Double Acting Telescopic Cylinder
Extending
To Extend:
High pressure oil is directed by the control valve into extend port (A). The oil passes through an inner (transfer) tube in the smallest plunger to the base of the cylinder. The pressure acts on the effective area of the largest piston (F) and extends all stages to the first plunger stop.
The next stage then begins to extend. The effective area of each stage is figured from the inside diameter of the next largest stage. Each stage extends in its turn to the plunger stop.
Oil trapped between the plungers escapes through internal port holes (C) in each plunger and returns to tank through retract port (B).
To Retract:
High pressure oil is directed by the control valve into retract port (B). The pressure is applied to the effective area of the smallest plunger (D) which retracts first. Each stage from the smallest to the largest retracts in its turn. The effective area for retracting each stage is the area of the plunger (D).
Oil inside the cylinder is forced out of extend port (A). Because of the area differential between the retract side and extend side the flow into retract port (B) must be multiplied by this differential to determine the flow out of port. It may be necessary to install a dump-to-tank valve to speed up the retracting cycle.