High and low tubing pressure actuated well safety valve

A well safety valve adapted to be positioned in a well tubing and close on either a predetermined high tubing pressure or a predetermined low tubing pressure comprising,

• a body,
• a valve closure member in the body moving between open and closed positions,
• a tubular member longitudinally movable in the body for controlling the movement of the valve closure member, said tubular member including a first upper, a second middle, and a third lower telescoping section, said first section including a piston exposed to fluid pressure in the tubing acting to move the first section in response to the fluid pressure,
• means yieldably urging the first section in a direction to open the valve,
• means yieldably urging the second section in a direction to open the valve,
• first releasable locking means normally securing the first and second sections together,
• second releasable locking means normally securing the second and third sections together,
• means for moving the third section in a direction for allowing the closure of the valve member when the second locking means is released.