stainless steel brick arches

[Peter DicksonParticipant @peterdickson]

I am trialing a stainless brick arch in my 5" loco at present and am interrested in feedback , efficienct vrs effect on drafting ..

[Peter DicksonParticipant @peterdickson]

effect on performance

[MICHAEL WILLIAMSParticipant @michaelwilliams41215]

Hi Peter ,

The brick arch in a full size engine has four main purposes :

(1) To increase the length of path taken by the combustion products in the firebox and thus ensure that combustion is more complete before products enter fire tubes .

(2) To protect firetube ends from the worst effects of burning and erosion from the combustion products and to further protect tube ends from burning by direct radiant heat from fire .

(3) To prevent any large lumps of coal from being drawn directly into the fire tubes .

(4) To even out the flow of combustion products so that at least approximately the same amount goes down each tube row and in particular to prevent all the combustion products from taking a short cut through lower tube rows .

There is a further minor benefit of reducing spark emission from the chimney .

An arch fitted to a model would probably give some degree of the same benefits as in full size but I doubt whether it would make much difference to actual efficiency .

One final note – a stainless arch needs to fitted so that as far as possible it is not touching any copper firebox plates and also fitted so that any inevitable distortion does not cause arch to jam or dig in to plates .

Regards ,

Michael Williams .

Edited By MICHAEL WILLIAMS on 29/05/2013 23:53:15

[Peter DicksonParticipant @peterdickson]

Thanks very much Michael,

I have located the arch on a set of pillars mounted on my drop down pivoted grate so it is well away from copper work..

I noticed during a recent steam test the heat deflected well back toward the backhead and have full radiant superheaters ..my concern at present is the additional drag! on the effective air through the fire.

I have opened out the blast nozzle to .400 as I have 1.5" Cylinders, 5/8 exhaust pasages and streamlined joints .

I thinks it an experementation process .

thanks again for your input..

Regards Peter

[John BaguleyParticipant @johnbaguley78655]

Hi Peter,

What was the original diameter of the blast nozzle and did the loco steam well with that?

You may well find 0.4" dia. to be far too big for 1.5" dia. cylinders resulting in too soft a blast and poor steaming. Harold Barton wrote a couple of interesting articles in ME in July/August 1989 in which he describes his experiments with loco draughting. One of his conclusions was that the maximum diameter of the blast nozzle should be 16% of the cylinder diameter, which in your case would be 0.24". Your 0.4" equates to 27%.

I've used Harold's ideas on several locos and turned what were poor steamers into good ones, so his articles are well worth a read.

John

[Peter DicksonParticipant @peterdickson]

John,

many thanks , I was very keen to reduce back pressure to a minimium however your illistartion is very clear as regards the .40, the original design diameter was .281 and this seemed to pull the fire toi bits!!

I tried the brick arch to improve efficiency and attempt to keep the fire in place , however somewhere in the changes I have lost all steaming capability .

I have used Greenlys 1-3 and 1-6 to gauge the blast and petticote pipe..

I think it time to re size the nozzle . I have designed a removable blast and blower head to have different nozzles . seems like a good job i did.

thanks agin for your input

best regards

[julian atkinsParticipant @julianatkins58923]

hi peter,

the late laurie joyce's GWR KING had a stainless brick arch and won IMLEC in the early 1970's.

so long as your free gas flow through the boiler is generous .400" blast pipe nozzle should be fine. see don young's E S COX, DONCASTER, and BLACK 5 and his write up of his design parameters in his magazines LLAS (last 5 issues).

cheers,

julian

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