Guys,
Yesterday I completed my 2nd flight on my Jet Legend T-45. At the time of defueling I realized that the wall of UAT compresses inward as I defueled. Like wise it inflates a little more than its normal shaps as I fuel it up. I have checked for all kinds of kinking and have also pushed air through the fuel vent that is coming out of fuel tank. It seams normal.... the fuel goes in and out of tank without any problem when pushing air manually my mouth. The problem starts as soon as I attach fuel pump to fuel and de-fuel.
Please let me know what could be wrond here.

Also there is no bubble coming in the fuel pump. There is no air leakage.

Regards
Asif

This is normal

Normally when you fuel & de-fuel the aircraft, you are pushing fuel through it at much higher rate than will be the case when the aircraft is flying. It's not a problem if during this "fast flow" the UAT bulges or compresses a bit, as long as it can sustain normal full-power flow rate.

If you are fueling or de-fuelling extra fast though, do keep an eye on the fittings as you may actually induce a leak - I've had a UAT start leaking at one of the brass nipples when over-pressurised like this.

[edit: fix typo]

Thanks
Gordon & bcovish. I think my pump is pump fuel at high rate. I am using 11v battery for 7.2v pump.... I guess I need to change my battery !!!!
Thanks guys.
Regards
Asif

Asif,

You identified your problem! Use a battery with voltage a little lower than the rated voltage of the pump and it will work slower and minimize any bulging or collapsing.

Steve,
I am glad I have realized, what was wrong ;-) I was really concerned with this issue.

Regards


Asif

Hey Asif - how are you doing? Its been a long time. Send me an email. Jim

FWIW I am using a 5 cell 6V battery on a Jersey Modeler pump to keep the stress low on the fuel system.

Hey Jim,
Nice to hear from you man!!!! its been long time. Will drop you and email.

Asif

Causeitflies,
I used to used same battery.... will switch back to 5 cell

Regards
Asif

Another fix to this without changing the battery is to put a T fitting in the pump inlet and outlet fittings with a manual festo valve plumbed in between them. The idea is with the Festo full open the pump just recirculates unto itself. As you close the valve more fuel is pushed to the tanks.

Why bother this route, well my Bobcat XL fills with abnormally high backpressures I attribute to small 1/8" brass and multiple tanks, then my Kingcat with 4.5L and larger would take forever with the Bobcat battery setup on pump thus, I went with the recirc bypass to tailor the fuel flow to optimal. .02

c/f
nice idea man!!!! ;-)

Asif