The lever action fire valve is held open by a flexible wire in which fusible links are placed. These will shear at a temperature of 160°F when the valve will then be snapped shut by heavy spring pressure.
Good quality Lever Fire Valve Kits, available in 3/8" and 1/2" BSP Female Threaded.
Each kit includes:
1 Lever Fire Valve Body
9M of Stainless Steel Wire
1 Eutectic Soldered Link