Parallel versus tapered boilers

[Bill Bedford]

Another factor to take into account with Tornado is that this is effectively a new design of boiler, being all welded, although it is built to the dimensions of the original type. It may be that expansion and contraction characteristics have turned out to be somewhat different in reality to that expected in theory hence the stay problem.

More likely it is differences in the thermal duty cycles. Working railway boiler rarely were allowed to become cold.

[richard]

The A1 Group have said as much. Despite its busy schedule, Tornado is doing much less work than a regular A1 would have done , but is experiencing many more thermal cycles.


Richard

[PGBerrie]

Working railway boiler rarely were allowed to become cold.

I was at the Verkehrshaus Lucerne yesterday and the guy showing the last 2-10-0 (Elephant) built for Swiss Railways said that after they had dropped the ashes, they built a small fire at the back of the firebox, so that it could be in steam again in the morning within 1 hour. If there was no fire it took 8 hours.

Peter

[60041]

More likely it is differences in the thermal duty cycles. Working railway boiler rarely were allowed to become cold.

I have often wondered if it would be worth fitting some sort of heater to keep the boiler warm between steamings, either an electric immersion in the boiler or an external heater such as a gas burner that could be put into the firebox after the fire was dropped.
It would cost quite a bit to run, but then again having to replace stays is not cheap either.

[Nova]

I seem to remember reading that Gresley claimed that the boilers on the A1/3/4 and V2/4's were actually coned not tapered. The original reasoning behind the coned boilers was to be able to fit the maximum diameter boiler possible within the LNER loading gauge.

Look at any GWR/LMS engine with a tapered boiler and you will see that the bottom of the boiler runs parallel with the running plate, Gresley's loco's boilers didn't.

Probably the best visual reference to Gresley's boilers would be the P1 class as the boiler was mounted high above the frames. Side on you can clearly see that the bottom of the boiler does not run parallel with the frames.

as a bit of side-by-side comparison to back up this point, here's a 28XX and a P1




wouldn't a coned boiler actually have an advantage over the tapered design due to it having a downward slant towards the firebox?

[Hatfield Shed]

Symmetrically coned is slightly simpler geometrically than an assymmetrically coned barrel, so there might be a small saving in constructional cost.

What advantage are you proposing for a gradient toward the firebox? Nothing obvious occurs to me, and the thermally driven circulation within the boiler is so vigorous as to outweigh other minor potential effects from the barrel shape.

[manna]

G'day Gents

The only advantage that I can think of is that there is a slightly larger 'face' area between the boiler and the firebox, (bigger heating surface).

manna

[Hatfield Shed]

But in respect of symmetrically or assymmetrically coned there's no necessary difference in that dimension. (The whole business of tapering for thermal efficiency gains is hooey until well over 2,000 boiler hp output is required for a UK dimension loco boiler. There's ample test data to demonstrate this, Doncaster was quite right to stay parallel for everything but wide firebox types.)

[billbedford]

Look at any GWR/LMS engine with a tapered boiler and you will see that the bottom of the boiler runs parallel with the running plate, Gresley's loco's boilers didn't.

Well, yes. The Gresley boilers were coned so that the smokebox could clear the middle cylinder.

[1H was 2E]

Please bear in mind when considering the boiler shape of taper boilers that this may not be reflected in the cladding. For instance, in the case of the Stanier moguls, the boilers were constructed with the front ring parallel and the rear one coned at a comparatively sharp inclination. The first 20 engines had cladding which followed this outline, but the later ones had cladding modified to give a gentler taper over the whole length of the boiler.

[4812]

The taper on Bulleid Pacific boilers was on the underside. No doubt there were good reasons.

[andro]

Perhaps the coned boiler with a horizontal axis would encourage sludge to accumulate at the firebox end, making boiler washouts a bit easier? That's only a guess!

[billbedford]

The taper on Bulleid Pacific boilers was on the underside. No doubt there were good reasons.

The Bulleid pacifics had a very high middle cylinder, and maybe they needed the casing to hide their ridiculously small smokebox.