Inspecting Tanks and Transfer Equipment

Pre-Trip Inspection and Leak Detection

Tank vehicles come in many different types and sizes. Because each design has its own plumbing, hardware, and structural layout, tank vehicles have special items that a driver needs to check during a pre-trip inspection. Drivers must check the vehicle's operator manual to learn how to inspect their specific tank vehicle properly.

On all tank vehicles, the most important item to check for is leaks. Check under and around the vehicle for signs of any leaking, including leaks from tanks carrying liquids or gases. In addition, the driver must inspect the tank's body or shell thoroughly for dents and leaks.

Carrying liquids or gases in a leaking tank is strictly prohibited by law. In fact, transporting liquids or gases in a leaking tank is a crime. If you drive a leaking tank vehicle, you will be cited by law enforcement and prevented from driving further. You will be cited and prevented from driving further, and you may also be liable for the clean-up of any spill.

Check under and around the vehicle for leaks, and check the tank's body or shell for dents or leaks. CDL test formats and passing scores vary by state; consult your state's CDL manual for test details.

Manifolds, Valves, and Compartment Management

A tank vehicle relies on an intricate network of piping and controls to load, contain, and discharge its cargo safely. Check the intake, discharge, and cut-off valves, and make sure they are in the correct position before loading, unloading, or moving the vehicle. These components control the direction and flow of cargo and prevent accidental discharges while the vehicle is parked or in motion.

Valves must be in the correct position before loading the vehicle, before unloading the vehicle, and before moving the vehicle down the road. Make sure the intake, discharge, and cut-off valves are in the correct position before loading, unloading, or moving the vehicle.

Some liquid tanks are not a single large vessel; instead, they are divided into several smaller tanks by solid walls called bulkheads. When operating a compartmentalized tanker, drivers must pay close attention to weight distribution when loading smaller tank compartments and when unloading smaller tank compartments. When loading or unloading the smaller tanks, pay attention to weight distribution; do not put too much weight on the front or rear of the vehicle.

Tank Internal Design: Baffled vs. Smooth Bore Tanks

The interior construction of a cargo tank strongly dictates how the vehicle behaves on the road. The excerpt describes tanks divided into smaller tanks by bulkheads, baffled tanks with holes through their bulkheads, and un-baffled tanks with nothing inside to slow liquid flow. Understanding how the inside of the tank is built allows a driver to anticipate how cargo movement will influence vehicle handling.

Baffled liquid tanks have bulkheads containing holes that let the liquid flow through. These internal barriers help control forward and backward liquid surge during acceleration and braking. However, drivers must realize that side-to-side surge can still occur in baffled liquid tanks. Baffles help control forward-and-backward surge, but side-to-side surge can still occur and cause a rollover.

Un-baffled liquid tankers, which are sometimes called smooth bore tanks, have nothing inside to slow down the flow of liquid. As a result, forward-and-backward surge is very strong in un-baffled tanks. Smooth bore tanks are usually used to transport food products, such as milk. Sanitation regulations forbid baffles in food tanks because of the difficulty in cleaning the inside of a tank that contains internal dividers.

Smooth bore tanks have nothing inside to slow liquid flow, so drivers must be extremely cautious, slow, and careful when driving them. Handling these vehicles requires extreme caution especially when starting and stopping, as the unrestrained wave action inside the tank can easily push or destabilize the truck.

Liquid Surge, Center of Gravity, and Rollover Prevention

Operating any liquid tanker requires specialized driving habits because of the physics governing fluid loads. Liquid surge results from the movement of liquid in partially filled tanks. Liquid movement in a partially filled tank can adversely affect handling; for example, liquid can surge back and forth when the vehicle stops.

When a vehicle with a partially filled liquid tank comes to a stop, the liquid can surge back and forth. When a surging liquid wave hits the end of a tank, it tends to push the truck in the direction the wave is moving. On a slippery surface, such as ice, liquid surge can shove a stopped truck out into an intersection even after the driver has brought the wheels to a complete halt. Because of these distinct physical forces, the driver of a liquid tanker must be very familiar with the handling of the vehicle.

Compounding the challenge of liquid surge is vehicle balance. A high center of gravity means much of the load's weight is carried high up off the road. Carrying load weight high off the road makes a vehicle top-heavy, and a top-heavy vehicle is easy to roll over. Liquid tankers are especially easy to roll over.

In fact, tests have shown that tankers can turn over at the posted speed limits for curves. Tankers can turn over at the speed limits posted for curves, so take highway curves and on-ramp and off-ramp curves well below the posted speeds. Instead, drivers must take highway curves well below posted speeds, take on-ramp curves well below posted speeds, and take off-ramp curves well below posted speeds.

Thermal Expansion and Cargo Tank Outage

Another vital principle of tanker operation is managing the volume of the cargo. A cargo tank must never be loaded totally full. Never load a cargo tank totally full; leave room for liquid to expand as it warms.

Liquids expand in volume as they warm. Because a tank is a rigid container, drivers must leave room in a cargo tank for expanding liquid. The empty space left for expanding liquid in a tank is called outage. Leave room for liquid to expand as it warms, and know the outage requirement for the bulk liquid you are hauling.

Not all liquids behave in the same manner. Different liquids expand by different amounts, which means different liquids require different amounts of outage. A driver must know the outage requirement when hauling liquids in bulk to ensure the tank is loaded safely for transit across varying temperatures and distances.