Chain guards still a thing?

[Questions]

Good morning,
I was out walking in Scotland for a few days and used a few foot crossings and farmers crossings.
I noticed none of them had chain guards on the decks.
Are chain guards no longer a requirement?

 

[John Webb]

Good morning,
I was out walking in Scotland for a few days and used a few foot crossings and farmers crossings.
I noticed none of them had chain guards on the decks.
Are chain guards no longer a requirement?

I'm uncertain what 'chain guards' are. Were these some form of protection against dangling coupling chains on goods wagons?
If so, then as there no such wagons about any more on the national network presumably they no longer needed.

 

[Questions]

Yes, they used to have them on every crossing. When I used to help my friend on the historic railway he volunteered with , we used to clean them up and re-secure the bolts.
They where metal deflector plates at both ends of each crossing if that helps, they used to take a right good hiding.

 

[davetheguard]

The only meaning I know of for "chain guards" is the cover over a bicycle chain that stops the bottom of your trouser legs getting caught in the chain and/or being covered in grease.

Clearly, that's not the meaning the OP is refering to! Can you describe it further @Questions ?

 

[Questions]

I will try and find a picture

But essentially it’s a metal deflector plate that goes on either end of a crossing in the track, sorry I can’t describe it any better.

 

[Ashley Hill]

Are these what you mean. Here’s a picture from Network Rail showing a crossing with the items indicated.

 

[Mcr Warrior]

Are chain guards no longer a requirement?

As @John Webb was wondering, what exactly do they protect against? Damage to the leading edges of crossing surfaces?

 

[LowLevel]

As @John Webb was wondering, what exactly do they protect against? Damage to the leading edges of crossing surfaces?

They bounce dangling couplings up rather than them getting caught under the boarding and destroying the crossing in the process.

 

[Questions]

Are these what you mean. Here’s a picture from Network Rail showing a crossing with the items indicated.
View attachment 178949

Yes !

That is it

Are they no longer a requirement?

 

[Gloster]

They shouldn’t be needed at all as nothing should dangle below rail level as it will hit a lot of other stuff and dash itself against points. So what were they for? Although the railway has long had a ’belt and braces’ attitude, are they really intended to prevent something that has come loose from catching, but if so why only in the middle?

 

[LYradial]

Wild guess, they are solar cells to power the little LEDs the mark the edge of the crossing.

 

[swt_passenger]

Wild guess, they are solar cells to power the little LEDs the mark the edge of the crossing.

The angled plates just show the word “STRAIL”, being the manufacturer of the crossing components.

 

[edwin_m]

They shouldn’t be needed at all as nothing should dangle below rail level as it will hit a lot of other stuff and dash itself against points. So what were they for? Although the railway has long had a ’belt and braces’ attitude, are they really intended to prevent something that has come loose from catching, but if so why only in the middle?

I assume it's a coupling that might be dangling, therefore it's in the middle. If it strikes a rail on a set of points then it will be pushed off to one side and probably just ride over the rail and swing back once it is pushed far enough - and a rail is a lot more robust than a crossing panel. AWS magnets have a similar ramp. TPWS grids don't but they are well below rail level. Facing point locks had these historically too, possibly because although they are well below rail level a coupling striking them could move the point blades under the train. This may also be one reason why modern point machines aren't between the rails and the actuating rods are often top of sleeper level.

 

[LYradial]

A bit about it here https://www.networkrailmediacentre....y-at-footpath-level-crossings-across-anglia-1

new warning system to improve safety at level crossings in anglia

In the photo, to me the ramps look a bit flimsy to me to act as protection

 

[Ashley Hill]

but if so why only in the middle?

Because that is where couplings hang. You will also find similar protecting mechanical facing point locks. Here’s a photo of one.

Photo RMWeb

 

[Questions]

Good morning, so to confirm, are the coupling guards a requirement or not on crossings?
Why do some crossings have them and some don’t?

 

[Ducatist4]

i thought their current usage would be to protect against damage from the AWS detector on trains passing over the crossing.

 

[Ashley Hill]

i thought their current usage would be to protect against damage from the AWS detector on trains passing over the crossing.

The AWS magnet on trains is fixed so doesn’t dangle. However,AWS ramps have coupling guards to protect the magnets. Here’s a photo of one showing the guard.

Photo Railsigns.
Where the AWS ramp is on a bi-directional line a guard is provided on both sides.

 

[skyhigh]

i thought their current usage would be to protect against damage from the AWS detector on trains passing over the crossing.

If the AWS receiver is that low there's a problem.

 

[Ducatist4]

I have no idea as i was unable to find anything online that showed how it worked under the loco. Anyone know of anything?

 

[Gloster]

The only thing that should be below the level of the top of the rail is the wheel flange. Anything else is going to catch on the rail at at every crossing and either damage itself or the track. Anything that does hang down must be secured so that it does not get lower than it should, all of which will be carefully calculated and adjusted. The AWS receiver and any other signalling equipment will be carefully adjusted: the top of the ramp itself will be just above rail level so that the bottom of the receiver can pass safely above the rail at every crossing, but touch the ramp when it encounters it.

 

[skyhigh]

I have no idea as i was unable to find anything online that showed how it worked under the loco. Anyone know of anything?

The AWS receiver is fixed in position under the train, at a height of around 4-6 inches above railhead (from memory).

It absolutely does not need a ramp to stop it hitting track objects.

 

[4COR]

The AWS receiver is fixed in position under the train, at a height of around 4-6 inches above railhead (from memory).

It absolutely does not need a ramp to stop it hitting track objects.

It would be quite tricky to negotiate pointwork if it did...

 

[edwin_m]

The AWS receiver is not intended to touch anything. It works by sensing the magnetic field as it passes a short distance above the magnets.

People suggesting otherwise may be thinking of the old GWR ATC system, which the ramp would push the receiver upwards to activate the brake valve, at the same time being energised if the signal was clear which operated another valve to cancel the brake application. In this system the ramp was above rail level and much longer than the protective ramp on an AWS magnet, to give a more gradual lifting (but even so probably wouldn't have worked at 125mph).

 

[saismee]

Mixed LO/LU lines use similar wooden ramps over TPWS loops to deflect the centre contact shoe on underground units. Not quite relevant in Scotland, but there's numerous reasons that a ramp would be added.

Considering TPWS was invented much later than AWS, it can be assumed that the lack of ramps (on TPWS loops) is due to older stock with the risk of dangling chains/couplers no longer being in use. AWS ramps are older, so it is likely just a leftover from their design. It's cheaper to install a mass-produced plate of metal than to justify removing it from the design.

 

[edwin_m]

Mixed LO/LU lines use similar wooden ramps over TPWS loops to deflect the centre contact shoe on underground units. Not quite relevant in Scotland, but there's numerous reasons that a ramp would be added.

Considering TPWS was invented much later than AWS, it can be assumed that the lack of ramps (on TPWS loops) is due to older stock with the risk of dangling chains/couplers no longer being in use. AWS ramps are older, so it is likely just a leftover from their design. It's cheaper to install a mass-produced plate of metal than to justify removing it from the design.

The top of an AWS magnet is significantly higher than the top of a TPWS loop. And putting a metal plate on top of or even within a TPWS loop is probably going to prevent it working.

 

[saismee]

The top of an AWS magnet is significantly higher than the top of a TPWS loop. And putting a metal plate on top of or even within a TPWS loop is probably going to prevent it working.

I don't understand what you are trying to say. TPWS loops still needed a ramp on mixed LU lines because the centre contact shoe would strike and damage it, so they added wooden ones. There's no reason they couldn't add wooden ramps to all TPWS loops, but it has obviously been deemed unnecessary because they don't have them. There is no reason to put a metal plate on top of a TPWS loop, and nobody ever suggested doing this? It absolutely would attenuate the signal and prevent it from working.

 

[swt_passenger]

I don't understand what you are trying to say. TPWS loops still needed a ramp on mixed LU lines because the centre contact shoe would strike and damage it, so they added wooden ones. There's no reason they couldn't add wooden ramps to all TPWS loops, but it has obviously been deemed unnecessary because they don't have them. There is no reason to put a metal plate on top of a TPWS loop, and nobody ever suggested doing this? It absolutely would attenuate the signal and prevent it from working.

An LU centre contact shoe would surely never drop far enough to hit a TPWS grid, as they have to deal with points I believe they cannot ever go much lower than the height of the fourth rail, and that is about 1.5” above the running rail.

I suspect it’s more likely the wooden section is there to keep the shoe at nearly the fourth rail height, for when it runs back onto the rail?

 

[saismee]

An LU centre contact shoe would surely never drop far enough to hit a TPWS grid, as they have to deal with points I believe they cannot ever go much lower than the height of the fourth rail, and that is about 1.5” above the running rail.

I suspect it’s more likely the wooden section is there to keep the shoe at nearly the fourth rail height, for when it runs back onto the rail?

You are right, I completely forgot about points and fourth rail height. This image (Harlesden Station) shows that the TPWS loop is much lower, the wooden ramp is more likely just to prevent any arcing to the loop. As the wooden part raises the height of the loop slightly, the ramps may just be there just as a precaution to prevent damage.

 

[edwin_m]

You are right, I completely forgot about points and fourth rail height. This image (Harlesden Station) shows that the TPWS loop is much lower, the wooden ramp is more likely just to prevent any arcing to the loop. As the wooden part raises the height of the loop slightly, the ramps may just be there just as a precaution to prevent damage.

I assume the shoe is held down by spring pressure to maintain contact with the rail. That being so, when it runs off the end of the rail might it momentarily bounce down below normal height before coming to an equilibrium?

I read somewhere that GWR locomotives that ran through onto the Metropolitan or the shared platforms at Paddington had to have a device to secure the ATC receiver in a raised position so it didn't foul the fourth rail. It might have been quite interesting in the cab if someone forgot to do so!

Noticed today near Derby chain guards fitted to modern sets of points. The mechanism was one of the type with (I believe) a rotating rod in the four-foot moving several stretchers simultaneously. Where they cross there is presumably some sort of rack and pinion arrangement, and each of these was covered by a metal guard ramped at each end. Sorry didn't manage to get a photo!