What is a power ASSISTED steering?
You can have either a “power assisted” rack or box, or “manual” rack or box. A power assisted unit is powered by a power steering pump. The pump sends pressure to the racks spool valve, the valve is incorporated with the pinion gear or input shaft to the rack. When you turn your steering wheel a shaft connected to it applies torque to the input shaft. As the amount of torque increases the valve gradually opens and allows the pressurized fluid to travel and push against a fixed piston on the racks shaft. The rack shaft is enclosed by a cylinder so the pressure builds up against the piston and pushes the rack shaft (either right or left). Since the amount of pressure from the pump is constant the degree or amount of power assist you feel is related to the amount of torque you apply to the steering wheel (the more torque the great the valve opens… to a point). Power assist is usually required and noticed when making slow turns. The faster the car moves the less amount of torque or power
