Brake counters are used to initiate greasing cycles in a centralized lubrication system on equipment that lacks a continuous supply of electrical current. The counter relies on air pulses through a compressed air line to mechanically open and close an air valve ahead of the pneumatically-activated lubricator. Brake counters are normally installed in on-road trailers and semi-trailers where electronic timers cannot be used.
The brake counter receives pulses from the signal air line before the relay valve (trailer reaction valve). Each time the vehicle brakes, the brake counter piston strokes and in turn rotates the operating cam. The number of brake applications is counted until a preset number has been reached. The operating cam then opens the air valve allowing compressed air to activate the lubricator.
Air from the lubricator is vented following another preset number of brake applications.