Speaking of dry pipe failures, I remember a fall SR Steam trip from Washington to Front Royal with 2-8-0 #722 in 1977. I was helping to coal the engine for the next day's Warrenton trip when 722 suddenly leaped forward on her own. Whoever was in the cab at the time (I think it was Dwight Browning) had the presence of mind to center the reverse and open the cylinder cocks. (the independent brake was allready set) After she stopped, we very quickly dumped the fire. The Boss (W. J. Purdie to all you "unwashed" who think that title refers to some singer named Springsteen...........:), ) then decided that we should go to dinner while she cooled off enough to open up the boiler. While we were eating the yard crew shoved her inside the Alexandria enginehouse. After dinner I spent a rather hot and sweaty evening helping Paul Brock pull the dome cover. The dry pipe was OK, but the throttle casting had cracked. Needless to say, that was 722's last trip for that year.

Gary -

Maybe a stupid question, but is that something that would have been inspected on a fairly regular basis during steam days? And could it have been foreseen?

Les

I think we have forgotten the extent to which mainline engines self destructed doing their jobs of hauling more freight than they were designed to with just enough running attention to keep them going in the 30s and 40s.

A railroad was fortunate to get a decade out of a firebox, much less a set of tubes - so internal boiler work was certain to have been more frequent back then by necessity. Platoons of skilled craftsmen did daily what we now consider to be unusually heroic efforts.

After steam died in the US and was relegated to tourist and museum operation, it was the unusual locomotive that EVER got a thorough inspection - until very recently, when regulations forced us to do what was long overdue in terms of determining how much locomotive was left in our locomotives.

I don't think runnung tests on the drypipe would have even occurred to the average museum or tourist railroad steam guy in the 1970s or 80s.

dave

I've always feared a dry pipe failure. That's when I always keep the johnson bar centered when not running! One time I thought there was a throttle leak when I went to center the johnson bar and it flung all the way forward with the throttle closed, but it turned out the johnson bar spring broke.

The front end throttle also keeps steam in the superheater elements when the engine is idle, and allows superheated steam to be provided to steam-using appliances like the air compressors and blower for improved efficiency.

I have been told - but no personal frame of reference - that keeping the superheater elements "wet" also helped prevent them from being burned out as quickly.

dave

Les, I'm sure that the dry pipe was inspected when 722 had boiler work. The Birmingham steam shop was always pretty thorough. But 722's failure was with the throttle casting itself, something that probably wouldn't have been detected without ultrasound.

Thanks all the for answers and the stories.

Am I correct to assume the idea of the dome is to make sure you pick up as "dry" as steam as possible? Would a locomotive like the Lafayette also have a dome throttle, it's just that the location is directly above the firebox?

In the case of the front end throttle, the source of the steam is still the dome, but throttle is physically located forward, up by the superheaters/closer to the cylinders?

Thanks again.

Bob

Gary -

Thanks. I was not questioning SRR's Birmingham Shop; I am sure they did a thorough job of inspection. No, my question was about steam shops in general during the Age of Steam and whether the throttle casting would have been checked for cracks during normal inspections.

Les

A dome throttle almost has to come out during an annual inspection, because even the skinniest guy can't wriggle around it into the boiler. It would probably be normal practice to lap the seats while it's out, so a crack is not likely to go undetected.



Dry steam - yes.

The basic difference between dome and front end throttles is the steam path:

Dome - throttle/dry pipe/superheater header/superheaters/delivery to cylinders.

Front end - dry pipe/superheater header/superheaters/throttle/delivery to cylinders.

Some locos with front-end throttles eliminated the dome in favor of a perforated dry pipe. Several of the CPR designs come to mind. And if you compare the NKP and PM Berks to the supposedly "AMC identical" C&O locos, you'll find that the dome on the flatland engines is farther forward.

JAC

[quote="Dave"]I have been told - but no personal frame of reference - that keeping the superheater elements "wet" also helped prevent them from being burned out as quickly.

dave[/quote]

Yes this helps to keep the units from burning but also having some flow through the units while sitting helps. If the blower or some other applaince is on SH steam then you have flow.

I seem to recall that 4501 suffered a collapsed dry pipe during her SR career-- yes?

The 1945 NYC Niagara locomotives had a slotted dry pipe (just like the CPR 1200s--not perforated), due to an enormous boiler and tight eastern clearances.

Documented in excruciating detail in the TRAINS article "Master Mechanic - Steam" (some time in 1976). The incident happened on a northbound move coming into Attalla, AL. '01 was towed back to Irondale, and a new dry pipe was installed piece by piece, through the dome, so as not to have to remove the front end, superheaters, and header.

JAC

Adam is right, the steam in the superheater units helps keep them from being burnt by flue gasses. This was the idea behind the superheater damper applied to the earliest superheated engines, it cut of draft through the superheater flues when the throttle was closed (for road locomotives) or the blower was on (switchers). However, I think the superheater damper was short lived, because its rare to see them applied after, say, the late '20s. Why was this? My guess is that it was found that the flue gasses didn't get hot enough to damage the superheater units when the locomotive was stationary. Anyone know for sure?
-Chris

Maintaining those frigging dampers along with all the other front end accutrements was purportedly a nightmare which never ended, or more job security than the machinists wanted, whichever you prefer. Or so I have been told.....they did seem unpopular and not too many even seem to have survived.

I read something recently about superheating - and how it didn't actually make any significant difference for locomotives which were not customarily worked at high output for extended periods. Makes me wonder if it is worth the extra cost for museum or short, light tourist railroad operations.

dave