Author Topic: Flash Steam Engine and Steam Coil  (Read 26512 times)

Offline gary.a.ayres

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Re: Flash Steam Engine and Steam Coil
« Reply #75 on: September 04, 2019, 02:13:30 PM »
George - Stunning work is in evidence on this thread.

As a steam neophyte I have a very long way to go, but flash steam does interest me I admit. I have the Westbury book, and have the other, newer book on order.

It strikes me that your thread here is another such rare and valuable ressource on the subject, and it will be most helpful to me when I start tinkering with this aspect of things...

gary

Offline K.B.C

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Re: Flash Steam Engine and Steam Coil
« Reply #76 on: September 04, 2019, 02:38:46 PM »
Hi Gary,
Like you when  I started I knew nothing about Flashsteasm and as there was nobody else in Scotland interested in the subject I started from scratch.
As you may know the flash steam enthusiasts are all down south of Hadrian's wall and are all racing round the pole at ridiculous speeds, however I didn't want to be involved in long trips South or getting kitted up with waders and helpers, I wanted to be able to sale from the pond side  and to control with rudder and a stop valve.
The 2- most informative books are Westbury's but the best is "Experimental Flashsteam by Benson and Rayman"
If you look up on the Net another source of info is "On the Wire `" so have a look there. I have a copy of an article by Bob Kirtley who held the world record of 120 m.p.h. at one time and he published the article and I can mail it to you for reference.
Now I don't know all the answers but when you get started if I can help I would be please to do so.

George.
Your never too old to learn.

Offline gary.a.ayres

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Re: Flash Steam Engine and Steam Coil
« Reply #77 on: September 04, 2019, 04:42:50 PM »
Many thanks George.

I live well South of Hadrian's Wall  but am actually from just North of it (Dumfries). I lived in your city for seven years too, back in the 80's.

Flash steam seems like a very arcane world to me, with little bits of knowledge hidden away in secret corners of the world (and internet).

I tend to have far too many projects on the go, and some of them sit untouched for years while others get full attention, so it's very possible that I will start experimenting with flash steam in the foreseeable future and then go quiet on the subject as I focus on something else, like a mill engine or whatever. Too many ideas, not enough spare time.

However, I have just bought an antique brass paraffin/petrol blowlamp on ebay to see if I can press it into service as a burner (I could have bought a new gas one but an old shiny brass one complete with embossed lettering on the tank seems like more fun). I have the Westbury book and the Benson and Rayman one is in the post to me. So let's see...

Your offer of advice is much appreciated. I won't hound you but I do in fact have a couple of questions for you at this stage if you don't mind:

- Is the vintage liquid fuelled blowtorch likely to be any good as a burner (it was only 16 quid...)? Westbury says a single flame isn't optimal but that people do use it, and I'm wondering if it might be adapted or augmented in some way.

- What is your view on copper vs stainless steel tubing for the boiler?

- Is there any kind of pump that can be pressurised by hand that is powerful enough to push water through a clack valve into the boiler while it is running an engine? I'm wondering about a primus stove type of pump but have no idea if that would generate anything like enough pressure. Or maybe some kind of hydraulic water pump combined with a pressure vessel to avoid having to pump non-stop... I am not averse to things electrical but I prefer to avoid them in steam applications if I can. I'm also aware that the pump can be driven by the engine once it gets going but that's quite far down the line for me. Any plant I make will be stationary, not on a boat, so it wouldn't matter if I had to hand pump it. I have a feeling that Westbury goes into this to some extent but I haven't read that far yet.

Your thoughts on these matters would be appreciated. No rush, and feel free to just tell me to go and read the books or this thread more attentively if you like!   :)

Best wishes,

gary

Offline gary.a.ayres

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Re: Flash Steam Engine and Steam Coil
« Reply #78 on: September 04, 2019, 05:14:28 PM »
*PS - I just looked ahead in the Wesbury book and on p 66 and p 67 he appears to answer my question about a hand-pumped pressurised feedwater system. I'd still be interested in your thoughts, of course, but no rush.

gary

Offline Old School

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Re: Flash Steam Engine and Steam Coil
« Reply #79 on: September 04, 2019, 07:54:45 PM »
The hand pump is only for priming at the start, as soon as the engine is running the pump on the engine delivers water at a set rate to keep the engine running.

I used to run tethered flash steam hydros but the light weight class 8lbs dry weight the engine and boiler etc are a smaller version of Bob Kirtleys steam plant. I broke Frank Juttons B class record a lwhile ago and I have his B class boat TNT.
Forget the Westbury flash steam book it is dated you need a copy of Experimental Flash Steam Benson and Rayman.

You can use either copper or stainless steel for boilers for the fast flash steamers stainless has been used in all the modern hydroplanes.
Alan Raymsn also wrote a booklet "High speed marine steam engine" based on a Stuart Turner 10v cylinder casting it a good source of info on slower flash steam plants I have copper flash steam boiler in a straight runner that gets up and planes with Raymsns engine.

Offline gary.a.ayres

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Re: Flash Steam Engine and Steam Coil
« Reply #80 on: September 04, 2019, 09:25:57 PM »
Thanks for the advice, Old School.

Funnily enough I just watched a youtube video on Bob Kirtley's plant, and very educational it was too.

I ordered the Benson and Rayman book yesterday - looking forward to it.

Re the hand pump - I was wondering about a hand-pumped  pressure vessel that would feed the boiler over a period of time, rather than a simple hand pump, in lieu of an engine-driven pump. Westbury seems to be saying that's an option, though I admit I need to look more closely...

Offline MJM460

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Re: Flash Steam Engine and Steam Coil
« Reply #81 on: September 05, 2019, 12:02:24 PM »
Hi Gary, Flash steam is indeed an interesting area for your experiments.  I have had the Bensen and Rayman book on my shelves for so long I can no longer remember where I bought it, but it only mentions first published in 1973 in the flyleaf.  I highly recommend it to you.

I can help with a few principals but I will leave it to those more experienced with the practicalities to talk about the practical issues of which I am sure there are many.

So a few principals.  You can definitely make a hand pumped flash steam unit for your stationary engine, and you will find that blowlamp quite satisfactory.  Remember Bensen and Rayman were into really high performance, but in their book, they also cover a more moderate plant for a non-racing model.

Think of a flash boiler as a boiler with a really large heat transfer area in the form of a single long water tube, and a very small water capacity.  You pump in water at one end and it comes out as steam the other.  The division between the water boiling section and the superheater section is not clear, and indeed varies with varying operating adjustments. 

Now, that boiler configuration means that you need a more steady flow water input than a standard boiler; an initial fill then operate until fuel runs out, preferably before water runs out, is not practical.  You have to maintain the water injection while the burner and engine run.

There was an excellent series of articles in ME many years ago on flash steam for a railway locomotive.  Someone with a more organised collection than I might be able to find the reference for you.  The author actually included a small pressure tank which he half filled with water to even out the flow, and a similar arrangement would allow you to hand pump the system, though you would still have to be pretty consistent with the pumping.  The tank goes on the inlet side of the coiled tube.

The length of the tube means there is quite a pressure drop along the tube, so the water pressure required is much higher than what the engine sees.  However, a lightly loaded engine does not need much pressure at the engine end, so it should not be too high at the inlet.

Remember, when water boils, itís volume expands about 1000 times.  You can get the exact figure from the steam tables if you make an estimate of the outlet pressure and temperature, but you donít have to pump a big volume of water.  And it takes much less work to pump water than it does to compress an equal mass of steam.  Itís not like running your steam engine on air with a bike pump.

So your first question, about pumping against the pressure.

Letís assume you need 50 psi at the inlet to the tube, like your present boiler.  If your engine has a piston area of one square inch it will be 1.13 sq. in. diameter, and the force on the piston will be 50 lbf.  Possible to pump with a similar diameter piston, but very hard work.  But you donít need to have a similar diameter piston on your water pump.  If you have say 1/4 inch diameter water pump piston, the area is only 0.05 sq. in. and the force required is only 50 x 0.05 = 2.5 lbf.  Easy!  And you donít have to keep up with the engine speed, you only need 1/1000 of the steam volume.  So even allowing for the smaller volume per stroke, you should be able to keep up with a moderate engine speed.  But you will soon work out why the normal is an engine driven pump.  So building that is part of the challenge.  I suspect that bought gears is the way to go for both you and I.

The Bensen and Rayman talk about the use of SS tubes and the length of tube required, so I will leave you to read the detail, but their early experiments were all with copper tube.  Their investigation of SS tubes was because they were chasing extremely high temperatures and pressures in their quest for performance.  Again a moderate plant should be OK with copper.  I will be interested to hear what those who have run racing hydroplanes have experienced.

I suggest one of the practical issues to come to terms with is how to start the plant.  Going from atmospheric pressure and temperature to running continuously involves a sudden pressure rise once the water starts boiling, and you donít want to push too much water direct to the engine if boiling starts part way along your tube.  Again, this is an area I am keen to hear about from those who have the practical experience.

Once the plant is running, the back pressure from the steam will compress the air above the water in that tank I mentioned.  The water level will fall as the steam is consumed by the engine, and you need to get pumping to keep the level in range.  Obviously a level glass is necessary.  And it is a pressure vessel so needs to be designed as such, and equipped with a safety valve.  If you pump intermittently, the pressure and hence engine speed, will vary, but I assume this will be acceptable for you, and a larger vessel than might be practical for a locomotive or boat will help with the hand pumping.  After a few runs you will have a better idea of how much air to leave in the tank before you first tighten the plug.  As the pressure rises, you have to pump more water to maintain the level, and do more pumping to replace that consumed.

Overall pressure and speed control is a heat balance.  The burner produces heat which will partly go up the chimney, and partly evaporate the water.  If the engine does not pass all that steam, the pressure will rise and the engine speed will increase.  Be ready to pull the burner out!  It needs to be easy to remove until you have some running experience.  And it is a good idea to start with a smaller or gentler burner.  Even start with your silver soldering burners for additional control until you feel comfortable with the system.  Some of those Bensen and Rayman used must have been frightening to be near.  As part of their optimisation they used figure 8 coils with separate burners in each of the loops, just to get in more heat.  Anything in the quest for more speed.  Needless to say their engines were pretty sophisticated as well. 

I am sure you will have more questions, but that should give you some of the basic theory as a start.  A great project to be thinking about.  I am not sure where you will decide to go from here, if you decide to do some experimenting, you may like to start a new thread of your own rather than resurrecting this one.  But really good to see some of those with practical experience in the area also coming in, and an interesting topic revived.   I suspect you will have quite a few following if you decide to carry it further.

MJM460


The more I learn, the more I find that I still have to learn!

Offline gary.a.ayres

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Re: Flash Steam Engine and Steam Coil
« Reply #82 on: September 05, 2019, 01:21:53 PM »
Wow... what an amazing response, MJM460!

A combination of theoretical treatise and practical manual in a single post. It pretty much answers all my questions at this stage, and gives me a great deal to take forward if I decide to pursue this past buying the blowlamp on ebay.  :)

Assuming I do, I will surely start a new thread on the subject.

Only one part of your post had me a bit puzzled - it's where you say   

'Once the plant is running, the back pressure from the steam will compress the air above the water in that tank I mentioned'

I had assumed that there would be a check valve between the water source and the reservoir. Am I to understand that this isn't needed (i.e. that the system will balance itself as long as the reservoir is a proper pressure vessel) and that a tap or globe valve of some kind will suffice?

Offline MJM460

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Re: Flash Steam Engine and Steam Coil
« Reply #83 on: September 06, 2019, 12:10:55 PM »
Hi Gary, thank you.  I have tried to point to some of the practical issues, but I emphasise that I donít have some of the important answers, particularly on the best way to start the system.  This is where it is especially important to get the benefit of practical experience.  Do you start heating the tube, then start pumping in water, or is it better to pump in some water, then light the burner?  I am still hoping that Old School and KBC might share some there experience in this and other areas of the flash steam plant.  They are the experts.

Sorry to have confused you with that sentence.  I see the accumulator tank which is pressurised with the system in operation as separate from an atmospheric pressure reservoir which would be on the inlet side of the pump.  So two vessels in the system as I remember it from the articles.  It looked like a well thought out system.  A piston pump includes a check valve as part of its basic function so pressure should not go back to the reservoir.  Sometimes in this sort of situation, two check valves in series are recommended.  I have not assumed a check valve or shut off valve after the accumulator tank, but it may be a good idea, or even necessary in practice.  That would require a slightly different start up procedure.

When the system is at atmospheric temperature and pressure, the pressure is the same all the way through.  I think that if you start pumping in some water, if the engine is in a position where the inlet valve is not open, or you hold the flywheel, you will start to compress the air trapped in the accumulator and in the long coiled tube.  When you get to about 15 psig, the volume of the air will be reduced by approximately half.  If you then light the burner, the pressure will increase throughout, forcing some of the water back from the tube into the vessel, so the pressure stays equal everywhere.  The engine will probably run on this pressure, but itís all about how you juggle the water input and heat input, to get it running smoothly without filling the engine with water or getting excessive pressure.  So you see the problems.  I am not sure whether the water starts boiling very slowly, or quickly flashes to steam over a length of the tube.  The latter will result in severe pressure spikes, and is best avoided.  Tapping into existing knowledge on how to deal with these problems is a better idea than trying it out without some knowledge of what might happen.  Perhaps I am over thinking it, but of course I am used to working out these procedures for full size systems, where the dangers are real.  It tends to make me cautious.  Startup is always more tricky than steady running.

Once the system is running, there will be a pressure loss along the tube so the pressure at the pump and accumulator will be somewhat higher than the pressure at the engine inlet, and you will have to pump to maintain a level in the accumulator to replace the water that is turned to steam and passes through the engine.

I hope that makes it clearer.

MJM460
The more I learn, the more I find that I still have to learn!

Offline Old School

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Re: Flash Steam Engine and Steam Coil
« Reply #84 on: September 06, 2019, 08:07:58 PM »
I have no experience of using a reservoir my plant the water was pumped directly into the coil. On the hydroplanes the boiler was heated to dull read by the 3 blow lamps, the the water was pumped in steam was generated instantly the pumped would almost look up, the the engine was started with a pull cord.

Somewhere on the internet is a simple flash steam plant for an oscillating steam engine using a small coil a pencil type gas blow lamp and a plastic pop bottle with water in it pressurised with air. My brother has built one of these and it works. Imwill get the details when I get back home racing tether cars in Poland this weekend.

Offline Admiral_dk

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Re: Flash Steam Engine and Steam Coil
« Reply #85 on: September 06, 2019, 09:58:43 PM »
Quote
I will get the details when I get back home racing tether cars in Poland this weekend.

Although I do find the original subject here interesting .... any chance of some pictures (perhaps in a separate thread) ?

Best wishes

Per

Offline gary.a.ayres

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Re: Flash Steam Engine and Steam Coil
« Reply #86 on: September 06, 2019, 11:51:29 PM »
Guys -

your input is greatly appreciated. Lots of knowledgeable people offering friendly advice is the truly great thing about this forum.

However, I do not wish to dilute George's impressive thread any further with my rookie questions, so what I propose is this: when the antique blowlamp arrives (hopefully early next week) I shall - as a couple of you have suggested -   kick off a new thread with a photo of it (and maybe a couple of other pics too)  along with a post in which I will try to respond to the good stuff you have posted above.

Hope that makes sense, and look forward to catching up with you in a few days.

Thank you!

 :ThumbsUp: :ThumbsUp: :ThumbsUp:

gary

Offline MJM460

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Re: Flash Steam Engine and Steam Coil
« Reply #87 on: September 07, 2019, 09:56:54 PM »
Hi Gary, that sounds like a good plan.  I look forward to your new thread appearing so the discussion can continue.

MJM460

The more I learn, the more I find that I still have to learn!

Offline gary.a.ayres

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Re: Flash Steam Engine and Steam Coil
« Reply #88 on: September 07, 2019, 11:02:03 PM »
 :ThumbsUp: :ThumbsUp: :ThumbsUp: :ThumbsUp:

Offline gary.a.ayres

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Re: Flash Steam Engine and Steam Coil
« Reply #89 on: September 08, 2019, 10:55:21 AM »
Well, I didn't wait for the blowlamp! New thread now underway...

http://www.modelenginemaker.com/index.php?topic=9294.new#new

Hopefully see you over there.

Thank you for your comments up to this point.

George - thanks for allowing me to briefly piggyback on your topic.

gary