An electrically operated needle valve was included in the order, however it is to be cancelled as the mechanical valve appears more feasible to the manufacturer.
As the motor switched modulator was already in experimental state of manufacture for the Signal Corps and Evans Signal Laboratories an order was placed for 3 of them with these characteristics:
To have a motor-driven commutator to contain 4 contacts alternately switching two different temperatures, pressure and a reference. Rate of switching will complete one cycle per minute. To report pressure accurately between 150 and 500 mb. with a pressure resistor to be of such a valve that with a large radiosonde frequency variation for a small change in pressure.
To have an adjustable contact variable between 250 mb and 400 mb with a factory adjustment of 300 mb. When the pressure arm reached this contact, a squib will cut a thread that holds the ballast diaphragm open.
The first mechanical dribbler was received on 20 April 1947 and is undergoing modification and tests before being flown on Cluster Flight #2. If it is successful, an order for improved models will be placed.
Another method maintaining a balloon at constant altitude is by replenishing the hydrogen in the non-extensible envelope as it is valved or as it diffuses. This might be accomplished by use of liquid hydrogen but not by use of chemicals due to their great weight relative to the small volume of hydrogen generated. The liquid hydrogen method is being investigated with a long range view. It does not seem too feasible, however, due to the difficulties of keeping the rate of evaporation of the liquid hydrogen low at the high altitudes, without extensive and heavy guard glasks of liquid air.
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