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

 

Edward L. Anderson
Anderson Electronic Enterprises LLC
305 Reefton Road
Weddington, NC 28104
http://www.andersonee.com
http://www.eicommander.com

From: Charlie England

Sent: Friday, February 25, 2011 6:00 PM

To: Rotary motors in aircraft

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

 

From: Charlie England

Sent: Thursday, February 24, 2011 5:18 PM

To: Rotary motors in aircraft

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