Contact devices on interior of tubes for detecting passage of carriers

Full Title

Conveying articles through pipes or tubes by fluid flow or pressure; Conveying articles over a flat surface, e.g. the base of a trough, by jets located in the surface > Conveying the articles in carriers having a cross-section approximating that of the pipe or tube; Tube mail systems > Other devices for indicating or controlling movements of carriers, e.g. for supervising individual tube sections, for counting carriers, for reporting jams or other operating difficulties > Contact devices on interior of tubes for detecting passage of carriers