Hydraulic Cylinders / Jacks - How it works

Hydraulic cylinders are powered through pressurized hydraulic fluids. These fluids are typically oil. Hydraulic cylinders have a barrel, in which a piston is connected to a piston rod. The piston has sliding rings and seals and the rod moves back and forth. The barrel is closed on each end by the cylinder bottom or cylinder head where the piston rod comes out. The piston divides the cylinder inside in two chambers - cap end and rod end. Hydraulic cylinder is the actuator or motor side of a system. The generator side of the hydraulic system is the hydraulic pump. The pistons push the oil in different chambers from reservoirs. If oil pressure in the piston rod chamber is approx zero, the force on the piston rod equals the pressure in the cylinder times the piston area. The piston moves instead downwards if oil is pumped into the piston rod side chamber and the oil from the piston area flows back to the reservoir without pressure.

Hydraulic Jack
Hydraulic jacks work on the basis of Pascal's Principle. This principle states that the pressure in a closed container is the same at all points. If there are two cylinders (a small one and a large one) connected together and a small force is applied to the small cylinder, this would result in a given pressure. This pressure would be the same in the larger cylinder, but since the larger cylinder has more area, the force emitted by the second cylinder would be greater. The greater the differences in the areas of the cylinders, the greater the potential force output of the big cylinder. An enclosed fluid under pressure exerts that pressure throughout its volume and against any surface containing it.