Bahamas

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Shop - The Bahamas Locomotive Society

 

I’ve just read in the latest KWVR mag that as part of the overhaul the loco will be fitted with air brakes.

 

Technically fitted with an air pump and combined brake valve for working air braked trains, the engine and tender will still be steam braked. I understand that the air pump will be located out of sight between the frames rather than under the driver’s seat as with 4871 and 5212. A sensible decision IMHO to future proof it as I’m sure the time will come when vacuum brakes are banned from the big railway.

 

Thanks for the detail.

 

We also have a Facebook page with pictures showing progress on the overhaul..

And of course a shop Shop - The Bahamas Locomotive Society any income from sales or donations helps with the overhaul or why not join us?

 

Out of interest, why do you think this? Granted the experience with Vacuum brakes is becoming more limited, but that is different from a ban? Surely as long as a train can be demonstrated to be stopped effectively, the method is not really a huge concern to railway inspectors. Not sure anyone has ever doubted the effectiveness of vacuum brakes.
Only air braked stock being available is probably more pressing than a vacuum ban - hence this work to Bahamas which will make it a very useful loco.

 

Vacuum brakes certainly are effective, less complicated and easier to maintain than a two pipe air system although less efficient as the maximum braking force is limited to atmospheric pressure, about 15psi I think. The air brake train pipe is charged to 72.5 PSI ( 5 bar ). I could be wrong but the problem is if anything goes wrong on an unassisted steam tour where is the nearest vacuum braked rescue locomotive? When Bahamas went over Shap a diesel loco was one block behind it but to do that regularly would be rather expensive.

 

That is a fact John, certainly seems to have been a concern over the last 10 years but it must be getting on 30 years since last there were any dual braked diesel locos active, apart from those operated by WC and more latterly VT of course.
Perhaps the consequences of a train stranded in section have become more onerous so precautions need to be greater?

 

The different air / vacuum (air pressure in reverse) are compensated by the use of bigger cylinders for a vacuum system so equalising the brake effort. A vacuum brake can be just as effective as an air system although slower acting, hence the need for vacuum experience. Ultimately, the effectiveness of the brake is the adhesion between the wheel and the rail, not the means of application.

 

I didn’t know that, I’ve always assumed that the faster action was because of the additional brake pressure

 

You either run it a block behind or put it on the back, still need to staff and fuel it.
This is no different for the last 20 years though, which is when EWS withdrew their last dual braked locos. Both West Coast and VT risk assess trips and act accordingly - Shap trips used to be unassisted due to the proximity of Carnforth and dual braked diesels.
I dont see any directive coming from HMRI on this anytime soon though.

 

The two systems work on very different principles and the mass of air to be moved in a vacuum system is much greater than in an air system, so it requires more time to, for instance, fill and drain a cylinder. Look tat the thickness of an air hose, which has to withstand about five times the pressure, and a vacuum hose and you'll see what I mean. There is far less air movement with the pressure system than the vacuum.

 

Maybe it isn’t which is why I used the term future proof

 

As I understand it, with two pipe air, one pipe acts as a ‘brake controller’ along the length of the train, and via the ‘triple valves’ actuates the brakes on each vehicle, these are then recharged from local reservoirs.
With vac, air is admitted and removed from the loco only, so it takes longer for pressure to rise along the length of the train and apply the brake, and vice versa to release the brakes on each.
This could be total rubbish as I’m trying to recall my Black Book knowledge from 50 years ago, so please feel free to put me right.