Jack is a small lifting height easiest lifting equipment. It has mechanical and hydraulic two. Mechanical jacks another rack and screw type two, because from the weight of small, laborious operation, generally used only for mechanical maintenance work in the process of building bridges not applicable. Hydraulic jacks compact, smooth, self-locking effect, it is widely used. The disadvantage is the limited lifting height, lifting speed is slow. Also known as hydraulic jack hydraulic jack is a plunger or cylinder used as rigid top piece of the jack. Simple lifting equipment lifting mechanism generally available only for lifting heavy objects. Simple structure, light weight, easy to carry, easy to move. By a manual or electric hydraulic jack hydraulic pump driven by a hydraulic drive system, with the cylinder or piston as the top piece. Hydraulic jacks can be divided into the overall style and split. Integral pump and hydraulic cylinder into one; separate pump and hydraulic cylinder separation, in the middle associated with high-pressure hoses. Hydraulic jacks compact, smooth lifting heavy objects, from the weight of the maximum of 1,000 tons, travel one meter, high transmission efficiency, it is used widely; but easy to leak, not long-term support heavy loads. Such as long-term support should be chosen self-locking jacks, screw jacks and hydraulic jacks to further reduce or increase the height profile jacking distance, can be made multi-stage telescopic. In addition to the basic types of hydraulic jacks, but according to the same principle can be converted into a sliding template jack, hydraulic lifting platform, tension, etc., for the construction of various special occasions. Hydraulic jacks are divided into general and special categories. Universal hydraulic jacks for lifting height small variety of lifting operations. It consists of: oil chamber, oil pump, oil chamber, piston, pump, valve and other major components. Universal hydraulic jacks work, as long as pull back and forth to shake, making manual pump to keep the fuel tank pressure oil, because oil tanks continue to increase, forcing the piston and the piston moves upward together with the above weights. Open the return valve, high pressure oil tanks will flow back into the oil chamber, so heavy with the piston will fall together. Special hydraulic jacks so dedicated tensioning equipment, in the production of prestressed concrete members when tension is applied on the prestressing steel. Special hydraulic jack, mostly double-acting. Commonly used feedthrough and a cone anchor two. Universal hydraulic jacks include: an electric hydraulic jack: pressure electric jack, electric hydraulic one thousand two large tonnage, manual hydraulic jack: thin jack, manual split jack 3, from the top jaw hydraulic machine works: hydraulic jacks are based principle Pascal principle, namely: Liquid pressure is the same everywhere, so that in a balanced system, the relatively small pressure applied above the piston is relatively small, and a large pressure exerted on the piston is relatively large, so to maintain liquid stationary. So passing through the liquid, you can get different different pressures on the client, so that you can achieve the purpose of a transformation. Our common to the hydraulic jack is the use of this principle to achieve force transfer.