What is the difference between pressure-independent and pressure-dependent valves?

Pressure-independent control valves (PICVs) integrate a differential pressure regulator with a control valve into a single body, automatically maintaining constant flow regardless of upstream/downstream pressure fluctuations. Pressure-dependent valves rely on the system's balancing valves and pump control to maintain a stable differential pressure; they deliver their rated flow only at one specific pressure condition. PICVs eliminate the need for most balancing valves and deliver true flow at any stem position regardless of system pressure changes, which per ASHRAE 90.1-2019 can contribute to significant pump energy savings through variable-primary flow strategies. The tradeoff is higher first cost — typically 2–3× per valve — and slightly higher minimum differential pressure requirements (typically 3–5 PSI for Belimo PICVs).