Boilers & Accidents

Re: posts #137 and #139 (@torgormaig and @Jamessquared ): Given the thread title is specific to Bulleid pacifics, a question please: Does the presence of thermic syphons (vs. conventional construction) make any significant difference to keeping a firebox crown covered under such circumstances?

 

It would have been interesting to have been on the footplate of 34095 on the 02.45 out of Waterloo, the Bournemouth Mail, on July 8th 1967. When I got back to Waterloo on the 08.25 from Weymouth there was a rumour that driver Gordon Porter was going to try for a last ‘ton’ on his final steam turn, so back to Bournemouth I went. I knew the loco was a good one as the Mail was the back working of the engine off the train I’d travelled up on.
He didn’t make it but had a good try down Christchurch Bank, pulling up about 400 yards the wrong side of the station with one emergency brake application from the mid 90s. It was a different age then and he reversed back into the station and as always happens with these incidents, even at silly o’clock in the morning, railwaymen seemed to appear from nowhere. Some years later Bert Hooker told me he managed to get away with it without getting a form 1.

 

That was always given as one of the main benefits of thermic syphons on Bulleid Pacifics.

The point about a Bulleid on a heritage line - certainly our line - is that you have an ample reserve of power relative to train weight, which makes the fireman's job easier. I always think that you are juggling depth of fire, water level and pressure, all of which depend on each other. On a big loco, you have a lot more flexibility of how you arrange those things. So for example, a Bulleid blows off at 250psi, but you are hardly going to lose time if you are down to 200psi. So if you have to keep it quiet at a station, arrive at 200psi and you have loads of headroom while the fire cools down. Whereas on say a small Chatham engine, they blow off at 160psi but you start to struggle below 140psi: you have far less headroom to play with.

Reference has been made to Imberhorne. For those that don't know the geography, the final approach to the summit is at 1 in 55, which follows about 9 miles of on and off climbing mostly at 1 in 75. There immediately follows a knife edge descent at 1 in 60, which only lasts about 1/4 mile (say 45 - 60 seconds) but by the bottom of which, you have to be slowed down close to 10mph; you then roll into the station, after which you have to keep the loco quiet for perhaps 20 minutes with only a run round to use any steam.

So the trick is to aim to arrive at the station with boiler pressure well down and maybe half a glass of water, and the fire fairly well burnt through. But three minutes before, you have been going up hill at 1 in 55 so need a decent fire and head of steam; and the water needs to be high enough that when you start heading downhill at 1 in 60 and braking, you don't lose it all out of sight down the front. It's a difficult balancing act, that takes skill from both sides of the footplate, not least in how the driver controls the speed over the top. If you have ever wondered why some drivers seem to roll off a bit before the summit, it is to avoid needing to brake down the other side.

In those circumstances, a big loco is rather easier to handle, because you can let the pressure go right down and still make it. I'd reckon on wanting at least 130psi at the summit on a Chatham engine, 30psi below the red line, and the fire dancing on the grate, water level out of sight at the top of the glass. On the S15 you can allow it down to about 160psi (the brakes might come on at 140) and the water in sight near the top of the glass (which means 1/2 glass at rest on the level). You can do it at 160psi on Camelot as well, but the red line is 225psi so you have loads of headroom to subsequently control the pressure. The U boat was rather more tricky, as it had less power, so you probably wanted about 170psi at the summit but only had 200 to play with at the station; it also had a habit that if it did blow off, it would do so for a long time before the valves reseated.

80151 is a doddle because it faces the other way round, so the water levels all work in your favour at the summit.

The Chatham engines on a big load are far and away the most satisfying when you get the firing right, but you do need a sixth sense about water levels - if you can see it at the top of the glass, it’s already too low.

Tom

 

This is reputed to be the case due to the syphoning of the circulating water around the firebox but in a low water situation I would think that the effect is minimal.

Tom is right about the resiliance of crown sheets to transient low water. My worry as a firemanis about dropping a plug which is a cardinal sin in itself. If that happens you still have a long time to take remedial action before the crown collapses. But you cannot take such action if you are unaware that the plugs have gone and on a loco that is working hard this is quite possible if everything else seems to be in order. The classic case involved a Duchess near Carstairs just after the war. Heading south they stopped there and requested a fitter from the nearby shed to come and examine a blow in the firebox. With a big fire on the fitter could find nothing wrong and so the train went on its way. Five miles down the line the crownsheet collapsed. Why? One of the guage glasses was clearly giving a false reading and so was isolated. Unfortunately they shut off the one that was reading correctly and relied on the one that reassuringly showed a healthy if incorrect level of water. Clearly the plugs had already gone by the time they arrived at Carstairs but as there was no suspicion of this it was missed completely, even when stationary. I guess that there was a 10 -15 minute period between the plugs going and the crown collapsing.

Peter

 

Like you say not something to experiment with but things would have to go drastically wrong for a period of time to collapse a crown. Water disappearing out of sight is never a nice feeling and if it's due to a brake activation such as an AWS fail to cancel, as a fireman you're just a passenger at that point, automatic reaction is to apply both feeds and that's all you can do but wait for it to come back! Time definitely goes slower in that moment, especially on a bigger engine with a long parallel boiler. I've never seen a plug drop but I have seen some fusible plugs in a pretty ropey condition and also patches of roof stays that have been upset by the 'tide going out'.

A lot of boiler explosions and crown collapses I've read about theres often been some confusion with water levels or a fault with the gauge frames which give a false reading. S160's spring to mind here. Imagine working an engine hard and being oblivious that the water was a lot lower than you thought and then...

 

Which is why if your gauge frames are showing different readings, you go with the lower one!

I've always remembered something I was taught years back which is 'the gauge glass doesn't show you the water level in the boiler, it just gives you an indication of where it is'

 

The Duchess involved at Lamington in 1948 was 46224 Princess Alexandra which claimed the life of the driver. The same locomotive had been involved in another similar incident in 1940, in the same area as it happens, when the fireman was scalded to death. Needless to say, 46224 had somewhat of a reputation amongst crews after those incidents - an 'unlucky engine' was a term I heard quite regularly when former BR men were discussing the class. Such incidents led onto certain restrictions involving 'passed' crews manning such locomotives. The top of the firebox on a Duchess is much higher within the boiler than a Princess Royal, this is reflected in the position of the gauge glasses on the boiler back-plate; the ones on a Duchess hold a much higher position - less water space. Consequently, waiting on the tide to return on a Duchess gained that bit more attention than a Princess Royal.



Princess Royal boiler.



Princess Coronation.

 

Sorry for perpetuating the thread drift, but there is a good point to be remained of here.
Water surging forward during braking and then coming back over an overheated steel firebox on a big 01 class pacific, was the final piece in the 1977 drama of Bitterfeld, East Germany.
But the whole tragedy had started a full 10 hours before, when the young inexperienced driver had blown the fusible plug due to low water of a slightly smaller cl. 03 pacific.
He then forgot to take enough water in Berlin before the return journey, they ran out of water but took the chance of reaching Bitterfeld, which they did, but booth guys on the footplate and 7 passenger died.
On the cl. 01 fusible plug did not blow, although the loco was fresh out of the workshop.
http://www.gerdboehmer-berlinereisenbahnarchiv.de/Statistiken/19771127-000002.html

 

Cant remember where i read it, but a taper boiler adjusts the volume of water around the tubes to reflect the temperature of the tube as a heating element... ie hotter at the firebox end, cooler at the smoke box end.?
The Bulleid boiler shape should be a natural circulator, the colder fill naturally rolling down towards the firebox end, and perhaps the thermic syphons a precaution against higher than normal temperature gradients around the throatplate, as well as for its crown covering feature. Does anyone know if Thermic syphons were ever tried in a copper firebox ? or does welded steel make them a much easier prospect

 

It was found post-war in Italy that the S160 2-8-0s had a design fault with the firebox staying. See P. M. Kalla-Bishop's book 'Locomotives At War' for more information.

 

There is also information on the S160's firebox problems in 'Over Here The Story of the S160'. ISTR that the original firebox plates were only 3/8" thick and that the FS replaced the fireboxes with 7/16" plate as a result of incidents where the crown stays pulled through an overheated crown plate . When the guys in Alaska restored the boiler of their S160 they followed suit and also changed the staying arrangement http://557.alaskarails.org/
Ray.

 

I thought the idea of fusible plugs was to blast enough steam into the firebox to cool the fire down if not put it out completely. If that didn't happen with that Duchess, it seems to me that the plugs were too small.

 

I used to think that was so. However I have learned subsequently that it is only supposed to alert the crew to a problem, not correct the problem.

 

That is a false assumption thought by many. Consider that if a plug is melted it means a lack of water so nothing to douse a fire. Even if there is water, it is at pressure and at a temperature much higher than 100deg c. Once in the firebox it is at zero pressure so will instantly flash off to steam. I’m afraid steam will not put out any fire or even dampen it down.
Another false assumption is that it will reduce the pressure. If you consider the size of a plug in relation to the size of the main steam pipe it is obvious it won’t happen.

 

Thanks (also to Wenlock) for the correction. I still find it surprising that a jet of steam into the firebox has minimal effect on the fire. Anyway if the intention is to alert the crew and the crew of the Duchess were indeed alerted but no-one realised where the "blow" was coming from, that still suggests that the hole where the plug had been was perhaps not big enough. Or would a more massive flow of steam into the firebox be like a blowback, with flames coming out of the firebox door?

Edit: BTW, as this thread has drifted so far, should most of the recent posts be moved to MIC?

 

And therein lies the difference between the two situations. The Clan Line crew knew that they were in serious trouble and acted accordingly. The Duchess crew had absolutely no idea that the plugs might have fused because they mistakenly believed that they had plenty of water in the boiler. A blow in the firebox can be due to any number of reasons and you try examining a firebox crown on a hot engine with a big fire on, especially if you have no reason to suspect the plugs may be the cause. It is not very easy.

Peter

 

It is plausible that a blown plug would extinguish the fire in earlier days, as on Sans Pareil at the Rainhill trials, but a big - and deep - firebox is a different matter. Looking into the firebox doesn't help; many people would expect to see a downwards jet of steam. Not so: firstly, steam (as opposed to vapour) is invisible, but in any case would be drawn towards the tubeplate anyway. The Big Lizzies had, I believe, three plugs, and while these would make a noise you wouldn't necessarily be able to distinguish it from a leaking tube, flue or possibly even a pipe in the smokebox. But the blows, even if they reached the fire, would have no effect on a big, deep fire which is still producing a vast amount of heat, as is the now very hot brick arch.

As a fireman I was told that in the event of a dropped plug, the things to do were start both injectors, close the dampers, shut down the blower, get rid of the fire by shovelling it out as quickly as possible (if this wasn't possible, shovel ballast into the firebox to absorb heat), and demolish and throw out the brick arch. I remember thinking at the time that some of these were not easy of accomplishment, but instruction as to how you would demolish a brick arch were not forthcoming.

 

With the internal deflector plate on a Bulleid can you even see the crownsheet? Clan Line is slightly different to most mainline locos as it has most of its work on the same route which doesn’t take it more than 30 miles from home. I believe at least three of the regular crew are MNLPS members so they are driving and firing their engine which must make some difference.

 

This was in reply to the two previous posts which in the time I was writing it have been moved to a different thread. Hopefully this will follow and be placed in the correct sequence, following posts #84 and #85 in the Boiler explosion thread.

Peter