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<< Lancair Builders' Mail List >>
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In a message dated 12/23/0 10:22:21 PM, you wrote:
<<If you use compressed air - even from a bicycle pump - BE CAREFUL! >>
This is true. I once ran a hydrotest on a small rocket engine casing before
I loaded it with solid rocket propellant. This gizmo was about 18 inches
long and about 2 inches ID. I filled it with water in case it failed. I
then had it in a blast chamber at the USAF Academy (where I was a Visiting
Professor at the time) and pressurized the case from the other side of the
blast wall. (I may be crazy, but I'm not stupid.) The flange on the end of
the casing failed, and while so doing snapped the bolts holding on the end
plate. I was then left with a tube of water with 160 psi air forcing the
water out one end with nothing to hold it down.
I realized something was amiss when I heard a very large BANG. I confirmed
my suspicion when I looked over at the cadet I was working with and his eyes
were as big as dinner plates. I then looked at the pressure gauge -- which
read zero -- and said "oops!"
It took us about five minutes to find the motor case. It was no longer
connected to the pressurizing apparatus (which was pretty substantial, by the
way). Our first clue as to what happened was the big dent in the ceiling.
The motor case had launched itself and ripped away from the pressure line,
then landed on the floor and rolled under a workbench. Just barely missing
the $30,000 instrumentation system that the department was storing in the
blast chamber.
They thought I was being reckless, and I thought they were being stupid for
using a blast chamber as a storage facility. Mostly they were just upset
because they hadn't realized that rocket engine testing was hazardous. (well,
duh!) Of course I had been following written procedures, but after this
incident, a Lieutenant Colonel had to sign them off...
So Dick Alden is right, pressure tests can be hazardous. I was planning on
being around the corner and only going to about 50 psi. And pointing it the
other way....
- Rob Wolf
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