Piper Sump Leaks

[JediNein]

Greetings,
For the technically minded, is there a certain drip rate from the underwing quick drains that will allow airflow to suck a tank dry?
Will the inside tank pressure vs. the outside pressure serve to seal a leak, say a piece of dirt trapped under the rubber plug in the drain?
Or does airflow act as a siphon, sipping out fuel until there is none left?
Would a damaged fuel vent cause a siphon in this situation where it would otherwise not cause problems?
I'm trying to figure out why one leaky sump did not drain a tank, the next one did, and the third one caused no problems. Yes, the mechanics have worked on the plane all three times.
Fly SAFE!
Jedi Nein

 

[EagleRJ]

I don't think the airflow would siphon the fuel out at a rate faster than the leak rate on the ground. Do you have the locking petcocks that stand away from the wing surface or the flush holes that you push the testing jar's pin into?

The fuel tanks' drains are intended to avoid negative pressure situations, but they don't provide much positive pressure either. The pressure in the tank is very close to ambient pressure. The rate of the leak is probably governed by things like temperature changes at altitude and the amount of fuel (weight) over the drain.

One thing is for sure. If you have a working leak, not only are you wasting fuel, your fuel consumption is unknown now. I wouldn't take the plane on any long trips until the problem is fixed!

 

[JediNein]

The plane is back in airworthy condition after replacement of both sumps and fuel tank vents. The sumps are the locking quick drains not the button-types like on Cessnas.

How large does the hole need to be to lose 25 gallons in 30 minutes? Is this leak easily visible on the preflight? What would be the equation?

How about losing 25 gallons in 90 minutes? Is this leak easily visible on preflight?

With the drain full-open, how long does it take to empty the 35 gallons tank when on the ground, such as before fuel tank maintenance?

Thanks!
Jedi Nein

 

[avbug]

25 gallons in 30 minutes is a rate of 50 gallons an hour. This is far from an airworthy condition, losing nearly a gallon a minute at that rate.

The curtis drains described run about fifteen dollars each, some up to twenty five or so. The o-ring on the drain end internally is not replaceable, nor is the drain repairable, per Curtis.

You should see no significant increase in fuel loss from that drain in flight, though a very slight increase in internal tank pressure will generally occur.

If the aircraft were losing any appreciable and measureable amount of fuel, much, much less than the amount described, it should have been grounded and repaired without any discussion.

Curtis drains either work, or they don't. If they don't, they need to be replaced.

Normally an open curtis drain will empty at a rate of one to three gallons a minute.

If you are attempting to drain the tank, usually it's easier and faster, to simply remove the drain until the tank is empty, or siphon through the filler neck.

If repeatable leakage problems occur, the tank most likely contains debris. All drains should be removed and the entire fuel system flushed. It should be flushed through a filter to determine what contamination is or has been in there. You should drain any fuel removed from the tank through a filter, too.

 

[JediNein]

Thanks guys!

I don't play around with my airplanes. The piper was already grounded, serviced, and returned to duty by a repair station, including removal and inspection of both fuel tanks. No definite cause was found for the leak other than a broken fuel vent, but that was on the opposite tank and the fuel trail was not from that vent.

Fly SAFE!
Jedi Nein