A hydraulic lift is a device for moving objects using force created by pressure on a liquid inside a cylinder that moves a piston upward. Incompressible oil is pumped into the cylinder, which forces the piston upward. When a valve opens to release the oil, the piston lowers by gravitational force.
The principle for hydraulic lifts is based on Pascal‘s law for generating force or motion, which states that pressure change on an incompressible liquid in a confined space is passed equally throughout the liquid in all directions.
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Hydraulic lifts work on a basic principle: to go up, a pump pushes oil into the cylinder, pushing the piston (which pushes the lift car) up. To go down, the valve opens and oil is allowed to flow back into the reservoir, and is pushed back using the gravitational force of the lift car. The diagram above shows this system.
When the valve is closed, the oil can only go from the reservoir into the cylinder. When the valve is open, the oil can only flow from the cylinder back into the reservoir.
The controls in the lift car make the pump operate, moving the oil. When a floor is reached, the pump is switched off and the lift car sits on top of the piston, held in position by the oil which is trapped in the cylinder.
The position, size and operation of the cylinder can be one of two options – ‘holed’ or ‘hole-less’.