GB1136031A - Rotary hydraulic machines, such as pumps, turbines and pump-turbines - Google Patents

Abstract

1,136,031. Centrifugal pumps; hydraulic turbines. DOMINION ENG. WORKS Ltd. Feb. 8, 1966, No. 5448/66. Headings F1C and F1T. In a hydraulic turbine, pump or pump-turbine in which fluid friction on the runner is reduced by introducing air into an annular space 22 adjoining the band shroud 17, the space 22 is bounded by an annular baffle 20. When injection of air through a pipe 28 commences, centrifugal separation takes place between the water and the air in the space 22, so that the water is expelled radially outwards from the space. In addition, an air-water interface 48 is established beyond the radially inner end of the space 22, between a radially extending annular surface 46 of an annular flange 31 projecting radially from the band shroud 17 and an adjacent parallel surface 45 on the baffle 20, the flange 31 acting as a centrifugal separation for this purpose. After the water has been expelled from the space 22, some air leaks from the space at its radially outer end and collects on the other side of the baffle 20 in an annular pocket bounded by an annular flange 42, as shown. The resultant depression of the water level in an annular space 23 reduces the water pressure between the surfaces 45, 46, thereby allowing the air-water interface 48 to move to the outer periphery of the centrifugal separator flange 31, as shown. In the stable condition now attained, water leaking from the runner periphery and passing, via space 23 and an annular seal space 30, to the draft tube 15 undergoes an increase in pressure head in an annular diffuser passage 41, this increase combined with the pressure head due to the height of water in the space 23 above the centrifugal separator flange 31 balancing the pumping action of the latter, and excess air leaks from the space 22 by breaking through the air-water interface 48 and passing via the seal space 30 to the draft tube 15. An annular wall 34 prevents air in space 23 from escaping through the seal space 30. Holes 37 permit interchange of air between the spaces 23 and 22 to allow the water level in the space 23 to change in response to change in operating conditions. The diffuser passage 41 may be omitted or replaced by substantially parallel annular passages containing radial vanes which are tapered in the direction of flow to provide diffusion. A similar arrangement is provided adjacent the crown shroud.