Black Five Superheaters

[johnharkness]

Hello all, My 3-5"gauge Black Five superheaters are leaking, will it make much difference to the performance by removing these and making a connection direct to the cylinders?. John.

[baggo]

Hi John,

You would probably notice a much wetter exhaust due to the lower steam temperature and an increase in water consumption. You would be better to replace the superheater elements if possible, preferably with stainless steel for a longer life,

John

[Shawki Shlemon]

I am generally a supporter of s/heaters and have fitted them to most ( not all ) of my engines . It is one of those subjects that people can argue about it one way or the other . You have a high pick up point and therefore you collect reasonable dry steam , if you think it is easier for you ,Why not try to by-pass s/heater and check the performance , it will be done faster and you will learn for yourself the difference .If not happy you can always fit one later and then you will be committed to one system or the other . My engines without s/heaters like LION & GEMMA perform very well (see my website ) .Certainly s/heaters improve engine performance but to what degree ,that is a question I can't answer .

[waggy]

Hi John,

If you decide to make the engine "wet", I'd advise leaving the redundant superheaters in place. Removal may upset the draughting of the boiler. The gasses from the fire will will take the easiest route from the fire to the smokebox, passing through the larger flues rather than the smaller fire tubes. The superheater tubes act as a baffle in the large flues, balancing out the gas flow fairly equally.

Waggy.

[Shawki Shlemon]

Very good point Waggy , I didn't even think about it . You have a good suggestion .

[ausdan]

Another alternative to the supper heaters

I read somewhere, that you could also use a long strip of copper twisted in a spiral , placed in the larger superheat tube, as it will act as a baffle and slow the hot gas down, making good heat transfer..

I think it helped the guys steaming issues

[steam4ian]

G'day.
Ausdan reminds me that the old gas water heater we had over the kitchen sink had a twisted piece of steel in the flue. As Ausdan suggested that would be a good alternative to leaving the superheater elements in the flue/s.

Do those who know more than me think a steam separator in the smoke box would help against carry over?

Regards,
Ian

[johnharkness]

Thankyou all for the suggestions, I have removed the superheaters ( they were in a bad state very thin and leaking) and the exhaust is much wetter especially for the first five minutes running. there doesn't seem to be any fall off of in performance, what I have noticed which is a bit odd that it is the steam pressure is harder to control (blowing off more) and the top of the smokebox is a lot hotter, suggesting the hot gases are passing through the superheater flues. The suggestion about putting spirals in the superheater flues sounds promising, I will try that and let you all know the outcome.

John.

[waggy]

John,

Glad the beast works as a wet engine.

As a little aside from the main topic, I was wondering what effect blanking off the superheater flues would have?

Just a thought. All the heat would have to go through the fire tubes, these usually in the lower half of the boiler, heat rising and all that! Would the boiler have a better evaporation rate?

What are the thoughts of our wise counsel?

Waggy.

[baggo]

Hi John,

out of interest I've put the boiler and cylinder figures for Doris into Jim Ewins' loco efficiency formula. On the whole the loco comes out quite well except for the tube factor (ratio of length versus diameter). The figures suggest that the tubes are far too long for their diameter. Your experience of the continual blowing off suggests that by removing the superheaters you have effectively increased the cross sectional area of the tubes and actually improved the steaming of the boiler! The fact that the smokebox is also hotter suggests that there is less restriction to the hot gasses and the fire may well be burning better as well. Looking at it another way though, the superheaters would have been absorbing some of the heat from the gasses and cooled them before they reached the smokebox.

Waggy - I would expect that blocking the superheater flues off completely would drastically reduce the steaming of the boiler as it would appear that the fire tubes are too small in diameter. Playing around with the figures suggests that reducing the number of fire tubes and increasing their diameter to say 3/8" inside diameter would improve matters greatly

John

[steam4ian]

G'day John.

"reducing the number of fire tubes and increasing their diameter to say 3/8" inside diameter would improve matters greatly"

Just a quicky for Saturday morning before the public running that afternoon!

It is also possible that the larger diameter flues are allowing more complete combustion. So IMHO any spirals should not go all the way back to the firebox.

As an armchair expert I am concerned about the lack of combustion space in many designs. Interestingly the most efficient loco in our club is a model of a Black 5 (actually its Midland red) which has a combustion space helped by the narrow grate but wide topped firebox. Any comments?

Regards,
Ian

[baggo]

Hi Ian,

I wasn't suggesting John should take a hacksaw to his boiler ;D It's probably something to think about for some-one building a Doris from scratch though.
Allowing the gasses enough time to burn completely is obviously important for efficiency and the larger superheater flues (less superheater elements) may be acting as small individual combustion chambers and helping in this respect. The small diameter fire tubes would probably quench the flames before this could happen. A lot of full size locos with long barrels were fitted with combustion chamber fireboxes extending into the barrels which had the effect of: allowing the gasses more time to burn, increasing heating surface, and reducing the length of the fire tubes.

John

[chris vine]

Hi John,

There was one full size locomotive, a long time ago, which had a combustion chamber half way along the tubes. IE tubes, then combustion chamber then the last length of tubes to the smoke box.

Knowing what we know now, that the combustion is effectively stopped when the gases are cooled on entering the small tubes, the idea was completely wrong.

Just think how difficult it must have been to make, let alone maintain!!!....
If I come upon which locomotive it was I will update...

Chris.