Definition(s)
Heat-Sensitive Lock-Open Device
Device installed on a surface safety valve (SSV) actuator to maintain the SSV valve in a full open position until exposed to sufficient heat to cause the device to release and allow the SSV valve to close.
Source: API SPEC 6A, Specification for Wellhead and Christmas Tree Equipment, Twentieth Edition, October 2010 (Addendum November 2012). Global Standards