Hydraulic

Hydraulic describes a method of brake actuation that uses a pressurized, incompressible fluid (typically oil) to transmit and amplify force, based on Pascal’s principle. In industrial brakes, this method is employed in two fundamentally different ways, defining the brake’s operational purpose:

1. Hydraulic-Applied (Active Braking): In this configuration, the brake is disengaged by default. To apply the brake, a hydraulic power unit (HPU) or a manual pump generates fluid pressure, which is transmitted through hoses to a caliper or actuator. This pressure drives pistons that clamp friction pads onto a disc, creating braking torque. This system is used for dynamic or service braking, where controlled stopping is required by an active command from an operator or control system. It is common on large wind turbines, rolling mills, and mobile equipment.
2. Hydraulic-Released (Fail-Safe Braking): This is the most common configuration for safety-critical holding applications. The brake is spring-applied by default, with powerful mechanical springs providing the clamping force. The hydraulic system’s role is to release the brake. The HPU generates pressure to work against the springs, retracting the pistons and allowing the shaft to rotate. If hydraulic pressure is lost for any reason (e.g., power failure to the HPU, a broken hose), the spring force is unopposed and instantly engages the brake. This fail-safe principle is essential for holding brakes on mine hoists, large inclined conveyors, and drawworks. A self-contained electro-hydraulic thruster is a specific, integrated device that perfectly embodies this principle for drum and disc brakes.

The primary advantages of hydraulic actuation are its ability to generate extremely high forces in a compact space and to transmit that force reliably over distances, making it the preferred solution for the most demanding high-torque industrial braking applications.