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Level switches in the fuel system for alarms - Yes, No, Why?

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wsimpso1

Super Moderator
Staff member
Joined
Oct 18, 2003
Messages
11,353
Location
Saline Michigan
The saga continues. First my setup. My fuel system has a couple wing tanks, a header tank, pumps to get fuel from the wings to the header, draw from the header to run the engine.

I already have capacitance fuel gages for the wings, but none selected yet for the header tank.

The idea is that things break, we do not want the engine to stop anytime soon just because something quit working... That includes fuel gauges.

Now we get to the point where we use your brains as well as mine. Yeah, your thinking is a welcome addition to my thinking...

Since running any pump dry is bad for the pump, I am thinking a low level warning on each wing would be a good idea. Yes, No, What made you say that?

Next how would you run fuel level sensing in the header tank? As long as the wing tank selected has fuel in it and the pump selected is running, the header tank should be full and circulating some fuel back to the selected wing tank. Do we really want a gauge showing quantity when it should always be full? Yes, no, Why did you select your answer?

I am thinking the header tank could be just fine with two simple level switches because if I can not add any more fuel to the header and the level has just started down, I have about 50 minutes at cruise speed or 100 minutes at max endurance speed. When the other triggers, I better set it down on the best chunk of dirt I can see;
One switch to tell you when the transfer pump is not keeping the header full;
The other to tell you that the engine is about to stop from fuel starvation. If you have a compelling reason to know how much is in the header tank, I want to hear that too.

Now, assuming we want alarm switches, which should we have?

There are float switches in the catalogs that run around $30. I do not know about you guys, but a limit switch with a float on a pivot stuck inside a fuel tank that might have some water in it and someplace difficult to access for replacement just sounds like an invite for trouble at several levels.

Industrial solid state switches with zero moving parts (and they are small too) exist that sense if we have liquid at them or not. They even come in materials that will stand prolonged fuel immersion. $129 for the fuel safe ones.

So which would you use and why?

There is the question of the week. Help is appreciated.

Billski
 
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