A gas flow control valve with pivotable damper blade usable in a regenerative thermal oxidizer (RTO) unit or other gas flow control application. The valve in one embodiment is a four-way valve with dual operating positions to control gas flow through four ducts coupled to the valve. To enhance positively sealing the blade to the valve housing in each position the seal, selectively actuatable electromagnetic clamps are provided which magnetically draw the blade toward the active blade end seat acted upon by gas pressure in a direction which tends to force the blade away from its seat. The blade is actuated directly by an actuator system via an operating rod to change position of the valve. A seal air system supplies pressurized air to the valve seats. A programmable controller automatically controls actuation of the electromagnets, seal air, and blade positional changes.

A fluid control valve is disclosed, comprising: a valve body defining an outer wall for a curved flow path through the fluid control valve; and a valve element defining an opposing inner wall and rotatable relative to the valve body about a pivot point through between a closed position a range of open positions. A separation between the first inner wall and the outer wall along a restrictor portion of the flow path varies between open positions. The first inner wall and the outer wall are cooperatively defined so that for at least some open positions the separation between the first inner wall and the outer wall is constant along the respective restrictor portion of the flow path.

A fluid control valve is disclosed, comprising: a valve body defining an outer wall for a curved flow path through the fluid control valve; and a valve element defining an opposing inner wall and rotatable relative to the valve body about a pivot point through between a closed position a range of open positions. A separation between the first inner wall and the outer wall along a restrictor portion of the flow path varies between open positions. The first inner wall and the outer wall are cooperatively defined so that for at least some open positions the separation between the first inner wall and the outer wall is constant along the respective restrictor portion of the flow path.