towerman
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Post by towerman on Nov 19, 2023 11:35:14 GMT
One thing I never found out why,when 67TS ran on the Hainault loop they had the rheostatic brake cut out,anyone know the reason?
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Post by t697 on Nov 19, 2023 16:50:45 GMT
I don't know for sure but being old enough to have done a little engineering on these in the 80's here are some thoughts:
The rheostatic brake had two notching relay settings, Rheostatic 1 & Hold which was a low rate without retarder control and a single higher rate used with each of the MIN, NOR, MAX retarder controlled rates.
I seem to recall that this higher rheostatic setting produced brake force roughly equivalent to braking the motor car at tare MAX. So in MIN the retarder hardly applied any (trailer) friction brake, in NOR some trailer brake and in MAX and with full passenger load the retarder fed trailer brake even higher and the there was spillover into the motor car brake cylinders via a Restricted Application Valve which kept the trailer pressure about 30lb/in^2 above the motor car brake cylinder pressure.
With the Hainault loop being mostly non-tunnel and subject to variable adhesion the rheostatic brake's adhesion demand being biased to the motor car (even if the ATO brake profile (spots) had been set to a lowish rate) may have led to or expected to lead to wheelslip/slide. The easiest way around that would have been to cut out the rheostatic brake. With that done, the retarder control used Application Trailer and Application Motor I seem to recall and the adhesion demand was then sensibly the same throughout the train.
Let's see if this jogs others' memories.
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towerman
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Post by towerman on Nov 19, 2023 17:59:53 GMT
Sounds possible,when they first started running(with Rheostatic cut in)there were a few complaints that the braking was too fierce.
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Post by t697 on Nov 19, 2023 18:37:39 GMT
Another point was that unlike later stocks like 73TS, C stock and D stock, the 67TS didn't have Field Injection. The result was that once the motors started to excite in braking they reached full brake current very fast, in less than a second typically from 'Proving'. This gave the impression of quite a snatch to the brake as it's faster than typical e.p. brake feed-up.
A modification was made to slow this down with brief field weakening on the similar but manually driven 72TS to suit them better to driving in the open.
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towerman
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Post by towerman on Nov 21, 2023 22:16:53 GMT
Remember one of stock moves from Hainault left from wrong end of depot,arrived at Northumberland Pk wrong way round.
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Post by bigvern on Nov 22, 2023 8:12:08 GMT
Also when the 67s went to Hainault the Victoria line melamine maps were removed and central line paper maps were glued in the frame.
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towerman
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Post by towerman on Nov 22, 2023 12:03:11 GMT
Shows how quiet the Underground was after the evening peak back in the 70s,the wrong way round 67TS unit was turned via Earl’s Court,High St & Gloucester Rd on a weekday evening.
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Post by t697 on Nov 22, 2023 18:00:28 GMT
Super. It's scary to think of the assurance assessments and approvals we'd have to go through for that sort of thing today.....
Then again, just maybe, with today's processes the route would be laid down so tightly it wouldn't have left the depot in the wrong direction, so it cuts both ways.
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Post by d7666 on Nov 22, 2023 19:53:04 GMT
Super. It's scary to think of the assurance assessments and approvals we'd have to go through for that sort of thing today..... Then again, just maybe, with today's processes the route would be laid down so tightly it wouldn't have left the depot in the wrong direction, so it cuts both ways. Anecdote that has SFA with topic. Way back in 1990s some of you may remember a railtour operator named 538 Railtours. Well that was me. 29/02/1992 I ran something called Liverpool Street Leapfrog - proving to be a perfect example of how on the day issues wreck the plan. The train was 33/TC push pull visiting GE suburban location involving 42*** reversals. The train was booked to go over the Graham Road curve, north/west bound from Liverpool Street on to NLL. A requirement - don't ask me why - was they insisted the 33 could not push over that section but could only pull. So the whole train was back planned from there to ensure it set off from Waterloo the right way round to achieve this. So what happened on the day. A points failure in the Stratford area led us to do two sides of one triangle, instead of the direct route. This inserted an extra reversal. So the 33 pushed over the Graham Road curve. We all survived. Like I say, nothing to do with topic. Just an example of the best laid plans............ ***42 not really; it was a high number; 42 is the answer to the universe |
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towerman
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Post by towerman on Nov 22, 2023 22:13:12 GMT
Was at Ruislip Depot in the mid 90s,67TS came back from refurb wrong way round.
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Post by hugbilly on Dec 8, 2023 7:33:18 GMT
A naive question from an amateur, but if the trains can be driven from either end why does it matter which way round they are ?
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Post by brigham on Dec 8, 2023 8:32:18 GMT
Propelling a train; that is, having the loco at the back, pushing, isn't as safe as hauling from the front. Anyone who had a Hornby set will confirm!
In order to save operating costs, it was decided to allow 'push-pull' working at express speeds, providing stringent standards of train and track were maintained.
Certain junctions do not meet the requirements, and so propelling at these points is not authorised.
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Post by bigvern on Dec 8, 2023 8:40:17 GMT
The 1967 Tube stock was traditional two ended A & D end train due to provision of electrical connections through the coupler, as the trains on the line wouldn't be turned in normal service. So the car wiring was simpler,
30xx cars A end & 31xx cars D end.
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Chris M
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Post by Chris M on Dec 8, 2023 11:11:54 GMT
To expand on that last post, with "handed" stock you can't couple an A end to another A end, only to a D end because the couplers aren't (electrically) compatible (e.g. an A end coupler might have a power connector on the left and a data connector on the right, a D end coupler would have the opposite so they can connect).
This is fine if the trains can't get turned round in normal service as the A end is always at the e.g. South end and so any unit can couple to any other unit. If one unit is the wrong way round though then it can't couple to any other unit.
Trains that are so get regularly turned round in service (eg S stock) have couplers that are "unhanded" i.e. they are designed such that any coupler can connect with any other. This is more complicated and thus more expensive (e.g. it requires duplicates of every connection).
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