A valve specially dressed for a particular well and kept current with maximum flow potential that can shut in the well if surface control is lost. Also called a storm choke an early subsurface safety valve
George E. King Engineering, 5000 Oilfield Terms: A Glossary of Petroleum Engineering Terms, Abbreviations and Acronyms, US 2010. http://gekengineering.com/Downloads/Free_Downloads /Glossary_of_Petroleum_Engineering_Terms_25_August _2010.pdf, (Oil - Amer) {593}