Line stopping or line plugging is a means of isolating a piping system to provide a shut off where none exists. This process serves as a control, or temporary valve, that can be removed after alterations or valve replacements have been made. With a hot tap previously made on a line, a line stopper is attached to a temporary valve, and the valve is opened. The line stopper is hydraulically or mechanically pushed into the line to seal the pipe. There are various types of line stopping heads.
A single line stop can be used to stop off and abandon a shutdown. Two or more line stops can be used in tandem to isolate and bypass many intersecting lines at once. Fluid in the line is bypassed, leaving a workable dead section to alter, repair or add a valve while service provided by this line is continued.