Issue with fire tubes blocking up 3.5″ Rob Roy

[Thomas Henderson 1Participant @thomashenderson1]

Hi,

I am hoping that someone will have had some previous experience with this and come up with a successful solution.

End of last year I bought a 2nd hand Rob Roy, bit more clapped out than I would have liked but it has forced me into learning and making parts along the way. The latest issue I'm finding is however through a deviation from the drawings, rather than wear and tear.

Whoever built the boiler has used 5/16" fire tubes with 7/8" superheater flues where the drawings call for 3/8" and 3/4" tubes respectively. Although a greater number of fire tubes have been employed, 9 instead of the designed 7, the small bores of these tubes means that I struggle to complete more than four laps of the track at Swansea before they block up with bits of coal and clinker and despite my best efforts, the fire goes out.

Granted, timing of my firing and riddling of the fire may be contributing factors but whether I've run it on grains, beans, brick arches in several stages of modification etc. etc. I still end up with the same result.

I've been considering fitting a coarse stainless steel mesh panel in the firebox with holes just smaller than the fire tube bores to catch this stuff and burn it off, will it work?

Or has anybody got any better suggestions other than replacing the boiler?!

Many thanks,

Tom.

[Thomas Henderson 1Participant @thomashenderson1]

[Werner SchleidtParticipant @wernerschleidt45161]

Hi Tom,

i have a Maxitrak Ruby boiler and chassis and build up my own housing for to have a german narrow gauge design.

Many years ago as i start my first driving i use the original grate and my fire was dead after four rounds on the track. I narrowed then the blast pipe and could drive a lot longer. But I found many clinker in the smoke box and the lower tubes were blocked after short driving. I was able to drive about four to six kilometers a day. Then the fire dies and i had many clinker in the smoke box. Often the smoke box was half full and the grate had 2 cm of clinker on it. So the air can not come to the fire. I had then the idea to make a new grate with small steel bars and as separator M6 Nuts that means 4.8 mm distance from bar to bar. The orignal was 2.5 mm the bar and 2.5 mm the slot to the next one. Now the fire worked super and i had to widen the nozzle from 4.9 mm to 5.1 mm. In addition i added a petticoat inside the smoke box and lower the mounting of the blast nozzle. The idea was to have draught over all tubes , not only the upper ones. This was developed in several steps and tries. The longest run i had with this loco was 23 km a day and the clinker in the smoke box are like sand now and it was only an amount of 2-3 cm height in the smoke box. This in the range of the lower tubes. Befor I had clinker half full of the smoke box and as big as peanuts. Shure with a 3.5 inch it is more difficult , but with my 5 inch Plettenberg loco, this is a narrow gauge tramway loco, i have a 5 inch chassis with cylinder and boiler from a 3.5 inch Gezina loco i made similar experience. I drove her for about 10 km a day with a similar result.

Conclusion widen up the air slots in the grate and and open up carefully in small steps the nozzle diameter, add a petticoat and lower the nozzle that the draught is for all smoke tubes. With this you get a better fire performance. My coal i burn was Ibbenbüren german anthracide coal this coal burns good but you need ever draught otherwise the fire dies.

I hope you can sort out something for you. Good luck

Werner

[Clive Brown 1Participant @clivebrown1]

Hi Tom,

if you haven't already done so, can I suggest that you give Welsh steam coal a try. Not too widely available these days but it can still be obtained.It's listed on Ebay, although I haven't bought any from there. In the past when I have run my Simplex on it I found the ash and clinker residue considerably less than with other domestic coals so it might improve your loco's steaming.

[SillyOldDufferModerator @sillyoldduffer]

I agree with Clive. Good Welsh Steam Coal was perhaps the best coal ever mined anywhere. It's a hard coal with few impurities and plenty of heat in it, considerably cleaner than ordinary domestic coal. (Anyone else remember Nutty Slack, dreadful stuff.)

Unfortunately most Welsh Steam Coal was mined and burned years ago and god isn't making any more. I suspect what's sold today is a hard coal mined in Wales, but not the Premier Cru. Might be worth trying other Anthracite coals, but coal is a natural product and results may vary.

Back when Grouping was new, the God's Wonderful Railway sent engines out to show ignorant northerners that Swindon methods were best. Sadly, engines that performed brilliantly between Wales and London, struggled oop North. After blaming the drivers, the reason was found to be the coal: GWR got theirs from South Wales, ideal for engines, and hadn't tested how well their locos ran on cooler dirtier coal from Durham and Yorkshire.

Model Engineers having bother getting coal isn't new: I have an ME mag circa 1946 in which LBSC complains bitterly about the cost of the inferior coal he has to buy… He was right, all the best coal was exported to buy food.

Dave

[norm nortonParticipant @normnorton75434]

Thomas

If the fire creates many fine pieces of unburnt material, and there is a strong draught carrying these products into the tubes, then those tubes risk being blocked.

Number one: do not poke or 'riddle' the fire bed as this will raise bits and pieces. Contentious subject as some drivers love to poke about while other wise heads will NEVER use a poker in three hours of steaming.

Number two: ensure there is only just enough blast from the exhaust to keep the steam production sufficient for running. If you see any sparks from the chimney the blast is too severe.

I don't disagree that Welsh Steam Coal is a lovely material but you should be able to steam well on anthracite grains (grains are smallest, then beans, then nuts)

Norm

Edited By norm norton on 13/06/2022 21:16:09

[Rex HanmanParticipant @rexhanman57403]

Hi Thomas,

I am not surprised that you are experiencing blocked tubes in your boiler. My Rob Roy, built to the published design, has always suffered from the lower four tubes blocking after a while. It's easy to tell when it happens, the production of steam suddenly decreases.

Last year at the Andover M E S we held trials of Ecoal 50. This is a fuel made from coal and ground up olive stones. It comes in briquettes that have to be broken up into pieces to suit the size of the loco. This is quite easily done with little wastage.

I found it burnt well and the engine liked it. More importantly, everyone who tried it, from 3 1/2" to 7 1/4", all commented on how fine the ash was and how clear the smokebox was at the end of the run.

I had no problem with blocked tubes at all using this fuel.

There is, of course, a down side. Many of us found the fumes a little acrid, streaming eyes and runny noses were the result, even though it is claimed to be "smokeless"

Ecoal 50 is readily available, Wickes sell it in 10kg bags, a quantity that would last for a long time in a Rob Roy. For the sake of £7 I would recommend that you give it a try. If you do, please let us know the result.

Good luck!

[Jon LawesParticipant @jonlawes51698]

My William (almost the same design) repeatedly blocks the lower three tubes. I've taken to carrying an old flue brush with no bristles to knock the grit out. Infuriating. I've slightly opened out the blast pipe to try to reduce it happening, I've not tried it enough to gain meaningful results yet.

I've thought about including a baffle in the front of my ashpan which curves up to slightly shield the lower tubes but haven't done anything about it yet.

If I do poke the fire i try to do it stationary with no blower to prevent anything getting sucked up.

Edited By Jon Lawes on 14/06/2022 10:48:18

[Steve AddyParticipant @steveaddy35670]

I did make a "brick arch" for a friend's Polly boiler. It was only mild steel welded to two legs at the front of the grate and not touching any of the boiler shell. It lasted remarkably well and made a big difference to the issue of blocked bottom row.

[duncan webster 1Participant @duncanwebster1]

Stainless will last better than mild steel.

Alternative, convert to gas. see doubletop unfortunately none of the links in that seem to work, but I have doubletop's email and could put you in contact if you're interested

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