The really frustrating thing about all this is that every installation is different (not to mention that it's only speculation as to what caused this particular power loss).

Sixties-era cars (carb, engine mounted fuel pump) had vapor lock problems all the time in hot weather. Modern cars, almost never (in-tank high pressure pump). Keeping the pumps as low & as close to the tank(s) as practical would seem to be the best path. Van recommends mounting pumps on the floor in the cabin. That means that the max lift would be maybe 3-4 inches, through a -6 line, and nowhere near the high under-cowl temps. There's a guy flying an injected Lyc on ethanol-laced mogas who never has a problem with vapor lock. He removed the mech pump and uses wingroot mounted electric pumps.

If it weren't for the maintenance related inconveniences, I'd seriously consider in-tank pumps, as others have done.

But we still don't know whether this is what caused the recent power loss....

Charlie
 
On 08/13/2011 06:20 AM, Ed Anderson wrote:

I should have added - the best overall approach - returning hot fuel to the heat-sink tanks and drawing new cooler fuel into the lines.

 

Ed

From: Ed Anderson

Sent: Saturday, August 13, 2011 6:47 AM

To: Rotary motors in aircraft

Subject: [FlyRotary] Re: vapor lock

Ok, Finn,  that was my guess as well. 

 

 That then brings up a question - my understanding of "vapor lock" is that it is caused by a low pressure area/combined with hot fuel on the EFI pump intake which cause the gasoline to flash to vapor - naturally the EFI pumps can not pump vapor - therefore as fuel is injected from the high pressure side of the pump (reducing pressure on that side), vapor can form there as well.  In any case, insufficient fuel is injected into the engine.

 

Since the injectors are still clicking open, it would seem that any vapor on that side of the pump already has a chance to vacate the line (through the injector) - so my assessment is that it is not the relief of vapor/gas from the high pressure side that remedies the problem, it's removing the gas from the low pressure side (pump inlet) and thereby permitting liquid fuel to be pumped that "cures" a vapor lock situation. 

 

So I am puzzled why a gas vent on the high pressure side would have much (if any) effect on vapor lock.  IF there is pressure on the injector side - I question whether it would be as high as pump pressure - and even if it were, the injector opening would provide a path for it to be release - not to mention the pressure regulator.  So as I said -I'm a bit puzzled as to the mechanism that a vent in the high pressure side prevents vapor lock.

 

In my opinion, there are two ways to reduce/eliminate the vapor in the low pressure side - either cool the fuel sufficiently (somewhat difficult to do) or to increase the pressure in the low pressure line forcing the vapor back into the liquid - ergo - use  a boost pump.

 

FWIW

 

Ed

 

From: Finn Lassen

Sent: Saturday, August 13, 2011 2:53 AM

To: Rotary motors in aircraft

Subject: [FlyRotary] Re: vapor lock

Hi Ed,

I believe it's simply a return to the tank from the high-pressure side via a very small orifice. How small I do not know.

Finn

On 8/10/2011 9:28 AM, Ed Anderson wrote:

 

The one I potential preventive measure/fix I have not looked into is the vapor by-pass/dump that I know a few folks are using.  I search the archive but could not find a description of this method - anyone care to provide one?