Class 90/91 - Coupler? Buffer?

[tpjm]

Been pondering something weird for the last couple of hours...

Can anybody tell me what the below component is, and its purpose? I’m sure if seen these on a 91 with Mk4s so I’m now intrigued as it looks like some kind of additional buffer.

 

[DustyBin]

It looks like the rubbing plate for the buckeye coupler, I believe 90’s and 91’s have these but I’m not 100% sure. You’ll see them on SR EMU’s though.

 

[jopsuk]

It's a sort of buffer- it's for the corridor connector on the coaches. It's not needed with the ones for Mark 4s, but if you look at pictures of the ones that were in the Great Eastern (and before that West Coast) operating pools you'll see them, but on the ones allocated to freight duties only you won't

 

[JonathanH]

Can anybody tell me what the below component is, and its purpose? I’m sure if seen these on a 91 with Mk4s so I’m now intrigued as it looks like some kind of additional buffer.

Rubbing Plate - a bit of explanation here https://www.railforums.co.uk/threads/mk3-creaky-gangways.201689/page-2#post-4478101 and here https://www.railforums.co.uk/threads/current-operating-status-of-86259-les-ross.112479/#post-2089763

Buckeyes cannot take compression forces so require a Pullman gangway or rubbing plate.

A rubbing plate won't be of any use on it's own anyway. It's purpose is to provide the absorbtion of compression forces (which would ordinarily be done by the buffers) to trains which are coupled with a buckeye type coupler.

 

[t_star2001uk]

It is called a rubbing plate. In the picture there will be a drop head buckeye that is in the down position. To couple using the rubbing plate, the buckeye needs to be raised and the outer buffers retracted.

 

[221101 Voyager]

Been pondering something weird for the last couple of hours...

Can anybody tell me what the below component is, and its purpose? I’m sure if seen these on a 91 with Mk4s so I’m now intrigued as it looks like some kind of additional buffer.

View attachment 83998

91's have this also. See my shots below. The 1st MK4 coach behind the 91 also has one of these bar things.






This shot isn't mine but illustrates it well.

 

[Whistler40145]

The rubbing plates were required when working in push pull mode on DVT sets to ensure a smoother ride when breaking and powering up from a stop

 

[221101 Voyager]

The rubbing plates were required when working in push pull mode on DVT sets to ensure a smoother ride when breaking and powering up from a stop

Well I didn't know that, thanks!

 

[Whistler40145]

Well I didn't know that, thanks!

With the 90/91 pushing from the rear of the train, rather working in conventional mode, there's more of a jolt

 

[coppercapped]

Buckeyes can take compression forces - it's one of the things they are good at! Think of all those 4TCs being pushed from Waterloo to Bournemouth in days gone by and the half of each HST being pushed by the rear power car...

The truth is much more prosaic.

BR adopted the 'Pullman' style intercoach gangway connection as used by both Gresley and Bulleid in their pre-war coaches for the LNER and SR for all its standard coaches from Mk 1 to Mk 3 together with the Buckeye coupler. The advantages of the 'Pullman' style over the the suspended, concertina type connection used by the GWR and LMS were that (a) it was wider internally and (b) the two halves didn't have to be connected manually when the coaches were coupled together, the outer faces being spring-loaded. As the buckeyes mated the outer faces of the gangway came together and were compressed by a couple of inches. Relative motion between the two gangways was damped by the use of friction material on one side of each gangway face.

This means that if a locomotive is coupled to a coach using buckeyes, the bottom end of the corridor connection on the coach would protrude two or three inches past the mid-point of the two couplers if there was no equivalent rubbing plate on the locomotive. Under these conditions it could hit other components on the end of the locomotive, especially when the ends of the two vehicles are moving relative to each other at speed or on curves, especially as the motion of the end of the free gangway is not damped by the adjacent one.

If the locomotive was coupled to the coach using a screw coupling the extensible buffers on the coach kept the ends of the vehicles further apart so the bottom of the gangway caused no problems.

So a locomotive (or indeed any vehicle) which is intended to be coupled using Buckeye couplers to coaching stock fitted with 'Pullman' gangways has to have the rubbing plate.

Edit: added (a) and (b) and (brackets)!

 

[Merle Haggard]

What has puzzled me is why some stock wass fitted with a buckeye but no rubbing plate. I think that the outer ends of B.R. Standard Tyneside electric stock was one example, and possibly the Trans-Pennine dmu and also some AC electric units. What hey all have in common is that none have corridor connections over the buckeye.

 

[Whistler40145]

What has puzzled me is why some stock wass fitted with a buckeye but no rubbing plate. I think that the outer ends of B.R. Standard Tyneside electric stock was one example, and possibly the Trans-Pennine dmu and also some AC electric units. What hey all have in common is that none have corridor connections over the buckeye.

Loco and stock is completely different to units, the loco will be producing force to push the stock

 

[norbitonflyer]

What has puzzled me is why some stock wass fitted with a buckeye but no rubbing plate. I think that the outer ends of B.R. Standard Tyneside electric stock was one example, and possibly the Trans-Pennine dmu and also some AC electric units. What hey all have in common is that none have corridor connections over the buckeye.

Probably because none of them was ever likely to be coupled to a unit with a gangway end. Non-gangwayed SR EP-stock (4EPB, 2HAP) did have rubbing plates because they could be coupled to, for example a 4VEP

 

[jopsuk]

if the Mark IV TSOE has a rubbing plate to match to the Class 91, why have they not been required for Class 90s and Class 67s working with Mark IVs in push/pull? Indeed, as the 90s on mark 3s had the rubbing plate, why didn't the Class 67s and currently class 68s working push-pull with them have plates fitted?

 

[Whistler40145]

if the Mark IV TSOE has a rubbing plate to match to the Class 91, why have they not been required for Class 90s and Class 67s working with Mark IVs in push/pull? Indeed, as the 90s on mark 3s had the rubbing plate, why didn't the Class 67s and currently class 68s working push-pull with them have plates fitted?

Don't forget several 90s moved to freight operators following the end of loco hauled on the WCML and had their rubbing plates and buckeye couplers removed

 

[43096]

if the Mark IV TSOE has a rubbing plate to match to the Class 91, why have they not been required for Class 90s and Class 67s working with Mark IVs in push/pull? Indeed, as the 90s on mark 3s had the rubbing plate, why didn't the Class 67s and currently class 68s working push-pull with them have plates fitted?

The whole idea of having drophead buckeyes, rubbing plates and retractable buffers is to allow them to couple to any loco that has either standard drawgear or buckeyes. As I understand it, if both vehicles have buckeyes, then the buckeyes must be used, but there is nothing to stop a 67, 68, a 90 without buckeyes or indeed anything else without buckeyes from coupling to a Mark 4 TOE.

 

[Merle Haggard]

Probably because none of them was ever likely to be coupled to a unit with a gangway end. Non-gangwayed SR EP-stock (4EPB, 2HAP) did have rubbing plates because they could be coupled to, for example a 4VEP

Thank you for that, I can see that logic. Presumably, for the converse reason, some non-gangwayed stock e.g. the late rebuilds of NPCCS were fitted with rubbing plates.

In my experience, non-gangwayed units have been used to assist another (failed) train from the rear, but the train being propelled was also non-gangwayed (AM10 - AM10) Maybe, hidden deeply in a General Appendix, is a prohibition of coupling to gangwayed stock.

It's also curious that non-gangwayed e.m.u. stock had buckeyes at the outer ends, but non-gangawayed d.m.u didn't.

TPO coaches had an offset gangway. The LNER was a universal user of buckeyes/rubbing plates for gangwayed stock, and I remember noticing the solution to the conundrum produced by the combination of these two features - though I cannot remember (it was a while ago!) what it was...

 

[dubscottie]

Buckeyes can take compression forces - it's one of the things they are good at! Think of all those 4TCs being pushed from Waterloo to Bournemouth in days gone by and the half of each HST being pushed by the rear power car...

Sorry, they can't. It's why there in the need for a rubbing plate. It's nothing to do with component damage etc.
When a buckeye fitted loco is pushing, it's the rubbing plate taking the strain not the coupler head.
Various non-gangwayed Mk1 EMU & DMU classes had fixed buckeyes and rubbing plates between vehicles for the same reason.
Its why a 67 uses a screw coupling when working with Mk3 stock and not its auto coupler. The coupler head & drawbar on the Mk3 can't take compensation loads.
Irish Rail/NIR found this out when they started using Mk3 vans on the Enterprise.

Pic of a bufferless, gangway less EMU vehicle with buckeye & rubbing plate here.
https://flic.kr/p/hnu2tM

 

[coppercapped]

Sorry, they can't. It's why there in the need for a rubbing plate. It's nothing to do with component damage etc.
When a buckeye fitted loco is pushing, it's the rubbing plate taking the strain not the coupler head.
Various non-gangwayed Mk1 EMU & DMU classes had fixed buckeyes and rubbing plates between vehicles for the same reason.
Its why a 67 uses a screw coupling when working with Mk3 stock and not its auto coupler. The coupler head & drawbar on the Mk3 can't take compensation loads.
Irish Rail/NIR found this out when they started using Mk3 vans on the Enterprise.

Pic of a bufferless, gangway less EMU vehicle with buckeye & rubbing plate here.
https://flic.kr/p/hnu2tM

The body of all BR's mainline rolling stock[1] was designed to take up to 200 tons longitudinal force applied along the centreline without permanent distortion and lightly less if applied diagonally at the buffers. A limit also existed for forces applied at the cantrail level.

A 70,000lb-force tractive effort, a typical maximum for a six axle locomotive, is 31 tons-force, well within the design limits of the coach.

[1] The 57ft non-gangwayed hauled stock built by BR was designed to a 100 ton end load and if I recall correctly the early DMUs had an even lower end loading.

 

[Spartacus]

The body of all BR's mainline rolling stock[1] was designed to take up to 200 tons longitudinal force applied along the centreline without permanent distortion and lightly less if applied diagonally at the buffers. A limit also existed for forces applied at the cantrail level.

A 70,000lb-force tractive effort, a typical maximum for a six axle locomotive, is 31 tons-force, well within the design limits of the coach.

[1] The 57ft non-gangwayed hauled stock built by BR was designed to a 100 ton end load and if I recall correctly the early DMUs had an even lower end loading.

The limitations of the coach aren't the problem, it's the limitations of the buckeye.

 

[delt1c]

Classes 33/1, 73 and 74 were fitted with them for Push pull operation, interstingly the Edinburgh Glasgow Push pull 27's retained screw couplings as did ( I believe ) the 47/7's which replaced them

 

[coppercapped]

The limitations of the coach aren't the problem, it's the limitations of the buckeye.

So you are saying that buckeyes can withstand a 30 ton-force load in tension, but not in compression?

What is the limiting component?

 

[dubscottie]

So you are saying that buckeyes can withstand a 30 ton-force load in tension, but not in compression?

What is the limiting component?

The locking pin. I cant recall the exact reason but I seem to remember that it has to do with the way the back of the jaw is shaped.
Also the drag/draft box may suffer damage from compression also.

 

[tpjm]

This is all really interesting stuff! Thanks everybody for your comments.

 

[delticdave]

The locking pin. I cant recall the exact reason but I seem to remember that it has to do with the way the back of the jaw is shaped.
Also the drag/draft box may suffer damage from compression also.

How do these numbers compare with the knuckle couplers used in North America & Australia? Are there limits to the number or weights of cars than can be pulled from the head-end, (rather than when the locos are distributed throughout the train)?

 

[gimmea50anyday]

Interestingly but the 68s when buffered up to the Mk5s don’t have rubbing plates (or Pullman buffers as they are also known) but they make use of the standard buffers and are screw link coupled.

 

[dubscottie]

How do these numbers compare with the knuckle couplers used in North America & Australia? Are there limits to the number or weights of cars than can be pulled from the head-end, (rather than when the locos are distributed throughout the train)?

I am not sure as they are built differently although the figures quoted here by coppercapped are for the end loadings on the underframe/body not components like buffers or couplings.
While Buckeyes and AAR couplers look similar and compatible, they are very different.
Broken knuckles are a daily occurrence in the US but unheard of here.
I think I can remember were I read about the pins. It may have been in an accident report.
The old braincells are going and I believe the issue is that on a buckeye, the pin would only be held by its own weight as its uncoupled from the bottom. It is held tight by the tension of the gangway or rubbing plate. Without them it could jump up and unlock the coupler if briefly in compression.
The uncoupling chain on them rings a bell also. Will have a look tomorrow.

Classes 33/1, 73 and 74 were fitted with them for Push pull operation, interstingly the Edinburgh Glasgow Push pull 27's retained screw couplings as did ( I believe ) the 47/7's which replaced them

The 27s could have been fitted but it was not worth it. The 47s would have needed major structural changes and added a few tons to the overall weight of the loco.

 

[ac6000cw]

How do these numbers compare with the knuckle couplers used in North America & Australia? Are there limits to the number or weights of cars than can be pulled from the head-end, (rather than when the locos are distributed throughout the train)?

The common 'Type E' AAR couplers can withstand about 2900 kN of force in tension (about 290 tonnes-force), limited by the 'knuckle' strength (the moving part) which is designed to be the weakest part (and is easily replaced in the field).

I can't find any figures at the moment for compression, but I would expect that strength to be higher as compression force is handled by the fixed part of the coupler. Certainly it's common when pushing heavy trains uphill to have up to 4 x SD40-2 or 2 x modern AC-drive locos on the rear, which can generate about 1500-1600 kN of tractive effort, but this limit on rear-end locos is mostly about limiting the lateral forces in the train which can cause 'flange climbing' and hence derailments in curves.

Note that the UK 'Tightlock' coupler (used on various BR EMU trains) is a derivative of the AAR Type H coupler, which now the US standard for passenger cars as it largely prevents the couplings separating vertically in accidents, which can happen with the Type E and older versions. It also has less slack when coupled.

Broken knuckles are a daily occurrence in the US but unheard of here.

I think that's largely because of the much longer & heavier trains which have a lot more 'slack', so are much more prone to slack running in & out. That can over-stress the knuckles and cause them to fail at some point in the future (due to stress cracks developing).

 

[nlogax]

I think that's largely because of the much longer & heavier trains which have a lot more 'slack', so are much more prone to slack running in & out. That can over-stress the knuckles and cause them to fail at some point in the future (due to stress cracks developing).

It's such a common occurrence in the US that spare knuckles are usually carried in freight locos.

 

[ac6000cw]

It's such a common occurrence in the US that spare knuckles are usually carried in freight locos.

Yes, and it's the usually the conductor's job to walk back along the train (in the rain and darkness of course!) to replace a broken one...

I did once see a freight go into emergency braking while passing Sandpatch Summit on CSX (loud 'pssst' and slack run-in noises propagating along the train). Unfortunately when it happened the train was crossing between the two tracks so it stopped blocking the whole line.... Took about 90 minutes to fix it - I don't know if it was a broken knuckle or just air hoses parting. Then it had to be reversed back through the crossover to clear one track for a several higher-priority intermodals to overtake it, before it could finally carry on over the summit and down the hill to Cumberland, MD.