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the cylinder (known as Bottom Dead Centre or BDC) the exhaust valve starts to open. As the piston now moves up the cylinder, the hot gases (consisting mostly of nitrogen, carbon dioxide, water vapour and unused oxygen) are expelled from the cylinder. As the Piston approaches TDC again the inlet valve starts to open and the cycle repeats itself.
The core of the valve stem is usually removable by unthreading it from the stem cylinder, though removal of the core is not usually necessary. The core prevents air from escaping the valve stem, and when depressed, it opens the chamber to allow air to pass into the tire or tube during the inflation process. Ad.