Abstract: A valve having metal-to-metal dynamic seating for controlling the flow of gas includes a valve body having a gas passage extending therethrough, a metal seat extending about the gas passage, a flexible metal diaphragm mounted in the valve so the diaphragm can be moved into and out of sealing contact with the metal seat to respectively close and open the gas passage, and an actuator operable for opening and closing the gas passage by way of movement of the diaphragm relative to the metal seat. The actuator includes a metal backing member forcedly contacting the diaphragm during closing of the gas passage on a side of the diaphragm opposite a side thereof which makes sealing contact with the metal seat. The metal seat and the metal backing member are configured such that the sealing contact between the metal diaphragm and the metal seat is a relatively narrow line of contact extending about the gas passage.