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<DIV><FONT size=2>Bob, </FONT></DIV>
<DIV><FONT size=2></FONT> </DIV>
<DIV><FONT size=2>it actually happens because the pump doesn't close like the
pressure demand regulator in a normal pressurized YS engine. Instead the pump is
a positive displacement pump and as such if the pressure is applied to the inlet
of the pump the pump has nothing to stop the flow. Yes the pump is actuated but
the pushrod, however the seal on the piston of the pump is not a seal. Instead
the pump uses some little check valves working against each other to control the
flow. These check little valves are referenced to internal pressures in the
engine one from the bottom crank case, and one from the top valve cover/airbox.
The pressure differentials inside the engine when it is running is what keeps
the flow of fuel under control at the given times. When the engine is not
running these little check valves don't have the pressure from the engine to
keep them in the right spot and by design the fuel will flow around
them.</FONT></DIV>
<DIV><FONT size=2></FONT> </DIV>
<DIV><FONT size=2>As a result the pressure induced by expansion of the tank
while sitting in the sun will cause fuel to siphon to the engine. The engine
will completely lock up with fuel...every open space that will allow fuel to
fill into the hole will. The engine will be completely full of fuel this goes
beyond a flooded condition.</FONT></DIV>
<DIV><FONT size=2></FONT> </DIV>
<DIV><FONT size=2>The only way to stop it is to keep the supply line from
allowing fuel to flow to the engine. There are many cases and often times that
you don't need to plug off or pinch off the line. But if the model is sitting in
the sun the tank will warm up and the fuel will siphon to the
engine.</FONT></DIV>
<DIV><FONT size=2></FONT> </DIV>
<DIV><FONT size=2>Its not an big issue use a fuel dot to plug off the tank until
its time to start or use one of those K+S little clips they are quick easy and
clean. </FONT></DIV>
<DIV><FONT size=2></FONT> </DIV>
<DIV><FONT size=2>Fancy things like the tettra valve also work well.
</FONT></DIV>
<DIV><FONT size=2></FONT> </DIV>
<DIV><FONT size=2>To be 100% factual the exact same thing will happen on a
140RX...except that the way the pump works on the OS 140RX it provides more
restriction to the flow than the pump on the YS DZ engine. Due to the less
restrictive flow nature of the pump it allows the engine to flood where as the
pressure in the tank of the 140RX setup would have to build to a much higher
value to over come the restriction in the pump.</FONT></DIV>
<DIV><FONT size=2></FONT> </DIV>
<DIV><FONT size=2></FONT> </DIV>
<DIV><FONT size=2>By the way one of the causes of this situation is many of us
are running a check valve on the vent line of the tank. This prevents the
overflow of fuel from the tanks vent line while carrying the model and during
flight. If the vent line of the tank was left open to ATM then this would be
much less of an issue. There are solutions like looping the vent line behind the
tank and other solutions as well. The check valve installed to allow air in and
nothing out is the cleanest and easiest, and lightest solution but you do have
to have a way to close the fuel off from the engine. </FONT></DIV>
<DIV><FONT size=2></FONT> </DIV>
<DIV><FONT size=2>I used to use a fuel dot....I would plug the line when not
running. Once it was time to run I would remove the dot throw it in the TX case
and then connect the line to a fuel filter that would take fuel to the engine
and pump. Now I use the little K+S clips they weigh nothing and work
excellently. they stay attached to the model and fly with it. Literally they
weigh about 1g additional to the model. looping the fuel tubing or installing
some aluminum tubing that loops behind the tank weighs more and complicates the
system further.</FONT></DIV>
<DIV><FONT size=2></FONT> </DIV>
<DIV><FONT size=2>Troy Newman</FONT></DIV>
<BLOCKQUOTE
style="PADDING-RIGHT: 0px; PADDING-LEFT: 5px; MARGIN-LEFT: 5px; BORDER-LEFT: #000000 2px solid; MARGIN-RIGHT: 0px">
<DIV style="FONT: 10pt arial">----- Original Message ----- </DIV>
<DIV
style="BACKGROUND: #e4e4e4; FONT: 10pt arial; font-color: black"><B>From:</B>
<A title=bob@toprudder.com href="mailto:bob@toprudder.com">Bob Richards</A>
</DIV>
<DIV style="FONT: 10pt arial"><B>To:</B> <A
title=nsrca-discussion@lists.nsrca.org
href="mailto:nsrca-discussion@lists.nsrca.org">NSRCA Mailing List</A> </DIV>
<DIV style="FONT: 10pt arial"><B>Sent:</B> Wednesday, December 12, 2007 9:09
PM</DIV>
<DIV style="FONT: 10pt arial"><B>Subject:</B> Re: [NSRCA-discussion] Fuel
shut-off gizmo</DIV>
<DIV><BR></DIV>
<DIV>I don't know much about the DZs (never owned one) but from what I
understand, one of the pushrods is used to operate a pump. Could the flooding
happen when the crankshaft is turned to one particular position? </DIV>
<DIV> </DIV>
<DIV>Bob R.</DIV>
<DIV><BR><B><I>Mark Atwood <<A
href="mailto:atwoodm@paragon-inc.com">atwoodm@paragon-inc.com</A>></I></B>
wrote:</DIV>
<BLOCKQUOTE class=replbq
style="PADDING-LEFT: 5px; MARGIN-LEFT: 5px; BORDER-LEFT: #1010ff 2px solid"><FONT
face="Verdana, Helvetica, Arial"><SPAN style="FONT-SIZE: 12px">Only the DZ
line requires the clamp. “requires” is probably too strong a word as I
have run mine successfully for a season without one, but even with being
very careful I still had it flood numerous times. The clamp or a shut
off is a very easy, Highly effective, highly recommended
fix.<BR><BR>-M<BR><BR></SPAN></FONT></BLOCKQUOTE>
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