Abstract: A bidirectional diaphragm valve is presented in which the flat, disk shaped diaphragm formed of elastomeric material is biased against the valve seat by means of a plunger which is not attached to the diaphragm. The diaphragm is clamped between the valve body and a bonnet member providing compression and confinement of the perimeter of the diaphragm, resulting in radial compression of the diaphragm which is expressed inwardly as the expansion and buckling of the central portion of the diaphragm whereby the valve opens passively in response to pressure from the flow medium when the plunger is retracted. The preferred embodiment of the valve is of miniature size and compact configuration adapted for use in multi-valve banks and all parts having wetted surfaces are formed of materials of suitable chemical inertness compatible with the fluid media.