Power steering units are mechanical steering gear units incorporating a power assist. Power steering for the recirculating ball type steering system consists of a pump, fluid reservoir, pressure and return hoses and steering gear. The pump, which is driven by an accessory drive belt, consists of an impeller, pressure valve, and fluid reservoir. Pump pressure builds only when the engine is running. The pump impeller turns, picking up hydraulic fluid from the reservoir and feeding it to the steering gear under pressure through the pressure line. The fluid is then returned to the fluid reservoir through the non-pressurized return line.
Power assisted rack and pinion steering system is very similar to that of the recirculating ball system in that its power cylinder and control valve are in the same housing. The power piston is part of the rack while the rack housing is the cylinder. The pinion housing contains the control valve. Rotating the steering wheel moves the control valve, directing pressure to both ends of the steering rack piston. The rack and pinion system uses a pressure hose from the power steering pump to the control valve housing, and a return line to the fluid reservoir.
It is important to keep in mind these pumps and motors will eventually wear out and the hoses will start to leak. You can postpone that day by having a power steering service which removes water and contaminants that can corrode power steering parts.
Mechanical parts can be bent or damaged from hitting potholes, curbs or rocks. If neglected, the damaged parts stress other attached components which starts a chain reaction of damage.
Steering maintenance is pretty straight forward - replace power steering fluid as recommended and replace worn or damaged parts right away to save you money in the long run.