1. Installed on the return air duct of the ventilation and air conditioning system, it is normally open. When the smoke temperature in the pipeline reaches 70 °C in the fire, it will be closed, and the smoke leakage and fire integrity requirements can be met within a certain period of time. A valve that acts as a fire barrier.

2. 70 °C normally open, WSDc-FK, (W) temperature sensor control automatically shut down, (S) manual open, (Dc) electromagnet control off, (F) air volume adjustment function, (K) valve closed or opened Valve position signal feedback function.