Double Block Working

andrew jukes

Re: Double Block Working

Postby andrew jukes » Sat Jun 29, 2013 12:47 pm

I think the safety justification is reinforced by the obvious concern of the LNER with the braking performance of the streamliners. There was a fair amount of development work on the trains' braking system and there were braking tests of the trains (wasn't Mallard's record run part of this?).

The problem is amplified by, as I understand it, the braking performance of a 240 ton train hauled by a 120 ton loco being significantly worse than that of a 480 ton train hauled by the same loco. (Need to trawl through my books to support this statement!)

Regards

Andrew

Armchair Modeller

Re: Double Block Working

Postby Armchair Modeller » Sat Jun 29, 2013 1:00 pm

Didn't the LMS almost have a very serious accident during their own speed record attempt in 1937, when the train hurtled at high speed through the complex track formation at Crewe station - it just couldn't stop fast enough. Makes me wonder just how safe it used to be in the days of, say, the GNR Stirling Singles on the East Coast main line. Dangerous times!

John Palmer
Posts: 825
Joined: Fri Jul 15, 2011 11:09 pm

Re: Double Block Working

Postby John Palmer » Tue Jul 02, 2013 1:24 am

andrew jukes wrote:The problem is amplified by, as I understand it, the braking performance of a 240 ton train hauled by a 120 ton loco being significantly worse than that of a 480 ton train hauled by the same loco. (Need to trawl through my books to support this statement!)

Regards

Andrew

In connection with acceleration of the 'Cheltenham Flyer', O.S.Nock records that the GWR carried out braking tests with a 'Castle'. The relevant tests were conducted on level track from a speed of 90 m.p.h. With what appears to have been a full emergency brake application, the stopping distance of a 12 coach train was 420' shorter than that with a 6 coach train. Nock apparently attributes this to the facts that the locomotive carried a certain tonnage of unbraked weight (no brakes on the bogie), and that the proportion of unbraked to braked weight was increased by the reduction in the number of coaches being hauled.

Some interesting responses to the query I raised on the LNER forum about instructions for working the high speed trains, but nothing dispositive yet. I'm beginning to wonder whether any copy of the Railway's instructions survives.

andrew jukes

Re: Double Block Working

Postby andrew jukes » Tue Jul 02, 2013 10:21 pm

Glad I didn’t imagine the poorer braking performance of lighter trains!

Here’s another wrinkle that double block working has to accommodate -

I have just about got clear in my mind that the streamliner would get two distants at caution before encountering a stop signal at danger and that this could be achieved by box B treating box A’s distant as its own, so it would only be cleared when B has cleared its own home and starter. B’s own distant would only be cleared when box C has cleared its home and starter.

But what if box B has an inner and outer distant? If both are treated in the same way, both will be at caution if C’s home or starter is at danger. This presents the streamliner’s driver with the two successive cautions that indicate the next signal (B’s home) may be at danger - whereas actually it’s C’s home that may be at danger. The obvious solution is for only the inner distant to be treated as C’s distant, but this then will violate the normal rule (built into my locking) that the outer distant must not be clear if the inner distant is at caution.

I suppose the answer is that the driver’s route knowledge will be so good that he will know that these particular two distants, if both at caution, should only be treated as a single caution - but that does seem to add a new layer of risk.

I will see if the Signalling Record Society, now I’ve signed up to their forum, can help.

Regards

Andrew

User avatar
Noel
Posts: 1975
Joined: Wed Jun 23, 2010 1:04 pm

Re: Double Block Working

Postby Noel » Wed Jul 03, 2013 8:56 am

Andrew, I think that the problem of inner and outer distants at B is not a real one in practice. The driver will be working up and down the ECML on a regular basis and will know what these signals are. I agree that the locking would prevent the outer being off if the inner is on; anything else would negate the normal purpose of the outer distant. He will be expecting to see both on or both off, unless the inner is cleared after he has passed the outer, in which case the message is the same as it would be in normal block working - the signalman has had an acceptance from the next box since the train passed the outer. The only difference is that in my suggested model the acceptance is from D not C.

Noel
Regards
Noel


Return to “Semaphore Signals”

Who is online

Users browsing this forum: ClaudeBot and 0 guests