In many cases, the power available from a back pressure turbine through which the whole of the heating steam flows is appreciably less than that required in the factory. In such cases, it would be possible to install a back pressure turbine to generate additional power. However, generally, the functions of both machines are combined in a single turbine. Such a turbine is shown in Fig. 7.21. The steam enters the turbine and expands through the high pressure stages before the extraction branch. Here, a certain quantity of steam is continuously being extracted for heating purposes, the remainder passes through the pressure control valve into the low-pressure part of the turbine.
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