What is a power ASSISTED rack?
You can have either a power assisted rack or box, or “manual” rack or box. A power assisted unit is powered by a hydraulic pump (aka 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 rack’s gear shaft. The rack shaft is enclosed in a cylinder so the pressure builds up against a side of the piston and pushes the rack shaft; right or left. Power assist is usually required and noticed when making slow turns, such as while parking. As a car travels faster there is less rolling side resistance so less torque or power assist is needed to turn the car.
