Unic URW295CR, Maintenance Manual

Page: 71 / 125

14.2 Function and Working of Cushion Seal
For the purpose of absorbing a piston shock to the stroke end, the 4-section boom and 6-section boom have the
cushion seal in the part of piston of the telescoping cylinder (2), while the 5-section boom has the cushion seal in its
telescoping cylinder of (2) and (3).
(1) Flow of Pressure Oil When Retracting
Cushion mechanism of the telescoping cylinder (2) for 4-section boom and that of the telescoping cylinder (3) for 5-
section and 6-section booms.
In the retracting process, before the piston gets in the plunger, the pressure oil in the chamber A flows through the
central part of the piston as shown in the illustration and returns to the tank without being squeezed.
At the same time when the piston gets in the plunger, the chamber A is closed with the cushion seal .
As a result, the pressure oil in the chamber A is forced to return only through a drilled 1 hole in the state of being
squeezed. Thus the piston shock at the stroke end is absorbed.
（１４−８）