I’ve always been a BVM/Hanson/Kingtech UAT user for no real reason in particular, just came into jets always using that style. On a current project I opted to try a Digitech, which really I have no complaints about with the exception of the fill port being at the 6 o’clock position on the face of the tank. So what I’m finding in contrast to my BVMs is it’s pretty dang hard while filling to get that last bit of air out of the top, but worse than that is if I don’t act quickly to disconnect my fill line after shutting off the pump it starts siphoning the fuel right back out of the bottom of the UAT. The model sits pretty tall and thus the UAT is higher than my pump station when set on the ground, nevermind the fact that I sometimes fuel my jets while on a stand or a table with the fuel jug on the ground. Obviously I could elevate the pump/can when fueling to prevent this, but I also thought about just rotating the UAT cylinder 180 degrees in its mounts to have the fill at the top, which would hopefully prevent this. Am I the only one that has this issue? Am I overthinking it?

Not all cylinder UAT are made with a fill line at the bottom...

https://www.ultimate-jets.net/collec...er-ufbk-series

Because bubble are at the top....so it stay submerged.....at least it’s what I think and this way you can empty the whole thing, which can be useful , I used them but don’t make them

I’m using a Digitech and have had great results. I rotate my Havoc nose up for a few seconds to clear all the bubbles out of the UAT when filling. I’ve been use the no-drip fitting from Jersey Modeler for years for my fill line to prevent dripping fuel on or in my jet so siphoning after disconnecting is a non issue.
JS

Never ever empty your air trap. You would dry out your air separator and risk lots of bubbles intake on the next run.

Sometime I wonder......... I only empty it when I do maintenance..........Ahah and I go no bubble on the next run

I can just imagine the mess if I decide to change a line with the thing full.....

You just have to be very careful when changing a line. I did this yesterday when changing a line and emptied the trap half way and didn't spill a drop. Next thing I know fuel is running out the nose door Who in the heck let go of that line?

LOL good one.......

Just turn your UAT nose up and change your line.

LOL or just empty the UAT and change the line.....

If it’s such an issue maybe they should sell them full with options for Jet 1-A, Kero or Diesel.... (joking ahah)

Right, I use the Jett-Flow fittings to shut off the flow when disconnecting, like I said it's only an issue when still connected and with the airplane higher than the fueling station. Which, since I'm working on a new build, the plane is on the bench and the fueler is on the ground. It just caught me off guard when I fueled the airplane, shut off the fuel pump, went to grab something else for a bit and came back to a bone dry airplane. Like I said I suppose I'm just overthinking it, will just have to adjust my practices.