Mode of Operation If the belt moves off its track, the tracking valve sensor paddle activates the tracking valve. The tracking valve directs compressed air to the appropriate double acting air bellows (left or right side). The air inflates one set of bellows causing the bellows to expand pushing the carriage and the tracking roller in the direction of the force. This action causes the belt to move back on track. Please see data sheet detailing our 316 Stainless Steel Tracking Valve (optional extra) (link)