Pneumatic Brake and Clutch Assemblies Information

Pneumatic brake and clutch assemblies are equipment drive components that consist of pneumatic brakes for slowing or stopping shafts and pneumatic clutches for connecting or disconnecting shafts. Pneumatic brake and clutch assemblies transmit force from one point to another point using compressed air or other gases. Engaging the clutch transfers power from an engine to devices such as a transmission and drive wheels. Disengaging the clutch stops the power transfer, but allows the engine to continue turning. Braking slows or stops the movement of the coupled shafts. Because they provide reduced breaking distances, pneumatic brake and clutch assemblies are often used in large motorized vehicles such as buses.

Clutch Specifications

Clutch specifications for pneumatic brake and clutch assemblies include torque rating, power, rotational speed, and maximum pressure. Spring-return clutches require power to engage. Spring-actuated clutches require power to disengage. A variety of engagement methods are available. Non-contact clutches uses methods such as magnetic fields and eddy currents. Friction clutches generate friction between contact surfaces. Wrap spring clutches transmit torque from the input to the output through a wrapped spring that uncoils to disengage the clutch. Hydraulic clutches with teeth engage only during stops or at slow speeds. Oil shear clutches achieve drive engagement through the viscous shear of transmission fluid between the clutch plates. Other plate-based clutches control torque with compression springs. Sprags, steel wheels that tip in one direction to wedge between inner and outer races, are clutches that can often transmit more torque than other slip or overrunning devices. Ball detent clutches feature a slip mechanism in which, upon overload, seated balls are dislodged and overcome springs or air pressure engagement. Similarly, pawl clutches overcome spring or air pressure engagement and rotate out of their detent. With roller detent clutches, rollers that are held in place by springs wedge between the inner and outer races to engage the clutch. 

Brake Specifications

Brake specifications for pneumatic brake and clutch assemblies include torque rating, power, speed, and maximum pressure. A variety of brake engagement methods are available, including friction, wrap spring, oil shear, toothed surface, and non-contact methods. Band brakes, the simplest brake configuration, have a metal band lined with heat and wear resistant friction material. Drum brakes, which are commonly used on automobile rear wheels, work when shoes press against a spinning surface called a drum. Disc breaks are constructed of brake pads, a caliper, and a rotor. During operation, the brake pads are squeezed against the rotor. Cone brakes are made with a cup and a cone, which is lined with heat and wear resistant material.  During actuation, the cone is pressed against the mating cup surface.


Selecting pneumatic brake and clutch assemblies requires an analysis of measurements and mounting configurations. Important measurements include diameter, the cross-sectional width of the assembly; length, the dimension along the axis of rotation; and weight. Shaft configurations can be in-line along the axis of the load, parallel but offset from the axis, or perpendicular (right angle) to the axis. Drive and load connections for hydraulic brake and clutch assemblies can use shafts that attach to bores or flanges. With some drive shafts that attach to a bore, the output is a drive component such as a pulley, gear, or sprocket. Often, these types of hydraulic brake and clutch assemblies are designed to accept several different drive components.