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George,
I'll add a bit to Colyn's post: Some (but not all) injected Continental engines are equipped with a separate, solenoid-controlled primer circuit that 1) powers the electric boost pump and 2) opens the solenoid, dumping raw fuel into the intake manifold when activated. I don't have this system on my TSIO-550E, but use the boost pump and mixture control to achieve a similar result. Some believe that dumping the fuel into the intake manifold via the primer circuit is better; I really don't know. My engine dumps fuel directly into the cylinders via the injectors when the boost pump is on and the mixture control is in; works well for both hot and cold starting--with different techniques.
I've not actually run a big Continental with a failed engine fuel pump, but the folks at the Continental engine class that Colyn and I attended last week advise that the engine should run at partial power when the aux pump is on "low boost" and will likely need to be modulated by the mixture control when on "high boost." The "should" means that this would be the expected performance; they were rather reluctant to commit to any specific operation not knowing how our fuel systems are installed/plumbed/configured.
Bob
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
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