the balloon and permits gas to be introduced into the
top of the cell first. As the balloon is laid out and
shotbags are positioned, this tube must be kept clear.
At the point where the bubble is pinched of£ the folds
of the balloon are carefully divided; the inflation tube
is made as free as possible with only one layer of poly-
ethylene above and one below it. The tube is then pulled
up above and between the arms of the releasing device or
the heavy shot bags, and the remainder of the fabric is
pinned down so that no shifting will permit premature re-
lease.
Depending upon the load to be lifted and the rate of rise
desired, a pre-computed amount of helium is fed into the
balloon (see Section IV, A). This amount is determined
by noting the equilibrium pressure and temperature of
the gas in each cylinder. A manifold is used to feed the
gas from the tanks to the inflation tube in the balloon.
Shown in Figures 26 and 27 this manifold system consists
of an adjustable number of flexible pigtails leading into
a main line of heavy copper tubing. This main line and
the fittings are capable of ~hstanding the full tank
pressure of about 2500 feet psi. Two pressure gazes are
included in the main line and it is thus possible to make
last-minute checks of the amount of gas (pressure) in
each tank. (Due to variable gage-calibrations, it has
been found necessary to establish the lift-pressure. ratio
of each gage before using it.) In the main line of the
manifold, two valves control the gas flow. The inflation
tube is often initially twisted when the balloon is first
laid out, A small amount of gas at very low pressure
Should be valved into the tube to strengthen it. In addi-
tion to the fine valve control required for this pre-
liminary gas feed, it is also nedessary for e manifold
valve to permit high gas flow from the tanks even when
the pressure is greatly reduced. For this, the coarse
globe valve is used.
Once the tube has been chedmd, inflation should proceed
as rapidly as possible. The balloon is outdoors and so
subject to buffeting by the wind. The limiting factor
of sr·eed of inflation is the vibration of the fabric
near the open end of the inflation tube.
A~ a result of the extreme cooling of the rapidly expanding
gas, the manifold and the tank valve generally become
coated with frost. Too rapid cooling may actually cause
the valve to freeze shut.
-44-