Pneumatic cylinder of a pneumatic lever-lift chair, and its assembly process

A pneumatic cylinder for use in a pneumatic lever-lift chair, and its assembly process, the pneumatic cylinder comprising a cylindrical casing having a top opening, a bottom opening, and an inward bottom flange projecting into said bottom opening, a stop plate mounted within said cylindrical casing and fixedly secured to the inward bottom flange of said cylindrical casing, and an inner barrel mounted inside said cylindrical casing, wherein:

• said stop plate has a plurality of raised portions at a bottom side respectively welded to the inward bottom flange of said cylindrical casing;
• said cylindrical casing comprises a dent formed around the periphery and stopped above said stop plate, and a plurality of inside annular flanges vertically spaced around the periphery above said dent;
• said inner barrel comprises a hollow cylindrical body, an outward top flange stopped above the top opening of said cylindrical casing, a plurality of longitudinal ribs equiangularly spaced around an upper part of said cylindrical body on the outside, a plurality of outside annular grooves vertically spaced around a lower part of said cylindrical body on the outside and defining a plurality of vertically spaced convex portion between each two adjacent outside annular grooves, a bottom flange, and a plurality of longitudinal exhaust holes through the outward top flange and bottom flange of said inner barrel at locations corresponding to said longitudinal ribs, the convex portions and bottom flange of said inner barrel having a respective circularly chamfered bottom edge, the annular grooves of said inner barrel being forced into engagement with the inside annular flanges of said cylindrical casing respectively.