Abstract: A valve which can be inserted in an existing pipe or similar line without disconnection of the line. The valve is separable into two halves which are clamped around the line. The valve handle is then rotated to drive a cutter through the line, and to position an expandable seal across the line bore. Flow through the pipe is thus terminated to enable downstream repairs or installation of new equipment. Retraction of the seal and cutter opens the valve to reinitiate fluid flow, and the valve can thereafter be used as a conventional shutoff valve, as well as providing an auxiliary "T" connection to the line if desired.