Jump to content
 

Max. distance of signal box from points/signal


Recommended Posts

My question is in the title.

On the layout I'm building I will site the signal box opposite the station platform where most of the pointwork is situated close together (6 in total), but approx. 100 yards (at 1:1 scale) along the line from the box are another 2 points and  a signal.

Could these be operated by the same signal box or is that too far, and another box would be required.

Link to post
Share on other sites

Not sure of your railway or period, but GWR mechanical boxes, in addition to the frame/push rod operated points, operated points at a distance using electric motors on the points with a hand generator in the box, later replaced by rechargeable cells.

 

Mike Wiltshire.

Link to post
Share on other sites

  • RMweb Gold

Another trick the railways used was to have sprung trailing points on loop exits. The facing part was within the 350 yards but the trailing part could be further away as it was unworked.

 

Signals were probably no further than 2000 yards due to expansion issues and the weight of wire the lever would have to pull. "Assister weights" were provided (on the LNWR at least) to ease this.

Link to post
Share on other sites

The present limit for mechanicaly worked points is 350 yards, that is by a conventional roding run. In the '20's and '30's there was a few installations that used the Continental "Double Wire" system, these in theory, could be any distance from the signalbox, but there would be a practical limit. Power points can be any distance from the controlling signalbox. There is no limit on mechanicly worked signals, but has Beast already said, the practical limit is approx 2000yards. For round figures in 4mm scale, 350yards equals 13ft 9ins, so unless you have an aircraft hanger, and a bank balance to match, the figures are pretty hypothetical.

Link to post
Share on other sites

  • RMweb Gold

Martin is correct for points, although with modern pway the distances have been reduced in reality. 350 yards is quoted in the Board of Trade Requirements of Feb 1925. Back in the 1885 Requirements the distances quoted were 180 yards for facing points and 300 yards for trailing points in main lines or safety points in sidings.

For signals the often quoted limit was 1760 yards for wire operation, but IIRC this was not laid down in the Requirements. Again the practicalities of this depend on the nature of the wire run. Curves and crossing of the lines reduced the practical distance, Besides assister weights mentioned by Beast, stroke posts were used to keep the wire taught for the first half or more of long runs reducing the amount of slack to be taken up by the lever.

Link to post
Share on other sites

  • RMweb Gold

Not sure of your railway or period, but GWR mechanical boxes, in addition to the frame/push rod operated points, operated points at a distance using electric motors on the points with a hand generator in the box, later replaced by rechargeable cells.

 

Mike Wiltshire.

The distance of hand generator points from the box was limited by the volt drop on the line wire or cables. The practical limit was about half a mile. The GWR used the Westinghouse Style C machine on these.

Link to post
Share on other sites

  • RMweb Gold

Beast, you don't mention the LNWR practise of working a Distant signal by two levers. I think this was uniquie to the LNWR, I have never seen it elsewhere. Mick.

 

And in one case 3 levers - Duston near Northampton for those interested.

 

I've worked a 2-lever distant, at Helsby on the down Manchester, the first lever takes up the slack, the second lever clears the arm, levers 44 and 45 on the diagram below.

 

post-6662-0-45526400-1379542282_thumb.jpg

 

Edit to add 3 lever distant box.

Link to post
Share on other sites

  • RMweb Premium

The limits are determined as much by what a man (until recently nearly all signalmen / signallers were men) could physically pull off.  Anyone who has tried to pull something like half a mile of wire or more will know that isn't easy; I remember watching the Dovey Junction up (Aberystwyth line) distanct being pulled off involving something crossed between wrestling and a dance move!  GWR boxes had slack adjusters to take up the wire slack but expansion over that sort of run could require multiple turns of the device before a signal would clear.  Similarly with point rodding there is a fair effort required to shift the metal which constrains the distance over which rodding is effective in addition to the expansion issue.

Link to post
Share on other sites

  • RMweb Gold

Expansion is not an issue with most point rodding as long as the compensation is done correctly. The biggest problem with it is if the sun and shade is continually shifting on different sections of the run. 

 

For long wire runs a stroke post was favoured on LMS lines. In this picture the box is to the right. The weight keeps the wire from the box to the stroke post taught, thus reducing the slack to being that between the stroke post and the signal only. The weight also compensates for temperature expansion and contraction on the first section of the run.

 

post-9767-0-21581300-1379546216.jpg

Link to post
Share on other sites

Expansion is not an issue with most point rodding as long as the compensation is done correctly. The biggest problem with it is if the sun and shade is continually shifting on different sections of the run. 

 

For long wire runs a stroke post was favoured on LMS lines. In this picture the box is to the right. The weight keeps the wire from the box to the stroke post taught, thus reducing the slack to being that between the stroke post and the signal only. The weight also compensates for temperature expansion and contraction on the first section of the run.

 

attachicon.gifCTT_310-1 (427x640).jpg

Agecroft Jn had a couple of these on the up main splitting distants. These signals were 1586 yards from the box round an S bend and the wire went under the tracks around half way. They both needed a mighty swing and I was warned during training that if I needed to take a second swing, leave it for 20 seconds or so before doing so. This was to avoid catching the device on the backswing. Needless to say eventually I forgot and on a second swing the lever momentarily locked halfway across and the wire went Twang! as I was in full heave mode :bb:. I ended up in a heap on the floor narrowly missing banging my head on a cast iron radiator. Only did that once.  :fool:

JF

Link to post
Share on other sites

Two minor comments....

 

Firstly, as has been pointed out already, the limits for mechanical point or FPL rodding were originally quite short, but have been extended in stages over the years. So you need to ensure that you adopt the right limit for your chosen modelling period.

 

Secondly, where a set of points was too far away for the limit at that time, then -depending upon the traffic requirements - rather than providing another manned signal-box it was quite common to have those points worked from a local ground-frame, the GF being locked from the signal-box. The locking might be mechanical or electrical (in later years) or simply by a key taken from the SB to the GF.

 

Once the increase in rodding limits brought those points within the reach of the SB, then the railway /might/ abolish the GF and work the points direct from the SB, or it might keep the existing method to avoid the cost of alteration if the traffic need was light (eg a rarely-used siding).

 

What period and what railway company are you modelling?

Link to post
Share on other sites

  • RMweb Gold

Agecroft Jn had a couple of these on the up main splitting distants. These signals were 1586 yards from the box round an S bend and the wire went under the tracks around half way. They both needed a mighty swing and I was warned during training that if I needed to take a second swing, leave it for 20 seconds or so before doing so. This was to avoid catching the device on the backswing. Needless to say eventually I forgot and on a second swing the lever momentarily locked halfway across and the wire went Twang! as I was in full heave mode :bb:. I ended up in a heap on the floor narrowly missing banging my head on a cast iron radiator. Only did that once.  :fool:

JF

The help weights under the box on long pulls could catch you like that. A Lineman I was working with in the late 1960s got some grief for disconnecting a distant signal without putting a Reminder Collar on it. The Bobby went to pull it and as he got it out of the catch it shot across and hit him. 

Link to post
Share on other sites

  • RMweb Gold

The distance of hand generator points from the box was limited by the volt drop on the line wire or cables. The practical limit was about half a mile. The GWR used the Westinghouse Style C machine on these.

And the Region was still installing them occasionally into the 1970s (presumably using refurbished equipment) - the hand generators were commonly known as 'hurdy-gurdys' in some areas and were rather satisfying to work because you could hear the lock drop in the point lever controller once you'd wound them enough.

 

I never found, or heard of, any problems with pulling mechanically worked points a long way out provided both they and the rodding run were in good order.  The most common problems with heavy pulls on points seemed to be poor adjustment (uncommon once they'd properly bedded) and lack of lubrication of the slide chairs although i did come across one or two instances of movement of stools in the rodding run although I think all of those were runs nearing the end of their lives;  the only exception was at one 'box where just about everything outside seemed to be moving, usually in different directions, which even made points close to the 'box very heavy.  

 

 

 

Two minor comments....

 

Firstly, as has been pointed out already, the limits for mechanical point or FPL rodding were originally quite short, but have been extended in stages over the years. So you need to ensure that you adopt the right limit for your chosen modelling period.

 

Secondly, where a set of points was too far away for the limit at that time, then -depending upon the traffic requirements - rather than providing another manned signal-box it was quite common to have those points worked from a local ground-frame, the GF being locked from the signal-box. The locking might be mechanical or electrical (in later years) or simply by a key taken from the SB to the GF.

 

Once the increase in rodding limits brought those points within the reach of the SB, then the railway /might/ abolish the GF and work the points direct from the SB, or it might keep the existing method to avoid the cost of alteration if the traffic need was light (eg a rarely-used siding).

 

What period and what railway company are you modelling?

Another thing here is that some Railways also set about rationalising the number of signalboxes after the distance had officially been increased.

Link to post
Share on other sites

  • 2 weeks later...

Archived

This topic is now archived and is closed to further replies.

×
×
  • Create New...