George,   I don't have the whole answer but maybe one of the engine experts will chime in.
I do know:
- engine pump does have a spring loaded bypass so that the boost pump can drive fuel through it if it fails.  (We learned that at the Continental Factory course this week).
- High boost is a speed function on the boost pump.  I have never seen a IV that didn't have one.
- I'm not sure what the primer button does (I have both) but I think it has special plumbing.   Many planes don't have this.
- I need to do some research to understand the relative outputs of the engine pump vs. the boost pump and how that will affect mixture in the event of an engine pump failure.   My expectation is low boost will not be enough and high boost will probably require a mixture adjustment.

On Jan 27, 2013, at 12:30 PM, George Wehrung wrote:

As a continuation to my previous post, referencing the build manual chapters 14 and 23:

Chapter 23: wiring:  denotes a Single Pole Double Throw rocker switch for the LOW-OFF-HIGH positions of the fuel boost pump.

Chapter 14: Firewall Forward, depicting the fuel flow does not show a separate routing for the fuel primer circuit.  So how does the primer function work?  Is it merely pushing a higher volume of fuel through the circuit?  I know it's necessary for hot starts to quickly circulate the cooler fuel to the manifold but does it somehow bypass the gascolator and the engine driven fuel pump?  This would make sense if it did as some aircraft call for pushing in the primer and possibly holding it in to keep the engine running in the event of an engine driven fuel pump failure.

So then why do I only have a low selection of the boost pump?  Should I replace my boost pump switch with a three-position LOW-OFF-HIGH switch.  Should I have the boost pump on LOW for takeoff, descent and landing?

Thanks again

George




--
For archives and unsub http://mail.lancaironline.net:81/lists/lml/List.html