Why is the main fuel strainer located at the lowest point in the fuel system?

The main fuel strainer is positioned at the lowest point in the fuel system primarily to effectively trap any small amounts of water that may be present in the fuel. Water is denser than fuel and tends to settle at the bottom of the fuel tanks and lines. By locating the strainer in this position, it can capture and filter out this water before it enters the fuel system, which is crucial for maintaining engine performance and preventing corrosion or damage to engine components.

This design is important because water can cause fuel system issues, including microbial growth, which can lead to further contamination of the fuel. Furthermore, by catching this water in the strainer, maintenance personnel can easily drain it out, ensuring the integrity of the fuel supply and protecting the aircraft's fuel system from potential failures.

While draining residual fuel may happen, and filtering out micro-organisms could be a concern, these are secondary benefits, as the primary function of the strainer is to prevent water contamination from affecting fuel delivery and engine performance. Monitoring the fuel flow rate is not a function of the strainer, as flow rate is typically measured elsewhere in the system.