Although hydraulic machines generally are associated with heavy-duty construction machines like bulldozers, forklifts and cranes, you can find hydraulics in smaller, simpler machines, too. Even the brakes in your car use hydraulics to operate. When you press down on your car's brake pedal, you're actually causing a piston to push against an incompressible fluid. This action is transferred to slave pistons located at each wheel, which cause the brake pads to press against the brake rotors and slow down the car.
Coil-hydraulic steering stabilizers work in a similar manner to normal coil springs -- compression coils try to resist when you turn the wheel of a tow vehicle, so that when you let go of the steering wheel, the springs bring the wheels back to their original position. The only difference in a coil-hydraulic system is a piston in the center of the spring that resembles and acts like a shock absorber in your car's suspension. Working with the coil spring, the hydraulic piston provides extra stability for the system by keeping the spring from snapping back into place too quickly.
What about purely hydraulic steering systems -- what happens without springs? See the next page to learn about hydraulic steering.