Inclined smoke tubes

I have just converted an old copper boiler drawing for a 1.5" burrell from copper to steel and noticed that it has the smoke tubes inclined to be 1/4" higher at the smoke box end than at the firebox end. Im not aware of this on any other drawings I have - is it normal? Does it serve a beneficial purpose?

I've seen it on several but not usually as much as on that one. Though my drawing says 1/8 "of lift

How much grate area do you loose going for thicker steel plate?

Edited By JasonB on 29/12/2017 16:07:12

On my Bassett-Lowke 1 1/2" TE the uplift is on the original drawing. As the original boiler was a riveted and soft-soldered design with the hornplates integral to the boiler I re-designed it to be a silver-soldered copper boiler with separate steel hornplates but kept the 1/8" tube uplift. It is quite a small boiler (3" dia) and I would have thought steel would not give a very good performance.

Sorry...working on two projects at the same time...its actually a 3" Marshall. I have done away with the incline as it would make things very difficult.

The fire/smoke tubes on most boilers are inclined. It helps the natural draft of the fire. Hot air rises.

On a traction engine, it is much easier to light a fire in the boiler if the nose is slightly uphill. If down hill the fire will smoke and not burn properly.

Paul.

Had a look through a few other traction engine drawings that I have and they all have inclined tubes including the ones with steel boilers so common practice. Problem with omitting the slope is you risk making the boiler harder to fire which will already have been compromised slightly due to using thicker steel.

EDIT, just had a look through half a dozen full size traction engine boiler drawings and all have sloping tubes some by quite a large amount. and in the case of a Robey they are angled so much that the tube plates are angled to suit!

Edited By JasonB on 30/12/2017 07:50:26

But surely if it were such a great idea it wqould have been the same in locos? And stationary boilers?

Not a loco expert but the design is used on portable steam engines. As well as inclining the tubes in the boiler, the whole boiler is often higher at the smokebox end than at the firebox end. This also ensured that water covers the firebox crown when the water level is low.

Paul.

Edited By Paul Lousick on 30/12/2017 08:47:37

This is just what I've gleaned from various books, but boiler design has always been a compromise. Do you want a boiler that produces a lot of steam quickly, or a boiler that uses the minimum amount of heat needed to produce a given quantity of steam? Actually what's needed is a boiler that produces steam fast enough to drive the engine properly whilst maximising fuel economy. Not easy. There are several compromises that can be applied to balance the efficiency and performance of a boiler, one of them being the diameter of the tubes.

A small diameter tube transfers a higher percentage of the available heat into the water than a big tube. It's more efficient, hurrah. But it also restricts the amount of hot gas passing and reduces the rate of steam production. It's slow - boo. However, the performance of a narrow tube can be increased by increasing the draught. The natural draught can be improved by lifting the tubes above horizontal, ideally making them vertical. In a steam loco that's inconvenient and draught is usually wastefully provided with a blower and a blast pipe. A stationary engine get's it's draught from a tall chimney, which is more efficient.

The problem with putting a vertical boiler or a tall chimney on a locomotive is lack of headroom. Tunnels and bridges get in the way!

So the compromise is to tilt the tubes, the downside being a more complicated construction.

In my reading I've not noticed inclined tubes being used in railway boilers. I guess the complication isn't worth it because a railway engine is usually moving with plenty of steam available for the blast pipe plus a blower available when stopped. The ability to pull and accelerate within gauge limits is more important than fuel efficiency, particularly as fuel and water are readily available. In comparison a traction engine is relatively slow. Also, fuel is not being quite so easily obtained on an open road. The circumstances might make improved natural draft through tilted tubes worth the extra trouble on a Traction Engine. Perhaps an expert can comment?

Dave

I think one of the ideas of sloped tubes is also the keep water over the tubes at the fire box end when climbing hills.

Ian S C

On a traction engine the whole boiler is raised slightly at the smokebox end. This provides a natural draft as the hot gasses rise and provides more water over the firebox crown. (the crown is the hottest part of the firebox and the first to melt if overheated)..

Because the takeoff for the steam chest is at the smokebox end of the boiler, the incline also helps to reduce priming (water enterring the cylinders).

Paul.

Well the first two loco boiler drawings I looked at both had inclined tubes too.

Boxhill and Conway.

I have recently finished a Super Simplex boiler, and that also has inclined tubes

Colin

On a traction engine the whole boiler is raised slightly at the smokebox end. This provides a natural draft as the hot gasses rise and provides more water over the firebox crown. (the crown is the hottest part of the firebox and the first to melt if overheated)..

Because the takeoff for the steam chest is at the smokebox end of the boiler, the incline also helps to reduce priming (water enterring the cylinders).

A good while ago I heard a local traction engine owner talk about a tour of the Western Lake District that he'd undertaken .

At least one down-hill section was taken in reverse, IIRC, Hard Knott with sections of 1:3 gradient.

(Little to do with the original post of course!)

With many designs of model boiler if you don't incline the tubes the bottom row fouls on the smokebox tubeplate flange (don't ask me how I know!). I suspect this is the real reason for inclined tubes, after all when lighting a model boiler fire we use a fan to create the draft, and once we've reached the stage where the gas in the smokebox is hotter than the outside air the natural draft is governed by the height of the chimney above the fire, not by slope in the tubes

I don't see how it can help crown cover if the tubes slope up, down or wiggle around. That is all to do with size of firebox and boiler and the designer positioning them sensibly. It does make some sense to incline the whole boiler up and thus the tubes go with it, but by no means essential. The rise of a few inches (full size) has sod all effect on the draught compared to a 6 ft chimney on a TE. You only have to close the fire-hole door and the 3ft hot head the firebox provides is enough to show the smoke where to go and a canny driver would have parked up back end to prevailing wind too.

But

If a designer showed the draft boiler drawing with tubes sloping downward, despite actually being functional, he would be laughed out of the shop, tubes level might just get by. Some things just wouldn't look right and I suggest most steam machines were designed in the days when engineering was as much about what looks right as what physics says would work.

It will be interesting to see what happens with my boiler - when we soldered the tubes into the firebox they had a big 'upward' slope on them and when I fitted them to the smokebox tubeplate yesterday I had to bend them down something like 3/4"! So they have a very noticable bend in them back towards the firebox.

I assume the draft will still pull the hot gas through. But I'd rather the tubes had stayed straight. Too late to do anything about it now so I have to hope for the best.

Boilers for Sentinel waggons (Sentinel spelling!) and locos were very efficient, and their tubes were inclined, (can't remember whether water or fire tubes), but obviously intended to improve circulation and heat transfer.

The Sentinel boiler was a vertical, rather than the horizontal locomotive type used for locos and Road Engines.

Howard