Oval vs Round - Buffered if I Know!

[Right Away]

The LMS Pacifics had ‘em.

So did their big Class 4 tanks. With some LMS influence brushing off onto the BR Standard designs, the 2-6-4 tanks and No 71000 were similarly equipped.

 

Why would various locomotive classes from the same CME/design team (so relatively late in the day) choose differing patterns of buffer heads? Aethetics? Surely it could not have been for a practical reason eg. reduction of the risk “buffer locking”,

 

 

[Nile]

6 minutes ago, Right Away said:

Surely it could not have been for a practical reason eg. reduction of the risk “buffer locking”,

Surely it was?

[LMS2968]

It was. The longer the overhang, the greater the chance of buffer locking. This doesn't really explain why the Brits got round buffers and 71000 oval; I doubt the extra three inches made a huge difference.

[Wickham Green too]

Nor why the 80000s had ovals and their 4-6-0 tender brethren didn't.

[Nile]

Just looked at some drawings. The tanks had an extra 4 inches of overhang at the back, compared to the equivalent overhang at the front of the tender locos. Would that be enough to warrant oval buffers?

 

My error, see below.

Edited September 2, 2022 by Nile
miscalculation

[Wickham Green too]

By my calculation, the 4-6-0s - in fact all the leading-bogie Standards apart from the Duke* - were 16'9'' leading coupled axle to buffer face whereas the 80000s were a tad under 16'2'' rear coupled axle to buffer face ..... according to drawings in 'Ivatt & Riddles Locomotives' ; Ian Allan, 1977.

 

* an extra 3''

[Nile]

Oops, I lost a foot in my calculations for the tender locos, so the plot thickens.

[Dave John]

Overhang yes, but surely the radius of curve that the loco was intended to work on would also figure in the calculations ? 

[Enterprisingwestern]

9 hours ago, LMS2968 said:

It was. The longer the overhang, the greater the chance of buffer locking. This doesn't really explain why the Brits got round buffers and 71000 oval; I doubt the extra three inches made a huge difference.

 

It would to me!

 

Mike.

[pH]

9 hours ago, LMS2968 said:

It was. The longer the overhang, the greater the chance of buffer locking. This doesn't really explain why the Brits got round buffers and 71000 oval; I doubt the extra three inches made a huge difference.

There’s always the exception! 🙂

https://commons.wikimedia.org/wiki/File:Britannia_pacific_70045_Lord_Rowallan_at_Carlisle.jpg

[LMS2968]

Similarly, the first two Stanier Pacifics 6200/01 were built with round buffers but soon received oval ones. In the 1950s(?) 6203 returned from overhaul with round buffers and ran thus for a while.

[Bucoops]

3 hours ago, Enterprisingwestern said:

 

It would to me!

 

Mike.

 

More likely your significant other? 😉

[57xx]

13 hours ago, LMS2968 said:

It was. The longer the overhang, the greater the chance of buffer locking. This doesn't really explain why the Brits got round buffers and 71000 oval; I doubt the extra three inches made a huge difference.

 

Tell that to the wife...

[The Johnster]

Found the level, then...

 

The design of a loco or any railway vehicle to prevent buffer locking is influenced by three factors; the length, the overhang, and the minimum radius of curvature the vehicle is allowed to run over.

 

Overall length over buffers of a big tank loco, such as the LMS and BR 2-6-4Ts, is usually greater than that of a tender loco without the tender, hence the provision of oval buffers on those tank locos but not the equivalant tender locos such as the BR standard 4MT 4-6-0 or Ivatt & BR 2-6-0, because the length over buffers of the tender loco is of an effectively articulated vehicle.  Other big tank designs such as the various Baltics usually had oval buffers for this reason.  Coaches tended to have oval buffers if they were longer, but this is not a hard and fast rule.  LNER, Bullied, and BR mk1 coaches, even the 57' suburbans, BGs and GUVs, had oval buffers, but GW had larger round buffers, even the 70footers. 

 

The LMS Princess Royal and Coronation classes were very long locomotives, resulting in their being given oval buffers at the front, but not on the tenders.  By contrast, LNER, Bullied, and BR Pacifics were shorter, even the LNER ones which had longer tenders, and had 'normal' round buffers at the front, excpept DoG.  I wonder if DoG, built as a replacement for Princess Anne, had Princess Anne's buffers; Crewe had a long-standing tradition of re-using parts!

 

Why use oval buffers instead of larger-than-standard round buffers?  They are slightly more expensive to make, and waste more material.  I really don't know the answer to this, but saving weight might have been a factor, particularly with coaches where it makes a significant difference on a long train.  Every ton hauled must be paid for in coal, so the 'range' of operations is affected as well; we've all heard stories of long-distance non-stop expresses arriving at their destinations having run on dust and momentum for the final 20 miles...

 

I have always considered that oval buffers give a 'look' to a loco, a suggestion of style, size and power, but, that said, plenty of 8P locos managed well enough without them.  The LMS and LNER Beyer-Garratts were the longest locos to run in main line service in the UK, but were of course articulated, that was the point of them, and the engine units were no bigger than 'normal' 2-6-0s or 2-8-0s.  Incidentally, the Robinson 04 2-8-0s had oval buffers...  Not all of this makes obvious sense, but perhaps they were designed for use on tighter curves than similar sized 2-8-0s elsewhere, or the overhang was greater.  But I think it is fairly safe to say that oval buffers were not used for stylistic or aesthetic reasons, unlike streamlining or air smoothing (though some of those may have had a role to play in smoke-lifting or reducing coal consumption).

[Steamport Southport]

On 02/09/2022 at 21:35, Wickham Green too said:

Nor why the 80000s had ovals and their 4-6-0 tender brethren didn't.

 

Sharp curves in certain areas they were designed to work. Even the Fowler Tanks had them and they were after all just a more modern version.

 

 

Jason

[melmerby]

Most GWR Autocoaches and Steam Railmotors had particularly large oval buffers.

[Wickham Green too]

20 minutes ago, Steamport Southport said:

Sharp curves in certain areas they were designed to work. ...

I don't think it's that simple ....... the Standard 4 4-6-0s had a slightly shorter coupled wheelbase than the 80000s so would be expected to be happier on tight curves - and the Fowler 2-6-4T was significantly longer in the coupled wheelbase than either of them !

[melmerby]

Some GWR hauled carriages had oval buffers, but not many,the longer ones usually had extra large round ones

[Steamport Southport]

37 minutes ago, Wickham Green too said:

I don't think it's that simple ....... the Standard 4 4-6-0s had a slightly shorter coupled wheelbase than the 80000s so would be expected to be happier on tight curves - and the Fowler 2-6-4T was significantly longer in the coupled wheelbase than either of them !

 

The 4-6-0s weren't suburban tank engines though. More used on cross country trains on mainlines such as the Cambrian and in the North.

 

It's also why the standard length of LMS non corridor stock was 57 foot. It's the longest that could be used in most areas. Some lines are still length restricted such as much of Merseyrail and why they are still using shorter 507 and 508 units.

 

Also if you look at the Stanier Tank in the NRM it even has rotating couplings to help it negotiate sharp curves.

 

https://preservedbritishsteamlocomotives.com/42500-lms-2500-br-42500/

 

 

Jason

Edited September 5, 2022 by Steamport Southport

[The Johnster]

1 hour ago, melmerby said:

Most GWR Autocoaches and Steam Railmotors had particularly large oval buffers.

 

Necessary because of the deeply bow-ended nature of the stock and the very long buffer shanks and housings.  There were some trailers acquired at the grouping with this feature as well, notably the Cardiff Railway's contribution.  Taff Vale and Rhymney auto trailers were flat ended and had normal round buffers, as did GW compartment trailers such as the Clifton Downs and 1953 'Cyclops' trailers.  None of these were built as trailers, though, they wwere in all cases conversions of previous loco-hauled non-gangwayed compartment stock

[HGR]

Bear in mind also vertical curves ... that being intentional at the top of an incline or bottom of a descent, resulting from the gradient changing over a short length of track. Overhang causes the buffer height to rise or dip particularly for long wheelbase or bogie centres. Then there's the unintentional vertical displacement resulting from poor track, dipped joints, and the like.

 

The more curvature that must be accommodated, the larger the diameter of buffer needed. Oval buffers are the optimum combination where vertical displacement is expected to be relatively low as for example with well-maintained track. Locomotives that typically find themselves on 'loose' or industrial track will normally have oversize round buffers.

 

The rectangular buffer appears to be a popular European take on the oval.

 

 

[melmerby]

4 hours ago, HGR said:

 

The rectangular buffer appears to be a popular European take on the oval.

 

 

Or the offset trapezoidal version on the Stadler/Vossloh locos (Class 68/88)

Edited September 6, 2022 by melmerby

[billy_anorak59]

10 hours ago, melmerby said:

14 hours ago, HGR said:

 

The rectangular buffer appears to be a popular European take on the oval.

 

 

Or the offset trapezoidal version on the Stadler/Vossloh locos (Class 68/88)

Or the 'clipped' buffers found on ex-gas turbine E1000/E2001 - probably could have made do with ovals?

[Wickham Green too]

1 hour ago, billy_anorak59 said:

Or the 'clipped' buffers found on ex-gas turbine E1000/E2001 ...

Nothing to do with Europe - they only got clipped when the loco left the W.R. with it's former broad gauge clearances.

[davefrk]

Then there were the locos which had 18'' buffer heads instead of the more usual 16'', Fowler 3mt tanks, Ivatt 2mt tanks, Ivatt 2mt tender locos and Royal Scots though the latter two only the front ones, some were replaced over the years with standard 16'' heads.