The H‑400OP Series is a compact one‑piece design for moderate pressure (up to 3000 psi) instrumentation panels and systems, which provides a fixed operating point. H‑400OP valves are normally closed. When the differential pressure between the inlet and the outlet is higher than the set pressure of the spring, the loaded poppet will move backwards and provide a free passage for flow through the valve. For vacuum applications, please select the H‑400HP series.