What is the difference between a mechanical jack and a hydraulic jack ? With the number of jack types that are available, it is important to
understand the difference between the two. Additionally, each type of jack offers its own benefits and drawbacks. Knowing which jack type to
use involves understanding the differences in the two types of lifting devices.
MECHANICAL JACKS
In contrast to hydraulic jacks, mechanical jacks use only physical means of raising and lowering their loads. Using mechanical advantage,
these jacks are commonly seen in the automotive industry for lifting vehicles and other loads.
A common type of mechanical jack is known as a [screw jack." With the use of a motor, or a lever that is cranked by an operator, a screw uses
the shape of its threads to raise or lower the jack. Depending on the type of jack, the screw itself may raise or lower the load, or a traveling nut
does the raising while the screw turns in place.
These jacks have many applications that include moving platforms on stages, changing settings on woodworking machinery, and adjustments of
radio telescopes. Other applications also involve the use of mechanical jacks and they provide some advantage over hydraulic systems.
Mechanical systems are normally self-locking. This means that when power is removed from the jack, the screw remains in the same position until
power is reapplied. Self-locking properties make these jacks safer to use than hydraulic units, since operators need not worry about loss of power.
Drawbacks of a mechanical system include the fact that they are not capable of lifting the same loads as hydraulic lifts. Additionally, levers that
provide mechanical advantage for manual operations can only reach a certain length before bending and becoming useless.
HYDRAULIC JACKS
Jacks using hydraulic power operate on the phenomenon that fluids produce the same pressure at all points when contained in a closed system.
With these types of jacks, a fluid is contained within a large and small container, both of which are linked by tubes. When a small amount of force
is applied to the smaller tube, the pressure on the fluid increases. This means that, within the larger tube, the same amount of pressure per square
inch is applied over a larger surface, resulting in an increased amount of force.
With hydraulic jacks, smaller amounts of force are capable of lifting loads which would otherwise be impossible. The principals behind this type of
jack was discovered back in the seventeenth century. Currently, it is used in a wide range of industries, including automotive, construction,
fabrication and health care. Hydraulic jacks are commonly used to lift vehicles in order to conduct maintenance.
While these jacks are capable of lifting heavier loads than mechanical jacks, they also have the drawback that the load will be lowered if the hydraulic
power is removed from the jack. Operators must take care to ensure that hydraulic power remains in place while they are working with the jacks.