Abstract: A method and apparatus for sealing a leaking valve on a compressed gas tank to accomodate safe transport of the tank and valve from the place of use in the field to a repair depot where the tank and valve may be safely serviced. The apparatus comprises a valve cap specifically designed for practice of the method. The method resides in the steps of placing the cap over the leaking valve and attaching the cap to the tank, filling the cap with a fusible substance in liquified form, the fusible substance having a fusion temperature in excess of ambient temperature but less than about 200.degree. F. and, upon cooling, solidifying within the cap about the valve, sealing off the cap, transporting the tank, cap and encapsulated valve from the place of use to a repair depot, at the repair depot converting the fusible substance from solidifed form to liquified form and draining the substance from the cap, and removing the cap from the tank and valve to accommodate safe servicing of the valve at the repair depot.