Hydraulic floor jacks come in a variety of sizes, capacities, and alloys, allowing for versatility of use and ease of storage and transport, but have you ever considered what exactly happens inside the jack that allows your strength to lift even a three ton vehicle? The answer is in the name, and is an ancient technique that has powered machinery since around 200 BC – hydraulics. The study of hydraulics spans a huge field, but in particular here, is the transmission of power using fluid; namely, the transmission of the downward movement of your arm, to the upward movement of your vehicle.
The handle of your floor jack connects into a yoke, which connects to a bottle jack unit, the primary working mechanism. Inside the bottle, or reservoir is a cylinder, and inside that is a piston. Below them, are a couple of channels, two check valves (comprising small balls on springs), and a release valve, and at the end of these, are the pump cylinder and the piston it contains, and connected to this is the attachment to the handle of your jack. Filling the reservoir is the hydraulic fluid, the essential part of the entire mechanism.
When you lift the handle of your jack, the pump piston rises, drawing fluid out of the reservoir and the pump cylinder fills with a certain amount of fluid. When you lower the handle, putting power into it, the pressurized fluid is constrained by the check valves and goes into a different channel, and fills the main cylinder, pushing the lifting piston up. Pump the handle enough times, and you can lift even a three ton vehicle. When you no longer need the jack to be lifted, you turn the release valve slightly, and it drains the fluid from the main cylinder back to the reservoir, allowing the piston to fall back to its starting position. In a floor jack, the bottle jack unit is parallel to the ground, and the piston is attached to an arm with special joints; the piston pushes the bottom of the arm forward, and the top of the arm rises, lifting the saddle and the vehicle with it.
Hydraulic floor jacks are an excellent example of the power of controlled, pressurized fluid. These jacks are a closed system and unless they develop a leak, they do not need to be refilled with hydraulic fluid, and they are so efficient that even someone physically weak can lift a car with one. A hydraulic floor jack is an essential part of a well-stocked garage, be it home or professional.
Here’s a good little video for those who are more visual: