Blast pipe to chimney hight.

[Phil Sutton]

Does anyone out there know if there is an optimum distance between the top of the blast pipe and the bottom of the chimney,or is it a case of trial and error ?

Thanks in advance,

Phil.

[chameleonrob]

home.ca.inter.net/~mguy/A%20Lempor%20Exhaust.htm
www.michaelguy.ca/lempor%20update%202006/Lempor%202006%20update%20page.htm
www.alanstepney.info/page19.html

As I understand it the best place for the blast pipe is level with the bottom of the petticoat pipe.

[greasemonkey]

Hi Phil
There was a good article written in model engineer about drafting. The writter did some experiments on his sppedy and got quite an improvement. I cant tell you the article info till I get home. Greenly recomended usign the 3:1 and 6:1 cones as described on Alans site.
Andy

[chameleonrob]

would that be Jos Koopmans? follow the from the bottom of alan's page that I linked above.

anouther link.
www.trainweb.org/tusp/exhaust.html

[greasemonkey]

I dont think so . The test were done on a speedy.

Andy

[alanstepney]

That might have been the work of the late Prof. Bill Hall.
Bill did lots of research on various aspects of steam engines, including draughting (in conjunction with Jos Koopmans) and various other aspects of engines.

Incidentally, Jos has earned a PhD for his work on draughting. Quite an achievement.

[waggy]

A friend of mine built a LUCKY 7 which has a stovepipe chimney approx six inches long, tapering outwards towards the top. He was a great experimentor and tried various ways of improving draughting and therefore steam output. He settled on a very long blast nozzle and no petticoat pipe as such.
The chimney base protruded into the smokebox by half an inch. The blast nozzle stopped one inch below the extension. I think the nozzle diameter was five sixteenths, not sure. The bore of the nozzle was taper bored, the base diameter of the bore approx one inch. This arrangement was deemed to "tune" the blast jet into a perfect diverging cone which matched the chimney taper.
Whether this was good luck or good judgement, I don't know. I never saw the engine but have heard from those who did that it steamed very well.

I would also say that air flow through the fire and tubes is also as equally important as good front end blast arrangements.
If the air can't get in, the gasses won't flow!

Waggy.

[chameleonrob]

I suppose someone should ask what Phil needs the info for.
know I'm answering a more general drafting queston than was asked but the whole of the front end needs to be considered as a unit. According to Porta the chimney should be tapered at 12o with the convergance point in the blast nozzle, when the chimney narrows down to the choke diamiter the should be a short parallel section dwon the the level of the blats pipe, the chimney should be as tall as possible. the only problem is trying to fit all this into what ever prototype you building.

rob

[ivanj]

I have just written an article for our club which I can email to you if you like It does, I hope clear up a lot of mystery about all this. You can calculate most of the values and it does make a difference - I have a Rob Roy that actually goes well now!!

[e-mail]

[steamjohn248]

Hello Ivan

We are just finishing off a long ago started Hercules and have got to the smokebox end i.e. peticoat and blast nozzle, we can do it to the drawings but we are always keen to tweak things if anyone has any inside knowledge they are willing to share.
My E is, [e-mail].

Many thanks

John

[Phil Sutton]

Hi.Thanks to one and all for your input.Winsons exhaust has more bends in it than a dogs hind leg,and I thought I could make some thing better.Also there was no petticoat pipe made for the 1400,so I bought a Didcot casting from Reeves.I needed to know the optimum distance so I knew how much room I had to play with.
A member of the old forum sent me one of his designs,but I intend to improve that if I can.Any other info or help will be gratefully recieved.
Thanks once more

Phil

[ivanj]

Steamjohn, Couldn't get your email to work - send me a link and will send you a copy of my stuff

[mott]

Phil, You ought to read Ivan's article on draughting the Rob Roy. It is applicable to the Winson14XX and will give you the formula for setting the position of the petticoat pipe, blast nozzle etc.(diam and height).Mott