118181 - WILLIAMS CONTROLS - Pressure Protection Valve- WM778A The WM778 series are normally closed pressure protection valves often used when an auxiliary system is supplied off a primary system. The valve will protect primary system air pressure by reclosing automatically at a nominal 70 PSI (482 kPa). The WM778 is available without a filter installed in its inlet port. The filter will reduce ingestion of contaminants. Cross references: WM-778-A