Heat Zone Valves are used to control the flow of water in hydronic heating systems. Each circuit of a heating system needs some form of control. The control can be independent circulating pumps or zone valves. There are many different types of zone valves, but they all share common characteristics. All zone valves have a valve body and an actuator. It is the actuator that moves to allow liquids to flow or to stop them from flowing. Electric voltage is applied to an actuator to make the valve shaft of the zone valve move. Valves that open or close too quickly can cause water hammer I a piping system.