The National Oceanic and Atmospheric Administration (NOAA) developed this
release valve to enable a more controlled descent of a balloon rather than the
typical burst and parachute method. Mike Manes describes it:
These photographs are of a valvedown device for latex balloons that was
developed at NOAA to produce a controlled near-constant descent rate, sans
parachute, for their vaporsondes. This prevents adiabatic cooling of the
airstream around the balloon from screwing up the PPM-scale water vapor
measurements in the stratosphere. NOAA uses a 4" diameter valve on a 3000 gm
balloon with a 5 or 6 lb payload, and regularly gets a 1000 fpm constant and
very smooth descent. There's still He in the balloon on landing, making visual
tracking a piece of cake. They also use a GPS-equipped cutter driver mounted
right at the valve to fire it at a predetermined MSL altitude.
We "cloned" a version for a 1200(?) gm bag, using 3" PVC pipe and an
acrylic valve plate. The plate is held in place with 15# monofilament fishing
line which is cut by a burner on ground command. During our test flight, the
cord running up the lift line got twisted like a double-knotted model airplane
rubber band, thus developing a bad case of air-gap-osis before we were able to
fire the cutter.
Mike Manes
