US Patent 7314080 Slidable sleeve plunger

An improved plunger lift mechanism comprises an internal hollow body having bypass orifices that, when exposed, allow fluid to pass through during plunger descent in a downhole tube to the bottom of a production well. A slidable sleeve slides along the hollow body to close the orifices, causing the plunger to rise and carry accumulated fluid to the well surface. In addition, the present apparatus comprises surface interfaces between a slidable sleeve and a mandrel to minimize a probability of mandrel and sleeve separation during the plunger's ascent phase and a risk of plunger stall.