Page 26 - Steam Turbines Design, Applications, and Rerating

Introduction 7

Figure 1.5 Single-valve steam turbine. (The Elliott Company,
Jeannette, Pa.)

Multivalve turbines (Fig. 1.7) automatically limit pressure drop
across the governing valves, thereby minimizing throttling loss.
The prime benefit of a multivalve turbine is the fact that the nozzles
forming a short arc are fed by a single valve, which will allow a better
velocity ratio than would result if all available nozzles were fed with
the same amount of steam. Valve gear designs will sequence valve
opening so that subsequent valves will only open when the previous
valve is wide open. Multivalve turbines are the wise choice if frequent
load changes or varying outputs are anticipated or when inlet volume

Figure 1.6 Single-valve steam turbine with hand valve indi-
cated by arrow. (Dresser-Rand Company, Wellsville, N.Y.)