A screw jack is a form of jack that is primarily operated by using a lead screw. It is used if heavy loads that can not be handled by human hands need to be lifted. Heavy vehicles and foundations of houses are the usual loads where screw jacks are used. The screw jack typically consists of a base that is quite heavy and can support an enormous amount of weight, a screw shaft that extends vertically from the base, and a lever which turns the screw.
When the lever is turned or moved the screw shaft will move upwards or downwards depending on the movement of the lever. The shaft will then be able to lift what is directly above it. The weight that the shaft can support can be very great. One of the greatest advantage of using a screw jack over other forms of jacks is that they are self locking which means that the moment that the lever is stopped in its movement the shaft will remain in place no matter how heavy the load above it is. This is something that is lacking in other forms of jacks. Hydraulic ones for example are in danger of lowering down under the pressure of its load once the counter pressure is removed.
There are two types of screw jacks that are commonly used today, these are the scissor screw jacks and worm gear screw jacks. Scissor screw jacks as the name would suggest have an appearance that is similar to a large scissor. It is mainly used in lifting cars. The bottom part of the jack is on the ground, while the top part fits under the vehicle. A screw is then inserted and is then turned which will cause the contraption to rise, raising the vehicle along with it. This form of screw jack can only be used for lifting smaller or lighter weights. The worm gear jack on the other hand can be used for lifting greater weights. This jack is just like an oversized screw. At the top is a platform for raising the load, while ratcheting motion of the lever is used to turn the screw.
If you are looking for some good screw jacks to buy for your own use, here are 3 of the best that you can get today:
JET SJ-5T 5-Ton Series Screw Jack
This is a very good mechanical jack that can be used for any type of lifting. It can hold up heavy loads for as long as you want it to and will not creep down slowly at all. It has a bell shaped base that can add to the support that it provides. It is equipped with a handle that makes it easy to carry and place. You can buy this screw jack for about $36. Also available up to 25 ton.
MIT Trailer Screw Jack
This is a 2000 pound capacity screw jack that can be used to raise the front of your trailer for an easy time hitching and unhitching it. Made from high quality steel that is given a weather resistant finish you can be sure that this jack will stand the test of time. You can buy this 1 ton screw jack for about $60.
Simplex Mechanical Screw Jack
This screw jack can be bought n 12 ton or 24 ton variations. It has a body made from iron and can hold up loads for as long as you need it to. You can get the 12 ton version for about $170. The only problem with these screw jacks is that they sell the lever bars separately.