As in any assembly, the individual parts of the Volkswagen power steering (PS) system relies on lubrication in order that they perform as one well-oiled whole. Collectively, the Volkswagen power steering system gives driver a tight rein of the vehicle. Through the steering rack, the driver is able to input the desired direction of the vehicle. When the steering wheel is turned left or right, the rack and pinion gear set turns the front wheels accordingly. To facilitate a smooth drive train operation, the power steering rack of the Volkswagen is fitted with a hydraulic pump that circulates lubricants. From the pump, these hydraulic fluids are charged and injected via the power steering hose. For the hydraulic fluids to reach every individual part of the drive train, they circulate in the system bearing up to 1,300 psi of boost. The Volkswagen power steering pump is typically a vane style pump driven by a belt connected to the engine. It contains a set of retractable vanes that spin inside an oval chamber, streamlining hydraulic fluid injection. The hydraulic fluid reservoir may be mounted on the pump itself for easy fluid flow, or the reservoir may be mounted remotely to isolate the oil from engine heat and maintain its optimal temperature range. The resulting flow of up to specs hydraulic fluid helps reduce steering effort, easing driver fatigue. In order that the hydraulic fluid is injected into the PS system at high pressure, the pump spin the vanes and pull hydraulic fluid from the return line at low pressure and force it into the outlet at high pressure. The amount of flow provided by the pump depends on the car's engine speed. The VW PS pump is designed to provide adequate flow even when the engine is idling. As a result, the PS pump inevitably flows in much more fluid than what is necessary when the engine is running at faster speeds. As failsafe to over lubrication, the VW PS pump contains a pressure relief valve to make sure that the pressure does not get too high, especially at high engine speeds when so much fluid is being pumped. A PS system is designed to give assist to driver only when force is exerted on the steering wheel. The component of the VW PS system that senses the force on the steering wheel is called the rotary valve. The key to the rotary valve is a torsion bar, a thin rod of metal that twists when torque is applied to it. The top portion of the bar on a typical VW PS system is connected to the steering wheel, and the bottom of the bar is connected to the pinion gear set that turns the wheels, so that the amount of torque in the torsion bar is equal to the amount of torque the driver is using to turn the wheels. The more torque the driver uses to turn the wheels, the more the bar twists. Some Volkswagen models use variable assist power steering systems, which provide more assist at low speeds and reduces assist at higher speeds. This provides the most assist when needed, reduces over-steer in emergency situations and provides better on-highway feel.