<< > > Herbert Boks wrote:
 > > >
 > > > Dear fellow rrrrrrrotarians,
 > > >
 > > > I want to ask for your thoughts/comments on the following.
 > > >
 > > > I am building a Cozy MK IV and will install a 3rd gen. 13B. I've spent
 > some
 > > > time trying to understand fuel systems for EFI engines, noting that
with
 > 2
 > > > main tanks, the need for return lines adds a lot of complexity to the
 > > > system. I'm thinking about electrically controlled fuel valves on the
 > > > firewall (2 valves and 1 solenoid or motor per tank). Since with EFI we
 > > > must have electricity to run the engine in the first place, the
 > inability
 > > > to switch tanks in case of a power outage is not really an issue. In my
 > > > opinion an EFI demands a backup electrical system in any case. I see
 > great
 > > > advantages in placing the fuel valves on the firewall:
 > > > - shorter fuel lines
 > > > - no need for a sump tank
 > > > - less fuel heat, because it runs back to the main tanks
 > > > - no fuel lines inside the cockpit
 > > >
 > > > There is the added risk of not being able to shut the valves when power
 > > > fails due to engine fire. I'm not sure how to address that yet.
 > > >
 > > > My understanding of EFI is rather superficial, so I may be overlooking
 > > > things. I may also be overlooking other side effects. What do you
think?
 > > >
 > > > Herbert
 > > >
 > > > Building PH-CZY (Ch.10)
 > > > Cozy MK IV #0769
 > > >
 > > > herbert@datamax.nl
 > > > The Netherlands

 Ed Anderson wrote:
 > Hi Herbert,
 >
 >     I faced the same challenge when putting a 2nd gen six port 13B in an
 > RV-6A.  I did not want to have to mess with return fuel lines and switches.
 > So I built a small rectangular (1 1/2x3x8 inches) aluminum tank out of
 > aluminum rectangular tubing by welding plates on both ends and AN- fittings
 > for fuel.  The high pressure EFI pumps (two) each have there own feed line
 > from the bottom of this tank.  The tanks is located low on the fire wall
and
 > is fed from two wing tanks by a single selector which switches between
them.
 >
 >   The two EFI pumps pull fuel from this header tank for the injectors and
 > returns unused fuel via a pressure regulator to the top of this same header
 > tank.  Any fuel actually injected creates a partial vacuum in the header
 > tank which pulls the fuel from the wing tanks to replace the fuel used.
 > This partial vacuum is substantial and will pull fuel up at least 24".  I
 > also have a boost pump in the low pressure portion of the fuel line to the
 > header tank for take off and landing insurance.
 >
 > It has worked fine for me.  The only two possible problems might be having
 > the header tank get too hot which could potentially create a vapor lock
 > (although turning on the boost pump should eliminate this problem should it
 > occur and of course placing the tank in some location other than the engine
 > compartment) and if you should have a leak in the tank then the partial
 > vacuum would suck air instead of fuel.  However pressure testing the
welding
 > should remove that problem.
 >
 >   I have 75 hours flying with this arrangement which requires no return
 > lines nor any multi port switches.
 >
 > Best Regards
 >
 > Ed Anderson
 > Matthews NC >>

This is a bad idea because vaopr lock is all but assured for a long
idle/taxi.  Those pumps put a lot of heat into the fuel and if its not being
burned its just getting hotter every time it goes around.
Jeff Spitzer

 
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