A gas spring-powered fastener driver includes a cylinder, a storage chamber cylinder having pressurized air in communication with the cylinder, a moveable piston positioned within the cylinder, a driver blade attached to the piston and movable therewith between a top-dead-center position and a bottom-dead-center position, the driver blade defining a driving axis, a lifter operable to move the driver blade from the bottom-dead-center position toward the top-dead-center position, the lifter is configured to engage the driver blade when moving the driver blade from the bottom-dead-center position toward the top-dead-center position, a bumper positioned beneath the piston in a vertical direction to absorb impact energy from the piston, and a valve positioned in the storage chamber cylinder. In response to the piston compressing the bumper while absorbing impact energy from the piston, the valve adds pressurized air from the cylinder to the storage chamber cylinder.