A method of cutting and removing a section of prestressed concrete cylinder pipe and then installing a replacement valve while the pipeline is fully pressurized uses a replacement valve body with two cylinders that match the openings of the cut pipe. Inside each of the two cylinders is a cut-covering assembly which includes a cylindrical elastomeric seal and a mechanical linkage to move the seal in and out of the cut pipe. The replacement valve body further includes a rotatable valve in a central portion of the valve, and when the cylinder ends of the replacement valve body are positioned adjacent the bores of cut pipe ends, the valve can be rotated to move linkage assemblies that control the elastomeric seals in and out of each of the cut-covering assemblies into the bores of the cut pipe ends, thereby covering gaps created when the pipe was cut and placing the pipe ends in fluid-tight engagement with the replacement valve body.