Pressure Control Valve On the Td6 engine, the pressure control valve is located at the high pressure pump. The pressure control valve regulates the fuel rail pressure according to the load status of the engine. If the rail pressure is too high, the pressure control valve opens, which enables some of the fuel to pass from the fuel rail to the fuel tank via a collector line. If the rail pressure is too low, the pressure control valve closes and seals the high pressure side from the low pressure side. The EDC controls an armature via a coil. The armature presses a ball into a seal, which seals the high pressure side from the low pressure side. When the system is not activated, the ball is returned by a spring. The entire armature is coated with fuel for lubrication and cooling. The pressure control valve has two control circuits: l One electrical control circuit for setting a variable pressure value in the rail l One mechanical control circuit for equalising high frequency pressure fluctuations. The electric control circuit compensates for slow pressure fluctuations and changes and the mechanical control circuit compensates for faster pressure fluctuations. With the pressure control valve not active, the high pressure present in the rail or in the high pressure pump output is exerted on the high pressure intake of the pressure control valve. Since the de-energized electromagnet is not present, the force of the high pressure is greater than the force of the spring, which opens the pressure control valve. The spring's design creates a pressure of max. 100 bar. When the pressure control valve is active (to raise the fuel pressure) the magnetic force and spring force must be increased. The pressure control valve is activated and closed until there is a balance between the high pressure force on the one side and the magnetic and spring forces on the other. The magnetic force exerted by the electromagnet is indirect proportion to the activation current (controlled by the EMS. Variation in the activation current is achieved by PWM. The PWM frequency is 1 kHz i.e. high enough to prevent disturbance from armature movements and/or fluctuation in pressure. Fuel Rail The Td6 engine is equipped with a common rail fuel rail. The common rail is located beside the cylinder head cover underneath the air inlet manifold. In the fuel rail, the fuel is subjected to high pressure and delivered to the injectors. The fuel rail feeds all cylinders and maintains its internal pressure at a constant value, even when handling larger quantities of fuel. This ensures that the injection pressure remains at a constant pressure when the injector is opened. Fluctuations in pressure resulting from the pump delivery and injection are dampened by the volume of fuel in the rail. In the Td6, the fuel rail pressure sensor is located atone end of the rail. The fuel rail is continuously supplied with fuel from the high pressure pump. The fuel is delivered from the fuel rail to the injectors via the injector connection lines.