Chrissi wrote:

I need to implement some form of cam /microswitch to manage the pumps as I do not want to have

some

situation where the pumps are on but the sump is not being fead. I was going to vent the sump

to the

tanks and vent the tanks, this prevents any vapor accumulation in the sump after initial

fueling.

If the pumps both draw from the sump, and the fuel valve controls which tank drains (i.e. not

force-fed

via another pump) into the sump, and the fuel rail excess is dumped into the sump, then it

really isn't

as critical for the fuel valve to control the pumps (versus Brian's system where it is much

more

important).  What is more likely to bite you, Chrissi, is that your system will crossfeed fuel

(via the

sump vent) when parked on non-level ground with full tanks.  This means that fuel may stream

out the low

wing's fuel vent.  Try to put the tank vents as high as practical.

Alternately you could use a six-port valve to return the vent to the draining tank(s), which

will also

allow the vent to be "off" when the supply is off.  But if you're going to go to the trouble

and expense

of the six port valve, you might as well plumb the fuel rail excess to it instead of the sump

vent.

Russell Kent

Russell, agreed, I have schematiced the heck out of this and it only gets worse, more complex, not
better. As it is , parking nose down adds more nonsense to venting.
Most use an "up and over, down the other side" vent schemewhere the high point is top of firewall,
some use a manifold block at top to link all vents together (2 from ea tank) then down to under
strake with forward facing diagonal cut tube (slight pos pressure)
Many of us are against extensive plumbing fwd in our canards, the big Andair takes that beyond
extreme and not practical to do with shaft and multiple universals.
The best to hope for is to be able to shut off the flow of fuel into the sump from the tanks, this
still does not shut off fuel from sump to engine except for pumps doing that.
Canards are strange beasts.
...Chrissi

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