AIR OVER HYDRAULIC SERVO (DIAPHRAGM); TYPE 16; STROKE (MM):

Brake chambers are used on truck and trailer air brake systems, located at
each wheel, where compressed air is converted into a mechanical force used
to apply the brakes and stop the vehicle.

They are also designed to apply the the brakes automatically in the event that
there is a loss of system air pressure. This happens because the air
pressure holding back the heavy parking/emergency spring dissipates
allowing the spring to extend the pushrod which in turn applies the brake.

There are designs to cover Cam Brake and also Disc Brake applications,
along with different sizes and strokes. the most common strokes are
standard and long stroke.