Al Gietzen wrote:

Perry wrote:

 

If you are flying and running only one h.p. fuel pump, and that pump fails, the engine will become silent only milliseconds later!

 

This is interesting.  As my circuit diagram is currently configured, I have a pressure switch in the fuel system which automatically turns on the backup pump if the pressure drops below about 30 psi. (don’t remember now the exact setting on the pressure switch).  Do you suppose that this wouldn’t react fast enough to keep the engine running?

 

  There is a manual bypass so I can turn the pump on if I want.  The idea was to turn on both pumps for takeoff, but at other times the backup would automatically kick in to keep the engine from stopping if the primary pump stopped; thereby avoiding rapid heart rates on the part of pilot and passengers.

 

Al

That's an excellent idea Al. Probably the best solution. The engine stutters and dies as pressure drops below 20 psi.

I just run both pumps all the time. (I get nervous if I turn one off, even at altitude). I can tell if one has failed because the pressure is slightly lower with only one pump on. Those Mazda pumps are extremely reliable. I use two junkyard pumps that probably had 100k+ miles in cars previously. No failures yet. I've also owned three 2nd gens with probably 200kmiles accumulated between them and no failures yet.

-- 
Perry Mick
http://www.ductedfan.com