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How do Hydraulic Lifts Work?

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We wouldn't have many of the modern conveniences that we do if it wasn't for hydraulic lifts. Dentist chairs, vehicle brakes, elevators, forklifts and a great variety of other machinery, are all examples of hydraulic lift systems. The exact mechanisms vary widely by application, but all depend on the same basic principle. Let's take a look at how and why hydraulic lifts work the way they do.

Hydraulic Lift Basics

Hydraulic systems all depend on the same principle; Pascal's law. In essence, this law states that when pressure is applied to an incompressible fluid, such as oil or water, and this fluid is held to a confined space, the pressure will be distributed throughout the fluid and is able to be multiplied. When correctly applied with careful engineering, multiplication of pressure is capable of lifting items of considerable weight.The main components of a hydraulic lift are a piston within a cylinder, an oil reservoir, a pump, a motor and a valve.

How Hydraulic Lifts Work

Generally, lifts depend on either an electric motor or air compressor to power a hydraulic pump. This provides the initial pressure to the hydraulic fluid inside the pistons. Multiplication of pressure occurs when fluid inside a narrow piston transfers pressure over a longer distance into a wider piston. Once in the wider piston, this pressure travels over a relatively shorter distance, and as a result acts with a greater amount of force.

To go up, the pump pushes oil into the cylinder which pushes the piston up. To go down, the valve opens and oil flows back into the reservoir, and is then pushed back using the gravitational force of the lift. When the valve is closed, the oil can only go from the reservoir into the cylinder. In reverse, the oil can only flow from the cylinder back into the reservoir when the valve is open. It may seem simple in principle, but this cause-and-effect relationship allows machinery to easily lift thousands of pounds.

Two Types of Hydraulic Lifts

There are two types of hydraulic lifts used in elevators. A holed hydraulic lift is a conventional lift. It requires a hole in the floor for the lift, while the cylinder which encases the piston and pushes the lift extends into the ground. The distance the cylinder extends equals the distance the lift car can travel upwards.

A hole-less hydraulic lift is one that doesn't require a deep pit for the cylinder. The pistons are direct action, and they're mounted on the pit floor in line with the bottom corners of the lift car.

This system operates like a jack and restricts the amount of upwards travel to around 98 feet at most. This system is not as commonly used, but it allows for use when a hydraulic system is required where the travel is short and the space is restricted going down.