Dry Pipe Failures

[Ken Fleming]

This link is for a PDF file from New Zealand addressing recent dry pipe failures and priming problems.  Very interesting.  My take away was using a small USB camera, with LED lights, to inspect the internals of dry pipes and could be used for other pipes.  Mount camera on something like an electricians fish tape and run down through the throttle valve for inspection.

http://www.nzta.govt.nz/resources/rail-safety-news/docs/rail-safety-update-issue-14.pdf

[John Kokas]

Really good article.  Nice to see that the NZ Dept of Transportation works cooperatively with groups to discover and remedy problems.  It's a shame that many times our own DOT/FRA prefers to "hammer" people first and then address issues later.

[Steve Smith]

Many thanks to Ken Fleming for calling attention to such an important article re steam locomotive safe operation. The bulletin the link takes you to also has an excellent article on the vital importance of avoiding too high a level of water in the boiler. It has a very clear explanation of how a water level too high can lead to a violent, uncontrollable wheel slip with resultant severe damage to the engine and quite possibly injury to the crew as well.

An unstated implication is that the crew has water level indicators that tell it like it is inside the boiler.

The article doesn't go into the subject of the reliability of the water level indicating equipment, but clearly, reliable level indications are a necessary precondition for maintaining proper level, since few, if any, steam locomotives had/have automatic systems to maintain that level. That job was the responsibility of the crew.

But for a long time in the history of the American steam locomotive, the water level indicators used were actually not very reliable, because what went on inside a boiler was not well understood. Then shortly  after WWI, the Bureau of Locomotive Inspection of the Interstate Commerce Commission conducted a series of tests to find out what happens to water level in various parts of a locomotive boiler under the various operating conditions. In 1920, Railway Mechanical Engineer ran a two-installment article describing the tests and giving the concluding, specific recommendations for the types of equipment and the placement of such devices on a locomotive boiler.

I have so far found and downloaded (from Google) five volumes of Railway Mechanical Engineer, 1916 through 1920. The articles on the water level indicating systems test and recommendations are in Volume 94 (Year 1920) pages 575 -579 and pages 630-633. I recommend them to anyone interested in either steam locomotive operating safety or the technical aspects of steam boilers.

The most--what term to use--dramatic?--item in the articles to me was the advice given in all sincerity by management and locomotive supervision prior to the tests and the report that in case of doubt the crew should trust the indication from the test cocks on the backhead in preference to an indication in the water glass. The tests showed that when the throttle is open and/or the safety valves are open the test cocks are likely to indicate a water level significantly higher than they should.

After reading the articles I believe I understand why crown sheet failures and resulting deaths, injuries and dollar losses occurred all too frequently, and persisted to some extent through the steam era.

 

[John McNamara]

The most--what term to use--dramatic?--item in the articles to me was the advice given in all sincerity by management and locomotive supervision prior to the tests and the report that in case of doubt the crew should trust the indication from the test cocks on the backhead in preference to an indication in the water glass. The tests showed that when the throttle is open and/or the safety valves are open the test cocks are likely to indicate a water level significantly higher than they should.

I don't understand. The first sentence seems to say that test cocks are the best indicators, but then the second sentence says that they aren't good indicators in some situations. Can someone clarify?

Thanks!
-John

[Steve Smith]

Sorry for the confusion, John. I should have given a bit more information. Problems existed and of course still exist, with water glasses as well, such as blockage in the lines from boiler to the glass. By the WWI era in question management and supervision were well aware of problems with water glasses but unaware of the problem with test cocks when throttle or safety valves are open, So they thought that test cocks were the safer alternative. I just imagined that it must have been dramatic for mgt & supervision to realize that, quite unintentionally, they had given advice that in all probability killed and injured locomotive crews through crown sheet explosions that occurred when a crew thought they were maintaining safe water level, as supposedly verified by using the test cocks, but instead had a level too low.

What got me looking into the whole matter was an article in the Summer 2005 NRHS Bulletin I saw in the Sheepscot station office about boiler explosions on the Milwaukee Road over the years. I couldn't make sense out of statements in it regarding the water indicting devices, but I noticed mention of the study and report by that committee of the ICC, so kept my eye open for possible mention of it, and eventually found the mentioned Railway Mechanical Engineer articles.

Last point, possibly of help should you look up those articles: After reading them, at first I wrongly concluded that the water column recommended in the report  (from which both test cocks AND water glass were to be tapped) was somehow a more reliable indicator of boiler water level than a water glass. I puzzled over that for a long time. Why would that be? It finally dawned on me that the column, as shown placed relative to the boiler in the accompanying drawings, was located so as to get the upper tap OFF THE BACKHEAD. That's the key.....OFF THE BACKHEAD. It's the upward surge (when throttle or safety valves open) in the space between firebox back sheet and the backhead that cause any indicating device with its top tap there to give a false reading.

I think--let the experts correct me on that if necessary-- that a water glass can be just as reliable whether tapped into an intermediate column or directly to the boiler, so long as the upper tap is not on the backhead, (of course assuming that the lines to it are clean and functioning properly and same for the isolating valves.



 

[Keith Taylor]

Another problem with test cocks (aka gauge cocks or tri-cocks) is they are inherently less than accurate due to capillary action drawing water up slightly where the water touches the back head. So a gauge cock will spritz water even though the actual water level is below the gauge cock opening.
Just as a tid bit of trivia...the funnel like object that the tri-cocks drain into is called a "tundish."
Keith