Suspended due to Poor Weather conditions

Quite a tribute to the advance of technology over about 35 years. 73TS was originally fitted with WSP which had to be taken off because it was so inadequate and one of the most unsung successes of S stock is its really good WSP.

It was mostly the electronic WSP controllers that limited the performance. Two types, about half the 73TS fleet each I think. The dump valves were standard Westinghouse products and themselves a good product although they probably couldn't pulse on and off as fast as ideal for slip control. The WSP controllers were pre-microprocessors. One from Westinghouse and I think primarily working on rate of wheel speed change as its slip detection. The other, Whitedown, primarily working on axle speed comparison as its slip detection. I may have over-simplified this summary. Every axle had a tacho head feeding pulses back to the control unit proportional to rotational speed.

Neither system was good enough. The detection, the correction and re-application regimes were too slow and the systems spent too long with the brakes released or near released. This meant they had to be arranged so that in emergency braking the dump valves were electrically isolated and no slip control could occur.
Typically a train would slip, WSP control would start, the T/Op would sense a reduction in overall brake rate, move the control handle to demand more braking until reaching Emergency at which point WSP would be cut out and likely lock the slipping wheels and cause wheel flats.

As mentioned, the equipment was first isolated entirely then later removed.

So d7666 are you possibly hinting that the RAT days could be numbered once the CLIP project is completed on the Central Line? But then again, they provided new ones to work with the S stock!

Maybe when they start scrapping 73TS they’ll keep some for RATs.

I would imagine a couple of 1973 stock trains for RAT duties would be maintained after their withdrawal.

There’s a lot of trees on the East End of the Central so like the Met, there is a heavier leaf load.

Are we assuming that the new Picc trains will no longer require the operation of RAT trains? The new trains will be to the latest standards and include auto-sand hoppers, as S stock, for poor adhesion conditions. However, there are still RATs operating on the Met. line!

This is a very complicated subject. The issue of DC motors vs AC motors is a red herring though. It is general LU practice on trains with WSP that, when wheelslide protection is activated, the dynamic brake is dumped and braking is carried out pneumatically.

WSP systems generally compare the speeds of all four axles on a car. If there's a significant discrepancy it determines there's slip. There's also another factor. If the system detects an unfeasibly high deceleration rate, the WSP determines that slip is occurring*.

The ATO/ATP systems add to the complexity.

On the axles with the ATP tachos, (two per train end) the system compares the speed between the two axles and looks for an unfeasibly high deceleration rate. If there's a discrepancy, in simple terms, the system decides it's lost and applies the emergency brake.

One of the reasons for a great deal of care of adhesion levels on the Central line is that it was LU's first ATO line operating in the open (ignoring the original trials on the District and Woodford Hainault). When originally delivered there was no WSP as it was believed that the dynamic brake would self correct in poor adhesion. In practice all trains tended to get wheel flats, and an excellent WSP was retrofitted. The original plan of open ATO was for the deceleration rate to be 0.75m/s2 which is very high for open running in leaf fall. Later an option for 0.6m/s2 was added - still high.

In comparison, Jubilee and Northern have much more control over braking rates and 0.4m/s is not uncommon. But, and there's a big but, these trains have a blended braking system. At low brake rates, the system tries to brake using the dynamic brake, and the trailer cars do little or no braking. But if wheel slip is detected, the dynamic brake is discarded and friction brake is applied to all cars. This means that brakes are suddenly applied on the trailer cars which can cause the issues described above with the ATP tachos.

Re S stock, a great deal of work has been done simulating the effect of sanders on S stock braking but as I understand it, sanding has yet to be commissioned. I hope I'm wrong!

And Elizabeth line trains always have a proper speed reference signal as the axles at the cab ends are unbraked.

* the very latest WSP systems have been further developed and they compare speeds of all axles on the train and operate dump valves appropriately. The very latest systems have another feature whereby the brake demand is adapted depending on the assessed adhesion which will vary along the train. The driver - or ATO - might be demanding a medium brake rate and the brake system will decide to apply a low rate at the front of the train, medium in the middle and high towards the rear. I don't know of any practical applications of this system but someone else might be along with more knowledge

Adding to my previous post:

The 1973 tube stock's lowest brake rate is pretty high - just under 0.6m/s2. With this brake rate and no WSP it's not surprising there are wheel flats

Reponding to spsmiler: Rail adhesion trains are part of the process of managing adhesion levels on the Metropolitan line together with foliage management, and leaf clearance. WSP and sanders will do a good job unless the leaf film is very tough/the coefficient of friction is very low. Under those circumstances, neither sanders nor the action of WSP will help.

Lastly, one 1973 tube stock car has operated through the Central line routinely. It's the track recording car.

Unless they use axle counters or something I do not know about I suppose that they will still use track circuits. All I do know is that the adopted solution will not require any special equipment on the train - beyond the train stops which nowadays all non automated trains using this route need. 

In the past I've seen LU Rat trains, Chiltern water jetter trains and Network Rail (or Railtrack) RHTT all passing through Rickmansworth - this short video shows the RHTT and Chiltern water jetter plus LU Track Recording Train.

re: the reply to me by 100andthirty about the Track Recording Train, so obviously the length of the 1973ts trains is not an issue for the Central line but the trailer possibly will not have any power collection shoes, whilst the two 1960ts DM's will have special 'high lift' power collection shoes, as these are needed for trains to pass through the original Central London Railway tunnelled section of the Central line. Even if unpowered.

The CBTC will see them via the axle counters in the same way that they see LU-operated trains in the CBTC area today. There is, naturally, a lot more to it than that, but it's the simple answer. There will not be track circuits, but it might be that the axle counters give more reliable detection than track circuits do in leaf-fall conditions where there is a strong possibility of rail head contamination.

Not a red herring. You have mis-read if you are refering upthread to my comments.

What I posted about DC v. AC was about wheel slip not slide; slip [wheel rotating faster] is under traction; slide [wheel rotating slower] is under braking; my posts say nothing about braking by any means, or slide, or WSP.

NR is also re-looking at plasma torch treatment. This autumn season there is a MPV carrying plasma torch kit under trial; it has been on a preserved line somewhere, they have got to the stage where it needed real live testing on a real line with real falling leafs.

Some with long memories may remember BR tinkered with plasma torch 50 years ago
www.old-dalby.com/Plasma%20torch.htm
and
www.traintesting.com/images/975018%20AND%20975019%20PLASMA%20TORCH%20CLASS%20101.jpg
you can just about see the torch flame immediately to the rear of the rear bogie of the leading car.

Just as a pedantic point, while LU RAT dispenses Sandite, NR RHTT dispense TrackGel, which is not quite the same thing. TrackGel comes in several variants, usually indicated by a two digit number; not sure if the same variant is used everywhere. IIMU RHTT do not dispense TrckGel over LU infrastructure.

re unexplained acronyms: IIMU = it is my understanding?

Are any of those actually acronyms?