The DPS17 is an SG iron pilot operated valve which combines the functions of a pressure reducing valve and a surplussing valve. It is suitable for steam or gases such as compressed air. The main pilot, fitted onto the main valve body provides control of downstream pressure. The surplussing pilot, fitted to the side of the valve is set to close the main valve should the upstream pressure fall below t he desired level. This facilitates the shutting down of the non-essential plant in order to either prevent overloading of the boiler or maintain the s upply pressure to essential plant.