A stock RAT sighting

I suspect only if it were an S4!

I really ought to have put the link in there, my apologies.

Here it be; www.flickr.com/photos/tubesnaps/14315542746/

Out of curiosity, what is the rationale behind using old stock for a RAT as opposed to just ordering more of the new stock? Surely it's expensive to have to maintain and source spares for a single unit of obsolete stock?

Isn't there one train of modern (well, from the 90s) that is used like that. Aren't there little aluminium plates in the vestibules where the tubes from the sandite hoppers go down to the wheels? I think it's 92ts, but that wouldn't make sense with the heritage sandite units on the Central Line.

Ahhh that would make sense, my "little aluminium plates" being one of your "various moifications".

A RAT is a Rail Adhesion Train - or Sandite unit. What it does is spray sandite (which is a mixture of sand and a few other things) onto the running rails, with the intention of reducing the problems caused by leaves on the line and improving traction. I believe (thus saith Wikipedia, anyway, although it presumably has the National Rail network in mind and LU may be a little different) that the leaves are first cleared by spraying jets of water onto the rails and then the sandite is applied. Sandite helps the wheels to grip better so you don't get the terrible slipping and sliding associated with leaves on the line, which can cause station overruns and SPADs. When train wheels go over leaves, the leaves basically get shredded and squished and the stuff that comes out of them and coats the rails is an absolute nightmare for trains, because the wheels will just slide like mad. It's like driving a car on black ice. Very nasty.

Plug.

Battery locos are in short supply, and can not be stationed full time. I believe the RAT train can be called out at any time if required.


A separate Sandite car could in theory be possible, but either way it would require power, someone at the controls etc.

In the olden days when Underground trains were made up of individual cars which could be mixed and matched as required it would have been possible to form a Sandite train from two standard (or even Standard) driving cars borrowed from the revenue-earning fleet sandwiching a special Sandite car. But these days trains are made up of units of more than one car each, which run in more or less permanent formations. For trains made up of three or more units it would be possible to replace a middle units with a suitably wired Sandite car, but now the C stock has gone the only line operating trains of more than two units is the Central Line. It is presumably cheaper to have a specialised unit to distribute the Sandite rather than have two extra units in the fleet to provide cover.

Note that de-icing also used to be done with specialist cars - the "sleet locomotives" converted from CLR tunnel stock. Nowadays de-icing equipment is mounted under certain members of the normal operating fleet. I assume there are reasons why sandite-spreading equipment cannot similarly be fitted under an operational passenger carrying car.

longer trains also have more axles, which is important as both leaves and sandite can sometimes insulate a train from the track. The more axles a train has the less likely it is to be completely insulated and thus invisible to track-circuit based signalling.

OK, that all makes sense, thanks. My question/suggestion was a bit influenced by seeing the short-ish Network Rail Sandite train passing through Amersham the other day.

Wonder what happened to the T Stock Sleet Loco/train down in Kent. Heard it was for sale. I suppose if it had been any good at its job, TFL could buy and restore it ready for when the A stock RAT became obsolete. :-)

The Green Goddess (3-car 960/117) was withdrawn at the end of last year's Sandite season.

A Network Rail RHTT runs using top and tailed class 66 locomotives (fitted with tripcocks) - beyond the LU boundaries this sprays water and applies Sandite, but only the former is done over LU sections.

Because that's done by the A stock Rail Adhesion Train. ;-)

Just Sandite.

Irritatingly, I'm struggling to find my source now, but I believe it has been preserved - I'll keep digging!