Tank vehicles

A commercial vehicle built to carry liquid or gas in a large tank.

Tankers carry milk, fuel, chemicals, or gas, and the cargo moves inside the tank, so the truck handles differently. The legal definition is a tank of more than 119 gallons, with 1,000 gallons or more in total. Hauling one usually needs the N endorsement.

Differs by state: The capacity definition is uniform in all manuals: an individual tank of more than 119 gallons and a total of 1,000 gallons or more. The tanks may be permanently or temporarily attached. Some manuals (GA, ME, PA, WY) still also print the pre-2011 rule, under which any permanently mounted cargo tank counted. Legacy tables in ID, MI, VT and WV do the same. Maryland's plain-language text joins the two limits with 'or'. A question that turns on a small permanently mounted tank gets opposite answers in those manuals.

Example: Rolling up to a red light with a half-full milk tanker, you brake early and keep steady pressure on the pedal.

Also called: tanker, tank vehicles, tanker truck

• baffle
• center of gravity
• liquid surge
• tank and hazmat endorsement
• tank vehicle endorsement

Liquid sloshing in a partly filled tank when speed or direction changes.

Brake, and the liquid rushes forward, then slams back. The wave pushes the truck the way it moves. On ice it can shove a stopped truck into the intersection.

Example: Stopped on a slick downhill ramp, you keep the brakes firmly applied until the wave inside the tank has settled.

Also called: surge

• baffle
• center of gravity
• rollover
• smooth bore
• tank vehicle

A perforated wall inside a tank that slows the liquid's forward surge.

Baffles are bulkheads with openings. Liquid still passes through, but slowly, so the forward surge is weaker. They do nothing for side-to-side surge.

Example: Driving a baffled fuel tanker, you still slow well before the curve because the liquid can swing sideways.

Also called: baffles, baffled tank

• bulkhead
• liquid surge
• smooth bore
• tank vehicle

A solid wall that divides a tank into separate smaller compartments.

Unlike a baffle, a bulkhead has no holes. Each compartment can hold a different liquid. Loading one end heavier than the other upsets the vehicle's balance.

Example: Unloading only the rear compartment at the first stop, you check that the front axle is not now carrying too much.

Also called: bulkheads

• axle weight
• baffle
• liquid surge
• tank vehicle

A tank with nothing inside to slow the liquid; an unbaffled tank.

Food-grade tankers, like milk trucks, are smooth bore because baffles are hard to clean. The surge inside is strongest. Starting and stopping need extra care.

Example: Hauling a smooth bore load of juice, you ease off the clutch at every light to keep the wave small.

Also called: smooth bore tank, unbaffled tank

• baffle
• bulkhead
• liquid surge
• tank vehicle

Space left empty in a tank so warming liquid can expand.

Never fill a tank to the top. Liquids grow when they get warm. Different liquids need different outage, and you must know the figure for your load.

Does not mean: Not a power outage; in tanker language it is the headspace left in the tank.

Example: Loading a tanker on a cold morning, you stop below the top because the product will swell in the afternoon heat.

Also called: ullage

• gallons
• liquid surge
• tank vehicle

The balance point of a vehicle's weight; higher means easier rollover.

Stack cargo high and the balance point rises. A tall liquid load raises it most. A high center of gravity means slow down more for curves and ramps.

Example: With pallets stacked to the roof, you take the exit ramp well under the posted speed because the load sits high.

Also called: high center of gravity

• cargo securement
• curve speed
• liquid surge
• rollover
• tank vehicle

The N endorsement a CDL needs to drive a tank vehicle.

You earn it by passing the tank knowledge test. The cargo does not have to be hazardous; milk and water count. Hazmat in a tank needs both N and H, written X.

Differs by state: The capacity test is printed identically in every manual: an individual tank over 119 gallons and 1,000 gallons or more in total. Some manuals (GA, ME, PA, WY) still also print the pre-2011 rule, under which any permanently mounted cargo tank needed the endorsement. Legacy tables in ID, MI, VT and WV do the same. Most manuals attach N to Class A or B and add Class C only for hazmat loads. Arizona and California name Class A, B or C without that condition.

Example: Offered a job hauling liquid fertilizer, you add the N endorsement before your first run.

Also called: N endorsement, tanker endorsement

• endorsement
• hazmat endorsement
• tank and hazmat endorsement
• tank vehicle