Level Control Valve

[Ocampo]

Hi all!

So, here's the thing. In my Twin Otter ground school we are currently studying up on fuel system. This aircraft has 2 tanks and a collector cell for each tank. The collector cell has the 2 booster pumps, a capacitance type measurement system for the fuel quantity indicator (as well as the other cells), a fuel low level float switch for the associated caution light and a level control valve.

I know the functions of all of the above items, but that level control valve is somewhat of a mystery to me, since there's not a description for that item on the manual...and since English is not my first language, things get a bit complicated at times. My initial thought about this valve is that it expels fuel to the outside if somehow the fuel tanks get over-filled. How close am I?

Thanks in advance.

[Gooneyone]

The engines are supplied from the collector cells. Fuel is stored in a collector cell and 3 other fuel cells (a total of 4 cells for Forward tank and 4 for Aft tank).
An ejector valve in each fuel system (or "tank"), "powered" by booster pump fuel pressure, draws fuel from the other 3 fuel cells to keep the Collector cell full. When the collector cell is full, the level control valve closes, thus stopping the supply of fuel from the other 3 cells. This is the only way to stop the flow of fuel into the collector cell as the booster pumps cannot be selected off in flight. As the Collector cell empties, the Level Control Valve opens to allow the Collector cell to be replenished.
This is intended to ensure that the Collector cell will be the last one to run out of fuel.

Hope this helps.

If you need a schematic, PM me and I will try to scan and send the one I have. Please note that I came off the Twin Otter about 15 years ago and have not kept current on any system changes.

[Ocampo]

When the collector cell is full, the level control valve closes, thus stopping the supply of fuel from the other 3 cells. This is the only way to stop the flow of fuel into the collector cell as the booster pumps cannot be selected off in flight. As the Collector cell empties, the Level Control Valve opens to allow the Collector cell to be replenished.
This is intended to ensure that the Collector cell will be the last one to run out of fuel.

Great! That's the answer to my question. Thank you very much, sir! Don't worry about currency on the aircraft...it seems it's the very same aircraft you last saw 15 years ago :E (It's perfect as it is IMO)

And yes, I'd like that schematic for further understanding of the system. Much appreciated!

[Gooneyone]

Just sent the schematic. Hope it helps

[Ocampo]

Got it. Thanks!