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Inflation Procedures for Pilot Balloons
Inflation of Balloons
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.
Pibal Time vs. Height Table (assumed height above surface).
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.
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: