The presently-disclosed subject matter includes valve covers. The valve covers can protect valves from exposure as well as from tampering. In some embodiments the valve cover comprises a cap that includes a top end and a side wall that is substantially cylindrical. Embodiments of valve covers also include a plug on an interior side of the top end of the cap that projects toward the opening of the cap. When the valve cover is installed, the plug can extend beyond an opening of the valve.