The Belimo ZONE24NC 24V Zone Act Normally Closed is a zone actuator designed primarily for HVAC applications. When not electrified, it operates as a normally closed valve, staying closed. When the actuator receives a 24-volt AC signal, it spins, allowing air to travel through. This enhances comfort and energy efficiency by accurately regulating airflow in various building zones. https://www.partshnc.com/24v-zone-act-normally-closed-3