Power steering does more than make life a little easier -- it makes cars a lot quicker. Before power steering, manufacturers could build a box with a quick gear ratio for rapid reflexes, or a much slower gear ratio for easier turns. But since tighter boxes made steering harder, they often had to install giant, school-bus steering wheels for extra leverage on them. The modern hydraulic steering system packs a load of power in a small package, and develops incredible pressures to do it.
All cars are different, and require different pressures. Heavy vehicles and cars with very quick-ratio steering boxes typically require higher pressures than lighter and lower-performing vehicles. At idle with the steering wheel static, a typical power steering pump holds about 80 to 125 psi in the output line. Yank the steering wheel a couple of times in rapid succession -- causing the pressure-release valve to flutter open and shut -- and a typical modern pump might momentarily put between 1,000 and 1,500 psi through the lines. Older and lower-performing pumps might run 850 psi of momentary pressure or less, while heavy-duty off-road pumps may sustain 1,600 or more. High-performance pumps can jump to 2,500 psi before the valve releases. and hold upward of 8,000 to 10,000 psi internally before bursting.