Generally, pneumatic tube transport systems are used to transport or convey materials between discrete points or stations. Many products, documents, and other items may be placed in a carrier which is positionable within a number of substantially hermetically sealed tubes of the pneumatic tube transport system. The carrier may then be propelled through the tube by creating a zone of relatively higher pressure behind the carrier than in front of the carrier. This pressure differential may be accomplished by creating a vacuum or zone of negative pressure in front of the carrier or by creating a zone of positive pressure behind the carrier.
Accelerator rings or seal bands have been provided on carriers to prevent excessive mass transfer of air between the front of the carrier and the rear of the carrier. Such seal bands thus create differential pressure between the front and rear portions of a carrier, which provides the force necessary to propel the carrier through the pneumatic tube system. Such accelerator rings or seal bands typically engage the inner surface of the transport tube to support the carrier body and to inhibit air flow between the front and rear portions of the carrier. In this regard, it is important to minimize friction between the seal bands and the inner wall of the tube to enable the carrier to move through the tube without requiring high differential pressures between the front and rear of the carrier. Such a desire for minimizing friction must also be balanced with providing an adequate seal to inhibit mass transfer of air between the front and the rear of the carriers. In this regard, a "loose" seal band which does not provide a good seal may travel freely, but may also perform erratically for varying payloads within the carrier. On the other hand, while a "tight" seal will inhibit mass transfer of air between the front and rear portions of the carrier, friction forces between the seal band and tube may be high, thus requiring increased system pressures of the transport tube. Such tight seals may also generate an excessive amount of debris from wear on the seal bands, which can degrade performance of the tube transport system and/or components, such as blowers and optical sensors therein.