The Upper Stage Tool Assembly is used in conjunction with a packoff and lower stage tool assembly.
Staged plunger lift is a method to get accumulated fluid from a lower depth to a point in the tubing where a plunger can effectively lift it to surface. A standard stage tool design is comprised of a bottom hole bumper spring located at the end of the tubing string, a plunger, a stage tool assembly, and another plunger above the stage tool assembly. The stage tool assembly has a dual acting seal assembly pack off to provide a seal to the tubing string and a standing valve to prevent slippage back through the spring.
The Upper stage tool assembly absorbs the shock of the falling upper plunger and also contains the standing valve to prevent fluid slippage down hole.