Letters To The Editor

Readers respond to the merits of helping youth; warn of the dangers of running pumps dry.

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Beware of Cold When Hydrostatic Vessel Testing
In relation to the article “Use Water to Check Vessel Integrity,” additional consideration in colder climates is to guard against the possibility of water being retained in or leaking into smaller, isolated
chambers, piping, etc. where extreme cold could cause rupture or otherwise damage equipment. 
Dave Mahan
American Refining Group, Bradford, Pa.

There’s Merit in Helping Youth Learn Engineering

I heartily agree with Mark Rosenzweig’s column, “Convince a Child to Explore Engineering." Recently, for seven weeks on Monday nights I have had the pleasure of acting as Engineering Merit Badge Counselor for Troop 87 of the Boy Scouts of America (BSA) here in Vernon, Texas.

BSA’s merit badge guide book did a very nice job describing engineering and developing activities to teach the boys what engineers do. It was a blast for me, and the highlight of my week. We covered statics, mechanics, lean manufacturing, heat transfer and chemical reactions including polymers.

The boys were very sharp and quickly picked up on the concepts. They thoroughly enjoyed each week (I could tell since no one was absent!) and several fathers enjoyed it, too. I suspect Vernon, Texas, will be contributing at least one or two engineers to the profession in the coming years.
Howard P. Elton P.E., technical manager
Rhodia Inc., Vernon, Texas

Article Brought Back Memories
I really enjoyed Andrew Sloley’s article “Troubleshooting: Take It To the Field." I have 37 years’ experience (pump and seals) of solving the same type of issues, and your article brought many of those back to mind.
Mike McCauley
Fluid Sealing Consultants, Inc., Schererville, Ind.

Running Pumps Dry Will Cure the Economy
I recently received a query about dry running pumps and I want to share my thoughts on how it could cure the economy. Following is the inquiry I received:
We have a Group II  pump, 2 x 3 x 8" with semi-open impeller, standard stuffing box, and a metal bellows seal. The pump has an externally supplied seal flush (1 gpm flow @ 50 psi). What mechanical or seal damage would result from running the pump for short periods of time (3-5 minutes) with only the seal flush supplying liquid to the pump?

Since very little detail was supplied, I had to make a few assumptions in developing an answer.

Let me assume that the non-flowing liquid supply to the pump gets re-established after 3-5 minutes and that it's being re-established suddenly, or instantaneously. (Parenthetically, I might add that five-minute delays announced at airports are, realistically speaking, delays more likely 50 minutes). Anyway, instantaneous re-establishing of flow would be like a one-ton stack of bricks hitting the impeller. I'm not sure how accurate the one-ton guess would be; but, for a fee, Midwest Research Institute in San Textonio (MwRI) could calculate it.

The impeller, having briefly tried to function as a gas compressor will, hopefully, not have been able to produce much of a vacuum. If the impeller pulls a vacuum and some air is sucked in from a leaking gasket, there might be an explosion. On the bright side: Industry spends much more money after than before an explosion.

Anyway, the impeller will probably be surrounded by a (very hot) vapor cloud and that vapor cloud, upon being hit by the ton of bricks (assuming MwRI agrees with the magnitude of one ton) will either condense, collapse, or move on — as a big bubble — in a piping system that had anticipated transporting only a liquid.

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