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Up Release and Tracking

Inflation Procedures for Pilot Balloons

Inflation of Balloons
When inflated a balloon is subject to fatigue, which can lead  to a low bursting altitude.  For this reason and to reduce the the loss of gas by diffusion, inflation should be delayed until just before the observation is to begin.

The tables below lists the recommended free lift for 10, 30 and 100 gram balloons in order to achieve the average ascent rates used in the time/height table below.  These are U.S. standard ascent rates1.  Users with Met Office Standard fillers (United Kingdom) use fillers that yield different ascent rates2.   The night time free lift assumes that a lighting device will be attached (~30 grams) to the balloon.  Note the ascent rates for these free lifts are approximate.   10 gram balloons are used daytime only due to the weight of lamp units and the ascent rates are specified for helium with the standard 45 gram nozzle (about 42 grams would yield similar results with hydrogen - however nozzles are not made at this weight.)

Note: Balloon chemistries and manufacturing lots are not constant.  These changes will effect the ascent rate of the balloon for a given free lift.  A single theodolite observation cannot account for up and down drafts in its assumed ascent rate.   Consequently ascent rate errors introduced by differences in the manufacturing of individual balloons is most likely not the limiting factor in the accuracy of upper level wind determination using a pilot balloon and a single theodolite.

10 Gram Balloons
Day   45 Grams
42 Grams
30 Gram Balloons
Day 139 grams (helium) 125 grams (hydrogen)
Night 192 grams (helium) 170 grams (hydrogen)
100 Gram Balloons
Day 515 grams (helium) 450 grams (helium)
Night 552 grams (helium) 482 grams (hydrogen)

Pibal Time vs. Height Table (assumed height above surface).

Min 10GM (m) 30GM (m) 100GM (m) Sec 10Gm (ft) 30GM (ft) 100GM (ft)
1 152 216 350 60 500 700 1150
2 293 414 670 120 960 1350 2200
3 433 612 980 180 1420 2000 3200
4 573 801 1285 240 1880 2630 4300
5 701 990 1585 300 2300 3250 5400
6 829 1170 1880 360 2720 3850 6200
7 957 1350 2170 420 3140 4450 7100
8 1085 1530 2455 480 3560 5050 8050
9 1213 1710 2740 540 3980 5600 9000
10 1341 1890 3020 600 4400 6200 9900
11 1469 2070 3300 660 4820 6800 10800
12 1597 2250 3580 720 5240 7400 11750
13 1725 2430 3855 780 5660 8000 12650
14 1853 2610 4130 840 6080 8550 13550
15 1981 2790 4405 900 6500 9150 14450
16 2109 2970 4675 960 6920 9750 15300
17 2237 3150 4945 1020 7340 10300 16200
18 2365 3330 5215 1080 7760 10900 17100
19 2493 3510 5485 1140 8180 11500 18000
20 2621 3690 5755 1200 8600 12100 18900
21 x 3870 6025 1260 x 12700 19800
22 x 4050 6295 1320 x 13300 20650
23 x 4230 6565 1380 x 13900 21500
24 x 4410 6835 1440 x 14500 22400
25 x 4590 7105 1500 x 15000 23300
26 x 4770 7375 1560 x 15600 24200
27 x 4950 7645 1620 x 16200 25100
28 x 5130 7915 1680 x 16800 26000
29 x 5310 8185 1740 x 17400 26900
30 x 5490 8455 1800 x 18000 27800

Use a nozzle and attach weights such that their combined weight equals the desired free lift for the balloon.  The free lift values can be used from the table above or obtained from another source.  The balloon is correctly inflated when its buoyancy is sufficient to float with the nozzle and weights attached.

Inflate the balloon slowly as follows:

1  Remove all excess air from the balloon by folding or squeezing it carefully by hand before placing the balloon's neck on the inflation nozzle.  Secure the balloon t the nozzle with a rubber band.

2  Ascertain that the diaphragm valve of the regulator is closed or in a position that will not permit gas to pass.  This is most often accomplished by turning the valve counter clockwise.  The regulator and gas line might be damaged in the cylinder valve is opened while the valve is opened at the time when the diaphragm valve is open.

3  On very rare occasions the pressure gages of a regulator can fail when opening up the gas cylinder.  Always stand to the side of the gages (perpendicular to the dials) when opening up the gas cylinder. Open the cylinder valve of the regulator fully.  Hold the balloon upright by the tip and slowly open the diaphragm valve by turning it clockwise until a pressure of not more than 7 psi is shown on the low - pressure gauge if you are using a nozzle with a valve on it.  (On these systems the valve is down stream from the rubber hose connections.  Pressure in excess of 10 pounds might cause the hose to slip off the nozzle and damage the film of the balloon.  In addition, the hose connection to this type of nozzle is not that secure allowing the user to remove the hose from the nozzle to get the proper free lift. ) 

The U.S. 10 gram nozzle has no valve.  The weight of the hose is taken into account and it is not removed from the nozzle to achieve proper free lift.  Consequently gas is controlled by a valve upstream from the rubber hose connections in many of these inflation systems. (I have used pressures of 15psi with a 10 gram balloon nozzle.  In my system the connections and tubing through the hand valve which are rated to over 150 psi, the hand valve reduces the pressure delivered to the rubber hoses of the system to a value much lower than 7 psi.)  

Open the hand valve (or valve on the nozzle to fill the balloon slowly.  Care must be taken when opening up the lower valve not to fill the balloon too rapidly.  10 gram balloons should be inflated in not less than 1 minute, 30 gram balloons should be inflated in not less than 2 minutes and 100 gram balloons in not less than 5 minutes.

4  When the balloon is partially inflated, turn of the gas (at the cylinder then the diaphragm valve for 100 gram balloons and the hand valve for smaller balloons) and listen for leaks.  If a leak is found reject the balloon.   Do not patch balloons except where lack of supplies necessitates their use. 

5  Continue with inflation by opening up the cylinder valve and then the regulator or hand valve as in step 3 above. Stop inflation when the balloon nozzle and weights just begin to float by closing the hand valve for 10 gram balloons and at the nozzle for 30/100 gm balloons.

6  For 30/100 gram balloons (or Met Office Fillers) close the cylinder and regulator and remove the rubber hose from the nozzle.  If the balloon should be slightly over inflated (because the hose added some weight), permit the excess gas to escape slowly through the nozzle.  If it is highly over inflated, it is advisable to reject the balloon and support the hose a bit during future inflations.  

image, Alex Belov holding the hose to a 10 gram pilot balloon nozzle during inflation of a Pibal

For 10gram balloons and the U.S. nozzle, the balloon is filled until neutral buoyancy is achieved lifting about 3 inches of hose.  The hose is not removed from the nozzle because its weight is intentionally included in the free lift.  The balloon is now ready to be sealed.

7  To seal the balloon, make three turns of a doubled, soft cotton twine around the neck of the balloon just above the inflation nozzle.  Pull the cord as tightly as reasonably possible and tie it.  

8  If a gas regulator was used close the cylinder valve and open the diaphragm until the pressure falls to zero.  The diaphragm valve should then be closed and left in that position until another balloon is to be inflated. 

The balloon is now ready for release!

1 Federal Meteorological Handbook No. 3 "FCM-H3-1997" has some errors in its ascent rates table.  These have been corrected here.  Additionally the heights for the 30 and 100 gram, (ft) have been adjusted to reflect a more accurate ascent than some of the published numbers (this was due to non-linearity introduced into the tables with the rounding off process employed before publishing the tables in FMH 3.).  If you are using this data for calculating the position of the balloon rather than just reporting the height of the wind profile, use the meter tables and convert the results to feet, then round off.  The results will be more accurate.  

1 Met Office Pilot Balloon Filler Data for Mark 8 and Mark 7 Filler sets:
(Fillers specified for Hydrogen only):
10 gram balloon nozzle, weight 20 grams - Ascent Rate 400ft/min
20 gram balloon nozzle, weight 61 grams - Ascent Rate 500ft/min
30 gram balloon nozzle, weight 72 grams - Ascent Rate 500ft/min
100 gram balloon nozzle, weight 230 grams - Ascent Rate 700ft/min

Navigation through Pibal Observation Instructions
Table of Contents Introduction Equipment Requirements Observation Site Setup Theodolite Setup
  Balloons Selection and Inflation Release and Tracking Computations