Mk3 loco-hauled - why only 110mph?

[Bomag]

As the signalling had not been changed on most routes  HSTs needed to stop from 125mph in approximately the same distance as non-HSTs do from 100mph.  My understating was that with DVTs more of the WCML could be run at 110mph and be able to stop in time. From my time in RCE Anglia there is apparently only a little scope for higher speed running on the GEML, which is possibly why they can run London bound with the DVT brake actuator turned off.

 

I may have missed a mention in this thread but BT10s have different suspension and damper setting for 125mph as opposed to 100/110mph.  There is apparently a small but noticeable saving in maintenance costs if setting are limited to the lower speed.

[Edwin_m]

6 hours ago, Pete the Elaner said:

All the focus so far has been on HSTs being able to apply/release braking more quickly.

MK3As do have C3 - 125 mph labelled on their data panels.

 

Mk3As were originally mainly deployed on the WCML, where it was deemed too twisty to go any quicker without sacrificing passenger comfort.

Surely if braking was the only obstacle, they could have designed something to ensure the brakes applied/released more quickly, such as introducing DVTs earlier & having these also control braking?

With 110mph being a restriction for curvature reasons, loco-activated braking was probably sufficient & anything further would be considered a waste.

There are now moves to get bits of the WCML, or at least the northern half that won't be bypassed by HS2, fit for higher speeds by non-tilting stock.  This is primarily for the HS2 compatible units that won't tilt, but things like Transpennine's new 125mph EMUs would also benefit.  So working backwards that raises the question of why it wasn't done in the 1970s.  I can only think that with APT on the way BR decided they should just order an updated version of their standard mixed traffic design (which became Class 87) and that with extra power it could be stretched to 110mph without a major re-design or compromising its other performance characteristics.  

 

Which then raises the question of why APT with tilt was considered for WCML instead of just speeding up conventional trains...  

[seraphim]

Just to add a little to this. The MkIII DVTs were, as new, plated for 125mph because that's what the contract said. There may have been some thinking about running with MkIVs, but nothing I was party to. On a DVT/Class 90 push-pull set, there was the facility to propogate the brake from both ends via the DW3 units on both the DVT and the Class 90 - thereby replicating the brake concept of HST. This was never done regularly on West Coast. The main reason was that Class 86 & 87 do not have the DW3 facility, and therefore the brake performance could vary depending what loco was ten coaches back. Relying on drivers remembering this was a risk too far. Moreover, there was no chance of Class 90 exceeeding 110mph in normal traffic - so what was the point? 

 

After the MkIIIs and 90s moved to Anglia, it would have been feasible to reinstate the DW3 facility. But, if driving from the loco, command of the DVT DW3 was via the rather unreliable TDM link. If you lost TDM, full brake application and a long walk to sort it out. So, the facility was never used, as said above. In principle, the loco DW3 could be commanded when driving from the DVT - for which the TDM link must work - but what's the point of a train with better brake performance in one direction than the other.

 

Turning to BT10s, there are several flavours, but there are BT10A and BT10B frames. BT10A are restricted to 110mph because of issues with frame cracking. Hence, most LHCS MkIIIs tend to have these bogies - obviously, HST can only have BT10B. There are no damper or suspension "setting" differences which are speed related - the bogie isn't that sophisticated. Bogie are set-up differently depending on which vehicle they will be fitted to, but that's mainly to ensure that ride heights are correct with different weights of vehicle sat on the bogie.

[Pete the Elaner]

10 hours ago, seraphim said:

Just to add a little to this. The MkIII DVTs were, as new, plated for 125mph because that's what the contract said. There may have been some thinking about running with MkIVs, but nothing I was party to. On a DVT/Class 90 push-pull set, there was the facility to propogate the brake from both ends via the DW3 units on both the DVT and the Class 90 - thereby replicating the brake concept of HST. This was never done regularly on West Coast. The main reason was that Class 86 & 87 do not have the DW3 facility, and therefore the brake performance could vary depending what loco was ten coaches back. Relying on drivers remembering this was a risk too far. Moreover, there was no chance of Class 90 exceeeding 110mph in normal traffic - so what was the point? 

 

After the MkIIIs and 90s moved to Anglia, it would have been feasible to reinstate the DW3 facility. But, if driving from the loco, command of the DVT DW3 was via the rather unreliable TDM link. If you lost TDM, full brake application and a long walk to sort it out. So, the facility was never used, as said above. In principle, the loco DW3 could be commanded when driving from the DVT - for which the TDM link must work - but what's the point of a train with better brake performance in one direction than the other.

 

Turning to BT10s, there are several flavours, but there are BT10A and BT10B frames. BT10A are restricted to 110mph because of issues with frame cracking. Hence, most LHCS MkIIIs tend to have these bogies - obviously, HST can only have BT10B. There are no damper or suspension "setting" differences which are speed related - the bogie isn't that sophisticated. Bogie are set-up differently depending on which vehicle they will be fitted to, but that's mainly to ensure that ride heights are correct with different weights of vehicle sat on the bogie.

 

It sounds a bit like chicken & egg. If 90s had a newer braking feature, then they could all have been deployed as Inter-City locos instead of only 15 with the remainder on mixed traffic, dedicated parcels & freight. The 87s & 86s could then have handled the Mk2 stock & non-passenger workings.

Wasn't TDM also a problem when introduced? I seem to remember that it was expected to work with the existing lighting circuits...but wouldn't do so reliably?

If the need was there, then I expect the problems could have been worked out.

The Mk2 workings raise another issue. These were limited to 100mph & not much older than the Mk3s. If they shared the main line with 125mph Mk3s, this would produce diagramming issues. The alternatives would be to build more Mk3s & cascade them elsewhere, or just stick to 110mph for the Mk3s & not worry about the extra cost of fixing the above issues with braking, which are not necessary for 110mph running.

[jim.snowdon]

I can remember that when the Mark 3s appeared on the WCML services, there was normally a Mark 1 full brake on one end of the train, and a Mark 1 catering car somewhere in the middle.

 

Jim 

[Pete the Elaner]

17 minutes ago, jim.snowdon said:

I can remember that when the Mark 3s appeared on the WCML services, there was normally a Mark 1 full brake on one end of the train, and a Mark 1 catering car somewhere in the middle.

 

Jim 

I believe they were in mixed rakes with Mk2s to start with, limited to 100mph.

When 110mph services were introduced, Mk3As were separated & buffets were introduced to replace the Mk1s, presumably converted from FOs & TSOs. Some Mk1 BGs were maintained specially for 110mph running. I have heard that these were a little rough to ride in, so passengers were not permitted to do so.

[DY444]

22 hours ago, Edwin_m said:

T  I can only think that with APT on the way BR decided they should just order an updated version of their standard mixed traffic design (which became Class 87) and that with extra power it could be stretched to 110mph without a major re-design or compromising its other performance characteristics. 

 

The Class 87 was designed from the outset to run at 110mph even though it was plated for 100mph when introduced.  The only thing that was changed for 110mph operation was the pantograph.

Edited November 19, 2019 by DY444

[seraphim]

12 hours ago, Pete the Elaner said:

 

It sounds a bit like chicken & egg. If 90s had a newer braking feature, then they could all have been deployed as Inter-City locos instead of only 15 with the remainder on mixed traffic, dedicated parcels & freight. The 87s & 86s could then have handled the Mk2 stock & non-passenger workings.

Wasn't TDM also a problem when introduced? I seem to remember that it was expected to work with the existing lighting circuits...but wouldn't do so reliably?

If the need was there, then I expect the problems could have been worked out.

The Mk2 workings raise another issue. These were limited to 100mph & not much older than the Mk3s. If they shared the main line with 125mph Mk3s, this would produce diagramming issues. The alternatives would be to build more Mk3s & cascade them elsewhere, or just stick to 110mph for the Mk3s & not worry about the extra cost of fixing the above issues with braking, which are not necessary for 110mph running.

 

TDM was a problem from the start, and was a problem when I stopped being involved with it about five years ago. The issue, as a colleague put it, was trying to transmit safety-critical train control digital signals down a comms line designed by the RCH in the 1920s to let guards turn on and off the lights from one place. It's worth remembering that when the Class 90s were ordered the railway was utterly skint. The freight locos were desperately needed to eliminate clapped out Class 85s and similar on WCML freights; redeploying all 50 to IC was never even remotely on the cards.