How does a little 50 lb tool lift a 900 lb object with just a few light pumps?
In: Physics
Fluids do not compress under pressure. So if you fill a hose with a fluid, and the hose and fittings can hold the force, you can push fluid through the system to move something on the other side. This makes hydraulics essentially flexible levers without the drawback of bend in solid levers. So your Jack is operated by a lever that exchanges distance for force (your lever travels farther in exchange for generating more force; torque) and transfers that force through the fluid that can’t be compressed and raises the cylinder. When the fluid pushes through, it opens a one way valve, and when that pressure is released, the valve closes, allowing you to charge for another cycle (the upstroke).
When you turn the little pin to lower the jack, you are manually opening the one way valve.
So, in effect, you are traveling your arm farther than the cylinder is raising and the difference is what generates the excess force. Similar to when you are trying to lift something heavy with a seesaw, if you just make the side you’re manipulating longer, you can lift more weight.
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