If you register, you can do a lot more. And become an active part of our growing community. You'll have access to hidden forums, and enjoy the ability of replying and starting conversations.

P2 Locomotive Company and related matters

Discussion in 'Steam Traction' started by class8mikado, Sep 13, 2013.

  1. Smokestack Lightning

    Smokestack Lightning Member

    Joined:
    Oct 14, 2013
    Messages:
    262
    Likes Received:
    91
    Gender:
    Male

    My knowledge and experience of steam locomotives is negligible compared to others on here, so these are genuine questions:
    It says on the website that "the internal design is slightly different to No. 2001's boiler, the precedent was set by No. 2006 Wolf of Badenoch which had a boiler with a firebox combustion chamber". What is a firebox combustion chamber and how does that differ from the previous five, and did it cure any steaming problems? As pointed out above Tornado doesn't seem to suffer such problems.

    Again as pointed out, 2007 will probably never be permitted to exceed 75mph, so why worry about its high speed capabilities?

    As to the valve gear, does the projected cost of £5m at least partly represent the trust budgeting for some development work being needed? It seems a big hike from Tornado even allowing for some inflation and an extra set of driving wheels.
     
  2. m&gn50

    m&gn50 New Member

    Joined:
    Mar 17, 2009
    Messages:
    136
    Likes Received:
    17
    It's the Franklinstein thread now. Everyone had their own generic 'rotary cam poppet valve gear' to save the pounds.
    Lets see it in proper Donnie terms of don't fix wot ain't broke.
    If Caprotti won't go, has anyone really explored the Lenz as it wor all made by the same people, and Bulleid explored and compared both sets in service before plummeting for t' latter, it's really the excess wear that wor a problem which could surely be put right wit' modern(or LMS standard!) materials/ceramics and regular planned maintenance ;-) then everyone's bl+++y happy(?). The Beardmore-Caprotti had a different design for inside cylinders, would this go(sorry for not even been able to explore this answer, its for those clever people?
     
  3. Sheff

    Sheff Resident of Nat Pres

    Joined:
    Apr 21, 2006
    Messages:
    7,568
    Likes Received:
    2,345
    Gender:
    Male
    Occupation:
    Retired Engineer & Heritage Volunteer
    Location:
    N Warks
    Heritage Railway Volunteer:
    Yes I am an active volunteer
    A combustion chamber is an extension of the firebox into the boiler barrel and was a feature of most successful large boilers towards the end of steam. It provides a number of benefits i) it does what it says - increases the volume available for the volatiles to combust in (ie gives extra time for the gases to mix with the secondary air)- so avoiding losses typically seen as smoke; ii) it allows for a shorter tube length, which gives both a lower resistance to gas flow, so improving draught on the fire bed, and also reduces the superheat loss on the final leg of the element (over-long tubes can cool the flue gases to the extent that they actually cool the superheated steam in the elements). Generally a tube length of 17ft was found to be optimal, as opposed to say 19ft on some locos.

    In the diagram below, the combustion chamber is the area between the base of the brick arch and the tube plate.

    http://www.trainweb.org/tusp/pics/firebox1.gif

    Hope that helps.
     
    Jamessquared likes this.
  4. Martin Perry

    Martin Perry Nat Pres stalwart Staff Member Moderator Friend

    Joined:
    Apr 15, 2006
    Messages:
    16,510
    Likes Received:
    7,753
    Location:
    1012 / 60158
    Heritage Railway Volunteer:
    Yes I am an active volunteer
    http://en.wikipedia.org/wiki/Firebox_(steam_engine)#Combustion_chamber

    Basically the rear tube plate was situated further forward to extend the front of the firebox and give additional space for the gases released from the coal to burn.
     
  5. Sheff

    Sheff Resident of Nat Pres

    Joined:
    Apr 21, 2006
    Messages:
    7,568
    Likes Received:
    2,345
    Gender:
    Male
    Occupation:
    Retired Engineer & Heritage Volunteer
    Location:
    N Warks
    Heritage Railway Volunteer:
    Yes I am an active volunteer
  6. class8mikado

    class8mikado Part of the furniture

    Joined:
    Jun 1, 2009
    Messages:
    3,610
    Likes Received:
    1,438
    Occupation:
    Print Estimator/ Repository of Useless Informatio.
    Location:
    Bingley W.Yorks.
    Heritage Railway Volunteer:
    No I do not currently volunteer
    " says on the website that "the internal design is slightly different to No. 2001's boiler, the precedent was set by No. 2006 Wolf of Badenoch which had a boiler with a firebox combustion chamber". What is a firebox combustion chamber and how does that differ from the previous five, and did it cure any steaming problems? As pointed out above Tornado doesn't seem to suffer such problems.'

    In terms of boiler lineage the A4, thompson and peppercorn A1/ A2 Boilers all followed the pattern of the last p2 (2006) boiler - as a result Tornados boiler already has this feature - indeed one of the intentions is that the boilers of the two locomotives, will be similar enough to allow interchangeability. So whats being said here is that rather than use the original 2001 style boiler (type 108?) for 2007 we will use a Tornado (118a? ) boiler which is very similar to no 2006's boiler (109 ?)...

    Seem to recall that High output under test being one thing, (being able to romp away with whatever they were hooked up to in service being another). and that tearing up the firebed was a bit if a problem especially with 2001 ( poppet valves giving a very sudden exhaust release) and that a number of draughting configurations we're tried. now if the boiler is the same as Tornados there shouldnt be these problems.... apart from the different valve gear changing the character of the exhaust. ? ( oh dear...)
     
  7. m&gn50

    m&gn50 New Member

    Joined:
    Mar 17, 2009
    Messages:
    136
    Likes Received:
    17
    FYI it's Lenz not Lentz-the T was added as some Brits failed to appreciated the nuance.
     
  8. Jamessquared

    Jamessquared Nat Pres stalwart

    Joined:
    Mar 8, 2008
    Messages:
    26,103
    Likes Received:
    57,427
    Location:
    LBSC 215
    Heritage Railway Volunteer:
    Yes I am an active volunteer
    And not just then. Beattie had a combustion chamber about a third of the length of the barrel on some of his boilers round about 1855, nearly 100 years BP (*) :)

    (To what extent he understood the theory, as opposed to coming up with the design by empiricism is a moot point, though presumably he had some kind of idea in his head that led him down that route, which after all complicated boiler construction - so he must have had a reason for trying it. See Tyseley Bloomer thread for more!)

    Tom

    * - Before Peppercorn...
     
  9. Smokestack Lightning

    Smokestack Lightning Member

    Joined:
    Oct 14, 2013
    Messages:
    262
    Likes Received:
    91
    Gender:
    Male
    Thanks all for the explanation. I couldn't understand what the firebox is if not a combustion chamber. I would have assumed that longer fire tubes would have been an advantage, to get maximum heat transfer into the boiler, but I can understand the futility of this if all they are passing is partially burnt solids and gasses. Less chance of sparks with this design of boiler??
     
  10. 242A1

    242A1 Well-Known Member

    Joined:
    Dec 3, 2006
    Messages:
    1,558
    Likes Received:
    1,299
    Come on Sheff you know it is the A/S ratio that matters. This explains why some of Wagner's engines had tubes of unusual i.d. unusual that is until you appreciate the tube length involved. So, Smokebox Lightning, the tube length is not particularly important. The A/S ratio is. The combustion chamber part of the firebox is felt to be unnecessary by some but others feel it helps to prevent the phenomenon of "birds nesting". You can use the combustion chamber to increase the firebox heating surface and to help address the A/S. You could also say that the increase in firebox volume would help improve particle combustion. But it doesn't, the particle speed is too high for the increase to make any significant difference. Less chance of sparks? No, you need to drive the fire hard if you are wanting to achieve a high power output. All that primary air being pulled through the fire bed takes a vast amount of fuel with it, frequently unburnt. Sometimes burning. Hence the spark arrestor in the Smokebox. When 50% of the fuel is carried over in its raw state the locomotive can produce no more power.
     
  11. Steve

    Steve Resident of Nat Pres Friend

    Joined:
    Oct 7, 2006
    Messages:
    11,930
    Likes Received:
    10,088
    Occupation:
    Gentleman of leisure, nowadays
    Location:
    Near Leeds
    Heritage Railway Volunteer:
    Yes I am an active volunteer
    Birds nesting of tube ends is generally associated with chlorine in the coal. Combustion chambers increase the length of the flame path before reaching the tube bank and help to ensure complete combustion. Once the gases reach the tube bank they are effectively quenched and any combustion of the gases stops pretty quickly. That's as I understand it, anyhow.
     
  12. Steamage

    Steamage Part of the furniture

    Joined:
    Sep 14, 2005
    Messages:
    4,736
    Likes Received:
    1,107
    Location:
    Oxford
    What's the A/S ratio?
     
  13. class8mikado

    class8mikado Part of the furniture

    Joined:
    Jun 1, 2009
    Messages:
    3,610
    Likes Received:
    1,438
    Occupation:
    Print Estimator/ Repository of Useless Informatio.
    Location:
    Bingley W.Yorks.
    Heritage Railway Volunteer:
    No I do not currently volunteer
    Off the top of my head its the ratio of the Area presented by the tubes and Flues ( allowing for the presence of the superheater elements ) in relation to their length, and its to do with effective heat transfer. the theory being that a wide short tube is too 'free' ( hot gas passes through quickly without giving up their heat)
    a long thin tube slows the passage of hot gas / allows the gases to cool too much which gives sluggish heat transfer... This is why the Boiler tubes on British standard Pacifics are distinctly 'non standard' ( they made them wider to get closer to the ideal ratio for a 17ft length.
    Pushing the tubeplate up the barrel to create the so-called combustion chamber also effectively shortens the tubes. Simply shortening the boiler has the negative effect of moving the centre of gravity of the vehicle backwards when it should ideally be slightly forward of the centre driving wheel(s)....
     
  14. b.oldford

    b.oldford Member

    Joined:
    Sep 29, 2009
    Messages:
    245
    Likes Received:
    55
    Gender:
    Male
    Location:
    Shropshire
    Heritage Railway Volunteer:
    Yes I am an active volunteer
  15. Sheff

    Sheff Resident of Nat Pres

    Joined:
    Apr 21, 2006
    Messages:
    7,568
    Likes Received:
    2,345
    Gender:
    Male
    Occupation:
    Retired Engineer & Heritage Volunteer
    Location:
    N Warks
    Heritage Railway Volunteer:
    Yes I am an active volunteer
    A/S - as Class8mikado says, is the ratio of free cross-sectional area for gas flow divided by the surface area available for heat transfer. I've been compiling a spreadsheet of boiler dimensions for 'modern' British designs, I shall now go away and calculate their A/S ratios !!

    ... and the results are in. . Note that different companies appear to favour different ratios across a range of boilers in the case of BR and Southern ...

    BR6, 7 & 8 : 1/350 (Tube length 17ft)
    WC & MN : 1/366 (Tube length 17ft)
    A4 : 1/388 (Tube length 18ft)
    Duchess : 1/440 (Tube length 19.25ft)

    Wagner suggests the ideal ratio is 1/400.

    ps - I fear this thread has gone the same way as that for 71000 !
     
    Jamessquared likes this.
  16. 242A1

    242A1 Well-Known Member

    Joined:
    Dec 3, 2006
    Messages:
    1,558
    Likes Received:
    1,299
    The theory runs that though the ideal is 1/400 using a ratio that offers less gas flow resistance, although it reduces boiler efficiency, allows the boiler to recover more quickly after a boiler mortgaging effort. BR locos were designed with a front end, exhaust system limit, that became saturated before the grate limit was reached. Good for fuel consumption but not so good if you were needing an extraordinary effort.

    I must agree with Sheff, this thread has gone off for a bit of an excursion. Thanks for posting the ratios, but the way, interesting that the A4 is closest to the ideal. Maybe we need a section for theory chat or similar.
     
  17. Jamessquared

    Jamessquared Nat Pres stalwart

    Joined:
    Mar 8, 2008
    Messages:
    26,103
    Likes Received:
    57,427
    Location:
    LBSC 215
    Heritage Railway Volunteer:
    Yes I am an active volunteer
    Maybe we need a "boiler design MIC" thread, because the Tysley Bloomer thread has also gone down similar lines, albeit about early boilers. So clearly there is an interest!

    Tom
     
  18. Sheff

    Sheff Resident of Nat Pres

    Joined:
    Apr 21, 2006
    Messages:
    7,568
    Likes Received:
    2,345
    Gender:
    Male
    Occupation:
    Retired Engineer & Heritage Volunteer
    Location:
    N Warks
    Heritage Railway Volunteer:
    Yes I am an active volunteer
    It would fit on the 'Not the 71000' thread or whatever it became? But agree we could do with an MIC thread for all these sort of non-loco specific techno-ramblings. Do we want to break it down into sub-sections eg boilers, or just let it wend its way as fancy takes us?
     
  19. class8mikado

    class8mikado Part of the furniture

    Joined:
    Jun 1, 2009
    Messages:
    3,610
    Likes Received:
    1,438
    Occupation:
    Print Estimator/ Repository of Useless Informatio.
    Location:
    Bingley W.Yorks.
    Heritage Railway Volunteer:
    No I do not currently volunteer
    Suppose you could bring it round by posting with the the Ratios for P2 2001, P2 2006 and intended P2 2007 ( Ie Tornado ) on that list ?
     
  20. Jamessquared

    Jamessquared Nat Pres stalwart

    Joined:
    Mar 8, 2008
    Messages:
    26,103
    Likes Received:
    57,427
    Location:
    LBSC 215
    Heritage Railway Volunteer:
    Yes I am an active volunteer
    Threads drift, so I guess let it wend its way and don't subdivide too much - in any case, I'm a firm believer in a holistic view of loco design: you can't separate steam production from steam usage, or the strength of the frames to absorb the power **cough cough** another LNER pacific...

    The ex-71000 thread is as good a place as any.

    Tom
     

Share This Page