Abstract: An expanding gate valve having a valve body defining a valve chamber and flow passages and having spaced sealing surfaces. Gate members are moveable within the valve body between open and closed positions and at the closed position having sealing engagement with the spaced sealing surfaces. A wedge member is positioned between the gate members and has at least one tapered surface having reacting engagement with a tapered surface of one of the gate members so that relative linear movement of the gate member relative to the tapered surface of the wedge member develops a lateral gate expansion force causing expansion of the gate members for tight sealing engagement with the spaced sealing surfaces.