cold air in hot fireboxes

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cold air in hot fireboxes

Post  32A on Tue 01 May 2012, 6:47 am

Hi all
new to the site and admiring all the excellent work going on out there,hopefully will be able to do justice to a 6" foden.
Having been involved with steam over the last 40 years ,full size rail and road plus galloper centre engine,and miniature 15" gauge downwards,i have never been a fan af dropping the fire at the end of the day unless putting a lid on the chimey to stop the draught through the firebox and cooling the tubes and boiler plates too quickly with the possibility of leaking tubes or stays.Have had to expand tubes several times after inexperienced handling.Whilst i understand why people are dropping the fire to be able to blow down a new boiler to get rid of the crud,i had to wash out the boiler on a full size engine after major boiler work some years ago now,would it not be better to put a lid on the chimney and let the boiler cool down gently?
What does everyone else think

andy p

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Re: cold air in hot fireboxes

Post  Graeme81 on Tue 01 May 2012, 7:46 am

i would agree...fire should never be dropped unless absolutely necessary...ie no way of getting water in to the boiler. it will cause tubes to warp over time and they may well start to weep. i have seen this in the past where a fire door was left open continuosly on a full size engine and the cold air blew against the tube plate - wasnt long til the tube expander was out! Neutral

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Re: cold air in hot fireboxes

Post  bjwlancashire on Tue 01 May 2012, 3:13 pm

I have to agree, always better to let the fire thin down, close the damper and push remaining fire against the tubeplate - put the lid on if you have one. Full size engines do it this way and miniatures with steel boilers and expanded tubes shoud be treated no differently.

Also, there is no need to blow down with any significant pressure on the gauge. If the water is still hot then it will still be holding the particles of crud so no need for drama, just draining while still boiling hot or with 5-10 psi should allow the crud to flow out nicely.


Brian

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Re: cold air in hot fireboxes

Post  highpressure on Wed 02 May 2012, 7:55 am

Also, there is no need to blow down with any significant pressure on the gauge. If the water is still hot then it will still be holding the particles of crud so no need for drama, just draining while still boiling hot or with 5-10 psi should allow the crud to flow out nicely.


Brian

You would have enjoyed a miniature a few years ago at Exbury then, if I remember rightly it was a 6" but if not then at least a 4", with well over 100 on the clock possibly approaching 150 he simply wound the blow down wide open and let the whole boiler go in about 3 minutes affraid affraid A lot of whoosing and steam everywhere, and I thought at the time that the release of pressure, contraction of the boiler and rapid cooling of the internals can't be good. Mad


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