Pneumatic Brakes Information

Pneumatic brakesPneumatic brakes, or air brakes or compressed air brakes, use compressed air generated by a compressor and stored in a reservoir. When the operator actuates the lever or pedal, a valve allows the compressed air to flow to a piston that engages the brake. A spring disengages the brake when the pressure is released. Different types of brakes use different methods to create the braking action that removes kinetic energy from the moving system or vehicle. Air brakes/pneumatic brakes are the primary method of speed reduction for trucks, buses, trailers, and trains as they are a very efficient way of stopping large and heavy vehicles.

Specifications

Performance specifications to consider while selecting a pneumatic brake include but are not limited to:

  • Torque Rating—The maximum torque rating for the brake should equal or exceed the application's requirement.
  • Power—The maximum power rating for the brake. 
  • Speed—The maximum rotary speed rating. This specification applies only to rotary brakes. 
  • Maximum Pressure—The maximum pressure for a pneumatic brake. 
  • Shaft Configuration—Brake may be mounted in-line, parallel, or right angle.

Types

Energy can be removed by a brake in several ways. Here are some different approaches to braking:

  • Band—Band brakes are the simplest type of brake. They have a metal band lined with heat- and wear-resistant friction material.
  • Drum—Drum brakes press shoes against a spinning surface. They are often used on automobile rear wheels. 
  • Disc—Disc brakes have brake pads, a caliper, and a rotor. During operation, the brake pads are squeezed against the rotor. Disc brakes have good heat dissipation properties. 
  • Cone—Cone brakes consist of a cup and a cone, which is lined with a heat- and wear-resistant friction material. During actuation, the cone is pressed against the mating cup surface. Cone brakes are not commonly used.

Several engagement methods are available for pneumatic brakes, including:

  • Noncontact—Braking action is achieved through a non-contact technology such as a magnetic field, eddy currents, etc. 
  • Friction—Friction between contact surfaces transmits power. This is the most common type of brake.
  • Toothed—Toothed contact surfaces transmit power without slipping or heat generation. Teeth are engaged only when stopped or running at a slow speed (< 20 rpm).
  • Wrap Spring—A coiled spring wraps downward onto the rotating element. The brake is disengaged when the spring is uncoiled via a control tang at its end.
  • Oil Shear—Braking action is engaged via the viscous action of the shearing of transmission fluid. 

Features

There are two brake operation methods for pneumatic brakes: spring actuation (engage) and spring return (disengage):

Spring Actuation/Engage—The spring engages during operation and requires power to disengage. Spring-actuated brakes are also called power-off brakes, fail-safe brakes, and safety brakes. 

Spring Return/Disengage—The brakes need power to engage. A spring is used to disengage the brake. Spring-return brakes are also called power-on brakes and non-fail-safe brakes. 

Though pneumatic brakes are most familiar to us as they are used in trucks and trains, they are handy to use in factory environments where compressed air is readily available. Brakes that are integrated into machine tools, conveyors, and other equipment can safely slow their operating components without taking on any additional weight that may be associated with a hydraulic system. Air brake equipment is much more reliable than hydraulic brakes. An additional advantage of pneumatic brakes is that the working fluid supply is unlimited and will never run out. Small leaks will not lead to brake failure.

Related Information

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Image credit:

Panoha / CC BY-SA 3.0