Discussion in 'Steam Traction' started by GSN, May 15, 2015.
He hasn't asked about livery yet !
Aaaaaarrrrrrggggghhhhhhh! You've done it now!!
I’ve no intentions of putting my hand in my pocket, if it’s not BR large logo blue.
Its funny you should mention that. Many years ago, I used to know the original owner of this locomotive, and it was his avowed intention to see the locomotive returned to traffic in early BR blue!
Im sure a heavy donation to the fund will sway intentions ...over to you Disgusted Tonbridge Wells !
The last few days we did have a couple of interesting #OnThisDay posts on the various GSN socials. Bit like buses historical dates always seem to come all once then none for ages.
The first being yesterday in 1955 General Steam Navigation returned to service following modifications as a result of the Crewkerne incident. The post mentions where we stand in our efforts to construct the crank and also a rather brilliant photo of GSN in original condition with a cut down tender and late BR crest. http://news.35011gsn.co.uk/2021/02/...to-service-following-crewkerne-modifications/
And today in 1944 was her naming ceremony at London Waterloo http://news.35011gsn.co.uk/2021/02/20/onthisday-in-1945-gsn-was-named/
The General Steam Navigation Locomotive Restoration Society feature in the latest Railway Mania podcast, episode 17. The 90-minute podcast features three of the Society Trustees, Andrew Collet, Steve Rapley (CME) and Graham Muspratt with Corwin Bainbridge discussing our project to restore 21c11 / 35011 back to original condition complete with Bulleid’s chain driven valve gear and air smoothed casing.
The Podcast looks at our ambitious project in detail, the Trustees answer questions and discuss: the history of 35011; the main issues arising from the project returning her to original condition including: the missing crank axle, replacement middle cylinder, the work being undertaken in cooperation with Loughborough University and the University of Birmingham students on drafting and smoke clearing arrangements; visibility from the cab; the potential liveries and dispels some of the myths associated with casing fires.
The Railway Mania Podcast can be found here
Cheers @siquelme I’ll have a look at that later, for anyone who hasn’t checked out Railway Mania yet, there’s some interesting topics it’s well worth a listen to.
Thanks @Matt37401, its a good listen and very informative. If you have any questions about the project this podcast pretty much answers everything.
Half way through listening to it ..real interesting , although I'm biased as a member/ shareholder , but great to hear from the sharp end of the society .......cheers
Thanks, although being one of our earliest supporters you are kinda biased lol
The podcast was very interesting but I was still unsure whether the "new" locomotive will have the original front end of the air smoothed casing or will it have the later "hood" in front of the chimney? I suppose they could actually start with one for a year or two and then change to the later style?
I was also surprised that they felt the original chain driven valve gear gave more precise valve timing over longer periods, when the rolling road tests in the 50's seemed to show the valve events were unpredictable at speed.
I think a lot of criticism that is customarily laid at the door of the valve gear is actually a consequence of poor maintenance of the reverser - a different issue.
Liked that and it gets you thinking about stuff;
is a synthetic rather than a metal construction be the answer to keeping the sump tight, could brush seals be used or would they just melt !
could use of a better boiler insulation allow the cladding to be positioned closer - an inch or two would be scarcely noticeable on the loco as a whole but allow a significant increase in cab window size whether early or later shape.
I would like to see the version where the casing sides came right down to the bottom of the buffer beam in front of the cylinders - but this particular Loco had a most unattractive version of that that (looked like it had been borrowed of Flash Gordons rocket)
Wasn't there an incident in a few years ago when Tangmere got stuck going up Hermerdon because its valve gear wasn't working right? Was that caused by poor maintenance?
I don't know - I'm not familiar with the incident.
The common criticisms of the Bulleid pacific valve gear were (1) it drifted and wasn't easy to keep set in one position and (2) it wasn't very controllable and would sometimes jump in the wrong direction.
The first of those is absolutely symptomatic of a steam reverser in which the cataract cylinder has leaked and has air in it. The second is a general problem of steam reversers which aren't especially precise in operation (in comparison with, say, a screw reverse). It was made worse on a Bulleid Pacific because the reverser was quite powerful but the valve gear components were light, so moved quickly. (It is also sometimes possible on a steam reverser to get the gear to move the opposite way to the way it is set to move if you open the control very carefully such that the cataract valve opens, but the steam valve remains shut: in that scenario, it will creep one way or the other depending on which way it is weighted, since the cataract valve is open, allowing movement, but the steam valve is shut, so isn't forced to move in a specific direction).
On the first ten Merchant Navies, the reverser was placed in a very narrow space under the boiler but above a frame stretcher; it must have been almost impossible to reach easily, so perhaps hardly surprising if keeping the cataract cylinder topped up was sometimes skimped. On subsequent locos the placement was changed to make that vital bit of maintenance easier to achieve; and a pilot valve was added to the steam supply to make the movement of the reverser more controllable. Those changes made the whole operation more consistent and reliable, but it was never going to be as good as a screw reverse if your objective is the ability to make very fine control adjustments.
I’ve never quite understood why any engineer would fit a complicated steam reverser to a main line engine. For a smaller engine that’s involved frequent shunting maybe but a pole reverse needs very little effort if you’re not trying to use it under power.
Having said that, I was talking to a driver at Bournemouth shed who was working the Blanford trip on the remains of the S&D in early 67. He had just found out that he had been given a rebuilt light pacific for the job; I’ll have a severe bout of w***rd wrist by the time I’ve finished today.
I know that the steam reverser had "issues" but I believe there were also other factors which add to the situation. Bulleid's valve gear has three major differences in its operation compared to the "traditional" and re-builds.
1 It is driven by two inverted tooth chains of 11.8 feet and 7.3 feet long and a three throw jockey shaft
2 It is a physically smaller system of radius rods, expansion links etc.
3 The 8:3 ratio rocker arms that move the valve heads
All these combine to give a lot more "lost" motion due to the inevitable clearances in the multiple joints. This is exacerbated as those joints wear in use - although the flood lubrication in the oil sump would reduce that wear with the improved lubrication.
So, at low speeds, this play would act to give (Slightly) reduced reciprocating valve motion.
But, at high speeds, I think that the considerable inertia of the valve head would start to overcome the friction of it's rings and the valve movement becomes more "jerky". It would travel slightly more and remain at its maximum travel for slightly longer as the various multiple clearances are reversed in direction. This could account for some of those rolling road results.
This could be why the originals were known to be so free running and able to attain very high speeds?
In modern terms Bulleid therefore created VTEC with his high speed, high lift, longer duration valve gear......
Obviously it would need either high speed photography or a good computer program to see if my suppositions are correct but mechanically it is hard not to see the justification.
I believe the video mentioned that the chain & drives suffered from both wear and stretch in their day which impacted their behaviour but with modern materials and standards of care, would be less apparent.
Is this the experience from other chain-driven pacifics we've seen in preservation - Tangmere comes to mind as a locomotive that was definitely worked hard in more recent times?
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