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.
Fortunately, even without an explosion, the local pump repair shop will be greatly indebted to you after dry running and will supply you with the customary reward of two dozen donuts on an expedited delivery basis. Krusty Goop donut stock values will go through the roof. In some instances, the local pipe fabricator shop also will express profound gratitude. That's because when the piping jumped off the rack and seven supports broke loose, you were able to keep the fabricator in business.
Your local bearing suppliers will benefit from a marked increase in bearing sales. When vapor bubbles collapse, they tend to exert an overload on the entire rotor system, causing bearing consumption to escalate. Occasionally, the faces of the bellows seal will crack, but not all the time. Also, occasionally, the welded seams in the bellows will fracture, but we can always blame that on the seal manufacturer's deficient Q/C.
There's even more good news. I believe there's the possibility (albeit remote) that all the pump and process design textbooks in the world (that usually caution against dry running) will have been proven wrong and will have to be recalled for revision. That will re-invigorate the book publishing business. The piping jumping off the rack has consequences that will activate both OSHA and the EPA. After exchanging suitable correspondence, they will be joined by the Provincial Air Control Board Task Force (PACBTF) and the SPCA — since both wild and domestic animals will have been frightened by the consequences of dry running. To become the new norm, an API task force would have to be convened.
Even if dry running pumps shouldn’t become the new norm matters will, inevitably, be investigated by teams of lawyers. The teams will soon arrive, golf bags and all. Extra bags now cost lots of money and airlines will finally sell 99.3% of seating capacity. Well, let's just say the airlines will be helped immensely by dry running pumps because lawyers travel in First Class.
The economy will finally recover and your plant manager will be given an award for being the “Business Leader of the Decade.” Regrettably, I will be vilified for having cost industry gazillions of dollars by claiming for decades that pumps shouldn’t be run dry. My reputation will be sullied and the mayor of West Des Moines won’t give me the keys to the city. Igor Karassik’s body will be exhumed and burned at a Run’em Dry Rally because he, too, was wrong.
Sorry, I digressed. Back to the subject: It used to be that process designers were obligated to design systems so that this dry running wouldn’t happen. Mechanical and chemical engineers used to determine what's reasonable and what's unreasonable. But times have changed. And so, we'll make that a story to be continued and examined another time.
Heinz P. Bloch
Serious Advocate of Not Running Pumps Dry
