What’s Wrong With Air Bags?

By LYNDON DOHMS, RET, API 653 Certification

High pressure flexible air bags can have some useful applications, but they are not well suited to lifting tanks safely or efficiently. Several hazards are evident:

Airbags, like car tires, are subject to instant blowouts. This significant explosion puts personnel in danger of injury from flying debris, and from the tank shifting unexpectedly. Hydraulic systems can develop leaks, but the effect is slow and non-hazardous, even if a person is standing right near the leak. We have time to close valves, and make other adjustments to ensure safety.

A tank lifted on airbags is like a tank resting on balloons. The airbags have limited contact with the bottom of the tank, and that contact decreases the more the bag is inflated vertically. This makes the tank highly susceptible to wind changes. When using airbags during a windy day, the tank will actually shift its horizontal position as it moves up or down, to the point where the support cribbing will no longer be centered under the load.

But MTS long hydraulic jacks contact the tank solidly in two places; both under the shell and 5m up the side of the shell, with or without welding. This provides rigid steel for vertical and horizontal support, and the foot of the jack is firmly planted on the ground rather than on wooden cribbing. We have had a tank fully elevated during a surprise windstorm of over 100km per hour, and had no noticeable sway.

Lifting and lowering with airbags is very slow compared to long stroke hydraulics. A tank that is elevated with airbags when a serious windstorm approaches cannot be lowered in a safe or timely manner. They just have to leave it up there. With our hydraulic system, however, a tank elevated 3m can be safely lowered to the ground in a matter of 20 minutes or less. Our highlift safety blocking is usually prefabricated, bolted together wooden cribs.

Unlike the MTS metered hydraulic system, an airbag system is not capable of lifting a tank in a perpendicular manner. This means that the tank on airbags is constantly tilted off balance and being subjected to unequal stress points during the lift. The wooden support cribbing below the airbags is also subject to these unequal weights, and can start a chain reaction failure if there is a weak timber in the wrong place.

Why take these risks? Airbags have not one advantage over hydraulics.