Pressurizing cap and method for using same

A method of pressurizing a container for racket-sport balls comprising the following steps:

• a) providing a container containing at least one racket-sport ball, said container comprising a sidewall that comprises an open end and an annular lip extending radially outwardly from the open end;
• b) providing a pressurizing cap comprising a sleeve comprising an inwardly facing sealing surface formed of an elastomeric material which forms a seal against the lip, and end panel secured to one end of the sleeve, said cap comprising an annular recess adjacent the sealing surface, said recess receiving the lip to hold the cap releasably on the container, the volume of the cap being no less than about one half the free volume of the container;
• c) placing the cap on the container with the sealing surface of the cap in sealing engagement with the lip;
• and
• d) pushing the cap along a stroke toward the container until the recess receives the lip to hold the cap in place, said lip sliding along and sealing against the elastomeric sealing surface of the cap through the stroke such that movement of the cap pressurizes the container around the racket-sport balls.