pump and the etficiency is considerably improved and it will be understood that the full range operable high specific speed pump of the invention can be safely driven over the full discharge range by using a prime mover selected from the shaft horse power at the best efiiciency point.

As described in the foregoing the high specific speed pump of the invention having a long and narrow passage 3 on the suction side of the impeller 1 which is located in a divergent pipe 2 can be driven by a smaller shaft horse power at the shut-01f point so that it enables to ettcct safety operation over the all discharge range without disturbing pumping quality.

From the above described principle it will be apparent that by reducing the smallest diameter (D of the restricted pipe on the suction side 5 of the impeller as shown in FIG. 9 the shaft horse power at low flow rates can be reduced similarly, thereby enabling the full range operation.

According to the experiments done by the inventors, by satisfying either one or both of the conditions that the impeller 1 is located in the casing 6 which is made as a divergent pipe 2 in the direction of flow and the length L of meridian line along the wall of casing 6 with the contracted passage 3 on the suction side 5 of the impeller is made more than 0.7 time the length L along the meridian section at the tip of blades of impeller 1 as shown in PKG. 5, or the smallest inner diameter D of the narrow passage 3 is made less than 0.9 time the diameter of the suction side of the impeller, i.e. the smallest diameter D at the tip of impeller 1, the desired object according to the above described theory can be attained and obtained the satisfactory result as a high specific speed pump enabling to make the shut-off power What we claim is:

A full range operable high specific speed pump which reducing the shut-01f horse power fulfilling the condiing a divergent pipe toward the direction of flow for reducing the shut-off horse power fullfilling the condition selected from the group consisting of L gofin and 1),;091),

wherein L represents a width at the tip of impeller blades as measured on the meridian section L the length of restricted pipe wall on the suction side of impeller taken on the meridian section (the length measured from the point (A) on the suction side of the tip of impeller blade to the point (B) at the smallest radius of inner wall of the restricted pipe on the suction side of impeller taken along the inner wall of the pipe), I), a diameter on the suction side of the tip of impeller blades and D an inner diameter of the smallest section of the restricted pipe on the suction side of the impeller.

References Cited by the Examiner UNITED STATES PATENTS 1,199,374 9/16 iagen 230-420 1,199,375 9/16 Hagen 230 1,321,538 11/19 Moody 103-89 1,430,141 9/22 Angus 103-89 1,460,423 7/23 Moody 103-89 1,502,865 7/24 Moody 103-89 1,578,843 3/26 Moody 103 89 2,245,989 6/41 Leathers 230-120 FOREIGN PATENTS 299,526 10/28 Great Britain.

505,078 5/39 Great Britain.

581,444 10/46 Great Britain.

JOSEFH H. BRANSON, ]R., Primary Examiner.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No 3 ,168 ,O48 February 2, 1965 Tomitaro Toyokura et a1.

It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 6, line 3, strike out "reducing the shut-off horse power fulfilling the condi" and insert instead comprises an impeller located in the water passage formline 5, for "fullfilling" read fulfilling Signed and sealed this 17th day ofMay 1966.

(SEAL) Attest:

ERNEST W. SWIDER Officer EDWARD-J. BRENNER Commissioner of Patents