Abstract: A reversible air seal construction for a carrier used in a pneumatic tube system, for use on a carrier of the type having a pair of air seal rings surrounding the carrier body spaced from each other and from the ends of the carrier. The reversibility is accomplished by means of spacers that may be positioned either outside of or between the two air seal rings so that two distinct spacings may be accomplished between the two air seal rings. The positioning of the spacer relative to the air seal ring is facilitated by means of an end adapter unit carrying a closure construction and arrangement for an open end of the tubular material-conveying carrier for the pneumatic tube system. The adapter unit houses a pivot mechanism including a cam member integrally molded with and forming circumferential axis of rotation for a disclike end cap which forms the closure for the tubular material-conveying carrier.