Air diffusers

A diffuser for controlling flow of air in an air conditioning system, the diffuser including an air flow control baffle, a first temperature sensitive element for sensing room temperature variations and including a body and a piston which move relatively to each other in response to temperature variations, a second temperature sensitive element for sensing duct temperature variations and including a body and a piston which move relatively to each other in response to temperature variations, a housing structure, the body of one of said elements being fixed to said housing structure, a pair of arms having inner ends and outer ends, the arms being pivotally mounted to said housing structure adjacent their inner ends and having their outer ends connected to said baffle, the arms protruding outwardly from said housing structure, each arm having a first cam surface on one side of its pivotal mounting and a second cam surface on the other side of its pivotal mounting, a control structure including a first control element having a first surface for bearing on said first cam surfaces and a second control element having a second surface for bearing on said second cam surfaces, the body of the other temperature element being fast with said control structure, a spindle opposite ends of which bear on said pistons to prevent the pistons moving towards each other, and spring means for resisting movement of the control structure as at least one of the temperature sensitive elements heats up, said spring structure comprising two co-axial helical springs arranged in series, an end of one spring bearing on a component with increasing force as said one spring is compressed so that said component is displaced, and the second spring bearing on said component so that as the component moves, it compresses the second spring.