In this answer to this question, "pressure refueling" was given as a reason to not worry about fuel vapors escaping when refueling larger aircraft.
What is pressure refueling and how does it work?
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2 Answers
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With a pressure fueling system, rather than fueling through holes in the tops of the wings, a fuel truck or fuel hydrant is used to push fuel into the airplane through a fitting at about 50 psi. The fuel fitting is generally in the right wing. A fueling control panel allows the fueler to fill the tanks to the amount called out by the flight plan.
These large aircraft still have an overwing fueling port for those times when the pressure fueling system is inoperative.
There is nothing to prevent fuel vapors from escaping to atmosphere.
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1$\begingroup$ Is that all it is? Essentially, pumping rather than pouring the fuel? How does this control vapours? $\endgroup$ May 16, 2015 at 17:28
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$\begingroup$ They're not pouring out the open "hole" where the fuel would go in; they're escaping through dedicated fuel tank vents? $\endgroup$– DJohnMMay 16, 2015 at 18:06
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2$\begingroup$ @DavidRicherby the connection is air and liquid tight. There shouldnt be vapor in the first place but if there is it gets pumped into the planes internal plumbing as there is no atmospheric venting possible at the refuel panel. $\endgroup$– caseyMay 16, 2015 at 19:27
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$\begingroup$ @casey help enlighten me. How to force vapor into the internal plumbing when you refuel tonnes of JetA at a time? Fuel will occupy space previously taken by vapor. Where does the vapor goes? $\endgroup$ May 16, 2015 at 21:32
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$\begingroup$ @vasin1987 on the way to the tank if there is any vapor in the hoses/plumbing it will be in bubbles suspended within the flowing liquid. Once fuel gets to the tanks there are vents in the wing to allow air out of the tanks as liquid fuel is pumped in. Also note the plumbing differs with different airplanes. Some (like the picture above) pump pretty directly into the tank, while others feature single point refuelling and fuel is delivered to various tanks from a single fuel connection and thus more plumbing is involved in the airplane. $\endgroup$– caseyMay 17, 2015 at 1:57
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I'm an Air Force fuel systems supervisor.
Yes...air is pushed out of the tank vents during fueling operations, but there are no flammable vapors in jet fuel until the fuel temperature exceeds at least 100 deg. F. There is odor, but not dangerous vapors until that temperature is reached.
The single point system is primarily necessary to reduce spills...it's a closed system that allows faster fueling with less environmental impact.
