Alloys of certain metals, such as Ni-Ti and Ni-Ti-Cu, can memorize shapes. Even when deformed, these alloys exhibit the property of returning to their original shape with temperature changes.
A shape memory alloy spring is used as a temperature control valve in water mixing systems, utilizing the properties of shape memory alloys.
Shape memory alloy springs can be used for fire dampers that close ventilation ducts in the event of a fire. When hot air is sensed, the spring shrinks, causing the butterfly valve to close.
It is used in valve bodies to prevent hot water from entering hollow fiber filters.