Types of Jack two
                                                                               Types of Jack (2)
                                        
Divided by structural features, it can be divided into rack jacks, screw (mechanical) jacks and hydraulic (hydraulic) jacks balloon pneumatic jack (pneumatic) four kinds.

1. A rack jacks: top rack driven by human heavy lifting by levers and gears. Weight is generally not more than 20 tons, long-term support heavy loads, mainly used in operating conditions inconvenient place or need to use the lower part of the heavy lifting claws occasions, such as railway track from operations.

2, screw jack: the human through the screw vice transmission, screw or nut sleeve cited as the top piece. Ordinary screw jack on the role of self-locking thread support weight, simple structure, but the low transmission efficiency, return slowly. Since fall threaded screw jack without self-locking effect, but equipped with brakes. Relax brakes, heavy to own rapid decline, shorten turnaround times, but this jack structure is more complex. Jackscrew long-term support heavy loads, maximum weight reached 100 tons, wider application. After loading on the lower level of the screw, but also to make the weight a small distance traversed.

3. hydraulic jacks: by manual or power-driven hydraulic pumps, hydraulic transmission system, with the cylinder or piston as the top lift pieces. Hydraulic jacks can be divided into integral and separate. Integral pump and hydraulic cylinder into one; separate pumps and hydraulic cylinders separated in the middle by a high pressure hose linked. Compact hydraulic jacks structure, smooth lifting heavy objects, from the maximum weight of 1,000 tons, travel one meter, higher transmission efficiency, therefore wider application; 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 the appearance or increase the height of jacking distance, can be made into a 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 jacks, hydraulic lifts, tension, etc., used in the construction of various special occasions.

4. balloon-type pneumatic jack.