July1999
Concept
Alargeshop aircompressorwas used
for the initial tests. The regulated shop air
hose was connectedto a needle valve for
controllingtheflowrate,andthentoa
silica-gel desiccator, and a flow meter for
measuringtheflow ratesbetween0-3
cubicfeetperminute.Theflowmeter
outputwasconnectedtothetankinput
portwiththediptube.Theoutputport
openedat the top of the tank. The output
port was connectedtoa 10foot length of
hosewiththeflameblockattheend.
Wherethehosewasconnectedtothe
output port valve there was an instrument
tap used to samplethe gas exiting the tank.
Theinstrumentconnectedtothesmall
sampling hoseindicates when the gas is at
theflammabilitylimits of2% and10%.
(See Figure 1 onpage 26.)
With this arrangement,airat aknown
flow ratewasinjectedintoa tankfull of
100% propane vapor at atmospheric pres-
sure and the resultant gas was monitored
for the time it tooktoreach10% and 2%
propanelevels.Withthisinformationa
curve was calculated that defines the per-
cent propane for any number of tankvol-
umes.
Test
A ten gallon aluminum Worthington
vertical tankwasused for the tankunder
test.Thetankwaspreparedbyfillingit
with 1/2 gallon of liquid propane and then
purgingtheair fromthe tankbyventing
vaporfromthetankuntiltheliquidhad
evaporated, the temperature was above 50
degreesF., andthe pressure was zero.
Anarea was chosenfor the testthat
hadcontroll edaccess,nostructures
nearby, a 3 to 5 mph wind, and no ignition
source within 200 feet. The test setup was
laid out so the output hose was downwind.
Thetestdataproducedthecurve
shown inFig. 2. Four tankvolumes pro-
ducesa tankcontent of 2% propane (the
lower flammabilitylimit).Byextending
the curve, the percentage of propane can
be obtained to10 tankvolumes.
The testwasrepeatedseveraltimes
and produced the same results.
Totestthesensitivityofthetestto
2, 3 cu. ft./min. The testresults were the
same.
IMPORTANT:Thetankinletand
outletportswereswitchedandthetests
werere-runat1and3cu.ft./min.The
resultsweredifferentdependingonthe
tankvalve configuration.There are sev-
eral valve configurations that open to the
topof the tank. If air isinjected through
these,theywillcause differentamounts
of turbulence.Theresultsoflow turbu-
lence is incomplete purging. Injecting air
through the dip tube producedconsistent
results regardless of the valve configura-
tion at the top of the tank.. The conclusion
reached was that theturbulence in thetank
at 1 to 3cu. ft./min., injected through the
diptube,wassufficienttoprovide com-
plete mixing of the propane and air in the
tank.
A 15gallon tank was connected and
severaltestswererun.Theresultswere
2% propane atfour tankvolumes.
MoistureOutofthe
Tank
During shipping one of the tankser-
vice valves must be open. At the comple-
tionof the trip it is assumed that the tank
has some water vapor inside. This is usu-
ally corrected by the introduction of a few
ounces ofmethyl alcohol. However, there
arerestrictionsonshippingalcoholwith
the tank.
AerostaticEngineering(SanJose)
makesasmalldesiccatordesignedwith
propane fittings that canbe connectedto
theopentankservice valve. Thisallows
the tank to “breathe” dryair, meeting the
shipping requirements. The tank can then
be filled uponarrival withno problem.
The desiccator can be used to dry the
purge air for the return trip. A small can of
freshdesiccantcanbeshippedwiththe
July1999
To ugh, high tenacity
1.9-o z. ripst op nylo n,
with a durable 3/4-oz.
po lyurethane co ating.
Our envelope is heavier
than most balloons and
harder to tear.
The mouth and skirt are
fla me-reta rda nt 6-o z.
Nomex®a nd fo rm a
heat -resist ant ring to
eliminate burns.
We sew the whole thing
up wit h feld seams,
double lock stitch and
load webbings from the
mouth to the apex.
We weave a mixture
of strong, resilient
rattan around a
framework of durable
and flexible nylon
rods. The floor is 3/4"
marine plywood.
Dense, hard maple 2"
X 2" skids and thick
skid leather protect
the floor. Heavy
suede leather trim on
the foam padded
railings and uprights,
conceals a web of
stainless steel cables.
The basket’s flowing
curves add strength
as well as beauty.
You never know where you may end up on a flight.
So we’ve designedintoHEAD balloons thetoughness
necessary to keepyou in the air, instead of in the shop.
Fr omtheskidstothea pe x— rugge dn essi s
engineered into everyHEAD balloon.
dualblast valve DBII burnersystem.
HEAD Balloon—a rugged yet beautiful design that can
takethe roughtreatment without showing it.
1-800-HEAD BALLOONS
Outside the U.S. (706) 865-3874
BALLOONS,INC.
2000Calendar
balloonists, this
calendar for the year
2000 is like a book
to be read very slowly,
two pages a month!
Edited byChristineKalakuka& Jane English
—Ed Yost
• The perfect landowner gift
• Sell to your passengers
www.eheart.com/balloon/blln2000.html
www.eheart.com
or call Village Books at1-800-344-0436
Balloon Publishing Co, 1241 High St, Oakland, CA 94601
510-261-4222, fax 510-261-7908, balpub@vdn.com
provides tags that are attached to the service valves indicating the
purge data.
The 12vDCColemanair mattresscompressorwastested
withthe smalldesiccator ona10gallontank. Thecompressor
produced1.33Cu.Ft/Minwiththevehicleengineoffand1.5
Cu.Ft./Min.withthe enginerunningata fastidle.Theresults
were the same. Remember the sparking brushes of the compres-
sor and the vehicle engine are sourcesof ignition.
Sincethere appeartobe notechnicalpurge criteria, it’sa
matterofjudgmenthowfarunder2%propaneyoufeelis
required. Youwillnote fromthe curve,8tankvolumesyields
.035%.With the1.33 Cu.Ft./min. portable air compressor it takes
9.98 minutes for a 10 gallon tank. For 10 tank volumes that yields
.0048%, and takes 12.48minutes.
John Terry, after 35 years with IBM, principally in the field
of testing, now has his own balloon repair station and technical
design business, Aerostatic Engineering, in San Jose, California.
John has a number of Supplementary Type Certificates and
a Parts Manufacturing Authority. He has a commercial balloon
pilot’s certificate and has flown balloons for about 25 years.
For more info rmation contact Aerostatic Engineering, Joh n
Terry, 495 E Brokaw Rd, San Jose, CA 95112, phone 4 08-441-
1919, email: jterry@terry.com
