2.1.1 Steam valve pressure drop
An example of this occurs in turbine governor valves, where the steam expands rapidly after passing through the valve, converting all its generated kinetic energy to frictional reheat. This has the effect of maintaining the enthalpy at the valve inlet value, but at the expense of a large increase in entropy and pressure drop. This is known as throttling and is used to shed load. More load is shed by reducing the valve area, so permitting less mass flow and increasing the pressure drop across the valve.