Valve assemblies optionally with inflatable bodies for modulating fluid expulsion from an inflatable body, without active user participation. Valve assemblies include, in separate components or in integrated form, a vent body defining an external orifice, an internal orifice in fluid communication with the external orifice, and an inflatable body interface. Extending from the internal orifice is a collapsible, hollow elongate member defining longitudinal and lateral axes. Sealing closure of the elongate member, which is preferably constructed from a resilient material, results from application of generally opposing mechanical forces across a lateral surface of the elongate member. Compression localizing members may be used proximate to the elongate member to increase closure performance. In addition, performance parameters can be varied by modifying the physical characteristics of the compression members (height, upper surface area, lower surface area, composition, density, use of localizing ridges, etc.) as well as locations of the compression members (proximity to other compression members, distribution relative to the cushion geometry, etc.).