Author Topic: Boiler suppliers and other bits suitable for (small) G3 live steam  (Read 1855 times)

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Offline jamiepage

If you don't mind I am going to pick up on another thread where a G3S boiler Inspector said in his opinion small boilers were unsuitable for G3 locos.

The statement is  wrong on so many levels that it shouldn't really remain unchallenged.

One significant issue is the fact it could dissuade new blood from trying G3 scenic railwaying by leading them to believe that G3 norms are somehow entirely different to G1 and 16mm norms.
In other words, more expensive, more regulated, just plain harder work.

Whilst that might be to some extent true for a large Pacific, it is utterly untrue for what could be seen as an entry level first scenic steamer of a smaller prototype.
'Ginger' encouraged this approach a few years ago, and it is still entirely correct.
Much already exists off the shelf in the G1 and 16mm world which could be easily used on a G3 loco.

For instance, this new supplier recently advertised plans for a batch of both Dee and Project boilers, fully certified, for a price iro a couple of hundred quid each.

I don't know whether there are any spaces left on those batches, nor how long those prices might hold, but they are also open for one- off builds.

I have one from their Dee batch on order. Modded slightly with the dome bush shifted to suit the prototype, it will slide into my small G3 0-4-4T nicely.

Since the order, I can say communication has been first class, and photos show a very high quality product. Proof will be in the eating, so I will report further when it arrives next month.

With an off the shelf (relatively cheap) batch built certificated boiler, plus off the shelf batch built single or twin cylinder blocks machined to various G1 designs, it would be extremely straightforward to collect the various bits to assemble a G3 scale steamer based on any number of smaller prototypes, without any boilermaking or much machining skills. And all with a bit more space (wriggle room)  between the frames than in G1.

 Such machined cylinders etc are already available from eg

I have used one of their ready assembled twin cylinder assemblies before, and was pleased with the standard of machining.

The 16mm world is also generating many items suitable for small G3 steamers. Whether Roundhouse boilers and gas systems etc, or 'after market' regulator assemblies etc, there is a great deal that could be used.

An ebay supplier occasionally offers G1 items such as 'Project' type water pumps.

MEL would almost certainly produce G3 scaled laser cut items to any design.

It is probably a slight stretch to say a G3 loco could currently be built with a screwdriver alone, but  people shouldn't be unnecessarily misled or discouraged. It should be no less accessible than  the other 'garden scales'.

If someone is looking for an entry level, or relatively cheap, live steamer for scenic railwaying, then G3 can be just as straightforward as G1 and 16mm. It's just a question of choosing the prototype.

(ps Another catalyst for growth is of course an opportunity to access tracks which is why an acceptance of the 'new' lighter touch code will help. Sure, people can choose who to invite, but if a Group or Society aims to encourage participation then maybe they should actually take any opportunity to do so. I note this morning that the Australian Rails in The Garden Group state it is likely they will move away from their current codes for Sub Miniature boilers. Their own investigations and risk assessments are leading them to a code which will 'probably not be dissimilar to those recently issued by G1MRA and 16mm Assoc.
So even Aussie Rules might be changing)

Offline Andy B

For further ideas and inspiration along these lines, there are some articles from old G3S Newsletters available on the G3S website (thanks Ian!):

Offline John Candy

I seem to recall that Adrian Booth converted a Roundhouse 0-4-0T into a G3 steam railmotor some years ago.

I was contacted just a few days ago by a potential convert to G3 from G1 who has been looking at material on and and is hoping to produce a small tank loco as per "Ginger's" series on the 0-4-4T.

He said he was encouraged by the "no nonsense" approach to construction and the fact that the boiler is of same design as one he is currently building for a G1 loco.

He watches (and has now joined) this forum and I hope this wrangling will not alter his views on G3.

My fellow Members, ask not what your Society can do for you, ask what you can do for your Society.

Offline jamiepage

So do I.

More fresh blood with his approach could do G3 a great deal of good.

Here's a G1 based G3 loco. under construction. Very much taken from Ginger's ideas.

Offline jamiepage

Here's a gross check for Small Boiler usefulness.

A representative small boiler could be one of the GWR Standard boilers. A small one, such as Standard 11 or 21, as used on Metro's, many absorbed locos, and many others.
These boilers are recorded as c. 16ft long overall, barrel and firebox with barrel diameters iro 4ft 3in..

In G3, c. 8.5 in. length, 2.25in dia.

A Project boiler, straight from the plan, has an overall length of 6.5 in., and a diameter of 2 in. It has a declared SWP of 60psi

Accepting the Project's diameter but increasing overall length to, say, 8in., results in a perfectly good  Small Boiler for G3 scenic purposes.
Plenty of room also for out of scale insulation within scale cladding.

Calculated 'capacity' of this extended boiler, c. 1.70 bar litre.

That calculation simply assumed the boiler was considered to be a simple cylinder, 8in long x 2in dia. It assumed the smokebox tubeplate was positioned as far forward as possible with no inset. 
No correction was made for displacement of firebox crown, fire tubes or other impedimenta.

So a good enough steam producer for small scenic locos and nowhere near the Small Boiler limit. Boilers like this can be purchased, ready certified, for something like £200- £300.

Offline MikeWilliams

I sometimes think we need a "like" button on this forum!

Offline John Candy

I sometimes think we need a "like" button on this forum!

Well, you asked for it.......let's hope it works!

I have activated for all boards, except those which are of the "announcement" variety (admin boards, buy/sell, etc.).

If you experience any issues, let me know.

My fellow Members, ask not what your Society can do for you, ask what you can do for your Society.

Offline IanT

A Boiler inspector is simply someone who has volunteered to undertake some fairly simple technical tasks. They are required to be competent and correctly equipped, such that they can undertake straightforward procedures that are very well documented. There is no qualification (or test) to become a BI as such - they are appointed but are of course expected to work/stay within their own competencies and experience.

The Society has about 6-7 BI's currently - and if you got them all in a room, I think you would find they probably have very different opinions about quite a lot of things - both technical and other. I certainly do not agree with everything Ralph says for instance - and I'm pretty sure he wouldn't support all of my views.

My point being that it's quite useful to recognise when someone is giving you a personal view - as opposed to an 'official' one - they are often quite different and it is misleading to confuse the two in my view.

Other than that Jamie - I don't disagree with you too much (and that has often been the case) - more the way you chose to make your points....


Nothing's ever Easy - At least the first time around.

Offline jamiepage

Sorry, but I'm not smart enough to see the 'off duty' distinction, Ian.

Were I surfing the net for G3 activity, wondering whether or not to dip my toe into scenic G3 live steam, I would sit up and take notice if I stumbled across a G3S inspector baldly stating on a public forum that a Small Boiler is unsuitable for G3.
I would take even more notice if said Inspector went on to call them a danger and declare he won't entertain them.

Like it or not, it is not unreasonable to also conflate an Inspector's opinions with his/ her organisation's, particularly when discussing boiler tests and boiler matters within the Society's area of influence.

And what an impression they give.

But perhaps G3S will enthusiastically embrace the 'new' code and use it to help show potential members it is no more difficult to get involved with G3 steam than it is the other 'garden' gauges.
Maybe it will encourage pockets of new G3 (small) steam activity and support new GTG tracks with Society insurance and guidance etc, all in isolation of  mandatory annual  visits to the Inspector cohort. (Not discourage such contact, but not mandate it either).
Who knows where relaxing the reins a bit might lead? Maybe Society activity will increase to the point where a BI just can't get to every GTG each year. Nor need to, at least for annual Small Boiler certifications.

Offline cabbage


You are very vocal in your opinions -but the one thing you have never done is provide is a mathematical first principles proof. So I will do it for you. This is a typical Gauge 1 boiler.

Given Parameters:

The wheels of a locomotive are 50mm diameter.
The bore and stroke of twin double acting cylinders is 25mm x 12.5mm.
The velocity of the locomotive is 1 metre per second.
Assume 100% admission and exhaust.
Working pressure is 5BAR.

I will be using the Greenly factor 100sq inches of heating surface per 100PSI with 1 cubic inch of water boiled per minute.

This translates to: 64,516mm2, 6.89BAR, 16.38mm3 per 60 Seconds. 

Revolution of wheels at 1mS-1 gives 381RPM thus:-

The volume of steam going from the boiler is Pi x R squared x H x Strokes x Number per minute

[Pi x 6.25 x 6.25 x 25 x 4 x 381] = 464,675,573mm3 of steam used per minute.

If we assume 5BAR this translates into a boiling temperature of 157 deg C and you would have to boil 14,796 mm3 of water per minute to produce this. At this temperature one volume of water produces 318 volumes of saturated steam.

The heating surface required would be  :- [5/6.89] x [14,796/16.38]

This would translate to a 25mm dia centre single flue of 98.49mm long. Which to simplify the maths we will call 100mm(!)

Looking at std tube diameters in 1.6mm seamless Copper.

50mm would give a volume of 196,349 – 49,087 = 147,262 mm3
The running time would be [ 147,262 /14,796 ] = 597 seconds until boiler is empty

The energy from the pistons is 0.1Nmm2 per BAR thus:-

[ 5 x 0.1 x 4 x Pi x 6.25 x 6.25 ] = 245Joules.

Now let us examine the boiler that I am using which is “Design No. 14” from KN Harris’s book “Model Boilers and Boiler Making”. This was designed originally for a 0-4-4 loco but I have adopted it for a 2-6-0 layout.

The total heating surface is 90,322mm2. The G1 boiler is 7,853mm2 even allowing for the difference in scale (and applying it) the same heating area would only be 19,323mm2.

Running through the same Given Parameters but using the size of pistons that I am using gives the following:-

As my bore and stroke is 30 x 22mm. Volume of steam required becomes:-

[Pi x 11 x 11 x 30 x 4 x 381] = 4,344,916mm3 per minute

Thus I have to boil [ 4,344,916 / 318 ] = 13,663 mm3 of water per minute.

Energy from the pistons is

[ 5 x 0.1 x 4 x Pi x 11 x 11 ] = 760Joules

From the above figures I feel that it would be impossible to power a G3 loco for any length of time with a small boiler as the quantity of steam required and the heating area needed to produce this preclude its fitting unless the loco does not have a long running time. I would prefer a larger less stressed boiler to one that is having to be thrashed… Axle pumps, tender pumps and injectors can be used to provide continuous feed for an undersized boiler. Only the tender pump is not parasitic on the energy produced by the boiler.

Let us also apply the basic rules of thermodynamics. A short fat boiler is more efficient than a long thin one due to the lower ratio of of Volume to Surface area. This is the volume of the container to the amount of external surface area to lose / radiate heat from. A larger boiler also has more defined circulation paths due to the volume of water and the depth of the water. Higher pressures reduce the amount of energy required to boil the water -thus a larger boiler system at higher pressure is more efficient.

My instinct is to follow the figures. IanT has said that of the boilers presented to the Inspectors only one shell was declared to be 3BAR litre. If I went to Borrowash track and declared my 5inch “LanyTank” to be 3BAR litre I would be laughed at. Looking at the figures I have decided that a G3 sized boiler in a G3 loco is the best option. Nowhere have I said that a 3BAR litre Small Boiler was dangerous -those are your words not mine. I have simply stated that 3BAR litre is not applicable to G3 as the boilers simply are too small and lack the evaporative power to be usable. This is my personal viewpoint and as proof that I held it to be correct before I became a Boiler Inspector I would present the time and effort required to produce Design 14 rather than buy a Project boiler.

Offline IanT

Jamie, when Ralph (Cabbage) kindly offered to provide boiler testing facilities in his neck of the woods - the Society didn't ask or require him to stop voicing his own opinions in this area. All they require of Ralph is that he performs the tests as laid out in the codes - which I am sure he will do very competently.

The "impression" people will get when they visit this site can of course be manipulated - something I am sure you would wish to avoid. I am therefore very pleased (and unsurprised) to see that Ralph is happy to debate you. I look forward to a lively conversation but please don't present any one persons views here as necessarily representing the Society as a whole or as an organisation.

I've seen and admired your work elsewhere. You decided to leave the Society - which was a pity but so be it. There are a lot of folk in the wider G3 community who don't feel the need to join the Society and that's fair enough - but as someone who has tried to help and support the growth of G3 and the Society - can I suggest the two are in fact linked. So whilst you don't have to agree with everything the 'Society' does (or does not) do, please stop the sniping...

OK - I'll shut up now. Over to you and Ralph - and then hopefully back to the main topic - which I think should be how to encourage the design, development and use of small live steam engines in G3.


Nothing's ever Easy - At least the first time around.

Offline MikeWilliams

Chaps, I have very little experience of actual running of live steam.  I have merely consulted with experts for the design of Venture, which has two cylinders made specially as an enlarged G1 design so they will take more steam than G1 cylinders.

The boiler is an enlarged G1 DEE as designed and proved by Dick Allen, but with the firebox reduced in size and the boiler slightly shorter to fit the LNWR 0-6-0.  So, it is only slightly larger than a G1 DEE and smaller than some G1 boilers for Pacifics and larger engines.

Roger Marsh has made the first boiler (coal fired), and many have seen it n test at Ampthill where it ran beautifully at scale speeds for at least half an hour.  It has run at least twice since then with similar success.
I guess it depends what you want from your Gauge 3 engine.  If you want to haul eight or ten coaches at 80mph for an hour, than the Venture boiler will soon struggle, but for pulling four 6-wheeled coaches or a dozen wagons at maybe 30mph for half an hour, then a G1 sized boiler appears to do the job very well.

Also, and probably more importantly, for older engines you just can’t fit a larger boiler without being grossly overscale, which is not what “scenic model railways” are all about.  Look at Roger Marsh’s tiny 0-4-0 saddle tanks – they run supremely well but only with very short trains and for a limited time, which is what the real version was built for.


Offline jamiepage

Over the last few days, in a thread discussing the 'new' Small Boiler regulation, you made many allusions to safety (or lack thereof).
Here's one from Wednesday.

As a host I have a duty of care to my guests. Some of my most enthusiastic guests (for no fault of their own) often have mental ages below 10...

In my first year of GTG I barred steam engines completely. It is my personally belief that the 3BAR litre rule cannot be ....

I suggested earlier that perhaps you should actually read and properly think through the 'new' code first, because I got the impression you thought Small Boilers were to become UNcertified, an impression rather confirmed by this-.

The insurance company simply insist that your equipment is safe. Certification ensures that!

However, if you now accept that size alone does not make a boiler safe or unsafe, and if you have accepted  the 'new' code which no longer mandates an annual visit to an Inspector such as yourself,  then there is no more to be said.

Turning to your mathematics, I'm afraid I'm reminded of the aerodynamics of a bumblebee.
I can admire the logic, the beauty even, in such calculations, but I confess I would get distracted from the theory every time a 'Project' puffed past in a scenic setting pulling a few coaches or wagons.

Shouldn't theory concede to empirical data?

The scaled size of a large prototype allows a large  boiler. Use the space and the loco will be able to carry out scaled express runs with heavy Teaks, in a SCENIC setting.
Logical, and all good G3 stuff.

But there is no logic in blindly over- boilering a small prototype for SCENIC railwaying. 
If someone wants to build a small G3 loco for scaled pottering or 'local duties', it is utterly unnecessary to  shoe- horn in an overscale boiler.

Unnecessary expense and complication, and to achieve what, in the SCENIC environment?

Many people would be delighted with a small, tightly radiused garden layout, and a small Tankie asthmatically struggling with the 'pick up goods'. (And if G3S gave them insurance and advice for GTGs, maybe the neighbours would join as well!)

Or indoor steam.

Show people how easy it can be to get involved with G3 steaming, and maybe their second loco will indeed be a Pacific with big boiler, cavernous cylinders and buckets of spare steam.


Offline IanT

Agreed Mike.

I don't really need to drag out my Henry Greenly's to know that if I widened the gauge of a 16mm engine by 18.5mm - it wouldn't change the overall characteristics of the engine. indeed Roger Marsh already has done exactly this and his engines run very well.

The member who has designed the <3BL boiler (that I mentioned previously) has cunningly (he is a very inventive engineer) shortened it - even though the outer cladding is longer (e.g. the internal boiler doesn't reach the same point as the external smokebox would suggest). His existing engines are also very efficient and will still tick along at 20-30psi - so he's confident that his boiler will produce enough steam to drive the engine and asked for the 'shell' test to be done at a Wp of 60psi. The combination of the shorter boiler and lower Wp will deliver a large G3 tender loco (SR but cannot recall what the actual loco is) with a <3BL boiler.

My view has long been that the issue of small boiler use in G3 is simply a legacy thing. Most published 2.5" designs (LBSC, Martin Evans, Don Young etc) were intended to be 'driver driven' - not scenic. You have to go back to before LBSC (pre-1930s) to find (mostly non-scale, spiritfired) G3 designs for scenic use. So it's not too suprising that most G3 loco stock comes with a large capacity boiler, operated at high pressure.

16mm have a legacy that is almost entirely small boiler/low pressure - so no surprise - there are lots of them around in 16mm - with maybe only a very few >3Bl engines about (large Garratts perhaps?). As the market for 16mm live steam grew - so did the demand for good quality commercial products - leading to the emergence of peope like Roundhouse. We are now seeing commercial live steam in G3 but generally they have been larger (Mainline) engines that can demand a larger price.   

However, there is absolutely no reason why excellent small G3 engines cannot be built (with <3BL boilers) apart from perhaps a lack of good/interesting small modern G3 designs. I think the dilemma is that we cannot interest the larger live steam commercial producers with our current demand volumes - so we first need to build a base of 'builders' to generate more interest in G3 live steam. I know many feel that 'building' stuff is going out of fashion and want RTR - but unless we are lucky enough to have some small firm make a giant leap of faith in this area - the 'owner-builders' have to first lead the way I believe.

What we need is more published designs for small G3 live steam engines (preferably easy to build) that can really start to move G3 away from LBSC's Passenger Hauling legacy...


Nothing's ever Easy - At least the first time around.

Offline jamiepage

I agree with every word of that.

Focus on what G3 is about.
The other 'garden gauge' Societies have tried to break down barriers to entry (safely) where they were perceived, and their membership and activity levels surely reflect that. And the manufacturers followed to everyone's benefit.
Unnecessary regulation or dogma helps no-one.

They have also undoubtedly benefitted by not having had their focus deflected in an entirely irrelevant direction by the needs of 'ride on' activities.

 If the number of people becoming involved with some kind of G3 activity  increase, I guess the manufacturers should follow.

G3 is nicely on the cusp of model railways and model engineering, and should be exploiting the best bits of both in a  SCENIC model railwaying environment.

There is a great deal to be said for , and interest to be had in, encouraging new ideas and techniques;  the greater the numbers of participants, the more likely we are to see them.
But to get there, I would suggest that currently one of the cheapest and simplest entry levels ways into (safe) G3 SCENIC steaming would be to utilise the economies of scale that purchasing a (certificated!) G1/ 16mm type boiler, and/ or other ex G1/16mm components, can bring, and using them in an appropriate design.
And bluntly, use the expertise built up around what does and doesn't work, and bring it to G3.
(As one example, the boiler, valve gear, cylinders, etc from a particular, currently available large G1 design fit almost perfectly within the outlines of a G3 small 2-4-0 I would like to build one day. Even the driver diameters are pretty well identical. And yes, the boiler is <3bar litre)

To discourage that particular approach is misguided.