The U-Cup RU3 is used as a rod seal for heavy-duty conditions in mobile and industrial hydraulics. It is installed with a fixed seat at its outer diameter. The rear dynamic sealing lip improves the leakage behavior and, at the same time, prevents the entry of contaminants from the atmosphere side. Compared with the RU2, the shorter inner lip is more flexible and can adapt better to the operating conditions and deflections of the piston rod.