Braking systems take advantage of the textbook offerings given by hydraulics — power, controllability and safety. Hydraulic brakes are fairly simple on the cover, requiring a hydraulic pump and a brake actuator. Vehicle braking systems may get by with only what are essentially two cylinders, one at the pump and the other at the brake. Depressing the brake pedal transfers force from the operator to the brake caliper actuator with force multiplication equal to the ratio of brake caliper area to the master cylinder area. For example, if the square area of the brake caliper cylinder is 3 in.² and the master cylinder is 0.5 in.², then the force multiplication is six times the effort of the operator’s leg.
Hydraulic brake applications go above and beyond the typical brakes of mobile machinery. Although it should be noted that mobile hydraulic machines employ braking technology so much more advanced than the above description, brakes are used in many more machines than those with wheels or tracks. Any machine with a load to be controlled safely may take advantage of a hydraulic braking system.
One of the standout applications is the braking systems for mine hoists. These advanced systems are powerful and sophisticated, which you would expect from machinery meant to keep both persons and equipment safe for long journeys up and down a mine. However, the mining industry puts safety ahead of all else, especially in underground mines, and this philosophy is evident with the braking systems used to hold the hoist cable drums.
When complete machine failure occurs, the brake actuators must default to the closed position to hold the drum stationary in the absence of power. Powerful springs inside large brake calipers maintain a braking force to hold the large drums and their subsequent loads stationary. Hydraulic pressure releases the brake, and at any time the hydraulic system fails, the brakes will automatically apply to slow and hold the hoist.
The force generated by industrial braking systems, such as those used in anything from amusement park rides to shipyard gantry cranes, is based on your standard area/pressure/force triangle. However, rather than a master cylinder and human-created force, a hydraulic power unit provides the power and control to braking systems. A full complement of redundant valves, pressure switches and accumulators intelligently plumbed offers precise control over the braking system to ensure they never fail, even in the absence of pump power.
Not all brake applications are spring-applied, operating more like the advanced-control older brother to vehicle brake systems. It’s reasonable to expect brake force up to 1000 kN (225,000 lb), which holds a load equal to that force plus the radius of the brake disc with a whole lot of safety factor involved. Smaller hydraulic brakes get by with compact hydraulic power units, while more sophisticated systems operate more in line with what’s done in the mining industry. From mountain bikes to skyscraper elevators, hydraulic brakes exemplify what makes hydraulic technology so durable.
Filed Under: Engineering Basics, Mobile Hydraulic Tips