Abstract: A gas metering valve is provided for selectively providing a series of different calibrated gas flow rates. The valve includes a valve body having a gas inlet, a gas outlet, a chamber situated between the gas inlet and gas outlet. The valve also includes a metering element located in the chamber. The metering element is formed to include a plurality of passageways for permitting gas flow from the gas inlet to the gas outlet. The metering element is movable relative to the valve body to position a selected passageway in communication with the gas inlet. The valve further includes a seal apparatus including a sealing disk in sliding contact with the metering element. The sealing disk has an aperture formed therethrough aligned with the gas inlet for sealing said chamber against the transmission of gas therethrough except when the metering element is oriented with the selected passageway in registry with the aperture in the sealing disk.