238,001. Carey, R. F. May 8, 1924. Maintaining vacuum in pump casing.-In revolving cylinder apparatus for the hydraulic transmission of power, means are provided for producing a vacuum in the enclosing casing B, and for sealing the casing against the entry of air. The casing is initially filled with Liquid, which is withdrawn by a pump E and delivered into a tank D, which serves for leakage replenishing and cooling purposes and seals the casing B. The pump E may be disposed as shown, or in connection with the lower end of a pipe of sutEeient length to contain a column of liquid to balance atmospheric pressure. In a modified form, the casing B is not immersed in liquid and grooves K around the shaft J are fed with liquid from an overhead reservoir.