1
A Description of the Standard Hydraulic Floor Jack
The hydraulic floor jack is a device that uses force to lift heavy loads. The hydraulic
floor jack is unique because it uses a principle called Pascals Law, a law of fluid dynamics, to
amplify force, which allows it to lift heavier loads higher than other jacks that use screw systems.
The hydraulic floor jack history begins in the 17th century when Blaise Pascal illustrated
the principle of the hydraulic jack 1. But it was not until mid-18th century that hydraulic jacks
began to be used more often. The hydraulic jacks that are most commonly used today are
evolved from Richard Dudgeons design. In 1851 Richard Dudgeon was granted a patent for his
portable hydraulic press 2.
This description explains to semi-technical individuals the structure, assembly, and
applications of the standard hydraulic floor jack.
The maximum lift heights and the maximum loads can vary from one jack to another jack
depending on the sizes of the hydraulic cylinders and lever arms. The concept of the hydraulic
floor jack is to reduce the amount of force needed to lift heavy objects.
Hydraulic floor jacks consist of various assemblies that work together to provide a
mechanical advantage for the users: (1,2) frame assembly, (3) handle assembly, and (4,5) wheel
assemblies.
"How Does a Floor Jack Work? - Floor Jack Advisor." Floor Jack Advisor. August 30, 2014.
Accessed November 21, 2015. http://www.floorjackadvisor.com/blog/how-does-a-floor-jackwork/.
2
Ibid.
Frame Assembly (1,2)
The frame assembly is the most important part of a hydraulic floor jack. The frame
assembly is where the load is supported. The frame assembly includes the power unit, which is
the most complex part of the jack, and the saddle.
The power unit consists of a reservoir, two piston/cylinders of different diameters, and
flow control valves. When the user raises the jack handle, hydraulic fluid is drawn from the
reservoir through a check valve and into the smaller hydraulic cylinder. The pressure increases
in the smaller cylinder when the user pushes the handle down, forcing the hydraulic fluid through
another check valve and into the larger hydraulic cylinder. The larger cylinder piston is attached
to the lifting arm of the jack which creates a lever arm that increases the mechanical advantage.
Due to the difference in diameters of the two piston/cylinders, the force is amplified
exponentially. A greater difference in surface area of the pistons results in a greater mechanical
advantage, allowing the user to lift more weight while using less force.
The saddle unit is the point of contact between the jack and whatever external object
being lifted or acted upon. The saddle has edges to prevent the object that is being lifted or acted
upon from slipping or moving laterally.
Handle Assembly (3)
The handle assembly includes the handle and the handle gear assembly. The handle
assembly is an important part in the hydraulic jack.
The handle must be turned clockwise to raise the jack. When the handle is turned
clockwise the release valve is closed. This allows the handle to be pumped to build pressure in
the hydraulic cylinders which raises the jack. The handle must be turned counterclockwise to
lower the jack. When the handle is turned counterclockwise the release valve opens, which
releases the pressure built up in the cylinders and consequently lowers the jack.
The handle connects to the handle gear assembly. When the handle gear assembly pivots
on the frame, the handle gear assembly uses the leverage from the handle to push the cylinders of
the power unit assembly.
Wheel Assembly (4,5)
The wheel assembly includes front wheels and rear wheels. The wheel assemblies mount
to the frame. The wheels allow the hydraulic floor jack to be easily moved.
The front wheel assembly consists of two wheels, a bolt axle, washer and nut. The front
wheels are fixed to rotate in one direction. The front wheels are often larger than the rear
wheels.
The rear wheel assembly consists of two wheels, two washers, and two nuts. The rear
wheels can rotate in any direction. The rear wheels provide the hydraulic floor jack the ability to
change directions. The rear wheels are critical because when they are combined with the front
wheels it allows the user to change the position of the jack without having to lift the heavy floor
jack.
Conclusion
The three major assemblies of the hydraulic floor jack work together to provide users
with a large mechanical advantage.
In an operating cycle, the handle is turned clockwise to close the hydraulic fluid release
valve. The handle is then pumped which forces the hydraulic fluid from the reservoir through
the small hydraulic cylinder, through another valve, and through the larger hydraulic cylinder,
finally pushing on the large piston and raising the lifting arm of the jack. Once the lift or
pressure is no longer required, the handle is turned counterclockwise which opens the hydraulic
fluid release valve and releases the pressure, which then lowers the lifting arm of the jack.
Bibliography
"Automobile Lifts Catalogue." Shanghai Hoton Auto Equipment. 2009. Accessed November 20,
2015. http://www.eqibao.com/english/cnauto/woding.asp.
"How Does a Floor Jack Work? - Floor Jack Advisor." Floor Jack Advisor. August 30, 2014.
Accessed November 21, 2015. http://www.floorjackadvisor.com/blog/how-does-a-floorjack-work/.
"Sears parts direct" JACK Diagram & Parts List for Model 875501340 Craftsman-Parts
Hydraulic-Jack-Parts. Accessed November 24, 2015.
http://www.searspartsdirect.com/modelpart/875501340/0247/1500165/50019102/00001.html.
Glossary
Check valve: an opening that allows fluid to flow in one direction
Hydraulic cylinder: a cylinder that uses fluid to function
Hydraulic floor jack: a mechanical device that uses fluid to raise or lower an object
Hydraulic fluid: a fluid that transfers power in hydraulic machinery
Jack: a mechanical device used to raise or lower an object
Operating cycle: an explanation of how the parts of the mechanism work together and what
actions are performed to make the item function as a whole through one cycle
