A diaphragm valve is provided with means to prevent wrinkling of the diaphragm and to accurately control the flow through the valve. FORGED STEEL VALVESThe valve has a body with at least one substantially flat valve seat on an exterior surface. Forged Steel ValvesPassages extend from an inlet chamber to the valve seats and from the valve seats to an outlet chamber. Each valve seat is covered by a diaphragm, overlying and extending beyond the valve seat, which in turn is covered by a cap. Bellow Seal ValveThe caps and diaphragms define control cavities overlying the valve seats which may be pressurized to force the diaphragms against the valve seats. Preferably, at least one of the caps supports a mechanical flow regulator which comprises a flexible backing member and means for moving the backing member towards and away from the valve seat, thereby controlling the freedom of movement of the diaphragm in the control cavity. Also, the diaphragm is preferably pretensioned and a rigid reinforcing member adapted to bear at least part of the tension in the diaphragm is attached to a portion of the diaphragm which extends beyond the valve seat.

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