How Does Hydraulic Power Work?

Hydraulic System Basics

Hydraulic systems work on the two most basic and fundamental laws of liquids: that they are incompressible, and that they'll assume the shape of their container. The most basic type of hydraulic system is the one that Archimedes demonstrated, namely that if you drop a two-pound weight into water, it'll displace two pounds of water. Now imagine that you filled a glass all the way up to the brim, suspended it over a larger container and dropped a two-ounce weight into it. Exactly two ounces of water will spill into the larger container, thus transferring the mass of that two-ounce object to the lower container by moving fluid into it.

Hydraulic systems work on the two most basic and fundamental laws of liquids: that they are incompressible, and that they'll assume the shape of their container. The most basic type of hydraulic system is the one that Archimedes demonstrated, namely that if you drop a two-pound weight into water, it'll displace two pounds of water. Now imagine that you filled a glass all the way up to the brim, suspended it over a larger container and dropped a two-ounce weight into it. Exactly two ounces of water will spill into the larger container, thus transferring the mass of that two-ounce object to the lower container by moving fluid into it.

Increasing the diameter of the slave cylinder relative to the master cylinder will result in a torque multiplication effect. For example, let's say that our master cylinder is one inch in diameter and the slave cylinder is two inches in diameter. Applying one pound of force to the master cylinder will transfer one pound of water to the slave cylinder. Since the slave cylinder is twice as wide, it can receive the same volume of water, but its piston will only move half as far. Because it expresses the same amount of force over half the distance, it pushes with effectively double the force of the master cylinder.

In reality, fluid transfer in a hydraulic system doesn't necessarily express as movement. If the pressure exerted on the master cylinder is matched by pressure pushing back from the slave cylinder, the assembly won't move. The system will, however, pressurize in direct proportion to the force placed on it and express a constant force relative to that. For example, we'll say that we have a master and slave cylinder with pistons exactly one square inch in area. Place 50 pounds of resistance against the slave cylinder's piston and push against the master cylinder's plunger with 50 pounds of force, and the system will pressurize to 50 pounds per square inch but won't actually move.