Abstract: A straight through flow diaphragm valve of the type in which a flow controlling diaphragm is operated by an actuating device for moving the diaphragm between fully opened and fully closed positions in respect to a flow passage through a valve body which is adapted to be installed in a fluent material carrying line, the flow passage geometry being so related to a shut-off ridge cooperatively related to the diaphragm across the passage so that the passage provides a substantially undiminished straight through flow path along the axis of the passage when the diaphragm is in the fully open position. An especially durable diaphragm structure is provided. The diaphragm is retained in a manner to prevent leakage where the valve must operate at elevated temperatures.