Two-port valve (motorised)
Also called: motorised valve, motorized valve, control valve, actuator valve, 2-port valve, fcu valve, zone valve
A two-port valve is the small motorised (actuated) valve on a chilled-water fan-coil unit (FCU) that opens to let chilled water flow through the coil and closes to stop it. It has two ports — flow in, flow out — and an actuator on top wired to the room thermostat: when the room calls for cooling the actuator drives the valve open; when the room is satisfied it shuts, and the coil gets no water. That is exactly why a mechanically-healthy FCU can still 'not cool' — if the stat isn't calling, the actuator has failed, or the valve has seized (common after long idle spells, or with dirty chilled-water-loop water gumming the plug), the coil stays starved even though the building's central plant is fine. It's a different part from a balancing valve (which sets the flow rate through the coil) and from the Y-strainer (which filters debris just upstream of it) — a weak FCU can be any of the three. Freeing or replacing a stuck two-port valve or its actuator is routine a water chiller service in Dubai work, and often the fix when one room stays warm while the rest of the building cools fine.
Related terms
Fan coil unit (FCU)
The in-room unit on a chilled-water or district-cooling system that blows cool air. The apartment equivalent of a split AC's indoor unit.
Chilled-water loop
The closed water circuit that carries cooling from the plant to every FCU in a chilled-water or district-cooled building.
Y-strainer
A Y-shaped in-line filter with a mesh screen that catches grit and debris in a pipe — on a chilled-water FCU it protects the coil and control valve from the muck in the system water.
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