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Thanks, Bill. Your points are why I haven't given that setup serious
consideration. And while $500 (for the Andair) is cheaper than a
crash, it isn't cheap enough to sound reasonable as a solution. :-)
With an inexpensive pump having anti-siphon features, it's making me
consider yet another option: a transfer pump for each tank, with no
selector valve at all. Of course, that means more (or at least
different) complexity, and more weight.
The L/R imbalance issue is about the same for an RV.
Without decisions, I'd have hundreds of hours flying by now....
Charlie
On 2/25/2011 5:40 AM, Bill Schertz wrote:
Charlie,
I would caution about your using a selector ‘normally’
and returning to only one tank. I believe that it puts too
much workload on the pilot, especially when you don’t have
max fuel. I don’t know about RV’s, but my experimental
(KIS) shows a definite development of the tendency to turn
towards the heavy tank when they get very far out of balance
due to uneven fuel content. At about 5 gallons difference in
the tanks, I start to have to apply steady pressure to the
ailerons to correct it. So, if you are getting low down to
half tanks, and start drawing from the non-return tank, it
might not take very long to deplete that tank with the
excess fuel being dumped into the return tank. Our pumps
move the fuel rather fast, faster (I believe) than the
certified planes that use that system. A prototype Pulsar
with the system as you described had this problem during an
early test flight when he started with ~10 gallons in each
tank, switched to the non-return tank, and ran out of gas
much faster than expected, couldn’t get the pump to prime in
time from the other tank, and had an off field landing.
Andair makes a nice duplex valve that returns the fuel to
the tank it came from. Costs a lot less than an off field
landing.
FWIW
Bill Schertz
KIS Cruiser #4045
N343BS
Phase one testing Completed
Sent: Thursday, February 24, 2011 5:18 PM
Subject: [FlyRotary] Re: Fwd: Fuel injector
pump cooling??
Ouch; I hadn't
thought about that. But I suspect that even a low pressure
pump would damage the tank if the vent is blocked. Thanks
for the data point on the fact that a high pressure pump can
be used effectively as a transfer pump.
Were you using a separate port on the main tank for your
transfer point? My tentative plan is to T into either the
regulator return, or (assuming an effective back/anti-siphon
setup), into the main supply between tank & engine pump.
Obviously, the anti-siphon feature would need to be bullet
proof to tap the supply line.
One option I've considered is to use the fuel selector
'normally', but have all regulator bypass return to a single
'main' tank. This arrangement is actually used in some
certified planes with injected Continentals, but I'm leery
of having my primary engine pump run dry for even a very
short interval as I empty an aux tank. I suppose that with
that arrangement, it would only run dry for a couple of
seconds ( :-> ), so maybe it would work out fine. Any
thoughts?
Charlie
On 2/24/2011 2:36 PM, Steven W. Boese wrote:
Charlie,
I initially had
my RV set up with a Facet transfer pump with an
external check valve. The check valve spring was
replaced with a slightly stronger one so that it
served both the anti back flow and anti siphon
functions. The high percentage of the time that the
Facet transfer pump was operating convinced me to
change to the type (not the exact part) of pump you
are considering. The pump seemed reliable but
after a couple of instances of transferring fuel out
the receiving tank’s vent in spite of a timer on the
transfer pump, I eliminated the transfer function
altogether. The possibility of applying up to 90
psi to the receiving tank if its vent malfunctioned
did not suit me. It would not take anywhere near
this pressure to fail the tank. The procedure for
leak testing the fuel tanks cautions not to apply
even a couple of psi to them. The limitation here
really was me, though, not the equipment.
Steve Boese
RV6A 1986 13B
NA RD1A EC2
From: Rotary
motors in aircraft [mailto:flyrotary@lancaironline.net]
On Behalf Of Charlie England
Sent: Thursday, February 24, 2011 12:23
PM
To: Rotary motors in aircraft
Subject: [FlyRotary] Fwd: Fuel injector
pump cooling??
Anyone see any issues with one
of the automotive in-tank pumps being used outside
the tank? Looking at the overall
pump/pickup/regulator/level sensor/etc assemblies in
most auto fuel tanks, it would appear that the pump
itself would be above the level of the fuel anyway
if the tank is less than 1/4 full.
I've been looking for a Facet transfer pump that has
both a backflow valve & an anti-siphon valve
(40257 is one) but they are very hard to find &
expensive when you find them. During my search, I
ran across this:
http://www.amazon.com/gp/product/B000BMBSS0/ref=pd_lpo_k2_dp_sr_3?pf_rd_p=486539851&pf_rd_s=lpo-top-stripe-1&pf_rd_t=201&pf_rd_i=B002YP4Q3Q&pf_rd_m=ATVPDKIKX0DER&pf_rd_r=1JFK34G48EBF5R93EB2Y
The application appears to be 87-98 GM products.
It appears to be very similar to the 'standard'
in-line pump that Tracy supplies, with the exception
of plastic components in the output end. Assuming that
it's a positive displacement gear pump, it should
supply both the backflow & anti-siphon features I
desire & at roughly $30 shipped, it's cheaper than
even the cheapest Facet 'solid state' transfer pumps.
I'm hoping that cooling/lube won't be an issue as long
as it isn't run 'dry' for more than a few seconds at
the end of a transfer cycle.
Charlie
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