1
William H Parker: Oil and gas well disaster valve control system. Del Norte Technology, June 1, 1976: US03961308 (23 worldwide citation)

A signal is transmitted through the walls of tubing extending down into an oil well in order to control a disaster valve at the lower end of the tubing. If the signal disappears, the valve shuts. In one embodiment, the tubing functions as the core of a transformer. In another embodiment, the tubing ...


2
William H Parker: Oil and gas well disaster valve control system. Del Norte Technology, July 26, 1977: US04038632 (16 worldwide citation)

A sonic energy signal is transmitted continuously through the walls of tubing extending down into an oil or gas well, in order to control a disaster valve at the lower end of the tubing. If the signal disappears, the valve shuts automatically. In one embodiment, the tubing functions as the core of a ...