When you need to lift a car to work underneath it or move a heavy piece of industrial equipment, you wouldn’t risk injuring yourself by trying to hoist it with your bare hands.
You probably would use a specialized lifting tool such as a hydraulic jack to safely lift and move heavy object. But how can hydraulic jacks allow users lift everything from crates to trucks to even houses?
The answer is right there in the tool’s name: Hydraulics.
How Hydraulic Jacks Work
Hydraulic jacks rely on force that is generated by pressure. While there are all types of hydraulic jacks, nearly all of them work on the same principle.
A hydraulic jack has two cylinders, one larger one and one smaller one, that are connected. As force is applied to one cylinder, due to this connection an equal pressure is generated inside both cylinders.
But because one cylinder has a larger area, the force produced by this cylinder also will be higher, even though the overall pressure produced in the two cylinders remains the same.
To lift heavy loads, a pump plunger will move a liquid through the two cylinders. Despite the hydraulic jack’s name, this liquid usually is oil, not water.
When the plunger is initially drawn back, it opens a suction valve ball which draws oil into the pump chamber. As the plunger is pushed forward, the oil then moves through an eternal discharge check valve into the cylinder chamber.
As the suction valve closes, pressure builds within the chamber, producing the force that can be used by the pump to lift heavy weights.
Bottle Jacks and Floor Jacks
The two most common types of hydraulic jacks used in industry are bottle jacks and floor jacks.
Bottle jacks resemble the type of car jack most people used to have in the trunk of their car. Shaped like milk bottles, bottle jacks can lift anywhere from a few hundred to a few thousand pounds, depending on their size and rated lifting capacity.
Bottle jacks are still widely used for lifting vehicles, but their use is increasingly spreading to other industries. For example, many hospitals will now use a type of bottle jack to move and lift heavy medical equipment.
Floor jacks use a shaft that pushes on a crank that connects to a horizontal lifting pad. Floor jacks generally have a higher range of vertical lift than bottle jacks.