Although 'external' chimney arresters can be fitted quite easily, they are likely to look disgusting on our pride and joy. However two things are to be remembered :

1. If you only occasionally run in public (and are willing to accept burned hair etc. in private), a single tea strainer will probably be accepted by the track officials, easily and readily cleaned, and will need to be, because not only will it trap rubbish from the fire, but also all the ejected oil from your cylinder lubricator.

2. On some traction engines the originals were often fitted with 'bee hive' arrestors, so it would not look out of place for a model to have one - but it would need to be the right 'size' to look right, although this might mean it is so small it creates back pressure in the smoke box.

'Internal' spark arresters are most easily fitted to a 'new' locomotive; and during construction, some consideration should be given to making it very straightforward to remove the spark arrester, as along with tube cleaning, it is one of those tasks which will need to be done after a steam-up.

Consider arranging for the whole chimney to be detachable from the smokebox. Depending on the design of the prototype, the flaring of the chimney base could conceal an extra large hole in the smoke box top, which could allow the petticoat pipe and arrester to be removed in one piece.

Screws, perhaps disguised as rivets, could hold the whole thing together. A design such as this would make cleaning easy and allow the largest area arrester to be used. Importantly though, such an arrangement would still need to be air-tight.

An alternate arrangement may be to make the top half of the smoke box removable to allow access to super heater joints etc. and this feature could be used to enable the arrestor to be removed. Remember however, that whereas access to super heater joints etc. is only rarely necessary; the arrester will need to be cleaned regularly. The bonus of this arrangement is much easier access for fitting regulator, superheater and blower fittings. The difficulty will be in regular re-sealing of the smoke box, and in keeping the smokebox paintwork in good order. Consider using chemically blacked screws instead of painted ones.

Design considerations

a] It should be remembered that any alteration inside the smoke box will affect the draughting. In many cases this is of little or no consequence as the overall efficiency is greater than required for good performance. However it should not be overlooked that a change of blast pipe orifice size or height which would compact the space available for an arrestor, may make it more restrictive to gas flow.

b] Every engine will have different blast characteristics - those with fierce blasts will tend to pull more sparks through the system - the shape of the chimney and it's height will also have an effect on how the exhaust is dissipated.

c] Cleaning will be essential - just look in your smoke box after a happy afternoon's running. The type of coal, and how hard you work your engine will also dictate how often you have to clean.

d] Determine what room is available in the smokebox. Is it possible to increase the space available by altering super heaters etc. How is access to the smoke box for tube cleaning, and also boiler testing (blanking etc.) Is it possible to improve the access ? All these areas should be explored because arresters will become a must and cleaning will be necessary.

If you are in the process of starting from new, at least the possibilities are more numerous and more easily engineered. There is no single solution and the ingenuity of every owner / maker will result in some very interesting designs.

But if you think all the above is too much, it's still easier than oil firing !

( Click to return to the Designs page. )