Class 03's and track circuit runner waggons

[gazthomas]

Hi all

Where track circuits in place before or after 03's were introduced? I ask, as if it was before you wonder why they didn't make them a little longer to obviate the need for a complentary wagon to trigger the track circuit.

 

[rebmcr]

That doesn't add up. Track circuits are operable with a single clip on a wire, never mind 3 shunter axles!

 

[GM228]

That doesn't add up. Track circuits are operable with a single clip on a wire, never mind 3 shunter axles!

Many rail vehicles around the world require TCAs to be 100% certain of activating a track circuit, clips on a wire are not guaranteed to activate a circuit!

 

[Emblematic]

The problem with the 03 is not only that it's very short, so potentially could get lost between track circuit blocks (particularly with jointless TCs which always have a gap between adjacent blocks,) but also it's quite stiff, so the three axles tend to form a three-legged stool, with one wheel on one side and two on the other bearing the load. This leads to unreliable TC operation, so a match wagon is a cheap and reliable fix, easier than changing an otherwise satisfactory design.

 

[Jamesb1974]

Deleted

 

[John Webb]

Track circuits have been around for over a hundred years. First proposed around 1860, it was in the 1890s that they became usable with reliability. The main line companies started installing them in quantity from around 1910; at St Albans South we have been loaned the box diagram from 1915 showing the first track circuits installed there.

 

[Dstock7080]

As an aside, London Transport aquired 3 0-6-0 Sentinel diesel shunter locos in 1971, these were too short (at 2.95m wheelbase) to operate track circuits and had to always run with a tender.

 

[Taunton]

When the 03 were introduced, several were allocated to Taunton, but in practice all worked at Bridgwater, 12 miles up the line, in the then docks and industrial yards. One waddled back to Taunton on the main line mid-afternoon most days for refuelling etc, without any need for additional match wagons. This went on for years without problem, just like their steam 0-4-0 saddle tank predecessors with an even shorter wheelbase had done for decades beforehand. The track circuits went in there with the layout remodelling of the 1930s, so were hardly the latest technology.

Quite how this became inappropriate I've therefore no idea.

 

[Emblematic]

When the 03 were introduced, several were allocated to Taunton, but in practice all worked at Bridgwater, 12 miles up the line, in the then docks and industrial yards. One waddled back to Taunton on the main line mid-afternoon most days for refuelling etc, without any need for additional match wagons. This went on for years without problem, just like their steam 0-4-0 saddle tank predecessors with an even shorter wheelbase had done for decades beforehand. The track circuits went in there with the layout remodelling of the 1930s, so were hardly the latest technology.

Quite how this became inappropriate I've therefore no idea.

Probably because the track circuits were not the latest technology - track circuits with insulated joints don't have gaps between blocks (just the width of the insulator.) CWR with joint-less track circuits do have gaps - I believe the LT spec. is a maximum of 9 metres, so if you're running very short stock there's a risk of being on-line undetected, which is unacceptable.

 

[gazthomas]

Thanks everyone for their insight