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Unusual drop-flap signal at Oban

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Unusual drop-flap signal at Oban

Unread postby mossend4 » Sat Oct 22, 2016 8:49 am

An enquiry from another forum – what is the purpose of the pipe and connector attached to this drop-flap signal at Oban signal box at this link? (Apologies for the crop and enlargement - it is an accidental capture in the foreground of a locomotive shot).

https://1drv.ms/f/s!AsRXEb3hnw8cmhz03FGaUZLgicCh

If you have ‘Signalling the Caledonian Railway’ by Jim Summers, page 94 has a photo of an elevated drop-flap signal with the same fitment at Oban Goods Junction.
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Re: Unusual drop-flap signal at Oban

Unread postby Mike Hodgson » Sat Oct 22, 2016 9:37 am

It's not gas-lit is it?
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Re: Unusual drop-flap signal at Oban

Unread postby Fast Line Floyd » Mon Oct 24, 2016 9:54 am

Mike Hodgson wrote:It's not gas-lit is it?

My thoughts also.
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Re: Unusual drop-flap signal at Oban

Unread postby mossend4 » Mon Oct 24, 2016 10:11 am

One or two members of the other forum thought that too. So far we haven't found written records for any gas-lit signals on the Caledonian Railway. The two photos are of signals at Oban, and there was a gasworks there. We have a verbal report of gas pipes discovered at Ayr (G&SW) which were also thought to be connected with signalling.

I personally had never heard of gas-lit signals.
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Re: Unusual drop-flap signal at Oban

Unread postby Pete2320 » Mon Oct 24, 2016 10:43 am

I don't think they were ever particularly common but certainly not unknown. They were of the era before the long burning oil signal lamp was invented and were largely replaced by the long burning lamps.

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Re: Unusual drop-flap signal at Oban

Unread postby MRFS » Mon Oct 24, 2016 11:02 am

I'm also convinced that's a gas fitment - the large round thing is a filter, I think.

There were *flashing* gas lit signals. Yep, extinguishing and relighting the flame. Eek.
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Re: Unusual drop-flap signal at Oban

Unread postby davidwoodcock » Mon Oct 24, 2016 11:18 am

MRFS wrote:I'm also convinced that's a gas fitment - the large round thing is a filter, I think.

There were *flashing* gas lit signals. Yep, extinguishing and relighting the flame. Eek.



Surely not extinguishing the flame but rather turning it down and then up - a comparatively simple task with a constant pressure gas supply.
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Re: Unusual drop-flap signal at Oban

Unread postby Mike Hodgson » Mon Oct 24, 2016 12:05 pm

MRFS wrote:There were *flashing* gas lit signals. Yep, extinguishing and relighting the flame. Eek.


Sounds like my central heating boiler. Probably more reliable than arranging for the drop-flap to keep moving. :twisted:
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Re: Unusual drop-flap signal at Oban

Unread postby Andrew Waugh » Mon Oct 24, 2016 12:44 pm

MRFS wrote:I'm also convinced that's a gas fitment - the large round thing is a filter, I think.

There were *flashing* gas lit signals. Yep, extinguishing and relighting the flame. Eek.


But this wasn't town gas technology.

Flashing gas lit signals used acetylene gas and AGA lamp technology. This was invented by Gustav Dahlen for use in unattended navigation lights. It was consequently *very* *very* reliable - railway signalling doesn't even come close. Navigation lights simply can't go out, nor is there a signal maintenance technician on call to fix them if they do. A couple of times a year, the supply ship would turn up, the crew would clean the bird poo off the light, change the acetylene bottles, service everything, and depart.

The complete system included a 'sun valve' which turned the light off during daylight hours, and valves that made it flash. The flashing is important - each light has a 'characteristic,' or particular pattern of flashes, so that mariners can reliably distinguish one light from another at night. And, yes, the gas was cut off and relit every time using a pilot flame. Dahlen, incidentally, won a Nobel prize for physics for the invention of the sun value.
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