S-Stock Delivery Question

[cso]

From talking to two people on the platform at Princes Risborough this evening when Train 39/40 arrived, S Stocks seem to arrive in two formats:

Class 20 - Class 20 - Barrier Wagon - S Stock - Barrier Wagon - Class 20 - Class 20

or

Class 20 - Yellow Wagon x 2 - Barrier Wagon - S Stock - Barrier Wagon - Yellow Wagon x 2 - Class 20


My housemate has a theory on why this might be... but I'm wondering if anyone here knew the answer?

[Deleted]

Brake Force. The 20s cannot operate the brakes on the S Stock, and therefore if only 2 Locos are used vice 4 then they need a few extra vehicles in the consist to increase the stopping power avilable. I'm not sure if GBRf run a train pipe through the S Stocks such that the Brakes can be applied on the rear Barrier Wagons / 20s

[Deleted]

GB have four Class 20s on long term hire from DRS for these workings.
At the moment one of them is broken so they are using the two MLAs (yellow wagons) each end to provide sufficient brake force as jn114 says.

I would assume that Bombardier install the temporary air pipe through the S stock to allow it to move and LU remove it once delivered..
The train wouldn't be allowed to run if there weren't continuous brakes.
It still doesn't have much brake force which is why it runs as a Class 8.

I've only even seen the two KBA barrier tanks so don't know if GB have a spare.
I would hope so for redundancy.

Andy

[cso]

There's definitely an air pipe which runs through the S-Stock when it's used with 4 wagons, as I saw it last night.

Also, my housemate's theory has been proved correct by your posts, so that's nice to know.

Thanks