Failed mechanical fuel pump field fix

[gereed75]

Just experienced a failed mechanical fuel fuel pump discovered at a fuel stop at a relatively remote field.

The pump still made good pressure but the leak rate was way too much to fly it.

Turns out that the KB fittings that most of us use to route the in/out fuel lines into the pump have the same 9/16-18 threads on both ends. Remove this fitting from the pump and it can be used to connect the in/out lines together, “jumpering out” a leaking mechanical pump.

You can then make it to civilization using the boost pump to fly, assuming you have a reliable electric boost pump.

Hope this helps someone in a jam.

[TS Flightlines]

yes they are the same thread, but different sealing surfaces. Flares vs. O'ring boss.
Better way to bypass is to have a AN815-6D handy. NO chance of a leak, unless you dont tighten it down. Keep one of these in your tool kit, or even tiewrapped under the panel. Just remember its there!


Tom

[AIR HOG]

Originally Posted by gereed75

Just experienced a failed mechanical fuel fuel pump discovered at a fuel stop at a relatively remote field.

The pump still made good pressure but the leak rate was way too much to fly it.

Turns out that the KB fittings that most of us use to route the in/out fuel lines into the pump have the same 9/16-18 threads on both ends. Remove this fitting from the pump and it can be used to connect the in/out lines together, ?jumpering out? a leaking mechanical pump.

You can then make it to civilization using the boost pump to fly, assuming you have a reliable electric boost pump.

Hope this helps someone in a jam.

I would be in a worse jam if the boost pump failed in flight...
But if I was camping in a remote forestry strip with a fire approaching it would be a useful option to keep in mind. Perhaps best to use it to taxi to a hangar.

[bhester]

How was this found? Someone outside the plane see fuel leaking?

[gereed75]

Tom, one of the fittings on my pump had a flare on one end and a flare with the o ring boss on the other end - nice!

Bobby, yes, the folks at this very small municipal field always come out to pump and they noticed it. I would probably have caught it as it takes a minute or so for the fuel in the system to back flow through the leak. It also is enough to leave a significant puddle.

I had always thought that a pump diaphragm failure would cause a small relatively insignificant leak. In this case the leak was estimated to be a gallon in four minutes at 1400 rpm during a subsequent ground run up. Needless to say, that was un-sat for further flight even though the pump was still making 25 psi!!

This happened at the end of a 2.5 hr cross country. Not sure when it started or how fast it leaked in flight, but I estimate 1.5 gallons were lost in flight using totalizer data. Engine never missed a beat.

[BruceW]

How many hours on the mechanical pump ???

[gereed75]

12 years and 550 hrs

[gereed75]

Correction - after getting the old pump out and looking at logs this pump is more like 25 years old and 1200 hours

I used the string/bungee method to hold the actuating cam up. Pulled the pump up pretty tight with the inside bolt. Then rotated pump up clockwise to get left side bolt in. Left just enough room to cut and pull the string. Worked like a champ.

A little over three hours from cowlings off to pump in without having to remove any other lines or equipment for access.

Thanks VAF for those tips.