A vacuum pump including: a pump body that includes an elastic sleeve; a valve stem; a valve pin that is surrounded by the valve stem with an end of the valve pin snap fitted to the valve stem; a piston that surrounds the valve pin and that is located inside of the pump body and sealed against the pump body; a plug; a ring that surrounds the pump body and the plug; a head cap that surrounds the valve stem and that is configured to move within a cavity of the ring; and a spring disposed between the valve stem and the stepped groove of the plug at a position radially outward of the valve stem.