Boiler advice needed .. .

[Martin DareParticipant @martindare17777]

I have just completed a Stuart Victoria stationary engine, my first build from castings. I originally planned to just run it from compressed air but my ambitions have grown to considering the live steam option.

The engine has a 1″ bore and stroke, ~13cc swept volume, x2 per revolution (double acting cylinder). @ 300rpm thats approx 7.8L of steam.

I am considering 3 boilers, but its impossible to know the volume of steam they could supply.

For burners I think gas via a regulator is the cleanest option giving instant heat control.

1. Pisces stationary Babcock type boiler 250Lx100wx370H  (inc burners) pressure vessel made from clevedonsteam.co.uk. Unlike its full size counterpart this does not appear to have a superheater, but I wonder if one could feed the steam outlet under the boiler to achieve this ??

2. Virgo Steam plant kit  250Lx110Wx250Hmm pressure vessel made from clevedonsteam.co.uk. This is a conventional flu type boiler which seems very inefficient to me. With such a low flu gas to copper area I would not expect large steam volumes, but never having had a boiler I have no clue.

3.Maccmodels horizontal 280L x 115 W x  444mm high. This is a complete kit so silver soldering is a must. This is one of the few boilers which gives clear information and technical info.

The door openings are 1-1/2″ high x 2-5/8″ wide. The water space is 3″ dia. x 8″ long, 44 cubic inch volume. The fire box is 3″ wide, 7″ long x 1-3/4″ high. It also has a cleanout door that opens to access the flues. It has five copper flues 5/8″diameter, 127 square inches of heating surface.

My current thinking is to go with #1, the babcock type. It can hold more water and level is not so critical. It has no internal flues to clean and is easy to inspect, plus it is already silver soldered.

I would very much appreciate any comments from owners/users.

I am planning to drive a dynamo, feed pump and governor via a gear drive from the crankshaft. I have also replaced the std piston oring seal with a graphited ptfe ring which was a worthwhile improvement.

Any advice or comments much appreciated.

Best regards

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[noel shelleyParticipant @noelshelley55608]

Compareing boilers and engines is far from straight forward ! You will only need a low pressure ie 30/40 psi, I have run a Stuart No 1, a very much bigger engine that yours to test on a prestige Hi dome pressure cooker – limited to 15psi ! If you belong a club see if you can connect your engine to someones boiler and get some idea of what you need. Boilers are expensive ! If your near me you are welcome to try it on my 6″ vertical boiler though this is bigger than you would need. Others here will be able to give guidance, I’m sure ? Noel.

[Martin ConnellyParticipant @martinconnelly55370]

300rpm seems far too high for a Victoria, I would be thinking 60 rpm would be a good target for max rpm. If you see a full size steam engine of this style the move gracefully rather than furiously. Remember also that faster running results in faster wear.

Martin C

[JasonBModerator @jasonb]

I’d say all three are a bit on the small side particularly if you want to use those sort of revs. The longer stroke engines are better run a bit slower

Looking through my old paper Stuart Catalogue they suggest the 504 or 4000 boilers.

The 504 is 3.5″ dia x 10″ long styles like the Pisces and the 4000 4″ dia x 9″ long and is the ctr flue type

[BazyleParticipant @bazyle]

For demonstration purposes you will need very little pressure. If you don’t have a compressor use a car tyre pump and spare tyre as a reservoir to see how little pressure runs the engine at a sensible speed. Simple calculations then give you the volume.

The book ‘model boilers and boilermaking’ by K.N.Harris is one of the reference books for model engineers and includes a number of designs and all the calculations you need. It is worth taking a bit of trouble to do the calculations and document them for future test certificates and insurance.
You might consider what would look right alongside it and having made your calculations make as simple a boiler as possible (because it is your first and to keep costs down) but clothe it in a shell if necessary to look the part.

[Martin DareParticipant @martindare17777]

Thanks for your interest and replies.

@ noelshelley >>Comparing boilers and engines is far from straight forward

I have found no information on this. Usage of steam by an engine is never quoted (say 200rpm/litres per min/pressure). Likewise boiler steam production capability, which will be influenced by the heat source size and the thermal efficiency of the transfer of heat from the flue gases to the copper.  For a beginner its a bit daunting.

@  martinconnelly  300 rpm was the max speed I would consider running, and for relatively short periods. I have been near to the large flywheel of a working full size stationary engine in one of the uk museums. When it was stopped it accelerated to (possibly by accident) to a very high speed, prior to stopping. The power to accelerate the flywheel that quickly was truly amazing.

@jasonb >> I’d say all three are a bit on the small side

The information from your old stuart catalogue is very useful. Its the first time I have seen any boiler size recommended for this engine. As you point out, the size is similar to the Pisces boiler, which I currently favor, and will likely settle on.

Best Regards

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[JasonBModerator @jasonb]

No. I said the style was similar to the Pisces.

The 504 has approx 60% more capacity than the Pisces and the 4000 is double the capacity. Heating area will also go up as the capacity does.

Heating is probably more important than capacity as you will need to be able to produce steam at least as fast as you are using it. Something like the 5″ one from Pendle with it’s twin burners would be a good candidate, why not drop Nigel there a line and tell him what you want to do and he will say what he feels will suit

[Martin ConnellyParticipant @martinconnelly55370]

You can also look at some videos by Keith Appleton. You can see him running a Victoria from a small boiler but it has a large burner and a water pump driven by the Victoria constantly replacing used water.

https://youtu.be/LtKeuWmjqSY

Martin C

[Martin DareParticipant @martindare17777]

@JasonB

>> The 504 has approx 60% more capacity than the Pisces and the 4000 is double the capacity.

How do you find out this information ? I do not even know how many heating tubes the pisces boiler has and had thought to ask Clevedon Steam, let alone how to get a comparison of the relative capacity (is capacity the volume of water, or of the boilers rate of steam conversion ?).

@martinconnelly

I have watched a large number of Keith’s videos, and found them to be very informative.

The info on the pisces boiler is minimal :-

” The Pisces stationary Babcock type boiler is designed to power mill engines etc. The pressure vessel is 3″ or 75 mm diameter and 9 1/2″ or 240 mm long. The casing is 4″ or 100 mm wide, 9″ or 230 mm long and 6 1/4″ or 155 mm tall. The height over the boiler is 7 1/2″ or 190 mm, with an overall height of 14 1/2″ or 370 mm. The working pressure is 60 psi or 4 bar. The boiler is supplied with heat from twin pan burners. The boiler kit comprises a tested pressure vessel in silver soldered copper, with the casing in unpolished stainless steel. It is recommended that the casing is painted with heat proof black aerosol. The boiler can be left copper or sprayed black to match. All boiler fittings are supplied, along with the twin burners, gas pipe and gas can valve. The steam stop valve can be used with either the 4 mm or 3/16″ coned unions supplied.”

Although it does come with a boiler certificate.

Many Thanks

Best Regards

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[JasonBModerator @jasonb]

Capacity is simply working out the volume from the sizes given, the amount of water will be proportionally less than the total capacity but it gives a good indication of the sort of size boilers Stuart recommend.

That boiler in Keith’s video even though Martin calls it “small” is larger capacity than either of the suggested Stuart boilers being 5″ dia by approx 9″ long (127 x 228) and has a capacity that is THREE times that of the Pisces. He also looks to be running at 120-150rpm and with no load so steam demand will be lower than when working at higher speed and loaded by the dynamo.

[JasonBModerator @jasonb]

There is quite a bit of info on this site about the various boilers Stuarts have produced over the years including details of the 504 boiler’s circulation tubes, superheater, and suitable burners.

[BazyleParticipant @bazyle]

https://www.abebooks.co.uk/book-search/title/model-boilers-boilermaking/author/k-n-harris/

[Martin DareParticipant @martindare17777]

@JasonB

Returning to your earlier statement :-

>> The 504 has approx 60% more capacity than the Pisces and the 4000 is double the capacity.

I cannot make that true. The Clevedon Pisces is 3 x 9.5” giving a volume ~ 350cc

The Stuart 504 as referenced at @ http://stuartturnersteam.com/boilers/500boilers/500boilers.html is 3.5 x 10”  ~ 500cc.

This implies the Pisces capacity is ~70% that of the 504, or the 504 has 30% greater capacity.

@bazyle

I have that book :-). But I have only skimmed it a while back. Although I am quite capable of silver soldering a boiler, I really feel that other demands on my time should have priority. Consequently, if I can buy a boiler with a certificate and no silver soldering I will be happy to do so.

I have looked at the second hand 504’s on ebay but you can never be really sure how good they are. ]

The pisces boiler comes with two burners and a gas can adapter. I may initially use this but will probably make a propane burner out of stainless steel tubing ( I have the tubing, the regulator and a small cylinder already “in stock” 🙂  ).

I have since found out that the Pisces has 4 water tubes and a central superheater tube, all external as it is a babcock design.

For me, it seems a very capable first boiler for my needs.

Thanks to all

Best Regards

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[JasonBModerator @jasonb]

You need to look at your calculations, I suspect you forgot to multiply by Pi

Keeping it metric and assuming 1.5mm wall

Pisces 76 x 241 external

3.142 x 3.65 x 3.65 x 23.9 = 1000cc

504 89 x 254 external

3.142 x 4.30 x 4.30 x 25.1 = 1458cc

I’d just roughly done it before using external sizes but easy to see the 504 is 46% larger, has six circulation tubes again 50% more than that of the Pisces and is also supreheated.

 

[Martin DareParticipant @martindare17777]

@jasonb

Yup, forget to use pi, however that does not affect the volume ratio. Would edit post but don’t seem to be able to ..

Pisces does have a 5th superheater tube, seems a bit like 2/3rds of a 504.

Best Regards

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[JasonBModerator @jasonb]

In which case how did you come up with “or the 504 has 30% greater capacity.”

500/350 = 1.43 so 43% larger not 30%

[noel shelley]

On noel shelley Said:

Compareing boilers and engines is far from straight forward ! …

Noel is absolutely right, to the extent I don’t think the 3 boilers mentioned can be compared using the information available.   Best that can be said is they’re similar and that the biggest will probably produce more steam than that smallest.

To size a boiler professionally, the engineer needs to know:

• how much steam at a given volume, pressure and temperature the engine consumes at operating load.  So the first question is how much work does the engine need to do.  Keeping it simple, this is given in Watts, ie rate of work, or power.
• The power output needed is used with other parameters to select or design an engine of the right size.   Size is determined largely by the swept volume of the piston, but that’s too simple.   The power output of a heat engine is determined by how much energy is extracted from the hot medium (steam), as it expands in the cylinder as the piston moves away.  If the cylinder was perfectly insulated, which it isn’t, the amount of energy converted from heat to motion is proportional to the difference between  input and exhaust temperatures.  So the designer has to allow for heat losses and many frictional losses, establishing how efficient the engine is.
• Knowing how much heat is needed by the engine to deliver it’s intended power output, allows the engineer to calculate the volume, pressure and temperature of the steam needed from the boiler.
• The volume of water and how fast it needs to be heated to generate that much steam can be calculated, again with due allowance for inefficiencies.   The amount of heat required to raise steam is also work at a given rate, so it too is power (measured in watts).
• Knowing the amount of heat the boiler needs to raise steam allows the firebox and tubes to be designed. to produce it.   The firebox has to consume a fuel of given heat value at a given rate to power the boiler.  Again inefficiencies have to be allowed for, but the firebox is designed to deliver the necessary power output by burning fuel at a given rate, in Watts.

Notice that every stage is qualified by the need to take account of inefficiencies, in fact these dominate the design of reciprocating steam engines, which are generally inefficient.   Heat is wasted in the firebox unless the fuel in completely consumed, heat disappears up the chimney because the tubes don’t transfer it to the water efficiently,  heat is wasted bringing water up to boiling point, the boiler shell soaks up heat and radiates it and so do the pipework, cylinder, piston and valve gear.  And then the moving parts waste more energy  in friction and the movement of their masses.   A big well-designed steam locomotive in tip-top condition might achieve 5% efficiency but less than 3% was common.   Small model engines are likely to be less than 2% efficient.

In practice engines and boilers are sized by experience.   The manufacturer would measure the steam volume and power output of his prototype engine on a dynamometer.   Similarly, boiler makers would measure the heat value of fuel burnt needed to generate a given volume of steam, making it possible customers to match boilers to engines and know how much the system is likely to cost them.

Vital in commerce for the engineer to match engine and boiler efficiently because fuel is expensive but that rarely matters when running models, where the power output and steam requirements of the engine are unknown, and boiler efficiency doesn’t matter because not much fuel is burned.

With models it’s usual to simply buy a boiler of about the right size.   With Stuart Engines, that was established experimentally over a 100 years ago, job done!  The alternative is quite complicated, basically needing some good books on Thermodynamics and a well-equipped workshop supporting an elaborate experimental rig.  Interesting, but rarely pursued I believe.   Quite a few owners have made dynamometers and measured the power output of their engines, but not much has been done with boilers, probably because they are difficult to improve significantly.

IMLEC is very interesting, and one of the few sources of information on model loco performance from fuel to power output actually hauling real loads.

To find out which boiler is best for your engine it would be necessary to try all the alternatives, taking measurements and comparing the results.  Probably not worth the effort unless something special is planned.  Normally model engines are only required to run for a modest amount of time for demonstration purposes, and they provide plenty of interest just doing that.

Dave

 

 

[noel shelleyParticipant @noelshelley55608]

Thanks Dave ! I had thought about writing something like that, you have saved me the job. Your mention of IMLEC and 2%, that’s a good engine ! In the context of the OPs question and the parameters he has given,eg 300rpm and generator (how many watts ?) + feed pump ! I would buy the biggest boiler you can, 6″ vertical multi tube, it may prove to be a little large for this engine, but you can always turn the fire down, what you CAN’T do is get more steam out of a too smaller boiler ! Take your bore and stroke, compare with other engines of a similar size and load and see what size/type of boiler they use, stationary or Locomotive. I would use a hand pump rather than crank driven feed pump, may be with an injector. Whilst gas is quick and easy there is a very real risk of Co if used indoors, it’s much more fun to use real coal and the exhaust can be used to draw the fire ! The 3 boilers that have been mentioned will all make the engine turn, but may be not at the rate and power you want.  Good luck.  Noel

[Martin DareParticipant @martindare17777]

@jasonb >>“or the 504 has 30% greater capacity.”

I probably should have said the pisces has 30% less capacity.

@sillyoldduffer Thankyou for very interesting and informative post. I am very new to this subject so perhaps you could enlighten me on the meaning of IMLEC?

@noelshelley I only need to generate 5W or so with a dynamo (or a stepper motor in a suitable shell), possibly less as its just for some trick led lighting using light fibres plus an optional mechanical governor load. I may do away with the governor and have a model engineer with his hand on a moveable throttle. This would be controlled by sensing the speed using a pickup in the dynamo, and some electrickery ;-).

One of the snags with the Victoria is that the flywheel and its support are on different levels to the base casting. On mine its 53mm. However this is quite a boon allowing a lot of room for hidden chicanery.

The 300 rpm was just something I estimated from running on compressed air, I would think 1/2 that speed would be adequate. I will do some tests with a mock up and see what the performance performance is with various loads.

Best Regards

Many thanks

picclock

[JasonBModerator @jasonb]

The different level issue is easily solved by changing the cast outrigger bearing support to a new one that can be made from a couple of bits of aluminium and suitable shaped to look like a casting.

You can then mount the engine on a hollow wooden base which make sit easy to hide wiring, pipework and anything else you want to keep out of site. This is my Victoria

[Martin Dare]

On Martin Dare Said:

..<br class=”bbp-user-mention bbp-user-id-44290″ />@sillyoldduffer Thankyou for very interesting and informative post. I am very new to this subject so perhaps you could enlighten me on the meaning of IMLEC?

…

IMLEC is the International Model Locomotive Efficiency Competition, a more or less annual event in the UK where several model locos compete for an efficiency prize – thermal efficiency.

Great fun and not completely scientific, but you might get a decent description of the engine, an account of the run, and they measure the coal consumption (heat input), work done, and distance travelled.  From this can be calculated the Specific Coal Consumption in lbs/HP/hour and/or Thermal Efficiency.  Spreadsheet results here.  Also, an account of each was published in Model Engineer magazine.

Perhaps the most striking feature of the competition is how inefficient model locomotives are, and that the reasons some do better than others isn’t obvious.   The 2022 results:

Best engine achieved an efficiency of 1.804%, whilst the least was 0.153% efficient – a range of 10 to 1!   Reasons not necessarily the engine is inferior: they include things like greasy rails, heavy handed drivers, fire too small or over-coaled, flanges grinding, valve timing wrong, mechanics slipping out-of-order, load larger or smaller than the engine’s sweet-spot, poor coal,  etc etc etc.   I think small defects  are amplified in small engines compared with big ones:  scale matters!

As far as I know, no-one has ever done a fully controlled scientific comparison or a completely modern redesign; for example most CAD packages can do thermal and other mechanical analyses, which might allow a modern loco to achieve peak efficiency by optimising everything.  Hard work though, and the law of diminishing returns applies.   Improving efficiency becomes progressively more difficult.

Dave

 

 

 

 

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