[135] Delockable non-return valve
The 4/2-way valve is
actuated, the hydraulic fluid passes through the non-return valve
against the force of the return spring and the piston rod
advances. When the 4/2-way valve is reset, the outlet on the
piston side is closed by the non-return valve, and the cylinder
remains advanced. The 3/2-way valve is now actuated, the pilot
piston is reversed and the outlet flow released; the piston rod
begins to retract. During the return stroke, the 3/2-way valve is
brought temporarily into its normal position. This causes the
outlet to be closed again, and the piston rod and load remain in
their current position. When the 3/2-way valve is actuated again,
the piston rod travels to its retracted end position.