[balloon-makers] Construction

David Barker dcbarker at dcbarker.karoo.co.uk
Wed Mar 12 06:35:51 CST 2003


Kasey wrote
< During a recent training flight with my instructor, we were going over
emergency procedures with the burner during flight. One of them was flying
with the tank valve, if the blast valve were to stick open. He held the
valve open, and I turned the valve nearly off, but kept it open a bit to
keep a flame. I think after only a few seconds, I looked at the valve and
saw/heard propane leaking out from the valve area. I know this was due to
there being large amounts of propane flowing through a not-so-large space,
but it was kind of statling...starteling.....startling....It made me
nervous. >

Cracking the valve open a touch to keep a small flame is the recognised
method to compensate for pilot light failure. A certain amount of cooling
will occur since the liquid propane converts to gas in the valve body hence
cooling it, but this cooling is generally insufficient to cause any problem
in the time needed to make a precautionary landing.

This situation is entirely different to opening the valve about a half turn,
which as I said will get very, very close to full fuel flow.  I have been
opening  valves in this way during these past 30 years with no problems!
It's easy enough to test.  Operate the burner, on the ground, and wind the
valve back until you notice a small drop in the size of the flame, then
check how much more turn is needed to completely close the valve.  The
minimum opening you need is a touch more than this.

If the stem seals on a valve are in poor condition leaks through the stem
can occur when the valve is in different stages of being open i.e. half open
it may leak whereas fully open it may not, or even vice versa.   Once the
stem seals are frozen due to the small leak the leakage will get worse.   I
suspect this was the cause of the leakage Kasey experienced and that the
valve was in need of some maintenance. Unless the icing is very severe
turning the valve off will stop the leakage through the stem.

Oh, and I also get nervous when there is a propane leak in the basket!

Best regards

David Barker
now, temporarily, at Burton Pidsea, UK





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