Control Valve
A motorized valve that continuously meters the flow of water or steam to a coil or heat exchanger, following a controller signal.
What does a control valve do?
A control valve is the device that meters the hot water, chilled water or steam sent to a coil, an exchanger or a loop. An electric or pneumatic actuator positions it continuously from a controller signal, turning a temperature setpoint into actual flow. It complements modulation on the generation side: the burner adjusts how much heat is produced, the valve adjusts how much of it reaches each zone.
Two-way or three-way
A two-way valve throttles flow and makes loop flow vary — the approach used in variable-flow systems. A three-way valve diverts unused flow through a bypass and maintains steadier circulation, which protects equipment sensitive to low flow. The choice follows the building’s hydronic architecture and pumping strategy rather than a blanket rule.
Flow characteristic and sizing
The flow characteristic describes how flow changes with valve travel. On a heating coil, output does not rise proportionally with flow: an equal-percentage characteristic compensates for that non-linearity and gives steadier control across the range. That only works if the valve is sized on the flow actually required — a valve selected on pipe diameter is almost always too large and will operate close to its seat.
Stable control and maintenance
A poorly sized valve hunts, produces temperature swings and wears out early. Verifying full travel, tight shutoff at the seat and response to setpoint belongs to routine inspection points, alongside checking an aquastat setting or the safety devices of a steam boiler.