ME vertical boiler

[duncan webster 1Participant @duncanwebster1]

About time for some iconoclasting!

If theboiler is to be gas fired there isn't much point having a water cooled firebox. The emisivity of a blue gas flame is very low so you don't get much radiant heat transfer, and the velocity is pretty low so you don't get much convective. I'd be tempted to have firetubes end to end, a firbrick tube to sit the boiler proper on and an outer tube so that the air comes down past the firbrick, and does a 180 degree turn to get up to the burner. Poke the superheater into the bottom bit where the flue gas is really hot

you can buy burners like that from a hillwalking shop to burn gas or petrol. I think you can get them to burn diesel, but never seen one in the flesh

[Neil WyattModerator @neilwyatt]

My boiler is a version of the Tubal Cain design, I made it about an inch taller.

The central flue has several water tubes and there is no firebox which makes it ideal for gas firing, it's also very simple construction. I rivetted right round top and bottom but really you only need 3 or 4 rivets to hold it lined up during silver soldering.

If I can make one, I'm sure Geoff can!

Neil

[doubletopParticipant @doubletop]

Posted by JasonB on 19/03/2018 10:07:11:

Gas

As you say any air needed for combustion would be drawn in as part of the burner in most cases so not sure what the holes are for.

The boiler looks remarkably similar the Sandy Campbell design.

http://www.modelengineeringwebsite.com/3%22_vertical_boiler.html

The holes in the side ar to allow the ceramic gas burner to draw in the secondary air. It would not be possible for the ~ 92% air required for combustion of the ~8% gas to be soley drawn through the holes in the jet assembly of the burner.

Pete

Edited By Doubletop on 23/03/2018 06:33:10

[nigel jones 5Participant @nigeljones5]

From my somewhat extensive research and development of gas fed burners I can say that a well designed burner needs no other air than that drawn in by the air holes adjacent to the gas jet, and that air should come from outside the combustion chamber to ensure it is a dense as possible. Taking air from inside a hot boiler as depicted is about the worst possible solution. I have tested all of my burners inside a completely sealed flue and all function adequately, needless to say that they function better with a chimney! There are several videos of burner tests both on youtube and on my website if anyone wants to see what they should burn like.

Nigel – Pendle Steam Boilers

[Ian S CParticipant @iansc]

Fizzy's got it, I;v been building gas burners for about 20 years, the jet and valve are Primus. The induction air should be a cool as possible, in some cases a shield is placed between the burner and the air holes. My burners are usually donut shaped to go around the hot cap of Stirling Engines.

Ian S C

[duncan webster 1Participant @duncanwebster1]

It would be extremely valuable if Fizzy (and IanSC) could be persuaded to write up their R&D. Design of burners is a black art as far as I'm concerned. I always thought you needed seconday air, obviously I'm wrong.

[nigel jones 5Participant @nigeljones5]

Hi Duncan. Much as I advocate the free sharing of information in this case I'm afraid that I need to keep my design to myself as it is a major selling point of my boiler and burner combinations. You are correct that absolutely no otrher air source than the 4 x inlet tube holes are required. The slits you see on my and others burners around the area of flame front are there to even out the harmonics caused by the burner. If you dont get these just right the boiler howls so much so that without ear-plugs you cant stand close to it – it hurts! I can tell you that making a ceramic burner is a doddle in design terms compared to a brass one – I make and sell both. There is a lot more info on some of the French model boat sites. Nigel @ Pendle Steam

[Howard LewisParticipant @howardlewis46836]

The boiler shown in the upper drawing with angled tubes owes something to the full size one designed for Sentinel steam waggons and locomotives. It was regarded as being a very efficient steam raiser. However, fuel was fed in from the top.

Probably not the easiest boiler for a novice to produce, but may be worth the effort in the long run.

Howard

[JC54Participant @jc54]

Coming a bit late to this thread, I am a complete newcomer to making a boiler or silver soldering. I started reading this series of articles at about the time that the pump was being finished. I have a need for an upright boiler for a project that I am in the process of drawing up and am going to attempt this boiler first as a learning exercise. I do agree that some of the articles do seem a bit long winded at times but for us complete beginners please remember that you cannot build the house until the foundations are in and correct!!!!! I have one problem in that I have ordered and recieved all of the back issues except for one. I am not sure if this is the correct place to ask but has anyone got a copy of ME 4578 19th January 2018 that they are willing to sell me? This is for Part 2 of the boiler build. Many thankc JC

[Andrew Wood 7Participant @andrewwood7]

JC54, this is a bit late perhaps but the best way, if you can do it is to subscribe to the digital edition and then you have access to all the back issues you want, several years worth anyway. I then print out the parts I need for the boiler and put them in a folder. Andrew

[Tim Taylor 2Participant @timtaylor2]

I'm jumping in a little late as well…….a couple things:

The combustion air on any boiler should be adjusted for proper fuel/air ratio – excess air improves combustion, but too much can dramatically increase the stack temperature and reduce thermal efficiency. On full scale boilers, on gas fire, we target for about 3% excess O2, which translates to about 15% excess air.

I'd probably also fit a simple superheater coil – easiest place to add it would be right at the stack….

Tim

Edited By Tim Taylor 2 on 20/01/2019 22:41:42

[JC54Participant @jc54]

Andrew, many thanks for your suggestion. A forum member sent me a copy of the part that I was missing. I am considering upgrading my account to digital when up for renewal. John

[Andrew Wood 7Participant @andrewwood7]

This is my first boiler and silver soldering project. I'm a bit behind on this but am in the process of silver soldering the boiler. I used the normal EF flux on the hand pump but on the advice of someone more experienced than me in the local model engineering society i switched to Tenacity 5 for the tubes and endplate assembly. This worked very well on the two endplates (except the whole assembly distorted slightly and ended up a bit out of square) but the flux forms quite a hard glassy like deposit and was more difficult to remove than EF flux. So i then reverted to the EF flux for the first set of bushes and that worked OK. When I came to the lower temperature solder for soldering the endplates into the barrel used EF Flux but this did not work so well as the flux became exhausted too soon and there was not enough solder to make a good fillet and it didn't give me any time to add extra solder. Although the endplate was a tight fit in the barrel it tapered in a bit leaving a larger gap towards the end. Cleaning up seems to take much longer than a dip in the citric acid for 20 mins and a soak in water as advised in the article. To get back to shiny or pink copper I have soak in the acid for hours alternating with washing and brushing off so I don't know if I've not got strong enough acid or am being too fussy in getting rid of all the brown oxide? Does the flux cut through a bit of the brown oxide or do I need to get it all shiny again for the process to work?

[Neil WyattModerator @neilwyatt]

Posted by JC54 on 07/10/2018 15:37:31:

I am not sure if this is the correct place to ask but has anyone got a copy of ME 4578 19th January 2018 that they are willing to sell me? This is for Part 2 of the boiler build. Many thankc JC

I would normally point you at:

mags-uk.com/magazines/filter/title/model-engineer.html?___SID=U&dir=asc&order=published

But back issues before March 2018 are sold out, I'm afraid.

Neil

[Neil WyattModerator @neilwyatt]

Posted by Andrew Wood 7 on 23/01/2019 12:34:45:

Does the flux cut through a bit of the brown oxide or do I need to get it all shiny again for the process to work?

Yes, as long as it is a relatively thin layer, in fact you can often see the oxide layer disappear under the centre of the flame when it is hot enough. The flux stops it reforming when the hot metal is exposed to air.

Tenacity flux is a good suggestion for boiler work, I would just leave it in longer/use more concentrated citric rather than keeping trying to scrub the flux off.

Neil

[Andrew Wood 7Participant @andrewwood7]

Thanks very much that advice Neil. Yes scrubbing and leaving in water don't seem to have much effect and you can't scrub the inside and any crevices. The supplier of the citric acid (CuPalloys) suggest 20 GM per litre. It sounds to me like a fairly dilute solution but I've no idea if this is particularly strong or not but presumably suitable for the purpose and works OK on EF. The tenacity flux supplier recommends Sodium hydroxide, an alkali, to remove the flux but I haven't tried that yet, maybe that would work better although it is a bit more hazardous?

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