... of USH piston rod seal, piston rod u cup seal,hydraulic piston rod seal,UPI seal,ect Hydraulic Seals - Introduction 1) Hydraulic seals describe ... moving. 7) However, a reciprocating application will need two hydraulic seals (double acting), one for each of the directions ... 8) The life of hydraulic seals is dependent on many factors including the maximum operating speed, maximum operating temperature, ...