Page:Model steam turbines; how to design and build them (IA modelsteamturbin00harrrich).pdf/22

18 the entrance and exit of the jet, the angle between the initial and final directions is somewhat less than 180°. If a Pelton type of wheel is employed, as in the Ratcau single wheel turbine and that of Messrs Riedler & Stumpf, this angle becomes 180°, but the steam nozzle has to be inclined, so that the

Fig. 7. -- Variations of Pressure of Blades with Different Speeds.

effective velocity of the jet is less than its absolute velocity, i.e. the velocity with which it leaves the nozzle. Fig. 7 shows the increase of pressure on the vanes as the peripheral speed falls below half the jet velocity.

From the foregoing it is clear that to design a turbine to do a certain amount of work all that is required to be known is the weight discharged in