Making a simple boiler.

[Gas_mantle.Participant @gas_mantle]

Hi all,

I've been thinking for a while about making a simple boiler to power small model steam engines. At the moment I've rigged up a temporary one using an old Kelly kettle and aquarium tubing, whilst it does work its far from ideal and does send as much water down the tube as steam.

I thought about getting some steel tube about 3 – 4" dia and about 6" long then firmly bolting 2 end plates on. I've no idea what sort of pressure something like that would generate but I can get tubing with 10mm thick walls.

If I was to use say 12 bolts to secure each end an apply some sort of sealant and a safety valve how I can I assess how much pressure is likely to be achieved and how much it will withstand.

I don't want to go down the road of getting a simple boiler checked for something that is only intended to power small models but surely 10mm thick walls will stand a lot more pressure than I'm likely to need ?

I'd like to buy a small pressure gauge and safety valve but wouldn't have a clue what spec I'd need.

Can anyone please offer any help ?

Thanks

Peter.

[Gas_mantle.Participant @gas_mantle]

[John RuddParticipant @johnrudd16576]

IMHO, the pressure you require your boiler to run at is a function of …what pressure is required by my model engine?

As a starting point for your boiler with bolted end plates you need to perform a hydraulic leak test, plugging any holes that would be needed for steam off take, relief valve sight glass pressure gauge etc…..if it stood a test of 80 psi for example, then a safe working pressure would be around half of that….then set your relief to say 50 psi….

10mm wall thickness is waaaaayyyyyy over the top…..Many small boilers that fall into the 'toy' category have a wt of 3mm or 10SWG in Copper, running at 50-60psi…..

These are just off the cuff comments, I'm sure other opinions will be expressed …..

[Gas_mantle.Participant @gas_mantle]

Thanks John,

I kinda thought 10mm would be overkill but as a beginner I'm being cautious that what I build is absolutely safe.

I've looked around at premade boilers but they seem to start at £400 whereas I'd rather spend £50 – 100 on materials and fittings and build my own so long as I can satisfy myself it's safe.

Part reason for thick walls was to allow me to bolt the end plates on easily and hopefully with enough bolts, get a good leak proof seal that isn't going to give under pressure.

[Steven VineParticipant @stevenvine79904]

Hi Peter

There are rules to be followed and you can test it yourself. You should do some calculations. Read the K.N.Harris boiler book.

How are you going to 'firmly bolt' the end plates on?

Steve

[John RuddParticipant @johnrudd16576]

Posted by Steven Vine on 29/07/2015 12:25:39:

Hi Peter

How are you going to 'firmly bolt' the end plates on?

Steve

I think his intention was to drill and tap the cylinder walls at each end and bolt the endplates in that way….

I was thinking 'flange' joint giving a wider area for the endplates……

Peter, you can buy 10gauge copper tube suitable for a boiler, copper sheet for endplates and the silver solder together after forming…..

Reading up on boiler construction would be a good start, helping to decide what type of boiler you want to build….and how you want to fire it ……meths/coal/gas?

If you keep the boiler below the 3bar-litre limit you can test the boiler yourself……

[Gas_mantle.Participant @gas_mantle]

Hi,

Yes my intention was to simply tap holes regularly spaced in the end of the tube wall, I thought if I used 10mm thick walled tube that would allow me room to use a decent sized bolts and if I used say 12 of them in a ring surely with some sort of sealant I'd get a decent leak proof seal ? I'm only wanting to power small engines so a bit of leakage shouldn't be a problem but if I can get a perfect seal then better still.

The idea of flange plates would help and it's something I'll consider.

The problem with going down the route of making a copper boiler is I have no idea how to solder nor do I have the equipment, if it was an option I'd do it.

I just thought a simple tube boiler would be easy for a beginner and if I'm careful there shouldn't be any risks.

Peter.

Edited By Peter Nichols on 29/07/2015 13:18:23

[Paul LousickParticipant @paullousick59116]

Hi Peter,

Sounds like you only need a small boiler at very low pressure if it will run from an old kettle. Making a boiler as you have described could generate far more pressure (depends how much you heat it) and could be dangerous. I would not recommend building one unless it is from a certified drawing and made to a design standard.

A friend of mine runs small engines from a steam cleaner. Available for less than $30 on flee-bay or hardware stores. (This was shown in an earlier post about using compressed air to run steam engines). Use a plastic hose that is pushed over the end of the steam outlet. Not clamped so it will blow off if there is too much pressure.

Paul.

(PS how do I show a link to a previous post in MEW)

[Ian S CParticipant @iansc]

Some others have used a coffee machine.

I suppose you could use the boiler suggested in the article you used to build your engine.  A pipe nipple, with caps screwed on each end, can't remember if you have that drawing.

Ian S C

Edited By Ian S C on 29/07/2015 13:35:08

[Michael GilliganParticipant @michaelgilligan61133]

Posted by Paul Lousick on 29/07/2015 13:17:09:

(PS how do I show a link to a previous post in MEW)

.

So far as I am aware: With Great Difficulty !!

The best I have found is to link to a specific page in the relevant thread, then add a comment describing which individual post on that page.

MichaelG.

[Neil WyattModerator @neilwyatt]

A wallpaper steamer is ideal if you want a fair volume of low pressure steam, noting that the 'boilers' have a built in safety valve (in some cases a an old style radiator cap). A heavy duty dimmer switch could be used to 'regulate' the steam rate.

Neil

[Ady1Participant @ady1]

The wallpaper steamer is a good low pressure starter, particularly since they have a built in safety valve

Easier than using say, an old pressure cooker yer mam used to make stew

edit: don't use this system indoors until you have some experience, the mess on the ceiling if it suddenly blows may irritate the missus slightly

Edited By Ady1 on 29/07/2015 15:02:13

[nigel jones 5Participant @nigeljones5]

hard to advise without knowing engine size but just buy a scrap mammod type thing off ebay? bolting the ends on wont work – not being defeatest but you will struggle to get it to seal. You stand a much better chance if you make it from steel. 4" dia by 6" long is a formidable boiler for a small engine!

[Gas_mantle.Participant @gas_mantle]

Hi,

I realise the wallpaper steamers etc will work but they aren't the same as making a 'proper' boiler, I'd really like to have a homemade one even if it's just a very simple one.

I did try over the weekend making one out of a metal thermos flask , I did need to cut the end off to get the inner skin out then blank of the open end but just by melting fishing weights I was able to cast the end plate to the tube. I was able to get a decent enough seal to power my small engine and the water stopped the lead from melting. Far from ideal but it worked better than you'd expect.

Surely by adding some sort of sealant between the end plates and the main tube and using 12 bolts per end I'll get a good seal won't I ? Or am I missing something here ?

I know a 4" dia 6" long boiler sounds a bit on the big size for small engines but if I wanted at a later stage to make bigger engines or multi cylinder ones presumably I need a reasonable boiler.

Peter

[Neil WyattModerator @neilwyatt]

If you want to make a 'proper' one within your budget, get a copy of Tubal Cain's Simple Steam Engines Vol;. 2 and make the vertical boiler in that. That's what I did, and I added an inch or so of extra height.

Neil

[AjohnwParticipant @ajohnw51620]

I don't think you would need to go to 10mm wall thickness. Even aluminium would take rather a lot of pressure that thick.

I sometimes wonder about using 10swg brass tube and screwing the parts together plus some automotive cylinder head type gasket glue.

It seems that the biggest problem with brass is zinc leeching out and high temperature with coal firing etc and isn't so bad with simpler heating even gas.

The simplest type of vertical boiler looks to be a tube within a tube, the heat being applied to the inside of the inner one. The gap between the outside of the inner tube should be fairly low extending about 1/2 way up the height of the boiler then on to a chimney. There are a few free designs about on the web. I would wonder if stuffing the inner tube moderately with wire wool would improve the efficiency.

I've managed to avoid making either a steam or a stirling engine for a very long time. Probably wont last though.

John

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[Gas_mantle.Participant @gas_mantle]

Posted by John W1 on 29/07/2015 16:46:02:

The simplest type of vertical boiler looks to be a tube within a tube, the heat being applied to the inside of the inner one. The gap between the outside of the inner tube should be fairly low extending about 1/2 way up the height of the boiler then on to a chimney. There are a few free designs about on the web. I would wonder if stuffing the inner tube moderately with wire wool would improve the efficiency

If I've understood you correctly that sounds like the arrangement I already have with the Kelly kettle. The kettle has a hollow bore through the middle and the water is held in a thin ring around it. The idea is it's an outdoor camping kettle that you light a fire in the middle of. It boils very fast because theres a lot of surface area exposed to the heat source but doesn't produce a lot of steam.

I assume the amount of steam produced is proportional to the surface area of water in contact with the air, the Kelly kettle has a small surface area in relation the volume of water, is that a true assumption ? I thought if I could make a boiler with a greater water/air surface area I'd get more steam.

I'll be the first to admit I'm only guessing here and would be interested to learn more.

[john carruthersParticipant @johncarruthers46255]

I keep meaning to make one of these flash boilers;

http://www.hobbydownloads.com/pdf/FLASH.pdf

from;
http://www.hobbydownloads.com/boilers.html

Edited By john carruthers on 29/07/2015 18:12:40

[JasonBModerator @jasonb]

The plates at the end of your proposed boilker may well be the weak points, you have not said what thickness you intend to make those. You will have a large unsupported area unless you add stays or use thick material.

Also hard to say if 12 fixings will be upto the job as again you have not given a size 10BA, M6 or anything between the two?

Nice groove around the end to take an O ring would be the ideal seal but would limit the size of fixings that could be used.

With the money you save on materials, buy a commercial safety valve with a low rating and you should not come to too much harm

[AjohnwParticipant @ajohnw51620]

if water boils it produces steam. The idea of the inner tube is to provide more area to catch heat than if for instance it just had a flat bottom. Another technique is to run a number of tubes up through what is basically a water tank. That can give a more effective increase in surface area to take in heat.

The catches with a boiler intended to produce steam at some pressure is that the boiling point of the water increases with pressure. As soon as steam is taken off heat is taken away as well so then the heating source has to have enough power to replace it. The bigger the engine being driven / the faster it runs the greater the heat loss. You shouldn't have any problem finding the boiling point at various pressures on the web. Sizing the heating to suit the steam output – currently black magical as far as I am concerned.

A far as I am aware the surface area of the water in terms of say the diameter of a vertical boiler has nothing to do with it's ability to generate steam. The main aspect is the surface area of the boiler that can take in heat from tit's source and how efficiently it does this. There may be some problem with water getting into the steam outlet due to it boiling and splashing about but as soon as it's pressure is allowed to drop it will boil. I think I have come across the term dry steam at some point. I suspect that relates to super heating it, maybe deliberately running it through something hotter than it's pressure related boiling point.

Other than principles this isn't really an area I know much about so if I did it I would have to suck it and see. One thing I would most certainly do is add a safety valve. In principle a candle flame could get the temperature of the water up to very high levels. It wont really boil if it's contained. The whole thing could explode.

Hopefully if there is something wrong in the above some one will comment. There was a book shop not far from me that had a lot of rather old books – steam plant information was in some of them and I can't resist looking at stuff like that.

Vertical boilers – I probably mention those as to me they are the only ones that can look nice especially with wood lagging. I'd guess to work out they have to be significantly bigger than the engine and proportioned just like the images of real ones that will be about.

John

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[frank brownParticipant @frankbrown22225]

On your DIY boiler, I would make the end plates thick and trepan a groove in each one to accept the thinner boiler shell and use external studding to clamp the ends on.

Frank

[John RuddParticipant @johnrudd16576]

Posted by John W1 on 29/07/2015 18:37:33:

. You shouldn't have any problem finding the boiling point at various pressures on the web.

 

 

John

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Look for steam tables…..these give the figures you may be looking for….or for future reference…

Edited By John Rudd on 29/07/2015 18:56:13

[nigel jones 5Participant @nigeljones5]

I tried this principal many years ago and simply could not get a good seal. When you drill/tap the holes you will distort the material around them. Machining copper tube in the lathe is a nightmare at best, so best avioded in thinner section. Where do you live – region – there will be someone on here willing to help. O ring is the way but you will need the ends reinforcing or staying, either option is not simple. What heat source do you intend to use? What tools/skills are at your disposal? On a scary note one of the first boilers I ever made was out of an old paint can – and it did what I wanted it too! But dont!

[Anonymous]

As has been said the boiling point of water varies with the pressure acting on it. In a closed volume, like a boiler, as the pressure rises so does the boiling point. Once the water reaches the temperature appropriate to the pressure within the boiler, it doesn't actually boil. You need to add considerably more heat, without increasing pressure, to convert the water to steam at the same temperature. Steam at this temperature is called saturated steam. An additional property of saturated steam is its dryness fraction, from 0% to 100%. At 0% there is no steam and all water droplets, at 100% there are no water droplets and all steam. Dry steam is simply saturated steam with a dryness fraction of 100%.

Superheated steam is different again. If we add more heat to the saturated steam we increase the temperature of the steam, but not its pressure. So in essence superheated steam is steam that is at a higher temperature than that needed to create steam in the first place, at the same pressure. Of course superheated steam contains more heat energy (enthalpy) than saturated steam, but I think one of the main reasons for using superheated steam is to prevent, or at least minimise, condensation in the cylinders.

Peter: Dream on if you think it is easy to produce a steam tight joint with a few screws and some sort of sealant. Been there, done that, with boxes for motor racing, and it still let water in, without there even being much pressure (water spray from the wheels) or elevated temperatures involved. It is possible to use O-rings to seal against water pressure, but it requires accurate machining of the grooves, and you need a lot of screws to ensure even clamping of the O-ring. Even then we had a couple of leaks due to almost invisible specks of dirt and that was only 3 bar; application being a liquid cooled heatsink for a power inverter.

Coincidentally I have been asked to do a design review tomorrow on an electronics box that needs to be IP67 rated. Should be fun!

Andrew

[AjohnwParticipant @ajohnw51620]

I suspect that the bolts would be the weak points providing thickness was as would be expected. The problem is the area of the diameter of the cores of the bolts used being equal or greater than the bursting point of the boiler itself. Just look at the number of rivets used on an old boiler on this page for similar reasons.

**LINK**

That's why I feel a sort of screw on or in cap idea would be better.

There is something like a flash boiler shown here – water tube boiler. The flash boilers are sometime called monotube boilers.

**LINK**

The curious thing about the tube boiler is the water in the tubes may not boil or needn't. Just heated to a point where it will boil when the pressure drops on the way to the engine it's driving. I can't see how it could work if the water boils directly in the tubes.

John

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