|
A 'sump' tank with the pumps in it
would be the best option, but difficult to achieve in a low wing
plane with 'wet wing' type tanks. The bottom of an RV-x fuel tank
is less than an inch above the bottom of the belly. Without a
sump, the risk of sucking air is huge, when fuel levels get
relatively low. Fuel *never* feeds at the same rate from both
tanks to a common destination, even in high wing planes like
Cessna's.
On 10/28/2014 10:37 AM, Ernest Christley wrote:
Charlie, could you not provide redundancy with a
on/off valve between the tanks? If one pump dies, turning
the valve on to allow fuel to gravity flow to the tank with
the good pump. Redundancy is provided by a pump in each
tank. Both run during takeoff and landing. If one dies,
switch to the other tank and run it low, then open the valve
to get fuel from the tank with the bad pump if you haven't
found an airport already.
On
10/27/2014 4:55 PM, Ernest Christley wrote:
This is the type that
I'm referring to:
Is anyone
familiar with electric fuel
selector valves as used in
automotive applications. I'm
trying to figure out how they
operate. Do they select one
line when power is applied to a
solenoid type plunger, and then
the other line is selected when
power isn't applied? Or does a
pulse of power switch them back
and forth? If they maintain the
currently selected tank when
power is absent, it seems to me
that this could remove fuel
lines and a leak prone selector
valve from a lot of cockpits.
Furthermore, the 6 port models
look like they could be plumbed
easily to handle return lines.
The ones I've seen actually use a motor to move the
valve (think screw jack), so they will remain in
last position. Reading your linked item indicates
that it works the same way.
'Traditional' engine guys have avoided them in the
past because they're plastic and they require power
(and they are an automotive product, so they can't
be reliable ;-) ). They are probably worth
considering, but I'm seriously looking at switching
to in-tank turbine pumps with automotive style PWM
control; no return line needed. Then tank selection
would be with a switch on the panel instead of a
valve. Downside is that for total redundancy, I'd
need 2 pumps in each tank. They are dirt cheap
(<$20 each), but controllers are around $75 ea
and switching gets pretty elaborate if there are
more than 2 tanks.
Charlie
|