This motion graphic was included as part of a computer-based training (CBT) module to demonstrate the correct procedure for taking a fuel sample from the sump at an aviation fuel farm. A common mistake was to leave the output valve open during the test (as shown on the left), in an effort to reduce system pressure. However, this approach often produced a misleading sample.

With the system depressurized, opening the drain allowed air to enter the filter housing, disturbing sediment that would then float upward—resulting in a cleaner-looking but inaccurate sample. In contrast, with the output valve closed (as shown on the right), pressure was maintained, and the true sediment load was forced out through the drain—providing a more accurate representation of the filter’s condition.