CDL Tank Baffled and Compartmented Tanks — Questions and Answers
Question 1: Compared with a smooth bore tank, what is the main handling advantage of a baffled tank?
- It has a lower center of gravity when loaded
- Less front-to-back liquid surge when braking or accelerating (Correct answer)
- It will not roll over on curves
- It needs no extra following distance
Correct answer: Less front-to-back liquid surge when braking or accelerating
Baffles have holes that slow liquid moving through the tank. This reduces front-to-back surge compared with a smooth bore tank.
A baffled tank has bulkheads with holes in them. The liquid can pass through the holes, but only slowly, so the baffles dampen forward and backward movement. A smooth bore tank has no internal barriers, so the liquid can move the full length of the tank. Baffles reduce the problem but don't remove it, and they do little to stop side-to-side movement.
Question 2: Which type of tank has no internal barriers to slow the movement of liquid?
- Baffled tank
- Compartmented tank
- Cargo-baffled tank
- Smooth bore tank (Correct answer)
Correct answer: Smooth bore tank
A smooth bore tank has nothing inside to slow liquid movement. Its liquid surges freely from end to end.
Smooth bore tanks have a plain interior, so a moving load of liquid can shift freely. Baffled tanks use bulkheads with holes. Compartmented tanks are divided by solid bulkheads into separate sections. Smooth bore tanks are common for products such as milk and other foods, where an interior free of baffles makes cleaning easier.
Question 3: A driver of a smooth bore tank slows quickly on a flat road and feels the truck being pushed forward. What is causing this?
- Liquid surging toward the front of the tank (Correct answer)
- The tank's baffles trapping air
- Liquid pressure dropping inside the tank
- Vapor expanding inside the compartments
Correct answer: Liquid surging toward the front of the tank
In a smooth bore tank, braking sends the liquid surging forward, and it can push the truck. Nothing inside the tank stops the movement.
When you brake, the liquid keeps moving forward because of its momentum. In a smooth bore tank it builds up and then pushes against the front of the tank. The result can push the truck ahead even after the brakes are applied. Drivers should brake early and gently, and leave a much longer following distance.
Question 4: How does a compartmented tank differ from a baffled tank?
- It has bulkheads with holes that let liquid flow between sections
- It has no internal structure at all
- It is divided into separate sections by solid bulkheads, so liquid cannot move between them (Correct answer)
- It can only carry one product
Correct answer: It is divided into separate sections by solid bulkheads, so liquid cannot move between them
A compartmented tank is split into separate sections by solid bulkheads. Baffles have openings, and these bulkheads don't. Each section holds its own liquid, and some tanks carry a different product in each.
Compartment bulkheads are solid, so the product in one section stays there. This limits how far any liquid can surge to the length of one compartment. Baffles only slow the liquid down, and it still passes through the holes. Because the sections are separate, a compartmented tank can carry several different products.
Question 5: Which hazard is NOT removed by baffles in a baffled tank?
- Any liquid movement at all
- Side-to-side liquid surge that can contribute to rollover (Correct answer)
- Front-to-back surge on a long downgrade
- Liquid sloshing when the tank is nearly full
Correct answer: Side-to-side liquid surge that can contribute to rollover
Baffles help with front-to-back surge but give little protection against side-to-side movement. Liquid shifting sideways on a curve can still raise the risk of rollover.
Baffles are mainly effective along the length of the tank, in the direction of acceleration and braking. In a curve, the liquid moves sideways and shifts the center of gravity toward the outside of the turn. Tank vehicles have a high center of gravity, so this can lead to a rollover. Take curves and ramps well below the posted speed.
Question 6: Why is a smooth bore tank especially hard to drive when it is only partly full?
- Partial loads cannot be weighed
- The liquid has room to build up a large surge from end to end (Correct answer)
- The brakes lock more easily when the load is light
- Smooth bore tanks leak when not full
Correct answer: The liquid has room to build up a large surge from end to end
A partly full smooth bore tank gives the liquid room to move over a long distance and build up a strong surge. Nothing inside stops it.
A completely full tank has little room for liquid to move. A partly full smooth bore tank has an air space and no baffles, so the liquid can travel the full length and gather momentum. When it reaches an end, it hits hard and can push the vehicle. Braking and accelerating smoothly matter most in this case.
Question 7: A driver is moving from a baffled tank to a smooth bore tank. Which change in driving is most appropriate?
- Brake earlier and more gently, and allow more stopping distance (Correct answer)
- Brake later because the liquid helps slow the vehicle
- Use the same following distance as with the baffled tank
- Accelerate more quickly to keep the liquid settled
Correct answer: Brake earlier and more gently, and allow more stopping distance
Smooth bore tanks have stronger surge, so braking should start sooner and be gentler. More following distance is needed.
With no baffles, liquid in a smooth bore tank can build up a large surge that carries the vehicle forward when you brake. Braking early and gently reduces the effect. You also need more stopping distance because a surge can push the truck. Quick starts and sudden stops are risky in any tank vehicle, and especially in a smooth bore one.
Question 8: Which statement about baffles is correct?
- Baffles divide the tank into separate sections that never share liquid
- Baffles remove the need to slow down on curves
- Baffles are what make a tank a smooth bore tank
- Baffles are bulkheads with holes that slow the movement of the liquid (Correct answer)
Correct answer: Baffles are bulkheads with holes that slow the movement of the liquid
A baffle is a bulkhead with holes in it. It slows liquid movement but does not stop it.
Baffles are installed inside the tank to reduce how fast liquid can move front to back. Because they have holes, liquid still passes through them. That is the difference from a compartment bulkhead, which is solid. Even with baffles, the driver must still be careful with speed on curves and with braking.
Question 9: A baffled tank is carrying a partial load. What should the driver expect compared with the same tank in a smooth bore design?
- No surge at all in any direction
- More front-to-back surge than a smooth bore tank
- Some surge, but less front-to-back than in a smooth bore tank (Correct answer)
- The same surge as a smooth bore tank
Correct answer: Some surge, but less front-to-back than in a smooth bore tank
Baffles reduce front-to-back surge but don't eliminate liquid movement. A baffled tank still has some surge, though less than a smooth bore tank.
The holes in the baffles allow liquid to pass, so surge is slowed rather than eliminated. A smooth bore tank has no barriers, so its surge is larger. A baffled tank is still a tank vehicle with a high center of gravity, so smooth control inputs are still needed. Don't treat baffles as a reason to drive faster or brake harder.
Question 10: Why can a compartmented tank still need careful handling when only some of its compartments are filled?
- Liquid in a partly filled compartment can still surge within that compartment (Correct answer)
- Empty compartments add weight to the front axle
- Solid bulkheads cause the remaining liquid to freeze
- Partly filled compartments reduce braking force
Correct answer: Liquid in a partly filled compartment can still surge within that compartment
Each compartment is a separate space. If a compartment is only partly full, its liquid can still move within the compartment.
Solid bulkheads stop liquid moving from one compartment to another. They do not stop movement inside a compartment that has air space. A partly filled compartment can surge and shift, and the movement can affect the vehicle's handling. Because each compartment is shorter than the whole tank, the surge is generally smaller than in a long smooth bore tank.
