Hydraulic Support Jack The work support jack is especially designed to support large work pieces and prevent distortion during machining operation. Its piston is extended fully from spring pressure of 14 pounds when not under load. Either the weight of the work piece or the clamping action sets the piston height. With hydraulic pressure applied, these jacks support a force up to 5,000 pounds. Support force is easily varied by controlling hydraulic pressure. This work support jack automatically adjusts to difference in material thicknesses.