PTO clutch/brakes are primarily made up of three major sub-assemblies.
Field/rotor assembly This is the coil, backing plate and rotor. The coil provides the magnetic flux that allows the clutch to pull in. The rotor provides the input rotation and is mounted on the input shaft.
Pulley/armature assembly This includes the armature disk, springs, hub and pulley. This is the output of the clutch. In some instances, a mounting flange is used instead of a pulley.
Brake assembly This includes the brake shroud, adjustment nuts and springs. By controlling the force against this brake shroud, the stopping time in the application can be controlled.
Engagement of the armature to the rotor is caused by the magnetic attraction between the rotor and the armature. The magnetic flux is transferred from the field into the rotor and then into the armature. The slots in the rotor and the armature are called banana slots. These slots allow the flux to contact the rotor and the armature in more than just two places. (A normal magnet only has a north and a south point of attraction.) By making multiple points of flux connection, the torque can be increased in this type of clutch. When the power is cut, the armature is released and pulled back against the brake shroud via the leaf springs. As the armature drags against the brake shroud, the blade is helped to slow to meet the manufacturer's stop time requirements. The shroud is attached to the backing plate via the studs. The backing plate is connected to a portion of the machine so that it can withstand the mechanical braking force. Depending upon the inertia of the system, the leaf springs can be adjusted in thickness to create a stronger torque to help meet the stop time requirements. This unit also has the advantage of being able to be adjusted as it wears. This can be a considerable cost advantage to the end user over the life of the clutch/brake.