REFLECTOR:RE:check valves
Chuck Jensen
reflector@tvbf.org
Mon, 28 Jul 2003 10:56:53 -0400
Another thing about check valves. They seem to always work perfectly when
being tested and fail when you rely on them. It's just another "thing" that
can break or malfunction. What's particularly bad about them, is there is
not indication of failure. And testing them is arduous in most
installations. Unless they are deemed essential, the parts shelf is a good
place for them. IMHO.
chuck
-----Original Message-----
From: reflector-admin@tvbf.org [mailto:reflector-admin@tvbf.org]On
Behalf Of Brett Ferrell
Sent: Monday, July 28, 2003 10:10 AM
To: reflector@tvbf.org
Subject: Re: REFLECTOR:RE:check valves
I'll bite. Although it *should* be OK, all thinngs being equal, I think
it's a bad idea because all things are never equal. There are a lot of ways
the tanks might get out of balance, and with open lines they can rebalance
themselves and avoid a lot of trimming.
I think in the example of the tip tanks, they're meant to be able to be
completely drained, and you wouldn't want them refilling in a steep
(uncoordinated) turn. You shouldn't routinely have the strakes running dry,
and even if you get a little undesirable cross flow, the moment arm isn't as
big a concern as with a tip tank.
Brett
Quoting Alexander Balic <alex157@direcway.com>:
> 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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