The Centre of Gravity is Moving Constantly

the centre of gravity is moving constantly

The issue in all tanker trailers is that the centre of gravity is moving constantly in the barrels and that does have a detrimental effect on stability. Experienced drivers learn though experience just how to handle the three trailer and any movement or sway which eventuates.

The Base Air system has the effect of reducing the effect of any sway and improving the suspension’s ability to keep the trailers upright along the length of the more than 50 metres long combination.. 

Emerald Carrying Company have fitted the Base Air on road train fuel tankers running out of its large yard on the outskirts of Townsville, which is home to the fuel hauling branch of Emerald Carrying Company (ECC). From this base the operation services fuel customers all over North and Western Queensland, covering the biggest runs across to Mount Isa, 896km to the West, and beyond. 

the centre of gravity is moving constantly


“When you look at what we do, they’re called dangerous goods for reason,” says Troy Sabin, the ECC Townsville Depot Trainer. “When you look at the adverse conditions that we drive in, when we look at our western roads, they can be less than optimal.

“What I’ve noticed with the trailers, with the standard air system, compared to what the Base Air fitted trailers do, is there seems to be a bit more stability there. It seems to get the airflow quicker, you know, as opposed to the standard system. 

“The quad axle triple is grossing out at 152 tonnes GCM, as opposed to the 136 tonnes achievable with triaxle trailers.You can see the difference in the way those trailers respond to what the driver is doing. Whether it’s at 70km/h at 90km/h here at 30km/h. You can see with that improvement to the suspension system, what an improvement it makes to the handling. You notice the difference straight away. You can see the difference when you sit behind them on the road.”

“This suspension now gives you more control or control over what’s going on,” says Troy . “It gives us the ability to stiffen up the suspension, where it needs it. It takes out the slosh factor. There’s less chance of that EBS coming on, if the suspension is stabilised. You have still got to watch what you’re doing, you can’t be a drone guy. You can’t just think ‘I’ve got this wonderful air system’.”

the centre of gravity is moving constantly

The BaseAir product comes in the form of a kit which can be fitted to both trucks and trailers. Initially, Martins were fitting the system just on the trailers, but later realised adding them to the prime mover’s rear suspension resulted in an even better solution.

In essence, what has been developed is an enhancement of the existing air suspension system. The normal system will be fitted with one height control valve (HCV). The combination of the HCV with the road conditions sees air flowing around a unitary air system to keep the truck chassis at the desired height from the road.

What the BaseAir system does is separate it into two parallel systems, one on the left and one on the right. When the truck is running in a steady condition, the two separate air circuits are selectively combined to have the same effect as we would expect from a standard air circuit.

This situation changes when the trailer starts to lean over. There are two HCVs, one on either side of the truck and when a discrepancy appears, the HCVs limits the movement of air from one side of the truck to the other.

At a basic level, in a normal system, as the trailer starts to lean to the left, for example, air would normally flow from the left across to the right, to equalise pressure across the unitary circuit. When this lean happens in the BaseAir system, the valves close and hold the air in the airbags on the left, to hold the trailer up and reduce the lean.

The Dual Pressure Protection Valve is placed at the point where the two separate circuits diverge at the connection from the air tank. The airlines to the two HCVs are the same length, as are the lines from the HCV to the airbags.

There is an extra airline in this system, the cross-flow line passing air from one side to the other, shut off and released by the HCVs on either side. Anytime the HCVs detect a lean of less than 1.5 degrees, the crossflow is fully open and allows air to flow feely between the two circuits, exactly the same as in a normal system.

Once that lean exceeds the 1.5 degrees the system will limit air flow, the cross-flow is no longer available, and the two sides of the suspension act separately. This is how the effect of holding the trailers and prime mover up straighter is achieved, by simply stopping the suspension from allowing the lean in the trailer when it reaches a certain level.


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