REFLECTOR:RE:check valves

[Alexander Balic]

I was thinking of this also- about using check valves in the lines from the
mains to the sump to keep the fuel always moving in the correct direction-
anyone else done this? any other comments on why is a good/bad idea?

-----Original Message-----
From: reflector-admin@tvbf.org [mailto:reflector-admin@tvbf.org]On Behalf Of
Larry Richter
Sent: Monday, July 28, 2003 12:33 AM
To: reflector@tvbf.org
Subject: Re: REFLECTOR:Low fuel light


Folks:
    Okay, I lurk too.  I have been building for a long time (forever?)
but do have plans to finish it (before I die of old age).

My flying plane is a 1948 Bonanza with Flight Extender tip tanks
installed in 1961.  I've been flying her since 1984.  This system uses
no transfer pumps .  There is a vent line consisting of a little tube
extending down into the slip stream cut off at an angle with the bevel
forward and a small hole on back side of tube ( to allow some venting if
the the front ices over- so I have been told).  This tube opens into the
top of the tank.  (Main tanks have similar vents).  About 1/3 of the tip
fuel is actually below the level of the fuel line in level flight with
the line going out to the tip tank inside the wing and then down into
the bottom of the tank.  This system has a check valve in each fuel line
from the tip tanks preventing fuel from porting/venting in the wrong
direction.  I have done all kinds of experiments over the years to try
to get the tip tanks to unport or malfunction.  To explain all of these
would make this email very long.  Suffice it to say,  it has been
totally reliable.   Proper (but very simple) maintainance is mandatory
to keep it working as the tip gas caps cannot leak and  the vents must
be open and working.  (My wife occasionally sees me kiss the tip
tanks--blow into the vent, feel the tank pressurize, and blow back at
you  when you let go).  Newer "improved" versions of this system
(Beryl'D Shannon is the latest) used various transfer pumps to eliminate
problems that do occur if the old system isn't maintained.  These
systems become maintainance nightmares as they age and fail and end up
in junk yards.  They can also give you little thrill if you are careless
and end up with 90lbs of fuel in one wing tip only to find out (too
late) that the transfer pump on that side has failed.  The only $
maintainance I have had to do was replace the O-rings in the check
valves 10 years ago when I discovered that they weren't "checking" after
most of the tip fuel ended up on the ground after parking overnight on a
slope with one wing higher.  And I had to replace the tip gas caps after
a certified mechanic "cleaned up them thar oily old gas caps n dried um
out real nice".  Want to ask me again why I am building my own airplane?

Sooo,
    My Velocity has vent lines as per (my) manual with main tanks and
sump vented to a common manifold on the front of the firewall.  I used
3/8 inch lines.  When I saw discussions regarding fuel sucking out of
leaking gas caps and draining the sump and opposite tank, I looked at my
50+ year old reliable lady and added the check valve to the lines from
the main tanks to the sump.  It seems to my simple mind that this should
be equally reliable.  The check valve would obviously cause a problem if
you expect fuel/air to go "backward" from sump to main tank.

larry richter

John Dibble wrote:

> Yes, I agree that the  pressure will be equal, under static
> conditions.  The problem is keeping the pressure equal under dynamic
> conditions like climb, descent, and leaking caps. If connected
> directly to the manifold, the sump pressure will change faster than
> the tanks because there is very little air space in the sump.
>
> John
>


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