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8.2 – Driving Tank Vehicles
Hauling liquids in tanks requires special skills because of the high center of gravity and liquid movement.
8.2.1 – High Center of Gravity
High center of gravity means that much of the load's weight is carried high up off the road. This makes the vehicle top-heavy and easy to roll over. Liquid tankers are especially easy to roll over. Tests have shown that tankers can turn over at the speed limits posted for curves. Take highway curves and on-ramp/off-ramp curves well below the posted speeds.
8.2.2 – Danger of Surge
Liquid surge results from the movement of the liquid in partially filled tanks. This movement can have adverse effects on handling. For example, when coming to a stop, the liquid will surge back and forth. When the wave hits the end of the tank, it pushes the truck in the direction the wave is moving. If the truck is on a slippery surface such as ice, the wave can shove a stopped truck out into an intersection. The driver of a liquid tanker must be very familiar with the handling of the vehicle.
8.2.3 – Bulkheads
Some liquid tanks are divided into several smaller tanks by bulkheads. When loading and unloading the smaller tanks, the driver must pay attention to weight distribution. Do not put too much weight on the front or rear of the vehicle.
8.2.4 – Baffled Tanks
Baffled liquid tanks have bulkheads in them with holes that let the liquid flow through. The baffles help to control the forward and backward liquid surge. Side-to-side surge can still occur. This can cause a rollover.
8.2.5 – Unbaffled Tanks
Unbaffled liquid tankers (sometimes called “smooth bore” tanks) have nothing inside to slow down the flow of the liquid. Therefore, the forward-and-back surge is very strong. Unbaffled tanks are usually those that transport food products (e.g., milk). (Sanitation regulations forbid the use of baffles because of the difficulty in cleaning the inside of the tank.) Be extremely cautious (slow and careful) in driving smooth bore tanks, especially when starting and stopping.
8.2.6 – Outage
Never load a cargo tank totally full. Liquids expand as they warm and you must leave room for the expanding liquid. This is called “outage.” Since different liquids expand by different amounts, they require different amounts of outage. You must know the outage requirement when hauling liquids in bulk.
8.2.7 – How Much to Load?
A full tank of dense liquid (such as some acids) may exceed legal weight limits. For that reason, you may often only partially fill tanks with heavy liquids. The amount of liquid to load into a tank depends on:
- The amount the liquid will expand in transit.
- The weight of the liquid.
- Legal weight limits.
Multiple-Choice Questions:
What have tests shown about tankers, and how should you manage it?
- Stopping distance will decrease as the liquid sloshes forward. Press the brakes with more of a "stabbing" motion to quickly slow the vehicle.
- Tankers will not turn over if you follow the posted speed limit signs in curves. Always stay at the posted speed limit for any curve
- Tankers can turn over at the speed limits posted for curves. Take highway curves and on-ramp/off-ramp curves well below the posted speeds.
- Tankers will be more likely to turn over if the center of gravity is low. Keep the center of gravity high when loading a tanker.
Never load a cargo tank totally full. Liquids expand as they warm and you must leave room for the expanding liquid. What is this extra room called?
- Drainage
- Outage
- Seepage
- Compartmentalization
Some liquid tanks are divided into several smaller tanks by:
- Luvers
- Mastheads
- Bulkeads
- Dykes
Describe unbaffled liquid tankers:
- They are sometimes called “masthead” tanks and they have wires inside to slow down the flow of the liquid from side to side.
- They are sometimes called “rodding” tanks and they have mastheads inside to prevent the liquid from sloshing side to side
- They are sometimes called “lockhead” tanks and they have completely separate tanks within the main tank to divide up the liquid
- They are sometimes called “smooth bore” tanks and they have nothing inside to slow down the flow of the liquid. Therefore, the forward-and-back surge is very strong.
Liquid surge results from the movement of the liquid in partially filled tanks. What are some characteristics of liquid surge?
- When coming to a stop, the liquid will surge back and forth
- If the truck is on a slippery surface such as ice, the wave can shove a stopped truck out into an intersection
- All these are correct
- When the wave hits the end of the tank, it pushes the truck in the direction the wave is moving.
Some liquid tanks have bulkheads in them with holes that let the liquid flow through. What are these called, and what do they do?
- They are called centuries and they help prevent pressure from building up in the tank
- They are called mastheads and they help prevent the sides of the tank from getting crushed inward
- None of these are correct
- They are called baffles and they help to control the forward and backward liquid surge.
What type of product do unbaffled tankers normally haul, and why?
- They transport chemicals because of the special anti-corrosive properties of the unbaffled tanks
- They transport chemicals to prevent the sloshing of the liquid from side to side
- They transport gasoline because they need to divide the tank into separate compartments for the different grades of gasoline
- They transport food products (e.g., milk) because sanitation regulations forbid the use of baffles because of the difficulty in cleaning the inside of the tank.
Hauling liquids in tanks requires special skills because of:
- The high center of gravity
- The movement of the liquid
- How easily they can roll over
- All these are correct
High center of gravity means:
- Much of the load's weight is carried high up off the road. This makes the vehicle top-heavy and easy to roll over.
- Sloshing will decrease the height above the road that the weight of the liquid is centered
- That much of the load's weight is carried low down near the road. This makes the vehicle top-heavy and easy to roll over.
- Gravity will center its influence on the liquid closest to the frame of the tractor
The amount of liquid that can be loaded into a tank depends on:
- All these are correct
- The amount the liquid will expand in transit.
- Legal weight limits
- The weight of the liquid.
A full tank of dense liquid (such as some acids) may exceed legal weight limits. For that reason, you may often only partially fill tanks with heavy liquids. The amount of liquid to load into a tank depends on:
- The amount the liquid will expand in transit.
- The weight of the liquid.
- Legal weight limits.
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