MEP-806B Aux Fuel system operation?

[fcbrants]

My apologies if this has been covered.

I used the Forum Search & Google Advanced Search to look for "Aux Fuel", but couldn't locate the actual threads (Google) or got hits on Every Page (Forum Search) that was picking up the sticky topics.

I think Google's advanced search is hitting on pages that have moved since the site was last indexed.

I just read the following info in my TM:

1.16.5.5 When the ENGINE CONTROL switch is set on PRIME & RUN AUX FUEL, it actuates the auxiliary fuelpump and transfers fuel from the auxiliary fuel supply to the fuel tank. The CIM shuts off the auxiliary fuelpump when the fuel tank is full and reactivates the pump as the level drops.
​

This is a really handy feature, but I'm curious what happens when the auxiliary tank runs dry? Will the Aux pump keep pumping, run dry, and burn out? You would think that the system was specifically designed to cope with that scenario, but I couldn't find anything in the TM that described what happened when the aux fuel supply ran dry.

Thanks!!

Franko

 

[Daybreak]

Howdy,
You are correct. That is a good question.

I would paraphrase, a lot would depend on the aux fuel source, your operating demand, and checking on the generator to ensure its smooth operation. Just as a example,because you have a 500 gallon aux fuel source sitting there, does not mean you never should look at the generator. Temp, load, oil levels etc. Times to shut down and change filters or oil etc.

The idea is the aux fuel source fills the day tank. The day tank is measured for each generator to run a day. The day tank gets down to about 1/4 full, it turns on the aux pump to fill itself to about 7/8 full and shuts off. That should net you enough time to monitor your fuel usage and have the next aux fuel source ready for use.

You could calculate the average fuel usage with your demand, and have a aux fuel source sized accordingly. Limits of course would be PMCS checks and oil change intervals

 

[Guyfang]

My apologies if this has been covered.

I used the Forum Search & Google Advanced Search to look for "Aux Fuel", but couldn't locate the actual threads (Google) or got hits on Every Page (Forum Search) that was picking up the sticky topics.

I think Google's advanced search is hitting on pages that have moved since the site was last indexed.

I just read the following info in my TM:

1.16.5.5 When the ENGINE CONTROL switch is set on PRIME & RUN AUX FUEL, it actuates the auxiliary fuelpump and transfers fuel from the auxiliary fuel supply to the fuel tank. The CIM shuts off the auxiliary fuelpump when the fuel tank is full and reactivates the pump as the level drops.
​

This is a really handy feature, but I'm curious what happens when the auxiliary tank runs dry? Will the Aux pump keep pumping, run dry, and burn out? You would think that the system was specifically designed to cope with that scenario, but I couldn't find anything in the TM that described what happened when the aux fuel supply ran dry.

Thanks!!

Franko

Yes, in fact this could happen. But I don't think it would, as the pumps are very robust. I have seen, (and heard) electric fuel pumps that ran 12-14 hours and did not damage themselves. Gen sets that ran out of fuel, and the crew never woke up, until the next morning. Pumps ran all night. If you think about it, how would you design a solution to the "problem"? I would put a thermal contact in the circuit. If the circuit got hot, the contact would pop. The military did not consider it important, or the pumps are not going to overheat. I would not worry about it. I would worry about the pumps over filling the set fuel tank, something I have seen several times. An event destined to make you unpopular with environmentalists the world over.