How Do Hydraulic Floor Jacks Work?
This is, to say the least, an interesting question. Even the non-professionals and regular do-it-yourself home mechanics know that floor jacks are designed to lift heavy items like cars, SUVs, and trucks. They might know a bit about the hydraulic design that gives these tools their power.
But it takes a bit more research to really understand just how hydraulic floor jacks perform day after day.
The key word here is “hydraulic,” a term that applies to almost every product, regardless of lift capacity, physical dimensions, and materials used to make the jack. This process is remarkable, in that the proper design and use of durable materials allows you to life a vehicle weighing 6,000 pounds or more.
The method is certainly not new. It was, in fact, used more than 2,000 years ago, when individuals discovered a way to create enormous power using fluids. According to the dictionary definition, the word “hydraulic” refers specifically to the process in which something is “operated, moved, or effected by means of water.” (Merriam-Webster). The word is created with two parts – “hydro” referring to water and “aulos” an ancient instrument that created sound when air was forced through small holes.
Water was the original fluid used, of course. The definition has since been updated to include pressure or resistance when a liquid such as water or oil is used. In basic terms, the handle of the floor jack connects to a cylinder which has a piston inside. Hydraulic fluid fills the reservoir. When the handle is lifted the piston draws fluid from the reservoir, filling the cylinder with fluid according to how much you move the handle.
Lowering the handle is the second part of the pumping action; the fluid is placed under pressure and directed to a main cylinder to push up a lifting piston. With enough fluid under pressure, you have the ability to lift thousands of pounds.
There are details to each floor jack design that add to or improve this rather simple process, including check valves and channels to direct the fluid power to the right place. Each jack has a release valve that can be turned by hand to drain fluid from the main cylinder back to the reservoir, to store it for the next task. The lift piston returns to its original position.
In a jack used to lift vehicles in a repair garage, for example, the bottle is parallel to the floor or ground. It’s necessary to design in an arm and joints to transfer the parallel motion to vertical motion. Basic lifting jacks, such as would be used to level a floor in an older home stand in the upright position, so the lifting action is simpler (more direct).
More on Bottle Jacks and Floor Jacks
All hydraulic jacks work on a force created by pressure. (It’s also possible to use a simple machine like the screw design to create lifting force. This is what makes a screw jack work efficiently.) With the hydraulic design, it’s necessary to have two cylinders, with one generally being larger than the other.
The science of hydraulics discovered so many years ago works when equal pressure is present in both cylinders. The force in one will be different than the force in the other because of the difference in size.
Pistons, sometimes referred to as plungers, move the liquid, first drawing oil into the chamber of the pump. When the plunger/piston moves forward, the oil moves through a discharge valve into the next chamber. It’s necessary for the valves to open and close at the right time to hold oil in the lifting cylinder. The oil can be returned to the storage cylinder or reservoir with a manual release of some type.
As mentioned briefly above, a bottle jack is a simpler version of the lifting jack. This design came into being in the early 20th century as the automobile become a common sight on the roads. Mechanics needed a safe and efficient way to lift the vehicles for inspection and repair. Creative individuals saw the milk-bottle shape as a likely way to provide the lifting power, with a vertical shaft and a flat surface that contacted the spot on the car’s undercarriage for stability.
This design also found use in industry, for bending metal pipe or for lifting material in a warehouse situation. This design is also used in construction, especially when it’s necessary to level and stabilize the settling floors of an older building. This same process, when performed in a horizontal position, gives rise to the modern floor jack, now widely used in the automotive and warehouse industries, to cite just two examples.
This design, with improvements in materials and valve details, allows a unit weighting less than 100 pounds to lift three tons, four tons, or more.