sufficiently to caaae.a Short between the electrodes, firing the squib
prematurely. If the distance is too large, however, therewill be too
great a height difference between the ttme of minimum pressure and the
time the electrodes are shorted. For instance, a spacing of 10 l!Uile would
delay the firing of the squib until the pressure reached 13.3 mb. above
the min~um pressure. At an altitude of 50,000 teet, the equivalent height
(standard atmosphere) would be about 2300 feet. It is obvious that tor high
level flights, a less dense rund lower freezing electrolyte tor the minimum
pressure gwitch ~11 be needed to obtain the desired sensitivity of 2000
teet.
By adding the pressure-activated automatic ballast valve to the
manual ballast valve, the complete patter.n of the solid curte in Figure 7
may be achieved ideally. At sunset the rapid cooling oaases descent which
cannot be canpensated for by the manual ballast valve. As soon as the seal-
off pressure of the automatic ballast valve is exceeded by the atmospheric
pressure, ballast flow is begun, Which restores the balloon to its ceiling.
The dashed curve in Figure 7 shows the action of a balloon when the
automatic ballast valve alone is used tor control purposes. In this case
the balloon ~11 si:rlk slowly from its ceiling (where full buoyancy just
equals the load) to the level where the e.utom tic ballast valve drops
ballast at a rate equal to the diffusion (the floor). It will be noted
that a flight which is controlled in this manner is less wasteful of
ballast and results in a correspondingly longer flight. lne "floor"
determined by this valve varies diurnally as the temperature (hence pressure)
of the air entrap}?ed in the diaphragm is affected by solar radiation. 'i'le
amplitude of this diurnal oscillation may be as much as 6000 feet. the nignt
level being higher than the day level.
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