Frangible shape memory alloy fire sprinkler valve actuator

Abstract

A temperature-activated valve for a conventional fire sprinkler utilizing a hyperelastic single-crystal shape memory alloy is described. The shape-memory element expands as it is heated, forcing a bolt to break, thereby opening the sprinkler valve. The devices described are less susceptible to accidental breakage than conventional actuators, and have fewer moving parts. Transition temperature of the shape memory alloy can be tuned to a narrow range.

What is claimed is: 
     
         1 . Method of making a thermally-activated sprinkler valve assembly comprising:
 tuning a shape-memory element comprising single-crystal shape memory alloy to exert a pre-determined force at a pre-determined temperature;   forming a temperature-sensitive actuator by coupling a frangible bolt to the shape-memory element so that the shape-memory element is compressed; and   coupling the actuator to a linkage, wherein the linkage is configured to couple with the valve of a fluid passageway having a valved outlet to oppose fluid pressure and maintain the valve closed.   
     
     
         2 . The method of  claim 1 , further comprising connecting the fluid passageway to a fluid source. 
     
     
         3 . The method of  claim 1 , wherein the step of tuning comprises tempering the shape-memory alloy by a heat treatment process that causes controlled partial precipitation of Al. 
     
     
         4 . The method of  claim 1 , further comprising coupling the linkage to the valve of the fluid passageway. 
     
     
         5 . The method of  claim 1 , wherein the step of coupling the actuator to the linkage comprises coupling the actuator between two brackets forming the linkage. 
     
     
         6 . The method of  claim 1 , further comprising matching the plateau stress of the shape-memory element to the ultimate tensile strength of the bolt.