230 STEAM TURBINES
pipe 7 and is intended to impinge on the back-motion vanes of the turbine, also has nozzles which point in directions opposite to those of the forward-motion ones. In the case illustrated, it will be seen, only the second turbine is applied to the back- ward motion.
Fig. 393.
In the style of construction adopted by Boella' (Fig. 394) the working wheel a has two vane wreaths, the outer one of which comes into action for the one direction of motion, while the inner one e with vanes of opposite cur- vature acts in the other direction. Between these vane wreaths protrude the covered leading apparatus d (only one is shown), each of which has one group of guide vanes for the radial impingement of the vane wreath b and another for the wreath c. In each of these leading apparatus is inserted a turning slide which can be actuated from the governing shaft e, and, according to its position, opens, to the steam streaming into the leading apparatus & in the direction f, first the one group of guide vanes and then the other.
Fig. 394. 2
A reversible axially impinged velocity turbine with two concentric working wheel vane wreaths has also been designed by Cassel (Fig. 395). The vanes 6 set with dovetail-formed feet in the wheel disc a have their inner parts e curved in E. P. 6420 of the year 1903.
2 E. P. 21,164 of the year 1901.
