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Locomotive Superintendents

Discussion in 'Steam Traction' started by Dunfanaghy Road, Feb 25, 2021.

  1. Jimc

    Jimc Part of the furniture

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    The official GWR reason was that any failure in the gear rendered the whole gear completely inoperable, and made it impossible to limp home on one side. The 4 cylinder locomotives were provided with an special link which could be used to hold the gear up out of use in case of a failure, whereas other lines simply provided instruction on how to achieve the same effect with blocks of wood and tying things up.
    Gibson, characteristically, has a conspiracy/cockup tale about how the gear was very difficult to set valve timing on and it would take days to do.
    I've also heard it said that the valve events weren't great because of the angularity problems alluded to above.
    All three could be true of course.
    The GWR gear was quite different to Deeley's design, which involved different length rods, so as cross connnected gears had been done before there is at least a doubt whether Deeley's patent would have been valid.
     
  2. Jimc

    Jimc Part of the furniture

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    I found an illustration of the Deeley gear in here.
    https://bisarchtest.files.wordpress.com/2017/03/july-newsletter1.pdf page 10.
    The issue with the cross connected gear is in getting the movement to the other side of the locomotive past the other set of gear. Its fairly clear from the drawing that Deeley did it by having one expansion link behind the other and accepting different length components on each side. What W H Pearce, Churchward's valve gear expert did, was rather more sophisticated. He introduced a pair of curved levers which crossed over but couldn't contact each other, which meant that on his implementation everything except the three dimensional shape of the levers was identical, and so the valve events were the same each side. Supposedly the two levers crossing past each other reminded the shop floor of a pair of scissors, and that was the source of the name.
     
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  3. pete2hogs

    pete2hogs Member

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    if only someone had come up with something simple. Like the Gresley/Holcroft gear for example ...
     
  4. Jamessquared

    Jamessquared Nat Pres stalwart

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    Just looking at the Deeley arrangement for a minute, I struggle a bit to see what the advantage was. Presumably it was narrow, which enabled the cylinder diameter to be maximised - but it seems a lot of complication to go to to achieve that. (Any comment @LMS2968 ?)

    Any pictures of the Churchward scissors gear?

    Tom
     
  5. Mr Valentine

    Mr Valentine New Member

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    There was a wooden mock-up made at the time, for which a couple of photos exist, although neither appear to be online. One appears in Nock's GWR Stars book.

    Googling 'Swindon scissors model' did throw up some interesting results, mind.
     
  6. huochemi

    huochemi Part of the furniture

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    From Nock's Stars, Castles & Kings.
     

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  7. Jimc

    Jimc Part of the furniture

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    Different aims. AIUI the idea of the cross connect gears was to provide a valve gear for two (inside) cylinders that eliminated eccentrics. This left more room for larger and stronger arrangements for the big ends. In the case of GWR No 40 we should remember she was effectively based on a Saint, with no connecting rods between the frames, so if two big ends were going on the axle then a lot had to come out. So a gear with no eccentrics must have looked ideal.

    The other part of the design was to derive the valve movement of the outside cylinders from the inside motion, which was readily done by having rocker arms, albeit very sophistically designed in detail.

    Holcroft had something different in mind. He wanted to reduce the number of components and simplify by having no inside motion on a 3 cylinder locomotive. With outside Walschaert's there was no concern about eccentrics, and so he used a much more complex arrangement of rockers to get the result he wanted. Have people heard Churchward's aside to Holcroft on seeing his model of his original three cylinder gear - roughly "Now all you need to do is work out a way of using one set of motion for both cylinders on a two cylinder locomotive and your fortune's made!"

    IMHO its certainly valid to say that outside valve gear would have made some aspects of design easier on the 4 cylinder Saint, since there is no issue with eccentrics inside. However as noted above it simply wasn't practical to have outside only valve gear on a Saint derived chassis, so a completely new chassis with very different wheel spacing and weight distribution would have been required. They could have had 4 sets of valve gear, but that seems to me to be bringing together the worst features of both layouts rather than the best.
     
    Last edited: Mar 7, 2021
  8. clinker

    clinker Member

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    I can't really see that Holcroft used a more complex arrangement, since the inside part of his valve gear was two 'swinging' links and three pin joints, operated by the existing outside Waschaerts via two knuckles and two more pin joints, OK simplified description, but fairly accurate compared to the principle and components of 'Scissors'. I'm also having a bit of a problem with valve events on Scissors, since the two 'engine' units running at 90 degrees does not allow 'Much' for the Lap and Lead functions of valve events.
     
  9. Jimc

    Jimc Part of the furniture

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    There's two stages, I think.

    One is to get the correct motion to the first cylinder- or rather valve.
    This requires either an eccentric or else motion from another crosshead 90 degrees out of phase (as with the cross connected gears). In the case of inside motion the cross connected gears save bearing space on the driving axle by eliminating the eccentrics. With outside motion I'm not sure cross connection has much to offer.

    The second stage is to derive movement to another cylinder which has no valve gear of its own.
    For this Holcroft's multiple rockers to get the inside gear 120 degrees out of phase with the outside were unavoidably more complex than Pearce's single rockers to get the outside gear 180 degrees out of phase with the inside.

    The subtleties of lap and lead are beyond me, but Don Ashton as linked above commented that there are issues with the valve events of a scissors gear.
     
    Last edited: Mar 7, 2021
  10. huochemi

    huochemi Part of the furniture

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    You seem to be suggesting that lap and lead in Walschaerts is achieved by an adjustment to the 90 degree angle - but I may be reading into your comment something that is not there. With Walschaerts, the movement of the valve in mid-gear (when it is imparted solely by the combination lever) is (lap + lead) x 2, the "lap and lead" component if you like. The drive to the scissors lever seems to be emulating a return crank/eccentric, and is concerned solely with the "cut-off" component i.e. the incremental valve movement when not in mid-gear.
     
    Last edited: Mar 8, 2021
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  11. 30854

    30854 Resident of Nat Pres

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    Enquiry: Could Churchward's decision to abandon scissors gear be related to his experiments with long travel piston valves?
     
  12. clinker

    clinker Member

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    When dealing with a Four cylinder design with cranks at 0-90-180-270-360 using two sets of valve gear is 'Relatively' simple, basically in-out up-down, on a three with pistons 120 degrees out of phase and two sets of valve gear it's a bit more invloved, hence the Holcroft type gear, which is still 'Simpler' than three sets of Walschaerts (Simpler as in fewer components/wearing points) Holcroft also designed a gear for a 'True' four cylinder (0-90-135-180-225-360) ie Eight beats to the rev, using two sets of walschaerts, which was obviously far more complex (Please don't ask me how it worked).

    Now WRT lap lead and cutoff, thinking of the eccentric/return crank at 90 degrees to the crank is a good starting point but with 'Simple' valve gears does not allow for valve lap or lead, with 'Walschaerts' these components are achieved via the combination levers, so looking at it now I can follow the 90 degrees of the scissors arrangement, and taking things a step further the scissors arrangement is also the opposite principle to the original Bullied oil bath valve gear where the combination lever arrangement derived it's motion from an eccentric rather than the opposite crosshead. This would make a great discussion in a Pub.
     
  13. MellishR

    MellishR Resident of Nat Pres Friend

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    That's exactly it. Instead of a return crank at 90 degrees to the main crank, you use the crosshead of the other cylinder, which likewise is 90 degrees out of phase. There is a wrinkle, that for one side the other cylinder is 90 degrees ahead while for the other side it is 90 degrees behind. You deal with that by having the valve rod for one side at the top of the expansion link for forward gear and the rod for the other side at the bottom for forward gear, as shown in the diagram at post #106. That in turn requires different linkages from the reversing screw or lever, also shown in that diagram.
     
    Last edited: Mar 8, 2021
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  14. clinker

    clinker Member

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    Yes, all clear(ish) now.
     
  15. bluetrain

    bluetrain Member

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    Thank-you for posting the interesting piece on Deeley’s valve gear as used on the Midland 999-class 4-4-0. It mentions that neither Deeley nor Churchward was the first to use a cross-linked valve gear, applications also being found in Belgium and USA. Ahrons comments that “the principle of this gear is similar to that of the Belgian Stévart gear, although Deeley’s gear was independently designed”. However, Stévart had got there 30 years before Deeley, as his gear had been used on a class of Belgian 0-8-0Ts in the 1870s.

    Tuplin’s book “Midland Steam” includes a lengthy discussion of both Deeley’s patent and the gear used on the 999-class. Some of Tuplin’s details are beyond my technical comprehension, but I will pick out a couple of key points. Given the prior use in Belgium, Deeley could hardly be granted a valid patent for the principle of cross-connected valve gear. Tuplin suggests that the key feature of Deeley’s patent was in fact not cross-connection at all, but a variation in the way that the Walschaerts levers are positioned and anchored. Quote “It was the pivoting of the combination lever on the pin in the die-block instead of on a pin in or near the valve spindle”. This is shown in the attached diagram.

    This patented feature was not in fact used by Deeley in the 999-class and is not known to have been used anywhere else.
     

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  16. Jimc

    Jimc Part of the furniture

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    I can only think Deeley must have had (an)other patent(s) that Tuplin missed. I cannot see that Pearce's scissors gear could be held to infringe on a patent for that development.
     
  17. Dag Bonnedal

    Dag Bonnedal New Member

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    The Deeley valve gear was also used by one of the major Swedish private railways: Stockholm Västerås Bergslagernas Järnväg (SWB), running NW from Stockholm into the mining district of central Sweden.
    They used it for both their variant of the private railways standard fast passenger engine H3, as well as their own fast goods variant of the same M3. In total 16 locos built 1910-1922.
    Here is a drawing of the gear used.
    SWB Deeley valvegear.jpg

    One of the passenger locos is preserved by NBvJ in Nora:
    https://www.nbvj.se/swb-h3-56/

    And here is the fast goods variant. Unfortunately none preserved:
    (Click for larger view, download with arrow in box.)
    https://digitaltmuseum.org/021018092002/stockholm-vasteras-bergslagens-jarnvag-swb-m3-64
     
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  18. Jimc

    Jimc Part of the furniture

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    That's rather interesting. If (and its a b***y great big if) I understand the drawing correctly its significantly different in detail from the drawing of the Deeley gear I found, and avoids the feature of having the expansion links one behind the other with consequent differences between the gears. It also, I think, avoids the issue of one side moving in the opposite direction to the other, since what think their designer has done is to have a rocker on the rod that replaces the eccentric introducing a 180 degree phase shirt on one side, but not the other. I think that deals with the issue of one cross head being 90 degrees ahead of the other and the other 90 degrees behind. Its also interesting in terms of what was in Deeley's patent, since its arguably even more different from the Deeley drawing then the GWR Scissors design is. Again, huge if, but if I understand it correctly I would think it the best of the three.
     
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  19. Dag Bonnedal

    Dag Bonnedal New Member

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    Jim,
    You are absolutely correct in you analysis.
    The only drawback, as I see it, is that the arms of 180 deg arms (#5/8) are short and thus introduce some error due to the larger angle of swing.
    The arms of the 0 deg arms (#1/4) are longer with less error.
    But with the connected horizontal links, the errors should be rather minute.

    As you say, it is different from the British cross drives (and the US Young gear). I have no idea of any patent issues, but it has always been called Deeley in Sweden.

    The drawing is from the standard Swedish steam loco handbook, Ångloklära. Given by SJ to all footplate men, 1949 edition. Very detailed for being such a handbook.
    Here you can download a number of handbooks from the Railway Museum (all in Swedish, but with OCR text. Thus you can use Google translate to read parts of interest).
    http://samlingsportalen.se/all/digitala_biblioteket_litteratur.html
     
    Last edited: Mar 12, 2021
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  20. LesterBrown

    LesterBrown Member

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    If the patent for Walschaert Valve Gear hadn't expired would both Deeley's and Churchwatd's have infringed it?
     

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