The FS220CI ('C' Strength) Series of spring applied brakes require hydraulic pressure for disc release. Braking force is provided by a stack (or stacks) of Belleville spring washers, capable of storing enormous force. When presurized the force moves the piston(s) to compress the spring washer stack(s), releasing the disc. The FS220CI Series features replaceable, high-grade friction material, cast ductile iron construction and Zinc plated grade 8 bolts. Buna-N seals are standard. Maximum hydraulic pressure rating is 2000 PSI Non Shock. Minimum hydraulic pressure to release brake is 1500 PSI.