…so the best explanation could be “they do that”.

 

Yeah…elevated fuel temps, high altitude/low atmospheric pressure, increased head differential due to climb attitude, vent restrictions (bugs and fuel stains), and the engine-driven pump trying to suck fuel uphill thru the restrictions of fittings, valves and twisting hoses & tubes all conspire to lower the system pressure.  When the system pressure is lower than the vapor pressure of the fuel, it boils.

 

I’ve also seen fuel lines and boost pumps leak air under suction that don’t leak fuel under pressure.

 

When (before) your Dukes pump goes, consider CJ Aviation ( www.cjaviation.com ) for a replacement or overhaul…

 

Neal  

 

From: Lancair Mailing List [mailto:lml@lancaironline.net] On Behalf Of Steve Colwell
Sent: Wednesday, September 24, 2014 6:13 AM
To: Lancair Mailing List
Subject: [LML] Mechanical Fuel Pump Oddities

 

Kevin,

 

I had the same problem on a warm day with warm fuel from an above ground tank.  My solution is to leave Low Boost on all the time.  The Dukes pump is not rated for continuous operation but mine is still running at 200+ hours.  Another plus is, if your engine pump fails on takeoff, Low Boost will probably keep the engine running (maybe at reduced power but still running).  I believe Continental recommends Low Boost above 10,000’ so the best explanation could be “they do that”.

 

Steve Colwell  IO-550 Legacy