Both cylinder 1 and piston 2 of the jack can travel. First piston 2 is placed on a support (Fig. a) and fluid is admitted into the upper end of cylinder 1, which is raised together with the load. When the cylinder reaches its extreme upper position, supporting beams of equal height are placed under the feet of the cylinder and fluid is admitted into the lower end of the cylinder. This retracts piston 2 into the cylinder and, when it reaches its extreme upper position, supporting beams are placed under the piston, repeating the process as required.
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