The element that manages the flow — blocking, throttling, directing, protecting and controlling — without adding energy to the fluid (class VA of ISO 14224:2016). Every valve in throttling service pays for it in head loss.
Types by function
(handbooks per type in Phase 1)
- Block (on-off) — gate, ball, plug, knife gate: full bore, tight shutoff; not made for throttling;
- Regulation — globe (the classic control geometry), needle (precision at small flows), diaphragm and pinch (corrosive/abrasive fluids — the body never touches the process), butterfly (large diameters, block AND coarse regulation);
- Unidirectional protection — check valves (swing, piston, dual plate): prevent reverse flow; their failure is hidden by nature;
- Relief and safety — PSV/PRV (API 526): the last barrier against overpressure — the classic hidden function, proven by bench proof testing;
- Self-actuated (regulating) — pressure reducing and flow regulating: they operate without an external actuator, using the process's own energy. Under ISO 14224 they belong to class VA — "regulators" are not a separate family;
- Control — the final element of the loop (IEC 60534), with actuator and positioner. The Control Valve handbook is one of the MVP's 5 assets (in production).
Reliability: seat sealing (internal passing), stem sticking, actuator/positioner and the mismatch between valve and process (cavitation and flashing in severe service) dominate the history.