Was going through the Ohio Central web site linked from a posting about the NKP move, and was looking at the images of the work on the 33.

I've realized that though I've heard of them before, I'm not clear on the purpose of location of a siphon as it is related to a locomotive boiler. Just what do they do, and where are they installed?

Greg

http://ocsteam.com/33/index.html

From the handy Trains.com Glossary Of Common Railroad Terms:

Thermic syphon
In a steam locomotive firebox, a funnel-shaped steel fabrication that connects the bottom of the throat sheet and the crown sheet. Water flows upward through the syphon, connecting the coolest and hottest parts of the locomotive boiler. Syphons improved water circulation in the boiler and insured more uniform temperatures in the boiler, increasing fuel efficiency.

http://www.trains.com/trn/glossary/default.aspx?list=4&fl=t

Thermic syphons are really just tubes running from the front bottom to the rear top of the firebox. The tube opens to the boiler at either end, allowing water to flow through. The tube is surrounded by the hot gases in the firebox; heat from the gases diffuses through the tube and rapidly heats the water inside. The heated water expands and rises, travelling up the tube and out above the crownsheet. More water from the bottom of the boiler is sucked into the other end of the tube, located down at the front bottom of the firebox. The result is a continuous flow of water from the bottom to the top of the boiler.

As for their purpose, think of a locomotive boiler with water in it. The hottest water will be found above the crownsheet (or top) of the firebox, and above the tubes--basically above all the heat-exchanging surfaces. The coolest water will tend to sink toward the lowest point in the boiler, which is the "mud ring" around the bottom edge of the firebox, and pool there.

With thermic syphons installed, water from the coolest part of the boiler is sucked in, heated, and expelled at the top. The net result is to heat the total water in the boiler to a more even temperture range, minimizing any thermal gradient from top to bottom. In addition to improving efficiency, it also reduces thermal stress on the boiler shell. A boiler shell exposed to a wide range of water tempertures from top to bottom will try expand unevenly--hot metal expands more than cold. An evenly heated boiler experiences less stress.

All this is book learnin' from me, though; corrections welcomed.

I hope Steve Z. will provide his great commentary about PM 1225's syphons, uttered in 1991, in WVA (and reported in the Aarne-Gram).

Steve? You're on.....

Howard P.

One of the most effective siphon designs was the patented Nicholson Thermic Siphon. One of our IRM members is John Nicholson, direct descendant of the inventor. That's neat.

Bob Kutella

That is neat. I've often wondered if there are any Vaulcains, Woodards, etc. among railfans.

I don't know if this counts but I'm married to a direct descendent of George Stephenson...one of her many good qualities!

Very interesting. LS&I 33 is equipped with the Nicholson Type Thermic Siphons. Were there other major manufacturers of them in the US?

Thermic syphons do well, especially in coal burners. Somewhere I had seen an addition once added to some locomotives...it cosisted of a trough that ran from the rear of the boiler(near the bottom of the syphon) to the front of the boiler. The idea was that it would pull water from as far away as the front flue sheet.
For oil burners, my money is on transverse arch tubes. It is amazing what a difference syphons make...

They also are used to support a Brick Arch. These increase the travel distance and increase stay time of the burning fuel in the firebox. This improves combustion efficiency. One of the problems with burning coal on grates is that, depending upon fuel volatility, often much more combustible gases and carbon fines are released from the fuel due to heating than can be consumed by the air available. Basically, it makes a lot of smoke that can't be burned. The brick arch also reflects heat ( refracts ) back at the fire. The combination of brick arch and overfire air jets, or simply air inlet ports, reduces smoke. Also, as we well know, unburned fuel causes sooting and long term efficiency reduction.

The mention of a brick arch brings up a question I have on the subject. On the oil burners I have seen with arch tubes or syphons few if any have had arch bricks. I assume this is because oil fires are hotter than coal but it would still seem to me the same properties exist that would make an oil burner more efficient with an arch. Can someone enlighten me on this subject?

Nicholson thermic syphons were installed on nearly all Western Maryland engines in part because they were said to provide some protection in the case of a low water situation by bringing a flow of water to the crownsheet. This was particularly important on a railroad with heavy grades.

Thanks for any information in advance.

John Bohon

Canadian oil burners have brick arches, eh? Burners are under the doors aimed at the throat below the arch. Don't know why we didn't go with this arrangement in the USA - probably maintenence costs.

dave

Here is one good reason against backfired oil burners.







M Austin


________________________________________________
"Are you sure you want me to crawl into this firebox?
14 of the last 16 locomotives I've inspected will never run again....."

M Austin to BCRail Executive

I've seen similar on hand fired coal burners before, much less oil. Is the worry the initial focussing of the intense heat on one limited area?

Wonder how long a set of arch tubes lasted?

dave

Matt,

You always have the most horrifying pictures of boilers. Could you please explain why a backfired boiler caused the condition pictured?

Phil

Air inlet in the standard CP back-fired configuration, has the main intake toward the front of the firebox under the brick arch. This forces the flames toward the sides and up over the top of the arch. This is a double whammy for the triangle of exposed side sheet. Not only does it see direct flames, but the area of side sheet forward of the brick arch is relatively cool for an inordinately high level. This causes greater thermal differentials than would be seen in a front fired version. (The 2860 had patches in the patches of this area.)
The above damage was on the 3716, which had just returned from a 5 day outing. It had suffered a bout of horrendous foaming about half way through the trip. Forcing the fire while the engine puked its guts film boiled the high heat transfer triangles. During film boiling, the water does not contact the sheet, consequently the sheet temperature goes past 1000F in a hurry with resultant deformation.
The back fired burner is more the result of Canadian regulation rather than heat transfer considerations. Converting a boiler from coal to oil, typically resulted in removal of the arch tubes. In the US, this was an alteration which required an Alteration Form 19 be submitted to the FRA. Under Canadian rules, a new boiler design is submitted to the government with a blank check, for review by a bunch Canadian Federal staff engineers. If ANY alteration is performed on a boiler, the ENTIRE boiler design is re-reviewed with the same intensity and COST as if it was a new design. Consequently, even minor boiler alterations were rare if accomplished at all.