Hydraulic Brakes Information
Hydraulic brakes use a fluid to transfer pressure and actuate the braking mechanism. Product types differ in terms of engagement, operation, and performance. Performance specifications include power, speed, torque rating, and maximum pressure. As a rule, the maximum torque rating for the brake should equal or exceed the application’s requirement.
Types of Hydraulic Brakes
The GlobalSpec SpecSearch Database contains information on the four major categories of hydraulic brakes: drum, disc, band, and cone.
- Drum brakes create friction by pressing the brake shoes against a spinning surface. They are mostly applied to the rear wheels to avoid significant heat buildup. They often have less drag than disc brakes when adjusted correctly.
- 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 and tend to be much more predictable than drum brakes at peak brake force.
- Band brakes are characterized by a metal band that’s lined with heat-resistant and wear-resistant material. These brakes are simple, compact, rugged, and can generate high force with a small input force, but are prone to grabbing, chatter, and loss of force when hot.
- Cone brakes are like band brakes in that they feature heat- and wear-resistant friction material, but are far less common. During actuation, the cone is pressed against the mating cup surface.
Brake Engagement Methods
Most hydraulic brakes use non-contact, friction, toothed, wrap spring, or oil shear engagement techniques. With non-contact products, braking action is achieved via magnetic fields or eddy currents. By contrast, friction brakes transmit power via friction between contact surfaces. Toothed contact surfaces transmit power with slipping or heat generation. The teeth are engaged only when the equipment is stopped or operating at low speeds. With wrap spring brakes, 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. Brake products may also achieve braking action via the viscous action of the shearing of transmission fluid (oil shear).
Brake Operation Methods
There are two brake operation methods for hydraulic brakes: spring actuation (engage) and spring return (disengage). With spring actuation, the spring engages during operation and requires power to disengage. Spring-actuated brakes are also called power-off, fail-safe, and safety brakes. With spring return products, the hydraulic brakes need power to engage and a spring to disengage. Spring-return brakes are also called power-on and non-fail-safe brakes.