Two-port valve
The Illustrated Guide to Mechanical Building Services, Third Edition (BG 31/2017), by David Bleicher, published by BSRIA in 2017, suggests that a two-port valve is: ‘A motorised valve which can be either on/off or modulating and is sometimes known as a zone valve. Pictured is a small two-port valve used on a domestic heating system to direct water to the hot water cylinder. The metal box on top of the valve is the actuator – an electric motor that moves the valve to the required position in response to signals from a control system.’
--BSRIA
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