Patent ID: 7784549

Claim:
A self-propelled swabbing device for use in removing liquid to surface from within an installed wellbore casing, said device comprising: a longitudinally extending plunger sized to fit within said wellbore casing, and having an internal surface defining an internal flow passage extending longitudinally therethrough; a seal between said plunger and said wellbore casing; a valve stem including a valve operative to be shuttled between an opened position allowing flow through said internal flow passage and a closed position to seal said internal flow passage when a set pressure is reached, said valve stem extending longitudinally through said plunger to form a piston and a sealed chamber; a biaser for biasing said valve toward said opened position; a snap-closed device for ensuring that said valve is fully open in the opened position; and a snap-open device for ensuring that said valve is fully closed in said closed position, wherein said snap-closed and snap-open devices comprise a member located on said valve stem, wherein one or both of said snap-closed device and said snap-open device includes a magnet.