Similar but different...... At school the physics teacher was showing that in a vacuum a feather and a ball bearing fall at the same rate... So he bought a big glass tube with a feather and a ball bearing in it. The ends where sealed (though one had a nipple on it to attach to the vacuum pump). So he slowly evacuated the glass tube (sadly not the classroom at the same time) and lifted the tube in the air. The ball bearing and the feather fell at the same time. The only problem was that the ball bearing fell into the nipple blocking it off. The vacuum pump went into overload so he placed the tube on the desk and camly switched off the pump (rather than slowly turning down the vacuum). The inward gush of air blew the ball bearing all the way along the tube, straight through the glass end plate, across the classroom and embeded itself in the wall. Luckily no one was in the way............ It took him a while to live that one down..... Ben ----- Original Message ----- From: To: Sent: Tuesday, August 27, 2002 3:31 PM Subject: Re: [EE]: The joys of electronics > We built a new air handler for a large office building. The air handler > had a 200 HP fan motor, which delivered 80,000 CFM at high pressure (5" > static). I got involved when we had to install a variable frequency drive > to run the 200 HP motor, and interlock it with the HVAC controls. > > Now this was one of the bigger air handlers the contractor had built. > Picture this, an airtight box, maybe 50 feet long, with a fan at one end > sucking air out of the box, various filters and cooling coils inside, and > a big wall of dampers at the other end. The dampers selected between > outside air and return air, and the controls picked whichever one used the > least energy to cool. > > Now one or the other damper *must* be open at all times, and one of my > jobs was to build the interlock that made this happen. My stuff worked > fine, but the contractor put tiny little motors on the dampers. I was > *inside* the air handler when the inevitable occurred. The 200 HP fan > kicked on, and both dampers remained closed. The walls began buckling, > and the whole wall of dampers began to move toward me with a noise like a > bulldozer was coming through them. . I had to hit the door (which opened > OUT) with my shoulder a few times to get out of there alive. I ran is > slow motion like one of those dream sequences in the movies to slam the > panic switch on the motor controls and shut the whole system down. > > > -- Lawrence Lile > > -- > http://www.piclist.com hint: The PICList is archived three different > ways. See http://www.piclist.com/#archives for details. > > -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.