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CDL · Liquid Surge

What is liquid surge, and why is it especially dangerous in a tank that is partly full?

Correct answer

It is the movement of liquid back and forth (or side to side) in a partially filled tank, which can push the truck in the direction the wave is moving and affect control, especially when stopping or turning

  1. A It is the foam that forms on top of the liquid and has no effect on handling
  2. B It is the movement of liquid back and forth (or side to side) in a partially filled tank, which can push the truck in the direction the wave is moving and affect control, especially when stopping or turning
  3. C It only happens in completely full tanks
  4. D It is a type of brake fade

Why this is the answer

Liquid surge is the wave action of the cargo moving inside a partially filled tank. When the driver brakes, the liquid surges forward and can shove the vehicle ahead even after the wheels slow; when the truck stops, the wave can rebound. Side-to-side surge in unbaffled tanks can affect steering in turns. Surge is most dangerous in a partly loaded smooth-bore tank because there is room for the liquid to build momentum. Drivers control surge by braking smoothly and early, increasing following distance, and being extremely cautious through curves, intersections, and on/off ramps where a surge can push the rig out of its lane.
Source: FMCSA CDL Manual 8.2.2 Liquid Surge

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