Abstract: A powered fastener driver including a storage chamber cylinder, a fill port, and a one-piece fill valve. The storage chamber cylinder encloses a piston cylinder and defines therewith a storage chamber in which compressed gas is stored. The fill port is in communication with the storage chamber. The one-piece fill valve is at least partially positioned within the fill port. The fill valve includes a slit, which, in a closed state, prevents gas in the storage chamber from being discharged to the atmosphere through the fill valve. In an open state of the slit, the slit permits the storage chamber to be refilled with compressed gas through the fill valve. A pressure exerted on a portion of the fill valve in which the slit is defined by compressed gas within the storage chamber maintains the slit in the closed state.