Driving liquid tankers isn’t dangerous, but it does require some advanced skills. With cargo that’s always moving, drivers need to stay a few steps ahead of the load, expecting and keeping that movement in mind. Inexperienced tank drivers get into trouble when they let their guard down and something unexpected happens.
That said, driving liquid tanks is immensely satisfying. It naturally makes you a better driver. You must be constantly aware of how the liquid in the trailer will react to any maneuver. From braking too hard or starting too fast, or driving too fast through a turn, liquid loads are very unforgiving.
There are dozens of types of liquid tankers. And they are often designed for specific types of cargo. There are tanks designed for transporting chemicals, food-grade products, dairy products, gasoline, diesel and light fuel oils, tanks for corrosive materials like acid, tanks for really hot products like liquid asphalt, and tanks for really cold products like liquid oxygen and liquid hydrogen.
Most commercial tank truck fleets operate a mix of equipment, usually including generic chemical and food-grade tanks. The tank barrels on these trailers tend to be made of stainless steel of varying grades, and they seldom have any internal baffles to minimize or prevent the dreaded surge. These tanks lack baffles, so they can be thoroughly and efficiently cleaned before each load. Baffles also add to the trailer weight.
Tanker sizes and weights
Most generic chemical tanks are sized to accommodate a variety of cargos. Generic tanks used for U.S. service tend to have capacities around 6,000 gallons (22,700 L). The number of gallons transported depends on the specific gravity, or density of the liquid. Water, for example, weighs 8.3 pounds per U.S. gallon. If you put 6,000 gallons of water in a tank it would weigh 49,800 pounds. With a load like that, you’d likely be overweight.
Sulfuric acid, on the other hand, can weigh nearly 16 pounds per gallon. So theoretically you could only fill the tank half way or less before you hit gross weight limits for the U.S. On the lighter side, some solvents such as naphtha or commercial alcohols can be as light as 6.5 pounds per gallon. You’d need a tank larger than 6,000 gallons to get a full-weight load.
In Canada, generic chemical tank trailers tend to be larger — around 9,000 gallons (34,000 L) — to carry more payload, but the same thinking applies. You can load less of the heavier cargos and more of the lighter materials. For the driver, hauling a half-full trailer of heavy product like acid can make for a very challenging ride. Not only do you have the optimum volume for heavy surge (half full), you also have a heavy wave of product sloshing around inside the tank.
Most commercial tank truck fleets operate a mix of equipment, usually including generic chemical and food-grade tanks.
Food-grade tanks are often made with a finer grade of stainless steel to facilitate proper cleaning. Some edible products can be hauled in stainless chemical tanks as long as proper washing procedures are observed. But the discharge valve fittings are often different, with the food-grade fittings designed for easier disassembly for thorough cleaning. Tanks designed to haul dairy products are stainless steel as well. They have fittings designed for use exclusively by the dairy industry.
Most chemical and food-grade tanks are insulated to keep the product warm. Many products, such as wax or chocolate are loaded at 150-200 Fahrenheit (65-95 Celsius) to help them flow better during loading and unloading. Should they cool in transit, steam coils located under the barrel will reheat the product during unloading.
Chemical and food-grade tanks are almost always washed out between loads at commercial tank wash facilities. They have different wash chemicals and procedures for cleaning out various cargo residues. Drivers are not responsible for actually cleaning the tank, but they are required to inspect it before leaving the wash rack to reload. Carriers provide training on how to inspect trailers. In most cases, the customer will inspect the tank again before loading it.
Sometimes little games are played with inspections, though. If the load isn’t ready when the truck arrives, the customer will sometimes reject the trailer, sending it back to the wash rack to be rewashed rather than pay a demurrage charge on a load that was not ready at the appointed loading time.
C’est la vie.
Dedicated tank trailers
Many types of tanks are designed to haul specific products, such as the B-trains you see hauling fuel to gas stations. These tanks are seldom washed out between loads unless something specialized is hauled. Loading gasoline into a compartment that previously held diesel fuel isn’t a problem because there is hardly anything left in the tank after unloading.
Such tanks have several compartments so they can haul mixed loads of regular and premium gasoline as well as diesel. With these types of trailers, the compartments are almost always nearly full, so there’s no surge to worry about, but their center-of-gravity is high, which demands extra care when cornering and maneuvering.
Tanks designed to haul acids and corrosive products have smaller capacities because the products are so heavy. A typical acid trailer for U.S. service might have a capacity of 3,000 gallons (11,300 L) because that’s all the product they can carry weight-wise.
Hot oil and asphalt tanks are usually made of steel or aluminum, insulated and designed to carry product up to 350-450 Fahrenheit (175-230 Celsius). These are hardly ever cleaned out unless they need repair.
A tanker driver’s duties
Tank drivers have a lot more on their plates than dry-van drivers. First, they have to be familiar with the equipment, how it works and how to inspect it. Cargo tanks have various safety features drivers need to understand, such as pressure relief valves, internal and external discharge valves. Drivers need to know how to quickly close the valves in the event of a spill or mishap during loading or unloading.
Drivers must be familiar with various unloading methods, and there are several. If the customer uses their own pump to unload, the driver simply connects the discharge hose, then opens the hatch on the top of the tank to allow air to enter as the liquid empties. Failure to do so will result in a vacuum inside the tank that can collapse the tank barrel.
Many tractors are equipped with liquid pumps so the driver can pump off the load. This involves running hoses from the trailer to the pump and from the pump to the customer’s tank. There’s some training required here, as improper use of the equipment can result in spills, unhappy customers, and possibly environmental consequences.
Some tanks — particularly acid and corrosive tanks — are unloaded using air pressure. There are no bottom discharge valves on such tanks to reduce the possibility of a leak or accidental discharge. Instead, hoses are connected to lines coming out the top of the tank, but run to the bottom of the tank internally. When air pressure is increased inside the tank, the product is pushed up the discharge pipe and flows to the customer’s storage tank. Pressure is carefully monitored to avoid opening pressure-relief safety valves.
Then there’s gravity, as is the case with gasoline delivery trucks. Hoses are connected to the truck and the underground storage tanks, and the product flows downhill from the truck to the tank. Drivers are expected to ensure there’s enough room in the tank to accommodate the amount of product being delivered.
Most gas stations still use dipsticks and tank calibration charts to determine how much room is in the tank. Many modern tank storage facilities now use internal sensors to measure liquid levels rather than dipsticks or eyeballs.
Loading the tanks
Loading tanks is a bit less complicated, but drivers still need to know exactly what they are doing. Most chemical and food grade tanks are loaded from the top through an open hatch. Pipes or hoses are dropped in, and the product starts flowing. Some facilities use their own loaders; some rely on drivers to do the work.
In some cases, the driver is responsible for dipping the tank to ensure the correct amount of product is loaded. For example, if the driver is to load 4,500 gallons into a 6,000-gallon tank, calibration charts for that tank will show the liquid level should be, say, 12 inches from the top of the tank barrel. The driver stops the flow of product into the tank when the liquid level reaches that mark.
Tanks are also frequently loaded by weight, so the driver would have to calculate how many gallons at specific number of pounds per gallon would constitute 45,000 pounds. There’s not a lot of room for error. Too light and the customer won’t be happy. Too heavy and the inspectors at roadside scales won’t be happy.
Shippers are never happy about having to pump off overages because the product is usually deemed contaminated so it can’t be pumped back into the storage tanks. It instead goes to the slop tank, and carriers are often billed for the spoiled product.
Petroleum tankers are almost all bottom-loaders. Self-sealing fittings connect loading arms to the tanker. The driver uses a keypad to enter the amount of product to be loaded into a given compartment, and then presses the start button. Various electronic crosschecks ensure the vents on top of the tank are open to prevent pressure buildup and to ensure the internal discharge valves are open to allow product to flow into the compartment.
Petroleum tanks did away with top loading years ago, for safety reasons, but it’s still done occasionally with certain commodities.
Some chemical products require additional safety procedures and precautions to prevent fumes from escaping to the atmosphere. For example, some products are reactive with the oxygen in air, so they are loaded in closed-circuit loops using nitrogen to fill the void in the tank. In such cases, loading and unloading is handled by experts, but drivers must be familiar with the special handling requirements in case some emergency arises in transit.
As one might imagine, there are tons of product-specific handling procedures involved, and in many cases, specific personal protective equipment required. There’s much for a tank truck driver to know about the equipment, the products, and the rules and regulations pertaining to the transportation of dangerous goods or food-handling requirements.
Pay and working environment
Annual earnings for tank truck drivers tend to be higher than van and reefer drivers. Often the mileage rates aren’t that different, but tank drivers see compensation for more of their non-driving activities, such as loading, unloading, and inspecting equipment.
Loading a typical chemical or food-grade tank trailer takes a few hours, but there can be additional waiting time for equipment inspections and lab approval before shipping or receiving the load. That time is often paid hourly, or at a flat rate that covers the time.
Petroleum tank drivers are often paid hourly from the beginning to the end of the shift, though some in longer haul service may get mileage, too.
Due to the nature of some cargoes, safety is pervasive in the tank truck sector. If you don’t like working in a highly structured environment, this may not be a job for you. Despite the elevated risks from dynamic loads, hazardous cargoes, sometimes-complex product handling requirements, the tank truck sector has one of the safest records in trucking.
As I suggested earlier, hauling liquid tanks forces you to become a better, more cognizant driver. There’s little margin for error on cornering or failing to account for the risks posed by the surging liquid in the tanks. You either drive the truck or it drives you. And the latter usually doesn’t end well.
Driving liquid loads
Tank truck drivers pioneered the art of progressive shifting long before it was considered a fuel-saving technique. Going slow and easy up through the gears keeps the liquid from surging violently back and forth. As you accelerate, the liquid flows to the rear of the tank, builds to a critical mass there and then surges forward. This repeats until the truck is up to a steady speed and the liquid settles down.
When upshifting with a manual transmission, drivers would shift gently from first to second, second to third, and then pause and wait for the liquid to surge forward. That’s when they’d slip into fifth gear to take advantage of the liquid’s momentum. Good tank drivers quickly figure out how to manage different types of liquid (thick or thin) and half-full or three-quarters-full tanks. They behave differently.
Stopping can be even trickier. When braking, the load surges forward. Gentle braking yields a gentle surge. Hard braking results in a hard thump from behind that can rattle your teeth. So, good tank drivers anticipate stops and begin decelerating much earlier. Generally gentle sustained brake applications are smoother than downshifting through the gears. That just perpetuates more movement of the liquid.
Perhaps the worst scenario is a hard stop on a slippery road. The surging liquid will often push the truck forward after it has stopped, possibly into an intersection or over the top of a car stopped in front of the truck. Twenty or thirty tons of liquid in motion are no match for a few dozen tires on slippery pavement.
Perhaps the worst scenario is a hard stop on a slippery road. The surging liquid will often push the truck forward after it has stopped.
Driving up or down a hill is challenging for the same reasons described above. If you downshift while climbing, the change in momentum will get the liquid surging forward then backward and can cause missed downshifts. Downhill braking gets the load surging forward, which will actually push the truck forward while you are trying to slow it down. That does your brakes no favors. Good tank drivers will slow down well before beginning their descent, pick a gear, throw on the engine brake, and use the service brakes sparingly or not at all to keep the liquid from surging.
And, of course, the liquid will surge sideways in a turn, throwing a lot more weight outward in the opposite direction of the turn. This clearly poses a rollover hazard. Drivers that go into turns too fast are at vastly elevated risk of a rollover — especially in a tall tank trailer that’s only partially full.
Tank carriers are having a hard time finding drivers these days, harder still than their van and reefer counterparts. The bar for “qualified drivers” is set pretty high in the tank truck sector. They don’t want cowboys or risk takers, and they are very reluctant to hire rookie drivers.
If you’re looking for a challenge and a job that keeps you on your toes, maybe tank driving is something to consider. I drove chemical tanks for more than 15 of my 20 years on the road. I can say truthfully if I ever went back to driving, I’d be looking for tank driving job.
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