TB500
Topic Author
Posts: 1
Joined: Sat Oct 05, 2019 11:48 am

Why is fuel drained?

Sat Oct 05, 2019 12:16 pm

Hello community,
today I was reading a document which is giving a basic explanation of the systems of an engine (Link: https://www.faa.gov/aircraft/air_cert/d ... _famil.doc). And as a component of the fuel system of an aircraft engine fuel drains where listed (page 9-10). However it was said that fuel is drained to "safely dispose of the fuel in the manifolds when the engine is shut down, and, in some engines, to conduct leaked fuel overboard."

But when I made some research on the internet I found this: https://www.youtube.com/watch?v=rNdLttyWenQ
(Title: Airbus A320 Fuel Tank Water Drain Valve Operation)

This confused me as the video says the purpose of those drains where to drain the remaining fuel (and water from condensation of the air in the tanks) from the tanks.

So my question is: Are there multiple reasons to drain fuel from the fuel system or are those all different type of drains? And -> When people talk about draining (NOT DUMPING) fuel what action do they mean?
 
Tristarsteve
Posts: 3595
Joined: Tue Nov 22, 2005 11:04 pm

Re: Why is fuel drained?

Sat Oct 05, 2019 4:38 pm

Two different things here.
The fuel in the engine manifolds is drained on shut down, usually into a small tank on the engine. This fuel is then burned on the next start up. Before about 1970, this fuel was dumped on the ground, but this practice was banned and engine fuel drain tanks were introduced.

Secondly, the fuel tanks in the wings have water drain valves. Water in suspension in the fuel settles out and ends up at the bottom f the tank. This is removed by opening the water drain valves at regular intervals, about every day or two, It is unusual if more than a few drops come out.
Also if these aircraft fuel tanks are being emptied for maintenance, the last few litres is drained out from these drain valves, after most of the fuel has been pumped out using the booster pumps.
 
Dalmd88
Posts: 2938
Joined: Fri Jul 28, 2000 3:19 am

Re: Why is fuel drained?

Sat Oct 05, 2019 7:45 pm

The purpose for the engine manifold draining is to prevent the unused fuel from dripping out of the fuel nozzles into the still hot burner sections after shutdown. It would not burn completely and build up a residue on the nozzles so the spray pattern would be wrong over time.

There are also fuel drains on the bottom of the engine that if you see drops coming out, it signify a internal seal on either the fuel pump or the fuel control is leaking. There are also hydraulic and oil drains for those components also.
 
strfyr51
Posts: 3937
Joined: Tue Apr 10, 2012 5:04 pm

Re: Why is fuel drained?

Sat Oct 05, 2019 9:53 pm

TB500 wrote:
Hello community,
today I was reading a document which is giving a basic explanation of the systems of an engine (Link: https://www.faa.gov/aircraft/air_cert/d ... _famil.doc). And as a component of the fuel system of an aircraft engine fuel drains where listed (page 9-10). However it was said that fuel is drained to "safely dispose of the fuel in the manifolds when the engine is shut down, and, in some engines, to conduct leaked fuel overboard."

But when I made some research on the internet I found this: https://www.youtube.com/watch?v=rNdLttyWenQ
(Title: Airbus A320 Fuel Tank Water Drain Valve Operation)

This confused me as the video says the purpose of those drains where to drain the remaining fuel (and water from condensation of the air in the tanks) from the tanks.

So my question is: Are there multiple reasons to drain fuel from the fuel system or are those all different type of drains? And -> When people talk about draining (NOT DUMPING) fuel what action do they mean?

fuel is drained from the Engine Fuel manifold after shutdown to prevent coking of the fuel Nozzles and causing them to clog. The EPA can is about 10 oz and empties on the next engine start .
 
Tristarsteve
Posts: 3595
Joined: Tue Nov 22, 2005 11:04 pm

Re: Why is fuel drained?

Sun Oct 06, 2019 11:38 am

The EPA can is about 10 oz and empties on the next engine start .


Like that you call it EPA can.
In 1971 when I was an apprentice working a stint in engine development, the EPA brought out a new rule about engine drains. Up until then the burner rail just emptied onto the tarmac on shutdown. I was tasked with finding out what we could do with the RR Spey. The solution was to route the drain pipe so it drained into the bypass duct. It was then blown out on the next start. Seemed a bit silly to me, but EPA said OK so thats what we did.

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