You may have heard stories about mothers who are able to lift a car that’s trapped on top of their child. Or Superman lifting a truck and throwing it at a bad guy.
But practically anybody has the power to lift a car, truck or other heavy vehicles … as long as they use a jack.
So how do jacks work, exactly? It’s not magic. Instead, it’s simply physics.
Hydraulic vs Mechanical Jacks
There are two basic types of jacks: Hydraulic and mechanical.
Mechanical jacks are the kind found with the spare tire of most cars. They also are used to jack up houses. Mechanical jacks use the power of leverage to incrementally lift a weight up a very small distance, such as a few millimeters or an inch.
Mechanical jacks use the power of leverage to incrementally lift a weight up a very small distance, such as a few millimeters or an inch.
Mechanical jacks are rated based on their lifting capacity, such as the number of tons they can lift.
But hydraulic jacks are usually much more powerful and can lift heavier loads. The most common types of hydraulic jacks found in warehouse and shops are bottle jacks and floor jacks.
The Power of Pressure
Hydraulic jacks use force that is generated by pressure. The way it works is this: A large cylinder and a small cylinder are connected. Force is then applied to one cylinder so that equal pressure is generated in both cylinders. But because one cylinder has a larger area, the force the larger cylinder produces will be higher, even though the total pressure within the two cylinders remains the same.
Hydraulic jacks use this principle to lift heavy weights. Pump plungers move oil through two cylinders. As the plunger is drawn back, a suction valve ball within the cylinder opens, drawing oil into the pump chamber.
But as the plunger is pushed forward, the oil moves through an external discharge check valve into the cylinder chamber and the suction valve closes, which causes pressure to build up within the cylinder.
Bottle Jacks
Bottle jacks were first developed during the advent of the automobile at the beginning of the 20th Century. They get their name from their distinctive shape, which resembles the milk bottles widely used at the time.
Today’s bottle jacks range in lifting capacity from a 100 pounds to several tons. They have a vertical shaft, which supports a platform known as a bearing pad that directly bears the weight of the object as it is lifted.
Bottle jacks are still used to lift vehicles, but they also have applications in the medicine to lift stretchers and patient lifts, as well as industrial applications, such as being used in pipe benders by plumbers, cable splicers by electricians, and material lifts for warehouses.
They also are widely used in agriculture and construction.
Floor Jacks
Floor jacks are horizontal rather than vertical. They have a shaft that pushes on a crank that connects to the lifting pad, lifting it horizontally.
Floor jacks provide a greater range of vertical lift than bottle jacks and are often found in warehouse and industrial applications.