The screw jack, also called the mechanical jack, is driven by a manpower through a screw pair, and a screw or nut sleeve is utilized as a jacking member. The ordinary screw jack supports the fat by the thread self-locking function, and the structure is simple, however the transmission performance can be low and the return stroke is Torque Arm gradual. The thread of the self-propelled screw jack does not have any self-locking action and is equipped with a brake. When the brake can be released, the weight could be quickly lowered by itself and the return time can be shortened, but the structure of the jack is certainly complicated. The screw jack can support heavy items for a long time, and the utmost lifting capacity has reached 100 tons, which is trusted. After the horizontal screw is definitely mounted on the low part, the weight can be traversed at a small distance.
Principle of use:
The mechanical jack is among the types of manual lifting tools. Its compact framework makes reasonable use of the rocking of the rocker to rotate the pinion. It really is operated by a set of conical gears to drive 
the screw to rotate and force the lifting sleeve so that the pounds rises or decline.
Instructions:
1. Before use, it’s important to check if the jack is normal, whether the components are flexible, put lubricating oil, and correctly estimate the fat of the heavy object. Make use of a jack of suitable tonnage and avoid overloading.
2. Adjust the method of supporting the teeth on the rocker. First of all, turn the rocker straight in the clockwise path by hand to help make the lifting sleeve quickly ascend the very best weight.
3. Insert the handle in to the rocker hole, move the handle along, and the weight will rise. When the reddish colored warning line appears on the lifting sleeve, the handle ought to be stopped instantly. If you want to lower one’s teeth in the opposite direction, the pounds will start to fall.
Precautions:
1. Generally keep the top of machine clean, examine the internal structure regularly, make the pinion in the rocker versatile and dependable, and lift the lifting sleeve openly.
2. The friction surface between the lifting sleeve and the casing must be oiled anytime. Other essential oil filling holes should be lubricated regularly.
3. To be able to consider the safety in use, avoid overloading, use illness, it is not appropriate to make use of multiple units to avoid danger.