What is the function of sumps and drains in fuel tanks?

The function of sumps and drains in fuel tanks is primarily to remove water and contaminants. Over time, water can accumulate in fuel tanks due to condensation, leaks, or other reasons, and this can adversely affect the performance and safety of the aircraft's fuel system. The presence of contaminants, such as dirt, rust, and microbial growth, can also interfere with the functioning of the fuel system and engines.

Sumps are designed to collect this unwanted water and any sediment that may settle at the bottom of the tank. The drained liquid can then be safely removed before it can affect the fuel quality or cause issues within the fuel delivery system. This maintenance practice is essential to ensure that the fuel used is clean and free from substances that could lead to engine failures or other hazardous situations during flight.

The other options involve aspects of fuel tanks that are important but do not focus specifically on the primary purpose of sumps and drains. Fuel flow enhancement, measuring fuel levels, and preventing evaporation are all relevant to fuel management but do not address the critical need for ensuring fuel cleanliness through the use of sumps and drains.