US1955070A

US1955070A - Draft tube

Info

Publication number: US1955070A
Application number: US653366A
Authority: US
Inventors: George A Jessop; Harold J M Ross
Original assignee: MORGAN SMITH S CO
Current assignee: MORGAN SMITH S CO; S MORGAN SMITH Co
Priority date: 1933-01-25
Filing date: 1933-01-25
Publication date: 1934-04-17
Anticipated expiration: 1951-04-17

Description

April 17, 1934- G. A. JESSOP ET AL 1,955,070

DRAFT TUBE Filed Jan. 25, 1933 4 Sheets-Sheet 1 INVENT R GEORGE A. E SSOP AND HAROLD J.M. ROSS ATTOR N EY 'April 17, 1934.

G. A. JESSOP El AL DRAFT TUBE Filed Jan. 25, 1955 7 4 Sheets-Sheet 2 ENTORS lNV GEORGE A. JESSOP AND HA ROLD J. M. Ros s MMDZL ATTORN EY April 17, 1934.

G. A. JESSOP ET AL 1,955,070

DRAFT TUBE Filed Jan. 25, 1933 4 Sheets-Sheet 3 Fig. 7.

Fig. IO.

ATTORNEY April 1934- e. A. JESSOP El AL 1,955,070

DRAFT TUBE Filed Jan. 25, 1953 4 sheets-sheet 4 Fig. l4.

INVENTORS GEORGE A.JESSOP AND HAROLD J\M. ROSS mwm ATTORNEY Patented Apr. 17, 1934 UNITED STATES PATENT OFFICE DRAFT TUBE Application January 25, 1933, Serial No. 653,366

23 Claims.

This invention relates to draft tubes and particularly to elbow types of draft tubes.

An object of the invention is to provide an improved draft tube in which the water will remain in full flowing contact with all surfaces of the tube.

Another object of the invention is to provide an improved elbow type of draft tube in which means are provided for splitting the water into a plurality of streams in order to prevent the formation of dead spaces in the bend of the tube.

Another object of the invention is to provide an improved elbow type of draft tube in which means are provided in the elbow portion of the tube for splitting the water into a plurality of streams so that the bent portion of the tube will be entirely filled with forward flowing, full velocity water.

Another object of the invention is to provide an improved elbow type of draft tube in which fillers are provided for splitting the water into a plurality of streams in such a manner that the velocity of the water is not increased.

Another object of the invention is to provide an improved elbow type of draft tube having a longitudinally extending vertical pier, in which the vertical pier is bisected for a portion of its length by a transverse or horizontal web which is so located that a plane passing through the upstream edge of the web and the center of ourvature of the elbow of the draft tube is at an angle of approximately with the vertical center line of the draft tube.

Another object of the invention is to provide an improved draft tube of the character mentioned, which is simple in construction, and reliable and exact in function under all conditions of service.

The invention also comprises certain new and useful improvements in the construction, arrangement and combination of the several parts of which it is composed, as will be hereinafter more fully described and claimed.

In the accompanying drawings:-

Figure 1 is a vertical longitudinal section through an elbow draft tube embodying the features of the present invention;

Fig. 2 is a horizontal section taken along the center of the draft tube, as indicated by the line 22 of Fig. 1, the transverse web across the central part of the draft tube being shown in elevation;

Fig. 3 is a view of the top of the draft tube, as

een from the line 3-3 of Fig. 1;

Fig. l is a horizontal section taken on the line 4-4 of Fig. 1;

Fig. 5 is a horizontal section taken on the line 55 of Fig. 1;

Fig. 6 is a transverse section taken on the line 8--6 of Fig. 1;

Fig. 7 is a transverse section taken on the line 7-7 of Fig. 1;

Fig. 8 is a transverse section taken on the line 8-8 of Fig. 1;

Fig. 9 is a transverse section taken on the line 99 of Fig. 1;

Fig. 10 is a transverse section taken on the line i010 of Fig. 1;

Fig. 11 is a transverse section taken on the line 11-l1 of Fig. 1;

Fig. 12 is a transverse section taken on the line 12-12 of Fig. 1;

Fig. 13 is a transverse section taken on the line 1313 of Fig. 1; and

Fig. 14 is an end view of the mouth of the draft tube.

Draft tube structures at present involve many important features that require careful consideration and analysis to meet and satisfy contingencies and demands in various installations in order to mantain the greatest eiiiciency possible in the operation of turbines and other analogous water power mechanisms, not only in primary placements, but also in repair or replacement work.

For various well known reasons, the runner or water wheel of a turbine or analogous power installation is practically always set at some distance above normal tail water elevation, and the velocity of the water discharged by the runner is comparatively high. It is necessary to have a draft tube to make use of the head or distance between the runner and tail water and to reduce the velocity of the water at the discharge end of the runner.

In general the function of any draft tube is to make use of the static head between the runner or water wheel, and the tail race and also to regain the velocity head at the discharge end of the runner by gradually, smoothly and efficiently converting this large velocity head into pressure head, so that it can become effective upon the runner or wheel itself. The effect of this change from velocity head to pressure head is to decrease the back pressure under the runner or wheel. The conversion of velocity head into pressure head must be done as efficiently as possible, and in order to accomplish this desirable result, it is necessary that the rapidly moving water in the draft tube remain in full flowing contact with the surfaces of the tube at all points.

In an elbow draft tube it is very difiicult to keep the water in full flowing contact with the down stream or upper face of the tube where the turn is made from the vertical to the horizontal, and if this contact of the water with all surfaces of the tube is not maintained, there will be a turbulency or eddy at the elbow, particularly adjacent the downstream or upper face of the tube, with material disadvantage in the effective operation of the tube.

It has been discovered that there is a higher velocity at the bottom and outside edges of the tube than at the top center from points starting well into the down stream curvature of the elbow and continuing to the outlet of the tube. This variation in velocity begins shortly after the tube starts to bend, and becomes a maximum at or near the end of the elbow and then decreases towards the outlet.

As the water flows downwardly through the tube from the entrance and is gradually turned from a vertical direction by the upstream curvature of the elbow, there is a natural spreading effect which increases and becomes more noticeable at what may be termed each section of the elbow organization. At the beginning of the upstream curvature of the elbow section the spreading effect is slight and becomes greater in the successive portions or sections thereof until it reaches its maximum at or near the final section where the elbow merges into the outlet or horizontal leg of the draft tube.

The velocities in these tubes, particularly when used for turbines under very large heads, are quite high, and the spreading action is therefore quite rapid and causes a large portion of the water to pass to the outside curved periphery of the tube at the final sections of the elbow or near the terminal of the latter situated adjacent to the horizontal leg of the tube outlet.

The water at the outside of the tube is therefore assuming a spiral motion but fiows forwardly along the tube at a more rapid rate than its rate of spiral revolution, the spiral movement of the water being insufficient to force or throw the water to the center of the tube and permitting a dead water space to be formed at the center of the tube, which should be filled or rectified by change of shape of the tube to eliminate eddies and partial voids.

In United States Letters Patent #1,71l,891 granted May 7, 1929 to George A. Jessop, there is shown an improved type of draft tube in which it was the intention to overcome the formation of a comparatively dead space at the center and top of the horizontal leg or outlet portion of the tube by flattening the elbow portion of the tube in breadth and expanding the same in width.

A second United States Letters Patent #1,'711,- 892 was granted to the same inventor on the same date as the above patent, for a modified form of draft tube having, in addition to the flattened and broadened elbow, the top of the horizontal leg depressed and supported by a longitudinally extending pier.

The general operation of the present tube within the length of the curvature is the same as that disclosed in the above mentioned patents, but in the improved structure there is a modification of structure to attain a more satisfactory and complete operation and thereby overcome the slight disadvantages present in the prior structures.

The improved draft tube is preferably formed of concrete or analogous cementitious material, but it will be understood that the same essential features of invention may be included in a metal or sheet steel draft tube.

The present invention consists essentially in providing a draft tube having an elbow, the area of which is so formed as to maintain the water in full contact with the surfaces of the tube, and also in providing such a draft tube which is gradually decreased in transverse vertical extent or breadth from a predetermined point above and fully through the turn or elbow, and increased in lateral or horizontal extent, and gradually widened towards the outlet extremity, a gradual increase in cross-sectional area from the upper inlet to the lower outlet extremity being regularly maintained. The center portion of the elbow bend is modified by filling in, or reducing the area by means of a horizontally or transversely disposed web or filler. The horizontal web or filler spans the tube from side wall to side wall and is spaced from the upstream and downstream Walls thereof. The horizontal web or filler may be formed integral with a vertical pier or web which, should the draft tube be constructed of concrete or other cementitious material, is formed integral with the main body of concrete. The front or inner edge of the horizontal or transverse web or filler extends substantially, but not entirely, around the elbow, and the rear or outer edge of said web terminates a short distance beyond the point at which the elbow or bend merges with the horizontal leg portion of the tube. The upper portion of the upstream end of the single vertical pier terminates near the downstream or outer edge of the horizontal or transverse web, while the lower portion of the pier underlies the web so as to provide a support therefor and terminates near the upstream or inner edge of the horizontal or transverse web.

Referring to the drawings and especially to Fig. 1, the numeral 21 designates a concrete or other cementitious structure in which the improved draft tube is suitably formed, the latter comprising an upper inlet extremity 22 over which the runner or wheel (not shown) is adapted to be mounted in the usual manner.

The structure 21 may be continued upwardly any suitable distance to serve as a base support for the installation of the remaining part of a turbine or other water power organization, and also for the purpose of supporting a power house in which the turbine unit or units are disposed.

The upper member 23 of the improved draft tube is shown as composed of sheet or other metal down to the point 24, the remaining part of the draft tube being shaped in the concrete or other material 21. It will be understood, however, that the upper member 23 of the draft tube, which may be specified as the inlet member, may, in some instances, be constructed or shaped in the concrete, and also the remainder of the tube may be shaped or entirely constructed of metal or other suitable material.

The upper inlet member 23 is concentric with relation to the axial line 25, which is also the axis of the runner or wheel and the turbine shaft above. The upper inlet member 23 also flares in a downward direction.

At a comparatively short distance below the plane or section on the line 4-4 (Fig. 4), the draft tube begins to assume an elliptical contour, and this configuration increases gradually through the elbow 26, to the plane of section 9-9, as indicated by Figs. 5 to 9 inclusive. In order to arrive at this construction, the curve 27 of the upstream or lower side of the elbow begins prior to the curve 28 of the downstream or forward upper wall of the draft tube elbow. The rear or upstream curve 27 comes from the vertical to the horizontal in an arc with a practically constant radius or in other wordawith a constant curvature. The curvature of the downstream or upper face of the elbow starts at a materially lower elevation than the upstream curve 27 when considering a vertical tube construction only. In other words, the curvature 28 of the downstream face of the elbow in the downstream direction starts much later than the curvature 27 of the upstream face. This downstream curve 28 of the upstream face is an easement curve, that is, at the beginning thereof there is a long radius of curvature and this radius is gradually decreased and becomes a minimum at or near the end of the curve, as at 29, and which in a vertical setting is at the horizontal.

This easement curve which, for the purposes of illustration, begins at or about the part of the draft tube elbow cut by the section line 5-5 and terminates at the point 29, is valuable and necessary in order to allow and assist the water to remain in full flowing contact with the downstream or upper face of the elbow portion of the draft tube, and thereby assist in maintaining a practically constant velocity of water at a given section of the draft tube.

By the term easement curve as hereinbefore referred to, is to be understood the well known engineering definition and which is a curve usually introduced between a tangent and a circular curve, and is a curve of varying radius, which leaves the tangent as a very flat curve and grows sharper and sharper until it has the'sarne radius as the circular curve, but in the present improved draft tube, instead of the curve terminating in a circular curve, it ends in nearly a straight tangent to the curve, as the bottom of the curve, or end of the elbow 26, is reached.

The maintenance of a constant velocity at all points in a given section of a draft tube, said section being taken approximately at right angles to the longitudinal center line, is necessary in order to maintain srnooth flow and therefore high efliciency in the tube.

Again, for the purpose of illustration, let it be assumed that the draft tube is divided into three distinct parts. The first part is the vertical section or inlet member 23 with a straight vertical center line immediately below the turbine runner. The sections at this inlet part or member of the draft tube are true, or approximately true, circles, as shown in Figs. 3 and 4, and for convenience of description, the words breadth and width will be applied to the different sections of the tube, the breadth being intended to mean the distance between the walls of the tube as cut by a plane passing through the longitudinal center line thereof, and by width ismeant the distance between the walls of the tube as measured at right angles to the foregoing plane, each measurement passing through the longitudinal center line of the tube.

The second part of the draft tube is the curved or elbow section 26, (see Figs. 1 and 5 to 11 inelusive). The breadth of the draft tube is a maximum at the end of the first part, and at the beginning of the second part or section or elbow 26. The breadth of the first part or inlet member 23 relatively decreases from its maximum at the entrance of the second part or section to its minimum at or near the end of the bend or elbow, as at 30. In other words, the upstream or lower face of the draft tube defined by the curve 2! approaches and gets nearer to the downstream or upper face of the draft tube defined by the curve 28.

At the same time the width of the draft tube is increased all along the bend or elbow 26, and this increase is such that the area of the draft tube is constantly increasing, as shown in Figs. 5 to 11 inclusive, so that the velocity of the water in the draft tube is continuously decreasing, or the velocity head is constantly being converted into pressure head.

The reduction in the breadth of the draft tube from the beginning of the upper end of the second section or part or elbow 26 is accomplished by making the upstream and downstream faces of the draft tube, or the lower and upper sides of the draft tube, in the curvature heretofore specified, and further because the curvature of the downstream or upper face 01' side 28 is started at a considerably lower point or later than the curvature of the upstream face 2'7.

The third part or section of the draft tube is the horizontal leg 31. Both the breadth and width of this leg can increase gradually, as shown in Figs. 1 and 2, and it is not necessary that both increase, in view of the fact that one, for instance the breadth or vertical extent of the leg, could remain constant and even be decreased, provided the width or lateral extent of the draft tube be increased a sufficient degree so as to maintain a continuously increasing area as the water approachesnearer and nearer the outlet 32, as shown in Figs. 2, 12, 13 and 14.

As hereinbefore indicated, from the entrance of the draft tube to the outlet thereof, the area is continuously increasing and therefore the velocity of the water is continuously decreasing.

As indicated by Figs. 6 to 11 inclusive, the opposite sides of the portion of the draft tube comprising the elbow 26 are curved, as at 33. and this curvature gradually merges or is changed into substantially straight or vertical side structures, as at 34, Figs. 12, 13 and 14. In this way the portion of the draft tube comprising the leg 31 may be made substantially rectangular in cross section and have, in addition to the vertical sides 34, a flat top 35 and bottom 36, (see Figs. 12, i3 and 14). The angular corners formed by the intersections of the sides with the top and bottom surfaces of the leg portion 31 may be filled with fillets 3?.

The water discharged from the turbine leaves the runner or wheel in the form or" a spiral having a relatively large pitch and enters the upper section 23 of the draft tube with considerable velocity. As the whirling water passes through the draft tube it becomes smooth or straightened out and its velocity gradually decreases, with the result that a full flowing contact will not be had of the water flowing along the curved surface 28 of the elbow 26, since the water tends to fall away from this face of the draft tube and descend toward the surface 27. This action of the water causes a pronounced shock which is transmitted back to the runner and affects the smooth operation thereof. Therefore, in order to prevent the formation of shocks in the water flowing through the draft tube and to also main tain the water in full flowing contact with all surfaces of the draft tube, especially in the bend or elbow 26, we have provided means for splitting the water passing through the elbow into a plurality of separate streams.

According to the present invention the draft tube is formed with a horizontal or transverse web or splitter 38 and a vertical pier or web 39.

The vertical pier or web 39 is located along the center line of the draft tube, as shown best in Fig. 2 and extends from the outlet 32 inwardly to a point well within the elbow 26.

The transverse web or splitter 38 is disposed in a plane substantially at right angles to the plane of the vertical pier 39, said splitter being located along the longitudinal center line of the draft tube, as shown in Fig. 1 and spans the draft tube from side wall to side wall, as shown in Figs. 2 and 7 to 12 inclusive.

As shown in Fig. 1 the inner or front edge 40 of the splitter 38 is located well into the bend of the elbow portion 26 of the draft tube, but does not extend to the vertical center line 25. Preferably the splitter 38 is so located that a plane passing through the upstream edge and the center of curvature of the elbow is at an angle of approximately 45 with the vertical center line of the draft tube and the outer edge or downstream edge 43 of the splitter 38 is in the leg portion 31 of the draft tube. The upstream and downstream edges 41, 43, respectively, of the splitter 38, may be rounded, as shown in Fig. 1.

When the draft tube is formed of concrete or other cementitious material the splitter 38 and the pier 39 may be cast integral with the walls of the draft tube. The vertical pier 39 in such case will also serve as a support for a power house structure and also strengthen the outlet leg 31.

As shown in Fig. 1, the upper inner portion 44 of the vertical pier or web 39 may terminate approximately at the point 29 heretofore referred to, so as to leave a clear space over the major portion of the upper surface 45 of the splitter 38, as shown in Figs. '7 to 10 inclusive. In order to support the splitter, the lower inner portion 46 of the vertical pier 39 may extend inwardly to a point adjacent the inner edge 40 of the splitter 38, as indicated at 47, Fig. 1. The front edge 47 may be substantially perpendicular as shown.

The thickness or breadth of the vertical pier 39 may vary as shown in Figs. 2 and '7 to- 14 inclusive. The portion of the pier 39 within the leg 31 of the draft tube may be thicker or wider than the portion 46 of said pier which extends into the elbow 26 and underlies the splitter 38. The narrower portion 46 of the pier 39 may gradually broaden and be joined to the thicker portion of the pier 39 by substantially flattened curved surfaces, as shown in Fig. 2. In this way the side walls of the pier 39 will have a stream line contour that will offer minimum resistance to the water flowing outwardly through the draft tube.

In operation, the water discharged from the runner enters the upper inlet member 23 of the draft tube with considerable velocity and more or less whirl. The stream of water passing downwardly through the draft tube will be divided by the splitter 38 and the pier 39 into a plurality of streams, the velocity of which will be gradually retarded as the mouth or outlet 32 of the draft tube is approached. Due to the contour of the elbow 26, the water passing along the curved surface 28 thereof will tend to pull away from said surface. However, this action will be prevented by the splitter 38, since the purpose of the splitter is to fill in the elbow 26 in such a Way as to eliminate from the draft tube the comparatively dead space at the center of the top of the horizontal leg 31 and obtain a more even distribution of the water over the remaining passages and also avoid a tendency to the spiral or whirling motion of the water along the side portions of the leg, the latter having at the top a substantially straight line construction. In this way the water will remain in full flowing contact with all surfaces of the draft tube.

In the Kaplan United States Letters Patent #1,467,168 issued September 4, 1923, there is shown a draft tube having an intermediate wall for increasing the breadth of the flow. Kaplans draft tube is of an entirely different construction from the present improved draft tube, and the intermediate wall which Kaplan has provided does not function in a manner similar to our splitter 38. In the Kaplan draft tube, the elbow is not constructed with surfaces curved according to our construction, and the intermediate wall which Kaplan uses is so constructed that said wall extends well up into the upper inlet portion of the draft tube. The upper curved surface of the Kaplan draft tube is formed with a comparatively long radius and the lower surface is formed with mostly straight surfaces, arranged substantially at right angles to each other and connected by a comparatively short curved surface, the radius of which is very much less than the radius of the opposite wall. Thus, in the Kaplan draft tube the elbow has more breadth in cross section than the balance of the draft tube, (see Fig. 12 of the above mentioned Kaplan patent). On the other hand our present draft tube is so constructed that the elbow is constricted in cross section, and this constricted portion is partly filled with the splitter 38. The splitter 38 does not extend up into the inlet member 23, but is located at a considerable distance therefrom, so that the shocks caused by the water passing through the draft tube will be muflled by the splitter and will therefore be prevented from travelling up the tube to the runner.

The advantage of having the splitter 38 come only approximately half way around the elbow 26, or less than the whole way, is that the shock loss is reduced or eliminated, because the further the splitter is from the runner, the more the water is smoothed and straightened out before reaching the splitter. The splitter must be far enough around the elbow to divide the water into approximately equal parts above and below the splitter.

In actual practice it has been discovered that there is no reaction on the runner by the water with the splitter 38 in the position shown in Fig. 1. Furthermore, by forming the upper and lower surfaces of the splitter with a curvature under no circumstances sharper than the contour of the easement curve 28, there is produced a shape which perfectly corresponds to the natural flow of the water flowing through the draft tube.

While one illustrative embodiment of our invention has been described in detail, it is not our intention to limit its scope to that embodiment or otherwise than by the terms of the appended claims.

What is claimed as new is:

1. A draft tube having inlet and outlet portions with an elbow therebetween, a transverse web spanning the portion of the draft tube intermediate the elbow and the outlet, and a vertical pier disposed longitudinally of the outlet portion, and extending from the mouth of the draft tube inwardly to the transverse web, the upper portion of the pier terminating near the outer edge of the web and the lower portion of the pier extending inwardly under the web and terminating adjacent the inner edge thereof.

2. A draft tube having inlet and outlet portions with an elbow therebetween, the elbow being contracted in breadth and expanded in width in a direction from its inlet towards its outlet, a transverse web spanning the portion of the draft tube intermediate the elbow and the outlet, and a vertical pier disposed longitudinally of the outlet portion and extending from the mouth of the draft tube inwardly to the transverse web, the upper portion of the pier terminating near the outer edge of the web and the lower portion of the pier extending inwardly under the web and terminating adjacent the inner edge thereof.

3. A draft tube having inlet and outlet portions with an elbow therebetween, the elbow being contracted in breadth and expanded in width in a direction from its inlet towards its outlet, a transverse web located in the contracted portion of the draft tube and extending from side wall to side wall thereof, and a vertical pier disposed longitudinally of the outlet portion and extending from the mouth of the draft tube inwardly to the transverse web.

4. A draft tube having inlet and outlet portions with an elbow therebetween, the elbow being contracted in breadth and expanded in width in a direction from its inlet towards its outlet, a transverse web located in the contracted portion of the draft tube and extending from side wall to side wall thereof, and a vertical pier disposed longitudinally of the outlet portion and extending inwardly to the transverse web, the upper portion of the pier terminating near the outer edge of the web and the lower portion of the pier extending under the web and terminating adjacent to the inner edge thereof.

5. A draft tube having inlet and outlet portions with an elbow therebetween, and a transverse Web disposed in the elbow and spanning the draft tube from side wall to side wall, the inner edge of the web being so located that a plane passing through its edge and the center of curvature of the elbow is at an angle of approximately with the vertical center line of the draft tube.

6. A draft tube having inlet and outlet portions with an elbow therebetween, the outlet comprising a substantially horizontal leg, and a web extending across the draft tube from side wall to side wall and disposed partly in said outlet leg and partly in said elbow, the inner edge of the web being so located that a plane passing through its edge and the center of curvature of the elbow is at an angle of approximately 45 with the vertical center line of the draft tube.

7. A draft tube composed of concrete or other cementitious material, having inlet and outlet portions with an elbow therebetween, and a web formed integral with the draft tube and spanning the same from side wall to side wall, said web being disposed in the lower part of the elbow, the inner edge of the web being so located that a plane passing therethrough and through the center of curvature of the elbow is at an angle of approximately 45 with the vertical center line of the draft tube.

8. A draft tube composed of concrete or other cementitious material, having inlet and outlet portions with an elbow therebetween, a transverse web spanning the draft tube intermediate the elbow and the outlet portion, the inner edge of the web being so located that a plane passing through its edge and the center of curvature of 9. A draft tube composed of concrete or other cementitious material, having inlet and outlet portions with an elbow therebetween, and a web formed integral with the draft tube and spanning the same from side wall to side wall, said web being disposed partly in said outlet portion and partly in said elbow and being located along the longitudinal center line of the draft tube, the inner edge of the web being so located that a plane passing through its edge and through the center of curvature of the elbow is at an angle of approximately 45 with the vertical center line of the draft tube.

10. A draft tube having inlet and outlet portions with an elbow therebetween, a transverse web spanning the draft tube and located along the center line thereof, and a vertical web disposed at right angles to the transverse web and located in the outlet portion of the draft tube, the inner edge of the transverse Web being so located that a plane passing through its edge and the center of curvature of the elbow is at an angle of approximately 45 with the vertical center line of the draft tube, and the outer edge of the transverse web being connected to the vertical web at the junction of the elbow with the outlet portion of the draft tube.

11. A draft tube having inlet and outlet portions with an elbow therebetween, a web spanning the draft tube from side wall to side wall, and a second web disposed along the longitudinal center of the draft tube in a plane substantially at right angles to the first named web, the inner edge of the first named web being so located that a plane passing through its edge and the center of curvature of the elbow is at an angle of approximately 45 with the vertical center line of the draft tube, the outer edge of said first named web being connected to the second web at the junction of the elbow with the outlet portion of the draft tube, the upper portion of the second web terminating near the outer edge of the first named web and the lower portion of the second web extending inwardly under the first named web and terminating adjacent the inner edge thereof.

12. A draft tube having inlet and outlet portions with an elbow therebetween, a transverse web spanning the portion of the draft tube intermediate the elbow and the outlet, and a vertical pier disposed longitudinally of the outlet portion and extending from the mouth of the draft tube inwardly to the transverse web, the inner edge of the transverse web being so located that a plane passing through its edge and the center of curvature of the elbow is at an angle of approximately 45 with the vertical center line of the draft tube, the outer edge of said transverse web being connected to the vertical pier at a point adjacent to the junction of the elbow with the outlet portion of the draft tube, the upper portion of the vertical pier terminating near the outer edge of the transverse web and the lower portion of said pier extending inwardly under the transverse web and terminating adjacent the inner edge thereof.

13. A draft tube having inlet and outlet portions with an elbow therebetween, the elbow being contracted in breadth and expanded in width in a direction from its inlet toward its outlet, and

a transverse web extending across the draft tube from sid wall to side wall and disposed partly in said outlet portion and partly in said elbow, the inner edge of said web being so located that a plane passing through its edge and the center of curvature of the elbow is at an angle of approximately 45 with the vertical center line of the draft tube.

14. A draft tube having inlet and outlet portions with an elbow therebetween, the elbow being contracted in breadth and expanded in width in a direction from its inlet towards its outlet, and a transverse web located along the longitudinal center line of the draft tube and extending from side wall to side wall and disposed partly in said outlet portion and partly in said elbow, the inner edge of said web being so located that a plane passing through its edge and the center of curvature of the elbow is at an angle of approximately 45 with the vertical center line of the draft tube.

15. A draft tube composed of concrete or other cementitous material having inlet and outlet portions with an elbow therebetween, the elbow being contracted in breadth and expanded in width in a direction from its inlet towards its outlet, and a web formed integral with the draft tube and spanning the same from side wall to side wall, said web being disposed partly in said outlet portion and partly in said elbow, the inner edge of the web being so located that a plane passing through its edge and the center of curvature of the elbow is at an angle of approximately d5 with the vertical center line of the draft tube.

16. A draft tube composed of concrete or other cementitious material having inlet and outlet portions with an elbow therebetween, the elbow being contracted in breadth and expanded in width in a direction from its inlet towards its outlet, and a web formed integral with the draft tube and spanning the same from side wall to side wall, said web being disposed partly in said outlet portion and partly in said elbow and being located along the longitudinal center line of the draft tube, the inner edge of the web being so located that a plane passing through its edge and the center of curvature of the elbow is at an angle of approximately 45 with the vertical center line of the draft tube.

17. A draft tube having inlet and outlet portions with an elbow therebetween, the elbow being contracted in breadth and expanded in width in a direction from its inlet towards its outlet, and means within the draft tube for splitting the water into a plurality of streams, said means extending up into the elbow and terminating at a point approximatel half way around the elbow.

18. A draft tube having inlet and outlet portions with an elbow therebetween, the elbow being contracted in breadth and expanded in width in a direction from its inlet towards its outlet, and a transverse web disposed in the contracted portion of the elbow for splitting the water into a plurality of streams, the inner portion of said web terminating at a point approximately half way around the elbow.

19. A draft tube having inlet and outlet portions with an elbow therebetween, the elbow being contracted in breadth and expanded in width in a direction from its inlet towards its outlet, a transverse web spanning the draft tube intermediate the elbow and the outlet portion, the inner portion of said web terminating at a point approximately half way around the elbow, and a vertical web disposed along the center of the outlet portion and bisecting said transverse web.

20. A draft tube having inlet and outlet portions with an elbow therebetween, the elbow being contracted in breadth and expanded in width in a direction from its inlet towards its outlet, a transverse web spanning the portion of the draft tube intermediate the elbow and the outlet, the inner portion of said web terminating at a point approximately half way around the elbow, and a vertical pier disposed longitudinally of the outlet portion and extending from the mouth of the draft tube inwardly to the web, the upper portion of the pier terminating near the outer edge of the web and the lower portion of the pier extending inwardly under the web and terminating adjacent the inner edge thereof.

21. A draft tube having inlet and outlet portions with an elbow therebetween, the elbow being contracted in breadth and expanded in width in a direction from its inlet towards its outlet, a transverse web located in the contracted portion of the draft tube and extending from side wall to side wall thereof, the inner portion of the web terminating at a point approximately half way around the elbow, and a vertical pier disposed longitudinally of the outlet portion and extending from the mouth of the draft tube inwardly to the web.

22. A draft tube having inlet and outlet portions with an elbow therebetween, the elbow being contracted in breadth and expanded in width in a direction from its inlet towards its outlet, a transverse web located in the contracted portion of the draft tube and extending from said wall to side wall thereof, the inner portion of said web terminating at a point approximately half way around the elbow, and a vertical pier disposed longitudinally of the outlet portion and extending inwardly to the transverse web, the upper portion of the pier terminating near the outer edge of the web and the lower portion of the pier extending under the web and terminating adjacent to the inner edge thereof.

23. A draft tube having inlet and outlet portions with an elbow therebetween, the elbow being contracted in breadth and expanded in widths in a direction from its inlet towards its outlet, a transverse web located in the contracted portion of the draft tube and extending from side wall to side wall thereof, the inner edge of said web being located at a point approximately half way around the elbow, and a vertical pier disposed longitudinally of the outlet portion and extending inwardly to the transverse web, the upper portion of the pier terminating near the outer edge of the web and the lower portion of the pier extending under the web and said pier being formed integral with the draft tube.

GEGRGE A. JESSOP. HAROLD J. M. ROSS.