[Balloon-makers] FW: micro-solenoid valve

Sat Dec 27 16:16:36 CST 2008

I lied, it was  April 1990.  See attachment.  Thanks for the link to the
German RC balloon reference.  I hadn't seen that before.  When I built my RC
balloon in 1987, I wasn't aware of ealier work.  Seems there were quite a
few in Germany prior to that.  I'll have to get some of this translated. 

That swagelok valve looks almost identical to the Hoke, might even be made
by them.  Yes, a four bar linkage is the way I actuated these valves as
well, although you could do it other ways too.  I used swagelok compression
fittings, and never had any significant problems with leaks.  Swagelok
valves and fittings are very high quality and rather expensive.  Aerostar,
balloon works, etc burners all use compression fittings (Swagelok and
Parker) as well as tapered pipe thread fittings so I am surprised you're
having trouble. Are you following maufacturers instructions exactly?  The
link for the valve you sent shows a brass valve.  Are you using brass
ferrules on stainless tubing?  I don't think you can do that, the ferrule
needs to be harder than the tubing.  I have never seen, tried, or heard of
any burner with soldered plumbing fittings although I can't see any reason
why it wouldn't work.  I'm not sure of the pressure rating of a sweated
joint but in a burner you have pretty good propane pressure as well as some
high thermal stresses so you need something rated.  I guess one reason not
to use soldered joints is that you would have a chance of a catastrophic
joint failure if you had a small leak and associated fire heating your
plumbing. 

The flame-heated propane vaporization coils I built were stainless 321
(Aerostar uses 321 in their burners), and I also played around with 316,
304, as well as copper which has an excellent heat transfer coefficient
compared to the stainless.  Most of the RC balloons I've seen available
commercially use small steel 1 Lb disposable cylinders.  The burners I made
were really for fairly large RC balloons, around 4500 cubic feet.  I used 6
or 10 Lb Worthington aluminum cylinders modified with diptubes to draw
liquid.  If I recall, the 10 Lb cylinder was good for around an 80 or 90
minute flight time.  

Pilot lights are really a challenge to make small, lightweight, and
reliable.  You're on the right track using a small torch or just copying a
pilot light from a full size balloon.  Do you have any balloon repair
stations in your area?  Maybe they would sell you an old pilot light or the
parts to make one.  I used a liquid pilot from an Aerostar, which is really
just a brass Sherwood regulator and a custom pilot head.  Although the brass
regulator is heavy, this approach has the advantage of using liquid,
requring only one cylinder valve and fuel line.  The torch burner you
mentioned will need vapor, necessitating a second cylinder or a second
withdrawal valve or a regulator to convert liquid to vapor. All of this will
be a weight trade for your specialized application.  

If you really want a challenge, you could mess around with direct ignition
(no pilot light) using spark via coil or piezoelectric but this is probably
more tricky than you'd be smart to take on at this point.  You're definitely
right about batteries getting smaller and lighter, and maybe that is a good
enough reason to use a solenoid valve.  I see that the DC version of the
ASCO valves draw about 7 watts each.  I assume you would need two of them.
Normally open valves would be dangerous in this application since a poor
connection or a dead battery would both result in propane flow.  Maybe you
could live with that for a low-flow pilot.  Still, I don't think I would do
it.

Servos driving microswitches driving solenoids, can't you get a circuit with
no moving parts which will eliminate the servo, microswitches, and all of
their associated failure modes?  One thing that stands out on the valve data
sheet you referenced is the ambient temp range of 15 to 140F.  Balloon
valves used for liquid propane need to be rated far lower, like -50F or
better since liquid propane flashes at -44 F at 1 atmosphere.  These valves
get cold!  Anything I ever tried that wasn't rated for cold leaked, and even
some that were rated for cold still leaked!  I forget what O-ring materials
are most compatible with liquid propane but these need to stay compliant
below -50F.  I think silicone is good at these temps, consult Parker's
O-ring handbook.

Good Luck!

Noah Forden

  _____  

From: Kyle Kepley [mailto:kyle at passfire.com] 
Sent: Saturday, December 27, 2008 12:45 PM
To: Noah Forden; balloon-makers at taleos.com
Subject: re: [Balloon-makers] FW: micro-solenoid valve

Hi Noah,

Thanks for the info.  I tried looking up your Balloon Life article in the
online archives, but they only go back to 1995 unfortunately.  My first
burner attempt was made using a valve similar to the one you linked to.
Here's the Swagelok valve I tried:

http://www.swagelok.com/search/product_detail.aspx?part=B-1GS4

I just put a servo in front of this and wired the servo arm to the valve
lever so that it would pull the valve open.  My design had other problems
with leaks though, so I'm going to rebuild the whole thing and try solenoid
valves this time.  I was using all compression fittings, which seem to be
very prone to leaking.   What is the best method to use for the plumbing?  I
have to keep the gondola construction to around 6 pounds, including fuel, so
I want to avoid heavy pipe fittings.   I was thinking about trying small
copper sweat fittings next.  I've seen some pictures of flexible tubing
being used also.  There's an entire book written on RC balloon making, but
unfortunately it's all in German and even when using the online translators
I have a hard time reading it.  It's downloadable for free at the link
below. The pictures of the balloons people have made are amazing!

http://www.pinguballon.de/main/main_e.html

What surprised me in that book were the small size of the propane tanks they
are using.  Maybe RC balloons aren't designed to fly very long?  I have one
of those green camping propane cylinders connected to my burner and it
empties out pretty fast.  I'm planning on carrying two of those in the
blimp.   I think my first burner attempt had too much output though and
that's why it went through fuel so fast.  The flame looks like at least 8
feet tall.  I took the regulator off of one of those camping stove burners
that screw directly onto the tank and added it to my burner to tone it down,
which seems to work.  My blimp is 9 feet diameter and 30 feet long, so I
can't have a giant flame shooting straight up or it will burn right through
it.  I need more like a two foot flame angled at 45 degrees forward and
backward.

Another area I had problems with was the pilot light.  I couldn't find
anything small and light, so  I finally just used a standard brass propane
torch head for the pilot light, which works great but is pretty heavy.  The
burner setups in the book linked to above all look compact and light, but
it's hard to see what they are using for the pilot lights.

One reason for going to solenoid valves is I want to have one servo control
both burners.  That's pretty easy to do by letting the servo arm make
contact with micro-switches that will power the coils.  Battery technology
has really come a long way in the last 20 years, as has the miniaturization
of servos.  I have a 7.4v lithium polymer pack that can output 2.3 amp hours
of current and it only weighs 114 grams.  The 6 volt DC solenoid I was
looking at is rated for 6.3 watts, so that would be over two hours of
continuous open-time before the battery ran out.  Here's the data sheet:

http://www.passfire.com/misc/8256_NSFR1.pdf

The company selling those, valve-store.com, actually quoted me 9 weeks
delivery time!  Unfortunately I can't seem to find anyone else selling them.

-Kyle

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