Model Boat Mayhem - Forum

Please login or register.

Login with username, password and session length.
Pages: [1]   Go Down

Author Topic: Too much superheat?  (Read 942 times)

mrsgoggins

  • Full Mayhemer
  • *****
  • Offline Offline
  • Posts: 183
  • Model Boat Mayhem Forum is the Best!
  • Location: Oldham
Too much superheat?
« on: July 29, 2017, 04:46:16 PM »

Thought I might share the following, for interest really.

I have just stripped down the steam plant on my picket boat to attend to a few niggles including blistered paint and oxidised steam delivery piping.
the boiler is a 31/2" return flue of my own design and build, having a feed water heater coil in the smokebox and a steam drier/superheater in the combustion chamber. A picture of the latter is attached and shows heavy oxidation of the copper superheater coil. The combustion chamber temperature will be high as there are no cross tubes in the main flue.
Normal operating pressure is 60 to 70 psi which is maintained during sailing and the 3/8" x 7/16" twin slide valve engine runs well despite blistered paint. The other picture shows one of the cylinder covers with significant bluing of the internal face. Valve chests and valves show similar colouring.
I suspect that the high temperatures occur only at low steam flows but I am remaking the superheater coil to reduce the length by about 50% and move it away from the blow torch effect of the main flue.
Logged
Chasing perfection but not running fast enough!

rhavrane

  • Full Mayhemer
  • *****
  • Offline Offline
  • Posts: 268
  • Steam passionate collector
  • Location: Saint-Mandť, Val-de-Marne, France
Re: Too much superheat?
« Reply #1 on: July 29, 2017, 05:38:43 PM »

Bonjour,
Your topic is very interesting because it raises a question "wet" or "super heet / dry" steam for our little machines.
Personally, as my boats are often too fast, I like using them at 2/3 bars (30/5 psi) with a wet steam to save autonomy and have lubrication even if there is no more oil in the lubricator after a while.
An old "knowing man" had told me that I even could use no oil as soon as steam was wet enough because there is not much effort at 2/3 bars.
My other concern would be that you can have flakes in your copper pipe when heated empty, not good for the plant.
I hope forum members will share their experience on this topic because, as often, we can find several answers to a question.
Logged
RaphaŽl
RaphaŽlopoulos Steam Lines UnLimited
Membre du Modele Club de Paris http://mycparis.fr/
Ma chaÓne YouTube:  http://www.youtube.com/user/rhavrane
Mes albums : https://picasaweb.google.com/104408627118165995713/

mrsgoggins

  • Full Mayhemer
  • *****
  • Offline Offline
  • Posts: 183
  • Model Boat Mayhem Forum is the Best!
  • Location: Oldham
Re: Too much superheat?
« Reply #2 on: July 29, 2017, 06:00:44 PM »

Hi rhavrane,
Thanks for your comments. There is no evidence of copper oxide reaching the engine but yes, it is a risk.
I saw superheat as a way of avoiding "lumps" of water being thrown out of the funnel and making a mess of my model.


Keith
Logged
Chasing perfection but not running fast enough!

steamboatmodel

  • Full Mayhemer
  • *****
  • Offline Offline
  • Posts: 236
  • Location: Toronto, Canada
Re: Too much superheat?
« Reply #3 on: July 29, 2017, 11:56:08 PM »


Hi Keith,
Most of our size engine are not designed to use real superheat (exceptions are those into flash steam). You should defiantly shorten and reposition you coil. What most of the modelers referee to as super heaters are really only driers, which is what we need in our models.
Regards,
Gerald.
Logged
Be wary of strong drink. It can make you shoot at tax collectors--and miss. Lazarus Long

hammer

  • Full Mayhemer
  • *****
  • Offline Offline
  • Posts: 426
  • Location: devon england
Re: Too much superheat?
« Reply #4 on: August 02, 2017, 09:59:17 AM »

That looks a great boiler. You obviously know what you are doing. But wouldn't a separator tank stop the globules of water going up the chimney? 
Logged

steamboatmodel

  • Full Mayhemer
  • *****
  • Offline Offline
  • Posts: 236
  • Location: Toronto, Canada
Re: Too much superheat?
« Reply #5 on: August 02, 2017, 04:19:33 PM »


That looks a great boiler. You obviously know what you are doing. But wouldn't a separator tank stop the globules of water going up the chimney?
That is why you use one, too stop the water and oil globules from going up the stack and hopefully allow only the steam to go up.
Gerald
Logged
Be wary of strong drink. It can make you shoot at tax collectors--and miss. Lazarus Long

mrsgoggins

  • Full Mayhemer
  • *****
  • Offline Offline
  • Posts: 183
  • Model Boat Mayhem Forum is the Best!
  • Location: Oldham
Re: Too much superheat?
« Reply #6 on: August 02, 2017, 05:00:44 PM »

Superheat was only part of the plan to avoid lumpy steam, other parts being a cyclone and a separate drains tank, all insulated to minimise condensation. It all worked fairly well so we shall see what happens now that I have reduced the length of the superheater coil by

Thank for the comments.

Keith

Logged
Chasing perfection but not running fast enough!

xrad

  • Full Mayhemer
  • *****
  • Offline Offline
  • Posts: 453
  • Keeper of the Sun Dried Tomato
  • Location: Ohio USA
Re: Too much superheat?
« Reply #7 on: August 22, 2017, 01:38:30 PM »

Your boiler /coil set-up looks fine. Start with air/gas mix. make it a bit richer or decrease flame front, this will lower temps.  looks like burner is running too hot.
Logged

mrsgoggins

  • Full Mayhemer
  • *****
  • Offline Offline
  • Posts: 183
  • Model Boat Mayhem Forum is the Best!
  • Location: Oldham
Re: Too much superheat?
« Reply #8 on: August 22, 2017, 06:06:41 PM »

Thanks xrad. I've shortened the superheater and run the steam plant for about an hour with no sign of "bluing" of the pipework so all should be well.
Logged
Chasing perfection but not running fast enough!

xrad

  • Full Mayhemer
  • *****
  • Offline Offline
  • Posts: 453
  • Keeper of the Sun Dried Tomato
  • Location: Ohio USA
Re: Too much superheat?
« Reply #9 on: August 23, 2017, 02:06:13 PM »

Your welcome.  Often in small locomotive boilers (example: Tich), the 'superheater' coil actually runs down into the main firetube to a depth of about 50%, does a 'U'-turn and then goes off to the cylinders.  However, these older designs were mostly made for coal, of which heat transfer/velocity is less than butane /propane mixes.  Anyway, you solved it!  That's what matters.
Logged

KNO3

  • Full Mayhemer
  • *****
  • Offline Offline
  • Posts: 1,140
  • Location: Vienna
Re: Too much superheat?
« Reply #10 on: August 26, 2017, 08:11:15 AM »

I have also found out that too much superheat isn't good for many model steam engines. For several reasons:
-many use orings which could be damaged,
-soft soldered connections can melt,
-the high temperature requires a very good lubrication and could stop or slow down a hydrostatic lubricator, which needs to be able to cool and is the type most often used in model steam plants.
I had some soft soldered pipe connections melt in my steam plant due to a long superheater (had 2 long coils). Then I resorted to shorten it to a U-shape and the problem was solved.
Logged

steamboatmodel

  • Full Mayhemer
  • *****
  • Offline Offline
  • Posts: 236
  • Location: Toronto, Canada
Re: Too much superheat?
« Reply #11 on: August 26, 2017, 03:12:39 PM »


What we need what most people call a super heater to do is not superheat the steam, but just dry it. the exception to this is those who are running flash steam, usually round the pole speed record . 
Regards,
Gerald.
Logged
Be wary of strong drink. It can make you shoot at tax collectors--and miss. Lazarus Long

xrad

  • Full Mayhemer
  • *****
  • Offline Offline
  • Posts: 453
  • Keeper of the Sun Dried Tomato
  • Location: Ohio USA
Re: Too much superheat?
« Reply #12 on: August 31, 2017, 01:31:10 AM »

KNO3, not to digress(or argue), but soft solder in not recommend for any steam fittings, especially those 'under' pressure.  even 'soft' solder w/600-700 degree melt point.  ~1100 degree silver solder is what most builders use.   There is always the argument that people have used soft solder without issue...... My rule is if it's too hot to touch or is under pressure, it gets silver soldered in my steam builds.
Logged

KNO3

  • Full Mayhemer
  • *****
  • Offline Offline
  • Posts: 1,140
  • Location: Vienna
Re: Too much superheat?
« Reply #13 on: September 07, 2017, 07:31:46 AM »

Recommended or not, there are tons of toy steam engines soft soldered by the manufacturer and sold with all legal tests, such as Wilesco. It was a Wilesco marine boiler where I had installed a superheater coil in the flue. That's how I found out how much it can raise the steam temperature.
Logged
Pages: [1]   Go Up