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Hi Ed,
Does your low pressure pump run all the time, maintaining some
positive pressure in your small header tank, or do you let normal
pressure differential draw fuel into the header once everything is
primed & functioning?
Th tiny header tank volume brings me back to an earlier thread I
started, about returning the bypassed fuel to near the pump inlet,
instead of back to the tank. If your header tank is less than a
pint, that's not much more than a decent fuel filter would hold. For
all practical purposes, it's what I drew up as one proposed
architecture. If you've had success with everything on hot side of
the firewall for so long, it's hard to imagine heat-driven vapor
lock being a real concern with all the components including the
regulator mounted in the cockpit where the bypassed fuel never sees
the heat of the engine itself. Makes it really tempting to just T
the return into the supply line & be done with it. If I did
that, I could get back to my 1st draft of valving: Van's 3-inlet
(Primary) valve would select L, R, or Aux; a 2nd Van's valve would
select L Aux or R Aux & feed the Aux port on the main valve. The
architecture returns to very nearly stock, with Van's intent of
having an alternative tank available if corrupt fuel happens in one
tank.
Even if I add a low pressure pump between the primary selector &
the injector pumps, it would still make life simpler, I believe.
It would be: Primary valve out>low pressure pump>T for bypass
return>T for 2 injector pumps>filters for injector
pumps(x2)>T for filter outputs>regulator>(output to engine)
and (bypass back to the 1st T after the low pressure pump.
I'm doubtful that the low pressure pump would even be needed, but it
might be a TSA- type 'feel good' about security against vapor lock,
as long as it runs all the time.
Charlie
On 2/25/2011 10:18 PM, Ed Anderson wrote:
So far I have around 560 hours on my two
tanks with a single selector switch and a facet pump between
tanks and my hi pressure section. I got around any return to
tank problem by returning all fuel to a very small header tank
holding around 1/2-3/4 pint of fuel located on the bottom of
my firewall. In effect it's almost a 'returnless' system
similar to that found on many modern automobile fuel set ups.
I do have the header tank and Hi pressure
pumps located in a fiberglass box covered with stick back
aluminum tape (for radiant heat reflection) and an blast tube
funneling cooling air into the box. Its worked fine for over
10 years.
All Hi pressure fuel elements are forward
of the stainless steel firewall in the engine compartment -
none in the cockpit area (my preference).
With my EFISM set to remind me of fuel
transfer at what ever gallon amount I want (I usually have it
set at four gallons which seems to provide a good set point
for balance in my Rv-6A). The alarm flashes and will not stop
until I take overt action to switch tank and punch off the
alarm. Not perfect, but simply, few parts and no way to pump
fuel out of a tank overboard.
While that is my preference, so long as it
a system is fundamentally safe and provides adequate
indication of fuel status and fuel system condition, any
number of designs can/will work - its all in what makes you
feel comfortable.
FWIW
Ed
Sent: Friday, February 25, 2011 6:00 PM
Subject: [FlyRotary] Re: Fwd: Fuel injector pump
cooling??
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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