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Date: Tue, 20 Dec 2005 18:22:08 -0500
From: Ernest Christley <echristley@nc.rr.com>
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To: Rotary motors in aircraft <flyrotary@lancaironline.net>
Subject: Re: [FlyRotary] Re: Fuel filter selection
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William wrote:

> Buly,
> I have read somewhere that the pumps shed small particles as they 
> wear, so there needs to be a high pressure filter after the pump.  
> Still need to keep water from getting to the pump also.
> Bill Schertz
> KIS Cruiser # 4045


Lots of people that all usually have very wise things to say, are all 
saying different things.

al p, you've broken the issue down, so may I pick on your analysis?  
Thank, you.  I thought it would be alright.

Debris killing the pump. 
You throw out a number ... 1 every 500 hours.  That's well and good, but 
we're talking about debris in the pump.  The only place that I see the 
debris coming from is the tank.  The most likely scenario is crappy gas 
from a bad station, or a windstorm at the beach.  Either way, both pumps 
are going down together, and taking you with them.  (Apologies if you 
fill your tanks seperately at different airports, but I only have the 
one.) Gasoline being one of the few items that are input to the plane 
regularly and since a lot of us are or will run auto gas, I'd move that 
move that risk component to a 6 or 7.  Losing power has the same effect, 
regardless of why, so I'd make the EFFECT component the same as you set 
for vapor lock, 6.  You might notice the bad gas; you might not.  So, 
the risk component can be set as high as you did for vapor lock, 7.  My 
guesstimate is that suck trash into your pumps will kill you as fast as 
vapor lock.

Water damaging injectors.
You got me there.  I would assume that the ratio to gas would determine 
if the engine kept running at all, but it no way do I see it as being a 
good thing.  Would the pump even be able to continue pumping after it is 
all 'frothed' up?   ie, would this be a sort of vapor lock in itself?  
Call it froth lock?

Vapor lock caused by pressure drop:
The PRM-81794 High Performance Filter Head is rated for 25GPM.  
Perma-Cool's website recommends its use for a filling station.   
http://www.perma-cool.com/Catalog/Cat_page26.html  I think it would 
laugh at our measely 25GPH fuel flows, adding no measurable 
restriction.  I assume it does this in conjunction with the fine 
filtering by using an extremely large filtering area (but that is just a 
guess).  With this filter and the electric pumps below the tank, I'll 
have 6 to 8 inches of head to the bottom of the tank.  More like 12 to 
15 with any reasonable quantity of gas to be leaving the ground with.

I agree with your vapor lock risk assessment.  They are as good as any 
I've seen pulled from thin air.  But I think you greatly underestimate 
the risk, effects and results of bad fuel.  In the software business, 
we're taught never to trust input from an external source, so I think 
the gas needs to be checked at the input.

So, the parts from Summit Racing will be here tomorrow, and I have a 
beautiful 45* flare tool, lots of fittings and lots of aluminum tube.  I 
think what I should do is go with the design that I was feeling good 
about, but follow your previous advice and put a pressure gauge on the 
fuel pump inlet.  A simple T that can be capped would be all that's 
necessary.

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