# How Does a Hydraulic Floor Jack Work?

Quite a few visitors to the site have emailed me asking, how does a hydraulic floor Jack work?, so I figured it would be useful to put together this quick, short post to help demystify the workings behind hydraulic jacks.

Anyone who has every used this type of jack knows it has a horizontal lift arm that is raised by pumping the handle of the jack.

The way this elevation occurs is the jack has a reservoir that holds hydraulic fluid. This fluid is drawn up by pumping the jack pump arm via the jacks pump. When you pump the jack handle in an up direction we create a suction force and then we apply pressure by pushing the jack arm downward which forces the now under pressure hydraulic fluid to move into the check valve.

The check valve then seals of the opening to the reservoir, preventing the fluid from moving back and pushes the pressurized hydraulic fluid into the Jacks main cylinder.

The main cylinder contains a ram piston which is driven upwards as the pressurized hydraulic fluid is forced into the main cylinder chamber.

When you are ready to release the jack, you simply turn a valve (the pressure release valve) which eases the pressure the fluid is under allowing the hydraulic fluid to return to the reservoir.

If your Jack is in good working order with no leaks it won’t need to have fluid added as it is a closed system.

It is the pressure that forms in this closed system that allows very small force from the user to pump the jack handle that results in very large weights being lifted with very little effort.

In scientific circles, this process works on the transmission of fluid-pressure or Pascal’s law (or principle) as its more commonly called.

From Wikipedia This principle is stated mathematically as:

“A change in pressure at any point in an enclosed fluid at rest is transmitted undiminished to all points in the fluid”

$\Delta P =\rho g (\Delta h)\,$

$\Delta P$ is the hydrostatic pressure (given in pascals in the SI system), or the difference in pressure at two points within a fluid column, due to the weight of the fluid;

ρ is the fluid density (in kilograms per cubic meter in the SI system);

g is acceleration due to gravity (normally using the sea level acceleration due to Earth’s gravity, in SI in metres per second squared);

$\Delta h$ is the height of fluid above the point of measurement, or the difference in elevation between the two points within the fluid column (in metres in SI).

Basically, the law states that pressure placed on a fluid is the same in every direction and across the entire volume of the fluid. You can read more about Pascal’s law here

The video below illustrates the principle using a hydraulic car lift

So hopefully this has helped you understand the actions and forces that make a hydraulic jack work. If you have anything to add, or have any questions let us know in the comment box below.