Great Western Coffee Shop

From JourneyCheck - 05 October 2017


Cancellations to services between Worcester Shrub Hill and Moreton-In-Marsh
Due to slippery rails between Worcester Shrub Hill and Moreton-in-Marsh the line towards Oxford is blocked.


Has'nt the leaf buster been out overnight ? Saw one at Bristol Parkway last Friday and thought, 'yes it's that time of year again'.

Seemed unable to get up the bank at Honeybourne. Indeed, services now running, but not stopping at Honeybourne until at least lunchtime, to give trains more of a run at the bank.

Similar problems between PNZ and PLY, with delays of up to 45mins

I had an opportunity to learn a little bit about wheel turning and wheel lathes on Thursday (and see one too) at a depot maintaining a mixed fleet of units (not HSTs, 16x or 180 units though).  Pertinent to this thread - some units are fitted with anti-slip systems and their wheels are reprofiled reasonably regularly across the year, whereas 153s do not have such a system and come the leaf fall season they become very firm friends of the wheel lathe, visiting in quite often - as this one here was doing.

Not sure if HSTs, 16x and 180 have anti-slip; I suspect not, but I also suspect (in the case of HSTs) that might be one upgrade too far at this stage in their lives. 

(http://www.wellho.net/pix/wheellathe.jpg)

Trivia question - why can wheel sizes on a 153 be up to 25mm different from each other on one bogie, but only a tenth of that on the other bogie?

All three do have WSP (Wheel Slip Protection) systems of varying sophistication.

Class 43 HST power cars have Wheel Slip/Slide Protection (WSP), a sort of traction control/ABS for trains.

The Mk3 carriage wheelsets, being unpowered, have no such system. These are often subject to wheel flats when braking on less than ideal rail head conditions. This time of year you'll find more than a few HST sets in traffic with at least one flat.

I noticed at least three flats on a GWR set passing me at Dawlish yesterday. Quite a racket from the outside. Inside, the resonance at certain speeds can be headache inducing.

The standard rules (GM/RT2461) are really about wheel slide during braking, and the risk of losing detection in track circuits, both of which are safety-critical. Traction sanding to prevent wheel slip is given much lower priority; though a TOC may be very concerned about it. Those rules say sanding should go before the third axle, and be followed by six axles, so don't apply at all to locomotives. Since an HST is a multiple unit in some respects, sanders do appear to be allowed by the rules. However, while manual application is allowed, automatic application based on the detection of wheel-slip is mandated - I'm not sure if HSTs are equipped so as to allow this.

Despite their lack of axles, classes 142 and 153 were given derogations to have sanders, following a couple of accidents and some tests in 2011.

No automatic sanding equipment is fitted to HSTs, the just have the WSP on the power cars which attempts to release the brakes momentarily to stop an all-wheel slide under braking, and under acceleration the engine power is restricted temporarily is slipping is detected.  Both systems work OK, but are by not brilliant in really poor conditions.  There's then the last resort of the jerry can full of sand kept in the power cars for manual application if you've ground to a halt - don't think that has a particularly high success rate either.  The key is to keep the vegetation well cut back, but NR have been very poor at doing that of late.

What happened to the Girling self-powered wheel slide protection that was fitted to HST trailer cars?

Agreed - and that's not just on the Cotswold Line.  >:(

This video has been posted today on the Facebook HST Enthusiast page showing mega slippage on Dainton! (Filmed in 2008).
https://www.youtube.com/watch?v=M3CJPgn7moo&feature=share

Blinkin' flip!

I mostly disagree. The key is keeping certain species in check, not the wholesale removal of all lineside vegetation.

It's particularly surprising given the wholesale surgery that's been carried out on Campden Bank over the past few years.

I’m not going to disagree with that, though NR have been very poor at doing that lately, too!


The area really cut back was the top bit by the tunnel, Campden Bank starts off OK where the old sidings and embankment are but you need to pick up speed there to 30mph or you could well be in trouble, as you then you hit the area beyond Poden Farm Crossing (now closed) and that’s where you start to slip badly and lose speed and you have over a mile until the next really open bit.

If you miss out the Honeybourne stop, you can usually hit the bottom at 75mph which gives you every chance, though you can still lose a large percentage of that if it’s really bad.

I know the tunnel itself has come to the rescue a few times as drivers have been down to less than 5mph before getting back normal traction in the tunnel.  I’ll be interested to see how IET’s cope with it.

Of course the speed lost and the height gained both affect total energy, with an equivalence that's not hard to work out (basic school applied maths). However, I don't recall coming across the numbers as a simple rule of thumb. Maybe that's because I've never needed to know in that way - do train drivers (like artillery officers) maybe have a version of this?  Or is it just experience (i.e. what happened over last year and many before)?

Anyway, it works out that 100 m of height converts to 100 mi/hr. It's the square of velocity that matters, so 50 mi/hr converts to only 25 m of height. For anyone more modern, 100 km/hr gives 40 m, so 200 km/hr gives 160 m. Or, for anyone less modern, 120 ft of height gives 60 mi/hr, and 160 ft > 70 mi/hr.

But that's only one factor in "will we make it up the hill?". You have to add the effects of traction from whatever adhesion there is and subtract drag from all causes.

PS: Campden bank looks to be a bit less than 100 m vertically from Honeybourne, rather less for the steep bit wherever you think that starts.
 

All down to experience, guesswork and a little luck.  It could all be looking good at the bottom, then you hit one of those fine misty rain showers that’s just started halfway up and suddenly you’re in trouble.  Though I don’t remember many problems ten or so years ago when trees were cut back further than they currently are.

The HST trailers are fitted with WSP. The Girling system was mainly fitted to MkIII LHCS. You also have a BR version but most are fitted with the Knorr-Bremse system.
You can normally see the wires on the outside of the bogie, normally painted orange when the wheelsets are overhauled.