Pilot Balloon Nozzle and Weight Set ML-373/GM (US ARMY)
This is a photograph of a ML-373/GM Pilot Balloon Nozzle and weight set produced in 1998. This set is used with 30 and 100 gram balloons and hydrogen (and possibly helium) for both day and night time (with pibal light) ascents. An interesting factor of this set is that it is recommended in the 1968 Army Technical Manual TM-11-6660-222-12 for use with Hydrogen only, however its weight/free lift falls in-between the NWS recommendations for hydrogen and helium. An alternate nozzle ML-472/GM system is suggested for use with hydrogen and helium. The ML-472/GM nozzle weight set looks identical to the ML-373/GM but is 7 grams lighter without weights.
A June 1997 US Army Field Artillery School Lesson Plan instructs ML-373/GM use with both hydrogen and helium. A phone call to the training division confirmed the use of the ML-373/GM nozzle weight set with both gasses. The nozzle itself weighs 132 grams (in-between the recommended weights for Hydrogen (125 grams) and helium (139) grams. It appeared as if the Army was sacrificing accuracy for simplicity.
Recent research has found that the Army was using an ascent rate of 200 Yards/ minute with 30 gram balloons (183 meters/minute). Other services were using an ascent rate of 180 meters/minute. This would account for the greater weight of the ML-373/GM weight set as compared to the 125 gram ML-472/GM nozzle which conforms to the ascent rate of 180 Meters/minute.
The nozzle has three weights 50, 70 and 443 grams. The 443 gram weight is used with 100 gram balloons (combined free lift of 575 grams).
The nozzle is double sided allowing for the use with two different balloon neck sizes. Pushing on the center bolt of the stop cock vents gas out of the balloon to the unused side of the nozzle allowing for controlled deflation of the balloon.
