Air distributor with automatically closable damper

An air distribution unit comprising means defining an air passage, a valve element movable between open and closed positions with respect to said passage, and means for moving said valve element between said positions, said moving means comprising slidably telescoped piston and cylinder members, one of said members being operably connected to said valve element, means for admitting pressure fluid into said cylinder member and for exhausting pressure fluid from said cylinder member, said one member moving said valve element toward said open position when pressure fluid is admitted into said cylinder member, a spring acting on said one member and operable to cause said one member to move said valve element toward said closed position when pressure fluid is exhausted from said cylinder member, the improvement in said air distribution unit comprising, a sensing tube communicating with said cylinder member and normally pressurized by said pressure fluid, first heat responsive means associated with said sensing tube and operable to vent said sensing tube to atmosphere when the temperature adjacent said heat responsive means exceeds a predetermined value whereby the pressure fluid in said cylinder member is exhausted to atmosphere by way of said sensing tube so as to enable said spring to move said valve element to said closed position, a detent movable between latched and unlatched positions relative to said valve element, biasing means urging said detent to said latched position, and second heat responsive means normally holding said detent in said unlatched position against the action of said biasing means and operable to permit said detent to move to said latched position when the temperature adjacent said second heat responsive means exceeds a predetermined value thereby to enable said detent to hold said valve element in said closed position independently of said spring.