72TS and C Stock unusual formation questions

I don't really know much about 72ts specifically, but I'll apply my C stock knowledge and see where that leads..........


Firstly, welcome to the forum; secondly, you'll never know if you don't ask!

I thought that they where all 7 cars, with a 4 car double ended unit (proper cab at each end) coupled to a 3 car single ended unit (proper cab cab one end, UNDM other end). On that basis, you'd only have one UNDM per train - if I'm wrong and there are two UNDM's in a train, well it's academic really as it makes no overall difference to how a train works. The basic answer (got there in the end! ;D) is that no modifications are necessary when two UNDM's are coupled together.

Yes & no! ;D ;D As I mentioned, the 4 cars (again, AIUI) have a proper cab at each end - meaning it's a complete train in it's own right - a three car unit with an UNDM at one end is not a complete train (hence why it's called a unit) as the UNDM is simply for use in depots to shunt around.

Can you see the answer to your next question?

Yes it's possible - that's how you make a train! The D stocks on the District are all three car units, does that help your understanding?

I don't know whether two 3 car 72ts units have been coupled, but like I say, there's no technical reason not to (well there may be one - see the C stock answer for more ).

Pass - but again it's equally possible (and again, the C stock answer may equally apply).

They have run as 12 cars - one train assisting another ;D ;D ;D

The optimum design for C stock is 6 cars, but yes, I believe 8 car operation was factored in. The reason the optimum is 6 cars (and here's the link with the 72ts I mentioned above) is the braking system.

Both stocks are fitted with similar braking systems - EP (electro-pneumatic) which is not fail safe, and Westinghouse (pure air only) which is fail safe. The EP brake is the normal service brake and uses retarders & rheostatic energy (the motors) as part of the service brake - these retarders & rheostatic characteristics are set up specifically for a set number of factors and if they're varied wildly [by using a different number of cars] the braking effect will be noticeably affected.

Because the fail safe secondary brake - the Westinghouse - uses pure air only, cases like that above where you end up with a 12 car train, mean that the EP brake has to be cut out as it would not work as intended.

Cutting out the EP brake isn't really a problem as we're trained & tested in the use of Westinghouse (in fact some would say, and I'm among them, that the Westinghouse is a better & more reliable brake anyway) - but the loss of the EP brake does create a problem...................the emergency passenger alarm relies on EP to stop the train ;D ;D ;D So if the EP is cut out, the train goes out of service - the only other reason why trains of different lengths can't operate is as you acknowledge:


Given the number of years these trains have been around, it's almost a forgone conclusion that it's happened.

EDIT: towerman posted while I was typing, so some of what I have said is wrong - if anyone else has corrections, feel free to make me look daft ;D ;D

This has got me trying to think whether 8-car trains have ever worked on the Picc? The only one I recall was the Victoria line tour. I, in common with many people, have seen 2 x 3-car 38TS units coupled together as against a usual 7-car.

When the C69 stock was first delivered it was tested as a 4 car unit on the District line I believe.
As has been said 3 car 72ts units could couple but there could be a few difficulties as all (bar 3299) are A ends to aid shunting in Stonebridge Pk depot. Remember that until the early 80s Mk1s and Mk2s were incompatable. I imagine that in a couple of years 3299 will be converted back into an A end UNDM and replaced by a 1967ts DM, but that is all to come....

So how did that come about then?

That is my understanding

The main change is with regard to the retarders - they basically consist of liquid metal (was mercury but I don't know if that's now changed) which moves between two contacts. If the train brakes too heavily, and the liquid moves far enough, the brakes will release and will reapply as the motion of the train allows the liquid to flow back. If you have travelled on a C stock and felt it 'rocking' as it brakes to a stand, you will have felt the retarders doing their job.

The retarders are therefore set up to work on the basis of six cars - if you then add more cars (or take some away), you change the characteristics such that the retarders become over/under responsive. As the retarders are a primitive version of ABS (anti-skid, if you will), it's important they are set up correctly.

I hate to disagree with you Colin but the retarders do not need to be adjusted if the length of the train is changed. We used to couple and uncouple various stocks in service with retarders ranging from Qs to As. The retarders are set to a specified angle according to the designed brake performance of the stock.

Also, on 67/72 and C Stocks the blowdowns are reversed so that if the e.p supply is lost they still allow max brake cylinder pressure. However, IIRC the reduced speed is required to prevent trains with failed e.p and thus without the benefit of retarder control from getting flats due to over braking with the Westinghouse.

A few comments on this thread I have worked a 4 car C stock from Hammersmith Depot to Edgware Road and back to Hammersmith Depot on a test run, although that was back in the early 1990's ;D
The reason why the EP is cut out if an assisting C stock is needed (making a 12 car train) is that there is a risk of the MCB tripping, due to the additional cars all now taking the electrical feed from the same cab.
The time when the retarders cause the EP to be cut out is when the train is being driven in reverse from the rear cab, as the retarders are now not going to work correctly, as the mercury will now be going the opposite way to normal
Colin - I would be willing to do your C stock refresher in March, but since I'll still be training for my new role at Loughton, that may prove a bit awkward ;D ;D

I had a very scary moment when I saw this thread; a C stock and 72ts would be a REALLY unusual formation

So if I understand this correctly, it makes no difference to braking performance how many cars are coupled, but if an excessive number are coupled, the additional power required to operate the EP brake circuits will cause a circuit breaker to trip. Is that right?

On that basis, would 8 cars be within the permitted current consumption for these circuits, but anything longer require the EP to be cut out?

I am sure that it never happened but there was of course the theoretical possibility that 1972 Stock and C Stock could have been one behind the other when C Stock ran to / from Neasden via the #-over south of / 'loop' north of Finchley Road. I wonder what the rules were regarding a train breakdown then? The Class 503 [?] DC trains had a coupling bar to enable a 1938 or presumably 1972 Stock to be pushed but the other way round was banned.

I never saw such a train but have at least one Bakerloo 1938 Stock 2 x 3-car (and photo'd one in train and bus red at Wembley Park). Tubeprune may confirm if any 2 x 3 car 1959 Stock was returned to the Picc from the Northern after loan say, or sent to Acton Works.

Were the 1956 Stock units coupled with 1959 Stock at any time or were they unable to so couple? I never paid much attention to this aspect when Hounslow West was the terminus and 1938, 1956, 1959 and 1962 Stock all mixed in service on the Picc!

The Aldwych shuttle 1962 Stock (Unit 1751) was used in main line service coupled to another unit and film exists of such a train at Turnham Green. Indeed the last Picc 1959/1962 Stock working was on 5th October, apparently with 1219 + 1728.

The cab roof ends also looked different, and the cars had more wood than the 1959 Stock

I thought it was only 59ts that were on Bakerloo.

The 3 trains of 56ts were all different. Metro-cammell built 1 train, Birmingham and Gloucester built one each. These differed internally by having deeper seat cushions

Here are some photo links:
www.londonrailways.net/56stock.jpg -Gloucester unit

www.users.globalnet.co.uk/~cign/rjwsite/index/02u1011.jpg -Gloucester unit

www.ltmcollection.org/images/webmax/db/i0000bdb.jpg -Metro-Cammell unit

As you can see, the Metro-cammell design was adopted in the end.