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  #51  
Old 09-03-2014, 02:02 PM
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Originally Posted by FasGlas View Post
Unless you're mounting a gascolator after the fuel pump where is no pressure, it's flow...
But you do mount the gascolator after the boost pump...
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  #52  
Old 09-03-2014, 02:08 PM
bjohnson1234 bjohnson1234 is offline
 
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But you do mount the gascolator after the boost pump...
Where you mount it makes no difference. Pressure and flow are two different measurements, like amps and volts. Just because you're pulling doesn't mean there is no pressure. Just like you in the wind tunnel, the gascolator can't tell the difference between a fuel pump before it or after it.
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  #53  
Old 09-03-2014, 02:08 PM
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Originally Posted by Toobuilder View Post
But you do mount the gascolator after the boost pump...
No. You mount the gasculator, on the firewall, from the fuel valve / tank. There's is no pressure. From the output of the gascolator it feeds the backup pump, from there to the mechanical pump. At this point you can collect any contaminants before it enters the pumps.
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  #54  
Old 09-03-2014, 02:09 PM
bjohnson1234 bjohnson1234 is offline
 
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Originally Posted by FasGlas View Post
No. You mount the gasculator, on the firewall, from the fuel valve / tank. There's is no pressure. From the output of the gascolator it feeds the backup pump, from there to the mechanical pump. At this point you can collect any contaminants before it enters the pumps.
My boost pump is before the gascolator.
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  #55  
Old 09-03-2014, 02:10 PM
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Quote:
Originally Posted by bjohnson1234 View Post
Where you mount it makes no difference. Pressure and flow are two different measurements, like amps and volts. Just because you're pulling doesn't mean there is no pressure. Just like you in the wind tunnel, the gascolator can't tell the difference between a fuel pump before it or after it.

So, if you disconnected the fuel line from the gacolator and let the fuel pour out, you're saying there's high pressure?? That is less fuel then the pump is FLOWING though it.
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  #56  
Old 09-03-2014, 02:26 PM
bjohnson1234 bjohnson1234 is offline
 
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So, if you disconnected the fuel line from the gacolator and let the fuel pour out, you're saying there's high pressure?? That is less fuel then the pump is FLOWING though it.
No, I'm saying that any amount of flow means there is some pressure. The peak of that pressure is the pump. In any case, it's irrelevant because the Usher gascolator can handle the pressure whether it comes from the mechanical fuel pump after it or the boost pump before it.
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  #57  
Old 09-03-2014, 03:12 PM
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Since this thread got a bit side tracked.. The question is???? Did you get your problem solved??
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  #58  
Old 09-03-2014, 03:18 PM
bjohnson1234 bjohnson1234 is offline
 
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Since this thread got a bit side tracked.. The question is???? Did you get your problem solved??
I think so, but I'm not 100% sure yet. It seems pretty likely that the engine quit because there was water in the air box. To fix that I drilled a hole in it and used filter grease to get a better seal on the bottom. I haven't ruled out a problem with the servo yet and I know I have a fuel boiling issue, but it's always been a minor issue at low rpm and has never caused the engine to quit.
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  #59  
Old 09-03-2014, 03:48 PM
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Quote:
Originally Posted by FasGlas View Post
No. You mount the gasculator, on the firewall, from the fuel valve / tank. There's is no pressure. From the output of the gascolator it feeds the backup pump, from there to the mechanical pump. At this point you can collect any contaminants before it enters the pumps.
That may be how you plumb your system, but that's not the norm in this world. Most boost pumps in this world are well inside the firewall, as close as practical to the fuel source. Boost pumps work much better pushing than pulling.
__________________
WARNING! Incorrect design and/or fabrication of aircraft and/or components may result in injury or death. Information presented in this post is based on my own experience - Reader has sole responsibility for determining accuracy or suitability for use.

Michael Robinson
______________
Harmon Rocket II -SDS EFI
RV-8 - SDS CPI
1940 Taylorcraft BL-65
1984 L39C
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  #60  
Old 09-03-2014, 07:06 PM
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AlexPeterson AlexPeterson is offline
 
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Quote:
Originally Posted by bjohnson1234 View Post
Where you mount it makes no difference. Pressure and flow are two different measurements, like amps and volts. Just because you're pulling doesn't mean there is no pressure. Just like you in the wind tunnel, the gascolator can't tell the difference between a fuel pump before it or after it.
Perhaps I'm not following this closely enough, but there is a big difference between pulling and pushing fuel through something. Yes, the pressure drop is only a function of flow and geometry, but the absolute pressure along the system will be different in your scenario. It is very desirable to keep the minimum absolute pressure along the path as elevated as possible.

At sea level pressure, 100LL boils at around 140F. Pull a little on it, as in the line upstream from the boost pump, and the boiling temperature goes down. The best place for the boost pump is right next to the tank. Indeed, cars put the pump inside the tanks.
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