The Importance Of Air

FASS works to improve diesel performance

December 2012 Column

Diesel Tech readers are always trying to get the most performance out of their trucks. As technology has improved over the years and decades, more and more information has become available about how to tweak and refit a truck to get better fuel mileage, more power and consistent stability from a diesel engine.

One area that has received a lot of attention over the years is the effect of air/vapor and other fuel contaminants. A leader in this industry is FASS, which stands for Fuel Air Separation System, and the engineers and other minds at this company seek to minimize the negative effects of air on your truck's fuel system, to improve fuel mileage save your injectors, reduce engine noise, improve throttle response and improve other areas of performance.


Brad Ekstam represents FASS, and has been working on diesel engines since as early as 1991.

"I was working on this out of my garage back then," Ekstam said.

As the FASS system was not developed until 2003, at this time Ekstam was developing a similar fuel system.

"We had a Cummins 444 engine that was operating inconsistently," he explained. "Sometimes it'd run real good, sometimes it wouldn't, and when it wouldn't, it'd fall flat on its face, the clatter was louder and the performance was much worse."

As the Cummins 444 was supposed to be the engine of its time for semi trucks, the truck was taken into Cummins for these issues and warranty work.

"Cummins kept checking for loose fittings, loose lines and leaks," Ekstam said. "The downtime was killing us, but eventually the shops told use they were looking for air in the fuel."

That was the breakthrough they were looking for. Eckstam and his coworkers took this information and applied it to the knowledge that when a suction side fuel filter is removed it is hardly ever full of fuel. This told them they going to always have this problem with conventional filter systems. Fortunately, a call to the Cummins Technical and Warranty Department would open a gold mine of information through a guy named Harold Webb.

Webb supplied them with a service topic written in 1965, on the subject of air in fuel.

"I used to be able to quote this word for word," Ekstam said.

The service topic explained that the source of vapor is fuel itself.

"Like water, fuel contains a certain amount of dissolved air," the service topic read. "Depending on fuel temperature, pressure on the fuel, specific gravity and the amount of aeration which the fuel has been subject to." This information told Eckstam that diesel engines have an inherent problem when it comes to fuel delivery in a real world environment. Fuel starvation is air and/or vapor in fuel

These many factors make the process of separating air and vapor from fuel a very difficult one, and a work that has been in progress for years.

Real-World Testing

One problem FASS has faced in dealing with this issue is that the test conditions for manufacturers' engines are not exactly real-world. For example, in a test environment, a fuel tank may be suspended 15-25 feet above the engine being tested, a far cry from the actual setup of the average diesel truck. These unrealistic conditions allow manufacturers to get great performance results, which are then published, leading people to believe there is no need for further changes to their truck's system.

Positive Flow vs. Vacuum

The boiling point of liquid, in this case diesel fuel, is directly related to the specific gravity (vacuum) which it is subjected to. As fuel is subjected to any kind of vacuum, vapor will be produced. As fuel is subjected to various degrees of specific gravity, vacuum vapors will be produced in various amounts and engine performance deteriorates as a result.

"For example, a dirty fuel filter vacuum, increases the vapor being produced," Ekstam explained.

An engine performs best with clean fuel filters, and as they restrict little by little, engine performance deteriorates little by little. Once the filter reaches a point of restriction to where the engine's maintenance guide indicates changing, or when you decide the lack of performance is intolerable, you'll change the filter, gaining back the lost performance.

Even with a clean filter flow is restricted, everyone understands this.

"Did you know that every 90-degree angle of fuel line fitting is worth about 13 feet of fuel line restriction?" Ekstam said.

This is why Ekstam suggests you should be using mandrel bent fittings especially when the FASS system is not being incorporated into your application. A 90-degree or "T" fitting introduces what is referred to as a liquid eddy current, which creates a restriction while introducing more entrained air and vapor. When the inside diameter is doubled, the flow is quadrupled. Manufactures have reduced the amount of air and vapor by simply enlarging the size of fuel lines along with fuel filters.

Stationary vs. Agitated

Fuel agitation is another major cause of air in fuel. This is one reason why a diesel engine performs better after the truck has been sitting for some time.

It is easy to notice how much smoother, stronger and quieter an engine feels at the start of a drive compared to other times when the engine has been running for hours upon hours. Studies from FASS have shown the amount of entrained air in fuel after 1.5 hours of traveling is equivalent to the vapor being produced from a filter with 11.5 inches of vacuum/restriction. Most engine manufacturers don't want to experience more than approximately 7 inches of restriction in a worst-case scenario.

Fuel Starvation

Air and vapor steal lubricating properties of fuel to the injection system. Fuel creates a barrier between the metal surfaces, like oil creates a barrier between the connecting rods and the crank shaft. Whenever there is a lack of lubrication, galling and scoring will occur from metal-to-metal contact. Some metal-to-metal contact will completely seize the operation of that component.

"Have you ever heard of a hung plunger?" Ekstam asks. "Lack of lubrication is the major cause of this situation."

Other Benefits

A lot of people just buy the FASS filtration system for filtering dirt and water, but they're starting to learn the importance of air. Some models of diesel truck seem to go through injectors one right after another, but after installing the FASS system, they discover that in addition to improved performance, they almost never have to replace their injectors.

"You never know where you're going to be when that injector goes, so making that last longer is a big deal," Ekstam said.

FASS is working hard to convey their message to the diesel truck industry, and what drives them is their belief that their product is superior and always improving.

"At one time our product was loud, because we didn't care much about sound coming off of semis," Ekstam remembered. "But now we're much, much quieter for consumer diesel trucks."



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