An air brake is build with two ducts and two air valves. If one valve is open, the other is automaticly closed. The pressure of the blower will do this automaticly, there is no need for an external control.

The valves are placed in such a way that when a carrier is sucked to the blower, the air will go through the bypass pipe.
The carrier will pass the tube switch, which shall switch off the blower. The carrier will be stopped by the air buffer in the tube. The rest of the air will flow through the bypass tube, and has no longer affect to the carrier.
By lengthening the bypass the inhibition of the carrier will be softer.

How does an air break work? Here an explanation »