Warbird Information Exchange

Flapper Valves
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Author:  Chipfire [ Mon Jul 13, 2015 10:09 am ]
Post subject:  Flapper Valves

I saw a report that fuel tank flapper valves were responsible for an unaccounted loss of power during an approach.

(Low fuel state following aerobatic flight using 20 gallon reserve tank position. Selected to RH restored power.)

3 in one tank and 1 in the other tank seized.

Is there an easy way to check flapper valve function without removing tanks?

Author:  rcaf_100 [ Mon Jul 13, 2015 12:26 pm ]
Post subject:  Re: Flapper Valves

Someone forwarded the same report to me, and the only references I can find online that includes 'T-6' and 'flapper valves' are in reference to the Texan II.

If I'm wrong, someone please correct me...


Author:  Chipfire [ Tue Jul 14, 2015 4:33 am ]
Post subject:  Re: Flapper Valves

It was a UK CAA Mandatory Occurrence Report related to a 1944 SNJ-7C registration G-BRVG
3 in one tank failed and one in other tank.
Report hints it may have been laid up for some time as it mentioned that there was sufficient fuel to cover valves during no-flying period.

There was previously fuel starvation on approach following aerobatics.

I would like to establish a good way to ensure flapper valves are okay without removing tanks or sumps - could boroscope perhaps but needs to be a tank safe probe.

Any ideas?

Author:  jdankos [ Tue Jul 14, 2015 7:19 am ]
Post subject:  Re: Flapper Valves

You should be able to reach them and maybe see them by removing the sump at the bottom of the tanks. I always thought the flappers just slowed down the sloshing of the fuel during turns etc. I think there are other openings in the ribs to allow fuel to transfer to the sump.

Author:  Matt Gunsch [ Wed Jul 29, 2015 7:58 am ]
Post subject:  Re: Flapper Valves

if you drain the tanks, you may be able to see them with a mirror and flashlight, but if they have never been changed, change them, they are flaps of rubber and I have found them broken off and laying in the tanks.

Author:  bdk [ Fri Jul 31, 2015 5:52 pm ]
Post subject:  Re: Flapper Valves

Ditto what Matt says. If you don't know when they were changed you should change them.

Author:  cessnaguy [ Mon Mar 21, 2016 10:13 am ]
Post subject:  Re: Flapper Valves

I knew someone whose engine quit when he nose over somewhat steeply because he had come up on his refueling airport sooner than expected. The fuel all sloshed away from the tank outlet because his flappers had rotted and fallen apart. After landing, the engine restarted fine in 3 point attitude. His wife was in the back seat and she wasn't happy.

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