The name “u-cup” is derived from its shape. U-cups seal on both outside and inside diameters. The small gland space they require make them a popular sealing solution. Typically, u-cups are employed for low pressure, low speed environments, both for hydraulic and pneumatic cylinders. Flared, flexible lips secure the seal, coming in contact with the rod or cylinder wall. To minimize friction, there is a clearance at the heel. The seal’s performance increases as internal pressure increases against the lips’ inner surface. For dynamic contact surfaces, the seal should have a finish of 8 – 16 RMS.