This invention relates to a fluid distribution valve (30) comprising a port select valve structure wherein the flow of fluid from a fluid flow source (25) is directed through a chamber (42) of a rotatable member (32) comprising a plurality of varying sized spaced ports (43) which align with ports (45) of a housing (31) at various positions of rotation of the member (32) to provide variations of fluid flow through the ports (45) of the housing (31). The valve (30) has particular utility as an air distribution valve in an air flow support mattress system (110).