Valve jam poses near-disaster for EEs

12/14/2010 8:53 AM EST

In steel mills, the cast bars would cool and have surface cracks. The surface was ground off with grinders to reach clean steel before rolling. These machines had large 300HP motors with huge grinding wheels. Hydraulics controlled the wheel position and therefore the power and amount of steel removed. Other hydraulics ran the steel back and forth under the wheel on what looked like short flatbed railway cars. Our controls were a mix of analog for the wheel position control and Motorola's 6800 series of 8-bit processors (all code written in assembler!) for the steel bar positioning.

As always, we designed and made the controls and shipped them to the mill. Once the hydraulics, mechanical apparatus and our electronics was installed, we would go to commission our electronics. Invariably, something would fail. A hose would break (wonderful fountains at 1500PSI!), a fitting would leak, a valve would jam, a belt would be thrown. Big red shutdown buttons were always nearby--and used. .

Late one evening we were busy trying to finish off an installation. The hydraulic control valve that raised and lowered the grinding wheel jammed. The three of us--my boss, a millwright and me--climbed the stairs up the tower to check to see what was jamming the valve and holding the wheel up. Judicious tapping with a wrench did nothing. The valve would have to be replaced. The hydraulic cylinder was holding up a heavy mechanism with a heavy grinding wheel, the valve controlled the cylinder.

It was the end of a long day and us electronics folks were not thinking clearly about hydraulics. Gathered around the valve on the catwalk, we helped the millwright loosen the valve. Quite predictably, it came loose and let loose a torrent of oil as the wheel dropped. We were soaked in oil. Fortunately it was not hot and of course the pumps were off. After the initial shock, a quick check that we all survived intact. We laughed at our stupidity as we wiped oil out of our eyes. We wiped away more oil and more again. No rags so we used our sleeves.

We stopped laughing as we noticed that none of us could open our eyes with all of that oil running over our faces. The mill was closed except for us--no shift that night. We sat there on the catwalk rubbing our eyes and eventually, chuckling at our mistake, we climbed down. Disaster dodged. .

We survived intact. Knowledge and experience in electronics does not translate into hands-on experience in other fields. I now leave the mechanical engineering to mechanical engineers, the software to the coders (I do write test code and sometimes that gets used, much to my chagrin). I find most people surprisingly competent at their job, whether it be a millwright or PCB assembler. I can wield a soldering iron but the best solderers are those who wield them eight hours a day. I can change a hydraulic valve but would greatly prefer a millwright to do it. Maybe we should have noticed that our millwright was tired or not confident in his work. Maybe we should have questioned the safety aspect. Maybe we should not have tried to rush to finish commissioning our controls. Maybe, maybe. Live and learn. .

My designs these days are a few orders of magnitude faster than the 6800 series, have progressed from ±15V supplies to +1.2V to +5V, use a fraction of the power and are always SMT. Thanks, but I can pass on the good old days of electronics from a few decades ago.