What Is a Jack?
A jack is a tool for lifting an object.
A jack can be operated in three different ways. Mechanical jacks rotate screws or gears, liquid-actuated jacks use hydraulic pressure, and air-actuated jacks use a compressor or other device to feed air into the jack. Typical mechanical jacks are ratchet screw jacks, screw jacks with bearings, and rack-driven jacks. Hydraulic jacks are mainly used for liquid-actuated jacks.
A jack with various load capacities (maximum load) is also available. These include small jacks with a load capacity of about 3kg for tabletop hobbyists and experimenters, jacks with a load capacity of 2-5 tons for use in automobile repair and construction sites, and lifts (jack) with a load capacity of 5 tons or more for use in factory installations.
How to Use Jacks
This section describes how to use jacks with a load capacity of 2 to 5 tons, which are used for many types of work, and explains the precautions to be taken when using jacks.
- Checking the installation point (contact point) of the object to be lifted
Determine the jack’s installation point on the object to be lifted. Some objects, such as automobiles, have predetermined installation points. If not, determine the installation point in consideration of the work area and load balance. Select a hard place for the installation point that can withstand the lifting force. - Installation of jacks
Select a level, hard, stable location for the installation surface. - Jacking up the object
Operate the jack to raise the object slowly. When raising the object, check the following points: The condition of the installation surface (whether it is stable or not), the installation point of the object (whether it is not being dug into), and the balance of the object (whether it is moving sideways or not). - Work
It is prohibited to start work immediately after the object is raised. The jacks are merely lifting the object, and there is a risk that the object will lose its balance and fall over. Work should be started only after fall prevention measures have been taken, such as supporting the object with rigid racks, etc. - Jacking down
Operate the jack to slowly lower the object. In the same way as when ascending, slowly lower the object while checking the condition of the installation surface, the object’s installation point, and the object’s balance.
How to Select a Jack
When selecting jacks, the most important factors to consider are the load capacity and height. Also, select the type of jack according to the work. The below information explains the advantages and disadvantages of each type and their uses:
- Load Capacity
The maximum weight that jacks can lift is called the load-bearing weight. It is important to select jacks with a load capacity greater than the weight of the object to be lifted. If the weight of the object cannot be exceeded with single jacks, multiple jacks should be used to lift the object. - Height
The lowest height that jacks can lift is called the minimum height, and the highest height is called the maximum height. Select jacks that can provide the necessary height for the work. - Merits and demerits of each type
The advantages and disadvantages of each type are as follows Select the appropriate type for the work area and the work to be performed
The advantage of the mechanical type is that it is lighter in weight and easier to handle than the liquid-operated type. Also, by using it horizontally, there is an advantage that the object can be moved laterally. Ideal for use when carrying a jack. The disadvantages are low work efficiency and the internal screws and gears are easily broken.
The liquid-actuated type is heavier than the mechanical type but has the advantage of high work efficiency. Recently, small types that can be easily transported are also available. It is mainly used in automobile repair and construction work. Disadvantages are that it cannot be used sideways and that handling such as oil leakage requires attention.
The advantage of the air-operated type over the liquid-operated type is that it can be used safely without risk of oil leakage or ignition. Today, various types are available: compressor type, exhaust gas type, and manual pump type. It is advisable to select the type that best suits the work to be performed. However, the disadvantage of jacks with a large load capacity is that they require a compressor, which can be cumbersome.