Low pressure or flat inner tubes can be the result of a faulty air valve. The air valve is part of the core assembly that fits inside the stem of a tire. The core is threaded tightly into place with the valve preventing air from escaping when the tire is filled with air. The end of the core features a release that, when depressed, allows air to escape from the tire and the pressure to be reduced.
Release pressure from the inner tube to prevent injury while working on the valve stem. Hold a core replacement tool with the long and pointed pressure release side of the tool extended outward. Press in with the tool to release air pressure from the inner tube.
Turn the tool so that the short slotted core removal side is extended outward. Place the tool on the core inside the stem so that is securely seated in place.
Turn the tool to the left or counterclockwise to loosen the core. Continue turning to the left to completely loosen and remove the core from the valve stem.
Select an appropriate replace valve core for the inner tube. Purchase cores from automotive and tire stores.
Thread the replacement valve core into the stem taking care not to cross thread the core as it is inserted. Tighten the core with your fingers and finish tightening the core in place with the same side of the core tool used to remove the old core.