First, a little motor theory. When a motor is ignited and first begins to
produce hot gasses (hopefully from the TOP slug), these gasses don't know where
the nozzle is. The gasses don't automatically begin to flow toward the nozzle.
Instead, the expanding gasses seek the path of least resistance. There is a
considerable amount of ambiant air in the cores of the unlit slugs which must
first be expelled out the nozzle. The longer the case, the more air there is to
expel, and the more resistance there is for the expanding hot gasses trying to
exit through the nozzle.
For the four longest 38mm motors, this resistance can cause the hot gasses to
briefly flow the wrong direction, upward away from the nozzle. The gasses escape
between the forward insulator and the top of the liner (remember, there is no
o-ring at this point) and begin to pressurize the area between the case and the
liner. This flow of hot gasses around the top of the liner can cause the case to
bulge and/or blister.
The solution to this problem is the forward seal disc. This aluminum disc
replaces the forward insulator. It has a groove around it's circumference into
which an o-ring is inserted. It then fits snugly into the top of the liner and
prevents the flow of hot gasses between the top of the liner and the seal
disc.
The forward seal disc is REQUIRED for the 29/240 (H-220 Kit Only), 29/360
(NEW) and the 38/480, the 38/600, the 38/720 and the 38/1080. The seal disc
o-ring is included with all reload kits for these four case sizes. Do not
discard the seal disc....only the o-ring is removed and replaced after every
flight.
The seal disc is included with any purchase that includes one of these four
case sizes (480, 600, 720, or 1080). Case damage caused by failure to use the
seal disc will NOT be covered by warranty.
