US3051441A

US3051441A - Dry band francis turbine

Info

Publication number: US3051441A
Application number: US51368A
Authority: US
Inventors: Robert S Sproule
Original assignee: Dominion Engineering Works Ltd
Current assignee: Dominion Engineering Works Ltd
Priority date: 1960-08-23
Filing date: 1960-08-23
Publication date: 1962-08-28
Anticipated expiration: 1979-08-28
Also published as: GB932632A

Description

Aug. 28, 1962 R. s. SPROULE 3,051,441

DRY BAND FRANCIS TURBINE Filed Aug. 23, 1960 2 Sheets-Sheet 1 ll VALVE INVENTOR. ROB EET S. SPJZOU LE ATTO New.

Aug. 28, 1962 s, SPROULE DRY BAND FRANCIS TURBINE 2 Sheets-Sheet 2 Filed Aug. 23, 1960 INVENTOR. ROBERT S- SPEOULE ATT PNEK United States Patent ()fiiice 3,051,441 Patented Aug. 28, 1962 3,051,441 DRY BAND FRANCIS TURBINE Robert S. Sproule, Montreal, Quebec, Canada, assignor to Dominion Engineering Works Limited Filed Aug. 23, 1960, Ser. No. 51,368 2 Claims. (Cl. 253117) This invention relates to new and useful improvements in hydraulic turbines and has particular reference to hydraulic turbines of the type known as dry band Francis turbines.

The principal object of the present invention is to provide new and useful arrangement for facilitating the introduction and maintenance of air in the space between the band of a Francis turbine and the fixed parts.

Another object of the invention is to provide an arrangement of the type set forth which is relatively simple and economical in construction.

Another object is to provide a device of the type set forth to provide a Francis turbine with seals which reduce leakage around the band to the point where it is possible to maintain air in the space between the band and the stationary parts.

Another object is to provide an arrangement of the type set forth wherein the need for a compressor to introduce air around the band may be eliminated or the power required by such a compressor is substantially reduced.

Other objects and advantages of the invention may be apparent from the following description taken in connection with the accompanying drawings wherein the preferred form of the invention has been given by way of illustration only.

Referring to the drawings:

FIGURE 1 is a fragmentary sectional view of a Francis turbine embodying the invention; and

FIGURE 2 is a fragmentary sectional view similar to FIGURE 1 but on an enlarged scale.

In an application of Martin J. Berlyn to which reference is made for further description of the turbine involved, for Dry Band Arrangement for Hydraulic Turbine Runner, Serial Number 834,357 filed August 17, 1959, and assigned to the assignee of this application there is described a method of introducing and holding air between the runner band and the stationary parts of a Francis turbine. It has been found that in connection with such construction that unless the runner band seal is much more effective than is common, a great deal of water passes through the space between the band of the turbine and the fixed parts and this water picks up an appreciable amount of air with the result that it has been found expensive to pump air into this space in suificient quantity to make up for air loss and to maintain the large proportion of air required for low friction at the runner band. This disadvantage is particularly apparent at part load operation of the turbine where there is considerable whirl at the discharge from the runner with the result that centrifugal pressure builds up in the space between the band and the stationary parts.

The principal object of the present invention is to provide a new and improved arrangement wherein the power required or necessary to introduce air at the necessary rate into the annular space to maintain the space substantially dry is greatly reduced or eliminated.

Referring more particularly to the drawings wherein similar reference characteristics designate corresponding parts throughout, the annular space 1 is found between the throat ring 7 and the runner band 6.

The upper band seal 5 is provided to maintain leakage of water into the annular space 1 to a minimum.

The turbine is also provided with an anti-circulation seal 4 adjacent to the bottom of the runner band 6. The pressure drop across this seal will be small so that the clearance can be generous or much greater than at the upper runner seal 5.

The space 1 is connected by pipes 2 which are connected to the space 1 through ports in throat ring 7 to an orifice 3 near the center of the draft tube 8 under the runner cone 9 and at this orifice 3 the pressure will usually be lower than in space 1 due to the presence of a vortex below the runner.

The air passage or duct 10 communicates with space 1 and a control valve 11 and is adapted to be connected to a compressor or air storage receiver or the like not shown.

The area between anti-circulation seal 4 and the adjacent surface of runner band 6 must be appreciably less than the area of pipes 2. With this construction it will be relatively easy to introduce air into space 1.

Leakage water through seal 5 and leakage water through seal 4 will be discharged through pipe 2 and orifice 3 into the draft tube maintaining the pressure in the space 1 close to the pressure at the orifice 3 which substantially reduces or eliminates the requirement of power to intro duce air at the necessary rate to replace the air which is carried away from space 1 by the leakage water passing through space 1.

The present arrangement will appreciably reduce the power required to supply air to space 1 when the leakage through seal 5 is sufiicient to carry away appreciable quantities of the introduced air. In installations which have suitable pressure at orifice 3 the invention will obviate the need of a compressor to supply air to the space 1 as the space 1 may be kept below atmospheric pressure. Whether a compressor is needed depends on the turbine design, the setting with respect to tailrace level, and the range of powers through which it is desired to maintain efficiency.

It will be noted that various arrangements of piping within the draft tube would operate satisfactory although it is desirable to keep the pipes to as small and as few in number as possible as they present some resistance to the flow in the draft tube. A construction which has been used satisfactorily is a tripod made up of three pipes 2 welded to a common head 12 at their apex and to three equally spaced points on the draft tube liner. The legs of this tripod are preferably at an angle to the horizontal, for rigidity. 'Other methods of introducing air close to the center of the draft tube have used pipes straight across or pipes cantilevered from one side of the draft tube.

It is pointed out that the aggregate area of the pipes 2 must be appreciably greater than the area between the seal 4 and the runner band 6.

It is contemplated'that this invention may be used for any Francis turbine equipped with seals which reduce leakage around the band to the point where it is possible to maintain air in the space between the band and the stationary parts. It will be of advantage where the draft tube pressure at the bottom of the band is not below atmospheric pressure and may be used either to eliminate the need for a compressor to introduce air around the band or to reduce the power requirements of such a compressor.

From the foregoing it will be seen that I have provided new and improved means for obtaining all of the purposes and advantages of the invention.

I claim:

1. In a device of the character described, a rotating runner band, a static throat ring, a close clearance upper band seal between said band and ring, a lower seal and an annular space between said band and ring, static duct means connecting said annular space to a zone of pressure at the center of the draft tube lower than the pressure immediately below said lower seal and an air inlet to said annular space.

2. In adevice of the character described, a rotating runner band, a static throat ring, a close clearance upper band seal between said band and ring, a lower seal and an annular space between said band and ring, static duct means connecting said annular space to a Zone of pres sure at the center of the draft tube lower than the pressure immediately below said lower seal and an air inlet to said annular space and means for supplying air under pressure to said annular space.

References Cited in the file of this patent UNITED STATES PATENTS 1,737,870 Telfer Dec. 3, 1929 1,823,702 Ring Sept. 15, 1931 1,860,618 Nayler May 31, 1932 1,898,023 Smys er Feb. 21, 1933 2,685,429 Auyer Aug. 3, 1954 FOREIGN PATENTS 486,923 Germany Dec. 11, 1926