The P series design is similar to the S series, which is designed for wet operation. The difference between the two models occurs in the bearings. P Series bearings are pre-lubricated and sealed and do not require external lubrication.
Torque ratings are based on the P Series disc pack operating in dry conditions thus requiring lower actuation pressure to achieve relatively high rates of torque.
Operation: Pressurizing the cylinder with fluid or air forces the piston to clamp and lock the friction and separator discs, and release springs. Torque is transferred through the clutch to the drive cup. When pressure is removed, the release springs separate the separator and friction discs and maintain a running clearance between separator and friction disc surfaces. Torque ratings are based on dry operation, thus requiring low actuation pressure to achieve high rates of torque.
Lubrication: P Series clutches and brakes are designed primarily for dry operation. Bearings are greased and sealed and do not require external lubrication.