UNDER ARREST! - By Graham Walker
This item explains the peculiar structure sprouting from Katies chimney in the photographs above! Having experienced two rather nasty burns on small children, I decided it was time to do something about it! My first quick-fix spark arrestor was just a simple square umbrella type affair, suspended about 5 above the chimney (above). This seemed to work quite well, but all the hot ashes and cinders were directed downwards onto the smokebox and the motion making a terrible mess. I therefore developed a Mark II. This was similar to Mark I but a little longer and incorporated a catchment tray thus overcoming the dirty motion problem and I think it was probably about 90% effective. The only time it was suspect was when working hard at high speed climbing the long bank away from the tunnel. So I embarked on a Mark III design made from 16 s.w.g. stainless steel. This was simply Mark II with a back-skirt fitted. This had the desired effect and I think it worked at around 99% efficiency. The only real problem was that the contraption was anything but railway-like in appearance. Certain of our members at Wortley Top Forge MES had been heard referring to it as a kipper smoker or a fish fryer....... and probably worse when I was out of earshot! During the winter, I tried to come up with a spark arrestor design that was more befitting a railway locomotive when lo and behold, a two-page spread appeared in The Model Engineer (Vol. 186 Feb 2001 page 122) by a Mr Alan Bibby.
The design is a stainless steel gauze about 16 mesh. This is formed into a cylinder and fits on to collar just under the blast nozzle and finished at the petticoat throat (see below). So I am now back to a Mark I smokebox type spark arrestor and it is now awaiting trials. It will be interesting to see how it performs!