Single Line Stop: Stops flow from one direction, such as when installing a hydrant valve. Double Line Stop: Stops water pressure from two sides, such as in a looped wall circuit, e.g. damaged pipe section replaced or main valve installed. Bypass option is available. Double Line Stop with Bypass Option: Whether it is 5 feet or 5 miles, you can permanently replace a line or cut in a valve on a transmission line or service line without customer inconvenience.