What is Common Rail?


A common rail is one of the most important components in a diesel and gasoline direct injection system. The main difference between a direct and a standard injection is the delivery of fuel and the way how this one mixes with incoming air. In the direct injection system, the fuel is directly injected into the combustion chamber, skipping the waiting period in the air intake manifold. Controlled by the electronic unit, the fuel is squirted directly where the combustion chamber is hottest, which makes it burn more evenly and thoroughly.

The main advantages of the common rail direct fuel injection can be summarized in reduction of exhaust and noise emissions, better fuel efficiency and improved overall engine performance.  The system consists of a high-pressure pump, injectors, a rail, and an electronic control unit.

The common rail is a long metal cylinder. It receives the fuel from the pump and distributes it to the injectors under extremely high pressure. The increase in the fuel pressure is a result of the latest engines’ design. Both, diesel and gasoline engines tend to become smaller and lighter for better fuel efficiency and improved performance which increases the fuel pressure and sets entirely new standards for the manufacturing of a high-quality common rail.

First, the geometrical accuracy of the component is of critical importance. Precise design contributes to better common rail performance. Even a minimal size or shape fluctuation could lead to failures. Defining the right parameters in the design phase is essential, but what really matters is strictly following them during the manufacturing process.

The material selection is also a point that shouldn’t be underestimated. Good mechanical properties ensure strength and prevent corrosion. The used materials are usually steel and stainless steel. The common rail for diesel engine is made of steel, while the common rail for gasoline engine is made of stainless steel, because the fuel is too corrosive and stainless steel possesses better resistance to corrosion than steel.

The quality of the common rail is of critical importance. Damage can lead to breakages and leakages, which can block the vehicle or set it on fire. Therefore

  • anticipating,
  • testing
  • and preventing


any possible common rail problems during manufacturing are essential. Forging has the biggest contribution to the efficient prevention of eventual component’s failures. Forging and in particular hot forging strengthens the material by closing empty spaces within the metal while deforming and shaping it with localized compressive forces. A forged common rail is stronger and possesses higher resistance to pressure and corrosion.

Setforge, the forging subsidiary of Farinia Group has a long standing experience in designing and exibiting a high-quality common rail manufacturing process. We work with best steel suppliers and offer a wide range of forging techniques done on state-of-the-art machinery and tools.

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