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CDL · Liquid Surge

When does liquid surge tend to be at its worst?

Reviewed by Jordan Morley, Editorial Lead at 247SimpleTests. Written by the 247SimpleTests Editorial Team from the official source material cited on every question.

Correct answer

When the tank is between 25% and 75% full, with maximum surge typically near half full

  1. A When the tank is completely empty
  2. B When the tank is completely full
  3. C When the tank is between 25% and 75% full, with maximum surge typically near half full
  4. D When the tank is exactly half full

Why this is the answer

Surge is worst at intermediate fill levels because the liquid has room to move freely while still carrying significant mass. A completely full tank cannot surge — the liquid has nowhere to go (and pressure relief valves prevent overfilling). A nearly empty tank surges less because the mass involved is small. The peak surge region is roughly 25% to 75% fill, with maximum often near half full. Loading practice for tank operations sometimes encourages either full or near-empty loads to minimize surge effects. Drivers who repeatedly deliver to multiple destinations face the worst conditions after the first delivery, when the tank may go from full to partially empty along the rest of the route.
Source: FMCSA CDL Manual 8.2.10 Surge by Fill Level

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About this topic: Liquid Surge

Liquid surge is the forward-and-back movement of a partially filled tank, strong enough to push a stopped truck into an intersection. These questions cover why it happens, how baffles and bulkheads limit it, and how to brake and stop to control it. This is one of 10 Tanker questions on liquid surge, each with a full explanation on a single study page.

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