292 STEAM TURBINES
parts of the naves of the turbine bodies, together with the fixed walls of the case, form chambers which are interconnected, and in which a mean between the high and low pressures is present. Further, for each turbine body requiring relief there is a chamber between two walls of the case which encircles the former. One of these walls abuts against a section of the nave, which has the same outer diameter as the central inlet for the corresponding turbine body. The other wall abuts against a section of the nave which has the same outer diameter as the central inlet for the next-following turbine body. In the case of the last of the turbine bodies, however, the above-named wall abuts against a portion of the nave, the outer diameter of which is equal to that of the central inlet for the first turbine body. The chambers gi m 020 0 Fig. 541. referred to are connected with one another by a channel. When in the case of marine engines the axial thrust of the working steam is only so far neutralized at the relief places that an amount equal to the back pressure of the ship propellers working on the turbine shaft remains over, the relieving appliance will work suitably when its relieving force varies with the thrust pressure of the propeller. Parsons (1896) endeavoured to produce an automatic alteration of the relieving pressure by the arrangement shown in Fig. 541,1 which is here fitted to a radial turbine, but may also be applied to an axial one. The turbine shaft is mounted by means of yielding rings (2)2 in a collar bearing, and is to a small extent free to move longitudinally. The relieving piston 7, together with the working wheels B, is fixed firmly on the shaft and moves with the latter in the axial direction. It is 1A, P. 553,932. 2 Compare p. 302.
