71000 Matters

As I quoted, direct from the horses mouth, rather than a magazine, post #34.

 

It was in reply to the question of the number of trips/tours, which I could not see answered by previous posts.

 

Some individuals and organisations are easier to deal with than others.

 

At the extremes of the slide bar there are no vertical forces to cause deflection (other than self weight) and, as LMS2968 says, the vertical forces reach a maximum at roughly the centre. The logical place to support them, therefore, is the centre. Between supports there is bound to be a deflection, dependent on the stiffness of the bar. The problem with three bar arrangements is supporting the bottom bars as things tend to get in the way so you end up with the top bar well supported and the bottom bars only supported at the ends. For locos mainly running in forward gear this isn't a problem. When working hard in back gear, it is.

 

Steve, I'm not a mechanical engineer, but I have seen the output of modelling work done on the BR pacific slidebar arrangement, which is supported by evidence of actual differences in wear on DoG itself between outside and inside cylinders.

 

According to D. W. (Bill) Harvey, when at Norwich they did have trouble with piston rods breaking on 'Britannias' which was eventually tracked down to the slide bar mounting bracket oscillating due to worn fasteners. As an experiment a scriber was fixed to the bars to prove this. Instead of just a vertical line a circle about the size of a pea was made indicating that not only the bars were moving, but the frame was flexing in the cylinder area also.

 

Eightpot - thanks for the reminder - I was scratching around trying to recall that.

 

As with most component designs the slide bar design will very likely have been borrowed from another drawing office, be it Doncaster, Brighton or Glasgow.
Nearly all the contemporaneous locos using this slide bar arrangement had either less cylinder power , a shorter piston stroke, or additional fixing points. You might expect the Brittanias to be the worst affected , followed by the Clans, 71000 and the standard 5's

 

The slide bars were designed at Doncaster. The mounting brackets were designed at Derby.
It is interesting to note that the slide bars for the caprotti Class 5s were designed at Derby. The front portion of the slide bars was a couple of inches shorter and bolted to a bracket cast onto the hind cylinder cover, as well as the mounting bracket.

 

Odd that only the Caprottis had this improved version isn't it. Does anyone know why - is it a date of design/build thing so incorporating operating experience perhaps? (Of course the 9F's also had the original version too IIRC).

 

It may just be that Derby had the drawings for the Caprotti cylinders from the last two black fives and just joined the dots... However the Selling point/ Justification for the caprotti was that it wasn't just efficient but would hold its settings/ require less maintenance than the walshaerts... not much point in having valve gear that you can leave alone for 50,000 + miles if the pistons need to come out every 20,000.

IIRC correctly Tyseley have not recommended the additional fixing point but instead are using a different construction of piston/ rod and a different approach to lubrication. Difficult to argue with this until its tested and if its GWR thinking maybe it will work... don't think anything on the GW ever this type of slidebar or had as much superheat as 71000 though

 

If the truth is known, 71000 was the victim of an experiment carried out on Britannias 70035-44 when they were built. These ten Brits were fitted with combined pistons and rods with just two piston rings on them and no spring loaded pads. The experiment was discontinued at the end of 1953 and separate pistons and piston rods were fitted, together with new front cylinder covers as per the rest of the Class. However, someone in the design department at Derby decided that similar combined pistons and rods should be fitted to the Duke, which it carried throughout its life, until now. As you say, it is reverting to the normal separate pistons and piston rods, with new front covers. This loco has never had any luck go its way.

 

Hmm, maybe the fact it's still with us, might that be considered lucky?

 

Yes, considering it went to the wrong scrapyard prior to being redirected to Barry.

 

Can you explain that plse - AFAIK both versions of the poppet valve 5's had the standard LMS two bar arrangement?

 

Yes, but doesn't the two bar arrangement have mounting points on the cylinders and a bracket 2/3rds of the way back... so if that was your starting point it might be a natural progression to leave the mountings feature ? and reposition it to mate with the new slide bar arrangement ?

 

Seems to suggest in SR that there is potentially going to be a more regular Q path available within the new timetable to allow more frequency in Shakespeares....

I would suspect you could possibly add another Castle, a King, a Saint, a County and a 47xx to that potential stable as I am not sure who else the GWS will be able to link up with?

Its all possibly down to demand, by the end of 2018 there is likely to be 3 main line registered Jubilees already, will there be enough work for them?

 

Mind you, from Tyeseley's point of view, a Jubilee can go places which an outside-cylinder GWR 4-6-0 can't. I'm not sure whether a Jubilee will fit on the Worcester-Malvern-Hereford line, but these days Castles and Halls most definitely don't. The two most recent main line trains to run over that route were both hauled by Bulleid Pacifics (I photographed the first, hauled by 34067 and travelled on the second, hauled by 34046). If Kolhapur does fit, it would enable Vintage Trains to run specials along a very picturesque line which their current working fleet - panniers excepted - can't access and which isn't that far away from Tyseley. Sadly, by the time 5593 turns another wheel under its own power, the semaphore signals between Worcester Shrub Hill and Malvern Wells are likely to be no more, but there will still be the combination of lovely countryside, a gem of a station at Great Malvern and a challenging 1 in 80 climb up to Colwall Tunnel.

Come to think about it, as this thread is about 71000, I wonder if it will fit on this line. No doubt within a couple of years we will know the answer.

 

Since Duke of Gloucester is a BR standard it should be relatively loading gauge friendly compared to a GW loco.