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In-cab AWS Equipment


Evertrainz
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When developing a 3D model of a loco cab (around 1960s era) I have stumbled upon a bit of confusion. Although the topic in question might be better suited to preservationists and the skilled locomotive restoring groups rather than the casual modeler, there are many overlaps between these communities so I've decided to ask here.

 

When looking at photos of AWS electropneumatic equipment located on the cab bulkhead among many classes, I can see two different "types", or "generations", of equipment installed. Generally when looking at the earlier diesel and electric cabs, there are usually four primary AWS bits located directly on the bulkhead - note that this excludes the fire bell:

- 'Clear' bell - large grey object mounted on a green backing

- Green warning horn - circular mesh-covered object that I think was operated by vacuum(?)

- Battery isolation and cab change end switches - Large box-ish apparatus usually painted silver, grey or blue

- Green electropneumatic valve

 

We'll call this the "modern" set.

 

 

However there seems to be a different set of equipment in certain locos, sharing many components:

- 'Clear' bell - large grey object mounted on a green backing

- Green warning horn - circular mesh-covered object that I think was operated by vacuum(?)

- BIS/change end apparatus: this time appearing more octogonal in nature

- Green electropneumatic valve, a more traditional box-like shape with raised surfaces, compared to the complex shape of the previous set

- Relay valve

 

Does anyone know if there's any way to categorize or separate these? In the former shot of the 31 bulkhead, we see the one set of equipment. However, in the preserved Ped 31018 at the NRM, there is the latter and less-common set of AWS equipment. Similarly as the preserved 40s have the "modern" set, there also appear to be some using the earlier set in these earlier shots.

https://www.flickr.com/photos/126693116@N06/43397270105/in/faves-125881805@N02/

https://www.flickr.com/photos/126693116@N06/37838142416/in/faves-125881805@N02/

 

Was the earlier equipment changed out in favor of modern equipment at some point? Was it down to builder? Region? I wonder if anyone involved in preservation have received a loco with the earlier set, and swapped them out for the "modern" set of equipment. 

 

Any ideas?

 

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The main difference you have is that the early locos show the Vacuum relay valve (vac only loco) where as on the late one the relay is that for a dual braked loco and is electro pneumatic as opposed to electro vacuum.  The change ends/isolating switch also changes slightly on  conversion from vacuum braked to dual braked.

 

It has also changed more recently with the installation of TPWS.

 

Al Taylor.

 

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