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Water in the Smokebox

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Alan maddern26/10/2018 19:12:17
4 forum posts

Hi I was wondering if anyone has any Ideas why I have a small amount of water in the smokebox of my 45 xx 5 Inch gauge after steaming? This is a new loco to me, Am I doing anything wrong? Any feed back would be much appreciated! Alan

Zan26/10/2018 19:57:01
161 forum posts
12 photos


Assuming it has passed the hydraulic boiler test, the source of the leak may be hard to find. Examine carefully and look for telltale white marks on the metalwork. Do not use anything hard to clean the smoke box or you may remove the marks. Check the superheater headers , blower, snifting  valve, exhaust blast steam feed to cylinders it could be any of these.

Another possibility is that as the engine is new to you, you could be overfilling the boiler and causing it to prime. Good hunting, but how much is ....a small amount of water?....

Sorry bad spelling from autocorrect 


Edited By Zan on 26/10/2018 19:58:51

Alan maddern26/10/2018 20:00:29
4 forum posts

Small amount is approx. a desert spoon full! Yep overfilling the boiler maybe next time I will only fill to a third of a glass instead of half a glass! Thank you for you Ideas Alan

Martin Shaw 126/10/2018 22:16:44
116 forum posts
37 photos


I suspect this is no more than exhaust condensing on the interior surfaces of the smokebox. I guess your boiler pressure is around 100 psi so it's not very hot to start with and the amount of heat drawn through the tubes is not enough to evaporate it away. I can only speak from experience of the full size item where water definitely indicates a leak, if you have eradicated that possibility then condensation is really the only cause. PS priming is of course a possibility.



Edited By Martin Shaw 1 on 26/10/2018 22:17:30

Alan maddern26/10/2018 22:52:37
4 forum posts

Hi Martin, Thank you for your advice! The loco is only around 8 months old it has passed the hydraulic and steam tests no problem, so it is possible its a priming or as you mention a condensation issue (Boiler pressure 80psi) I will check the pipe connections to the Blast pipe and Super heater before I steam her again!

Thank you again Alan

duncan webster27/10/2018 00:19:56
2542 forum posts
49 photos

The flue gasses in the smokebox cannot be colder than the water in the boiler, and at 80psi that is about 160C. Blind guess flue gas 200C. Yes the walls of the smokebox will be cooler, but cool enough to get condensation?

Zan27/10/2018 01:19:29
161 forum posts
12 photos

Any condensation would be small fry with the heat from the flue gasses which would soon evaporate that. Another thought.... could it be due to condensation in the pipes during cooling down of the engine? Easy to eliminate by checking the s box during a run.  Or try to chock the loco apply the brakes , crack the regulator and examine the s box but take care! Have somebody with a hand on the regulator!

Edited By Zan on 27/10/2018 01:22:47

not done it yet27/10/2018 07:19:40
4500 forum posts
16 photos

Stop guessing. Fill with liquid and test hydraulically. It might not show where it is leaking from, if there is one, but will soon determine if it is a leak, or not. If a leak - start worrying; if no leak - revert to guessing the origin.

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