A hydraulic floor jack is a fundamental tool in any repair shop. It uses a horizontal cylinder and a pivoting lift arm to raise cars off the ground. When you pump the jack handle, it forces hydraulic fluid into the cylinder, extending the piston and lifting the saddle. The jack rides on steel wheels, letting it roll forward as the arm lifts to keep the load centered over the base.
Never work under a car supported only by a hydraulic jack. Jacks rely on rubber seals to hold the fluid pressure. If a seal leaks or the release valve is bumped, the car will drop instantly. Always lift the car to the desired height, place solid jack stands under the vehicle's frame pinch welds, and lower the jack until the car rests securely on the stands before crawling underneath.