The Steamboating Forum

Hi Steamboating Friends

SBA member John Emmett and I have got together and created a website devoted to mono-tube steam generators. Why you might ask? Well the technology is light, inexpensive to build and electronic controllers are widely avaiable for little money. Despite all that I can only find five boats in the SBA Members' fleet that use mono-tubes. Thus we hope to spread the word and encourgae others to use this technology.

However, the aim is not for John and I to create stuff and push it to you. We would like to think that those of you who have views and expertise would be willing to share that by writing. The advantage of a website over a paper magazine is that you can be more wordy if you wish, clearly illlustrate your data and so on. There is no contraint of an A5 magazine.

If anyone is interested we are to be found at https://mono-tube.org.uk/.

Regards

Pete

That link should be https://mono-tube.org.uk/

Hi Bart

Thanks for that. Posted late last night and did not check. Now correct.

Best wishes

Pete

Hi Pete,

Sounds wonderful! Will Lamont boilers and the like be allowed on the site as fellow travellers? I have a hot water pressure washer coil I had made with the intention of running my 20' boat with it. If I every have a minute to make some progress on the d**n thing I'd love to share it with the web site.

Cheers!
Scott

Hi Scott

That sounds like a good idea. Why not submit some preliminary material and photos explaining what you think could be done with it. We could then add to that with what you actually do when time permits. You may also get a series of good ideas from other folks to make the task easier than you had expected. If you like, float the idea here and I can copy it over and expand it somewhat for the site.

Best wishes

Pete

On my list of "things to try" is a hot pressure washer coil, fed by a variable speed 12V DC hypro pump, and controlled like the Herreshoff coil boilers in terms of a maintaining the water level in a well insulated steam separator drum. If the steam got too dry/hot, the water level drops as it evaporates in the superheated steam; the reverse would be true if the steam got too wet. A thermodynamic steam trap could take care of the overflow from the steam separator on startup; this could also be used to quell steam production.

As I'm sure people are aware, controlling monotube boilers is tricky. These sorts of experiments are best carried out on a test bench .

- Bart

Hi Bart and Friends

That sounds an interesting idea. If one's budget is a bit constrained an alternative to the Hypro brand are Chinese cordless pressure washer pumps that are available from AliExpress - (https://www.mono-tube.org.uk/index.php/ ... cilliaries)

I would be interested to see a diagram of your idea as I have not fully understood it, being a paper pusher rather than and engineer.

Best wishes

Pete

Hi Pete and Bart,

I am also considering a similar overfeed/underfeed with accumulator plan. I was thinking of a more analog system with a double-acting feed pump where one side of the feed pump would always feed the coil, but the other side would have a bypass controlled by a stanley type or similar water level control. That way, the coil gets a continuous feed, and when the water level drops, the feed would double as the bypass closed.

Unlike your 12V idea, I'm not sure my plan would be flexible enough, as it would only have a 2x difference between minimum and maximum feeds.

The other possibility I was batting around was a procon vane pump (like the ones used on restaurant soda fountains and espresso machines) as a circulating pump, and then just a conventional feed pump to supply the whole thing. The feed pump would be plumbed to the front end of the coil, so that it could function as an overfeed flash boiler to at least limp home if the recirculating pump failed.

I'll share pictures of progress as soon as I have any progress to picture!

Cheers,
Scott

Isn't the biggest draw of a monotube boiler the fact that conventionally it contains only a small amount of superheated water at any particular moment, and so the damage due to a rupture is less likely to be catastrophic? Would a water level/steam separator drum remove that advantage?

Hi Elver

Thanks for the question. I will offer you my incomplete understanding so If I am not correct, hopefully some our better informed readers will chip in.

We start with a small diameter tube which if competely filled with water would not contain very much. The tube is heated at the same time that water is pumped into it. Thus at the inlet end we have coolish water. Somewhere along the middle, or possibly later, the water changes from being water to being wet steam. This gets hotter in the last stage of the tube and thus emerges into the water separator as a mixture of steam and water droplets but mostly steam. Some designs pick up that steam and run it through a superheater to ensure that it is dry. The water droplets are accumulated in the separator until the operator decides to drain them down. (See the diagram for Sirius 6 which is http://www.mono-tube.org.uk/index.php/h ... e-sirius-6) You will note from the photo that the whole separator is about the size of a small mug. This is a description of the 'over-fed' design where more water is pumped in than is needed to create steam. This is probably the safest design as the steam never reaches very high temperatures provided the feed water flow continues. So, in terms of the total water content, the water separator is not a large element and the water is cooling but I agree that it is still under pressure. Under this configuration the actual amount of water is significantly less than that found in water tube and fire tube boilers.

Wally Mounster in Australia designed a built a mono-tube boiler with a very long tube which meant that the steam coming out at the far end was around 500 C. This was his design temperature as he ran uniflow poppet valve engines which could cope with that sort of temperature. Those of us who are not high quality engineers like Wally are, I suspect, much happier to run with wet steam and thus not needing to worry about cylinder lubrication of our slide valve engines.

Regards

Pete