In a steam-using plant, steam is often generated at high pressures and reduced locally to provide heat for each steam user. This is usually done to minimize the diameter of steam distribution piping and enable more cost-efficient steam delivery.
A common way of lowering pressure is by throttling down the size of the steam passageway. For the most basic pressure reduction, it is possible to simply use a conventional globe valve in a fixed partly-open position, or by inserting an orifice plate into the flow of steam. However, any fluctuation in the flow rate would be accompanied by a corresponding fluctuation in pressure. To avoid such circumstances, pressure-reducing valves (PRVs) can be used to provide precise control of downstream pressure. They automatically adjust the amount of valve opening to allow the pressure to remain unchanged even when the flow rate fluctuates.