API Standard PS40 Hydraulic Disc Brake for Drilling Rig Brake System JC40 Disc Brake Actuator consists of the brake disc, working calipers (normally open calipers), safety calipers (normally closed calipers), and caliper frame. It is divided into service brake and safety parking brake. 1. Brake Disc Installation position: Both sides of the JC40 drum, with a single-side wear limit of 5mm.Structure: Air-cooled structure, friction braking reference surface. 2. Working Calipers