Mark Hickey wrote in message . ..
For those of you lucky / affluent enough to afford a pressurized
aircraft, here is the way NOT to test yours:

http://disastercity.com/kc135/


This is why whenever possible pressure testing should be
done with water, rather than air. Not an option in this
instance.

A former cow-orker of mine used to work for Cleveland Pneumatic
Tools which, in addition to aircraft landing gear, made these
big whatchamacallems, pressure chambers like deep sea divers
might sit in for a few hours to prevent the bends. Anyhow,
he saw one fail hydro testing one time. Said it looked like
a small tsunami as the water swept accross the shop. Had they
tested it with air it might have killed everyone in the room.

Back in another life when I was a contract engineer for a company
that made radiation monitoring equipment our QA technician was
hydrotesting a 'volume' for one of my jobs and I stopped
by to see how it was going, and also to be sure he didn't
have the radiation detector inside when he filled it with
water. He told me that he must have trapped an air bubble
in the volume because it took many strokes of the pump to get
the volume up to the correct pressure (225 psi
IIRC). I stepped back a couple of feet and explained to him
some of the differences between compressible fluids like air
and incompressible fluids like water. Then I pointed out that
1) if the volume he was testing failed the test badly it just
might explode, and 2) the air bubble reduced the sensitivity of
the test rendering the result invalid anyhow.

He was unimpressed and I went back up to my office. Later that
day another engineer told me what he saw happen next. The
technician had installed a short piece of tubing and a ball
valve to be used to drain the volume. The end of the valve
pointed straight out horizontally from the volume. So when
the time was up he went and got a bucket, held the bucket
under the end of the valve expecting to catch the water as
it dribbled out, and opened the valve. The water shot
accross the room hitting an oscilliscope on a wheeled cart
and knocked it over on its side.

I think he understood some of what I was trying to explain
after that.

--

FF