| abstract |
The vapor plug can be inserted into an open end of a pipeline. It comprises a hydraulic cylinder carrying a vertically disposed, elastic, resilient seal ring. The cylinder may be hydraulically actuated to expand the ring radially to seal the bore of the line. The hydraulic lines to and from the cylinder chamber may be blocked to lock the plug in the expanded mode. A plunger valve, responsive to pipeline pressure, controls a hydraulic fluid passage connecting the ends of the cylinder chamber. When the plunger valve is in the closed mode, it prevents fluid moving between the chamber ends. When the valve is moved by pipeline pressure to the open mode, fluid can move freely between the chamber ends, thereby permitting the ring seal to contract, to unseal the bore. The plug may then be pumped down the line and recovered at a pig trap. |