Abstract: A valve arranged for radial fluid flow from its inlet to its outlet has a spring-loaded diaphragm covering a valve cage member having a central opening communicating with the valve inlet surrounded by a plurality of peripheral openings communicating with the valve outlet. The valve cage member is downwardly concave and a valve top member closing off the valve body has an upwardly concave surface which is substantially the inverse of the concave surface of the valve cage member. Accordingly, the diaphragm moves from a zero flow configuration against the valve cage member to a full flow configuration against the valve top member symmetrically without stretching.