A weld cylinder having a single piston arrangement is provided. The
cylinder has a movable retract piston assembly with the piston arranged
within the retract piston assembly. The piston supports a rod that is
movable between home, intermediate, work, and advanced work positions.
The rod moves rapidly from the home position to the intermediate position
however, the rod moves more slowly from the intermediate position to the
work position to reduce the impact force a cushion valve supported by the
retract piston assembly and a cushion trip valve supported by a front
block cooperate to increase the rate at which the rod moves from the work
position to the advanced position so that weld force increases rapidly to
minimize increases in cycle time. With both the cushion valve and cushion
trip valve move from closed positions to open positions, the rate of
fluid flow through the retract piston assembly to increase the rate at
which the piston moves within the retract piston assembly.