<P> In 1838 William Joseph Curtis filed a British patent for a hydraulic jack . </P> <P> In 1851, inventor Richard Dudgeon was granted a patent for a "portable hydraulic press" - the hydraulic jack, a jack which proved to be vastly superior to the screw jacks in use at the time . </P> <P> Hydraulic jacks are typically used for shop work, rather than as an emergency jack to be carried with the vehicle . Use of jacks not designed for a specific vehicle requires more than the usual care in selecting ground conditions, the jacking point on a vehicle, and to ensure stability when the jack is extended . Hydraulic jacks are often used to lift elevators in low and medium rise buildings . </P> <P> A hydraulic jack uses a liquid, which is incompressible, that is forced into a cylinder by a pump plunger . Oil is used since it is self lubricating and stable . When the plunger pulls back, it draws oil out of the reservoir through a suction check valve into the pump chamber . When the plunger moves forward, it pushes the oil through a discharge check valve into the cylinder . The suction valve ball is within the chamber and opens with each draw of the plunger . The discharge valve ball is outside the chamber and opens when the oil is pushed into the cylinder . At this point the suction ball within the chamber is forced shut and oil pressure builds in the cylinder . </P>

Who is expected to use the hydraulic jack
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