... usually need to be higher friction seals than pneumatic seals but often operate under lower operating ... Rotary applications need only one hydraulic seal (single acting) because it can seal in the one ... reciprocating application will need two hydraulic seals (double acting), one for each of the directions.8) ... , WR, BRT, RYT, DB, TAY, VB, TC Pneumatic Cylinder appropriative seal:PGY, PNY, GLY, PSD, PDU, ...