Patent attributes
A safety valve features a flow tube operated flapper for the normal open and closed positions that can be obtained with one or two control lines to a principal operating piston. Pressure applied to the piston moves the flow tube to rotate the flapper open behind the flow tube. Release of pressure to the principal piston allows a closure spring to return the flow tube up to let the flapper close. A secondary piston can drive the flow tube with applied pressure through a control line. Cycling the applied pressure in combination with an indexing mechanism allows the flapper to be locked open and then released to normal operation. The pistons act as backup for each other as they both drive the flow tube. The flow tube has a clearance fit to the body in the locked open position to exclude debris from the flapper.
