Unusual 'doorstops' on Mk3 EMU doors?

[southern442]

I believe they only exist on classes 455 and 317, and the (delightfully funky) class 210 units had them too. No other sliding door stock built around that time, including the PEPs, have them. I call them doorstops because they look like doorstops but they don't seem to serve any actual purpose whatsoever. There are little trenches cut into the bottom of the doorways for these to run along. There is an example photo here and what I am talking about is at the bottom of the doors. Can anyone shed any light on this?

 

[3141]

The lower edge of the doors of London Underground trains used to run in grooves. These could get blocked by rubbish and cause a door to stick or fail completely, resulting in the train being taken out of service. They later changed to top-hung doors.

Perhaps classes 455 and 317 have top-hung doors but these "door-stops" and the grooves in which they run are there to keep them in line and to reduce door flapping caused by air pressure when one train passes another at speed, or when a train enters a tunnel. There would be much less likelihood of a blocked groove preventing a door from operating as there would be far less weight pressing down into the groove if the door is hung from the top.

 

[southern442]

The lower edge of the doors of London Underground trains used to run in grooves. These could get blocked by rubbish and cause a door to stick or fail completely, resulting in the train being taken out of service. They later changed to top-hung doors.

Perhaps classes 455 and 317 have top-hung doors but these "door-stops" and the grooves in which they run are there to keep them in line and to reduce door flapping caused by air pressure when one train passes another at speed, or when a train enters a tunnel. There would be much less likelihood of a blocked groove preventing a door from operating as there would be far less weight pressing down into the groove if the door is hung from the top.

This is a good explanation, however they seem to have similar 'flapping' issues as the other Mk3-derived units, so they are not very good at solving that issue. But the idea that this is perhaps an early trial of top-hung doors makes sense. Later units don't have these, so I assume either they decided not to bother for later designs or they figured out how to do it more discreetly.

 

[AMD]

Also found on the 150/0s

 

[TEW]

The last batch of 455s, the 455/9s, don't have them, so they were quite a short lived part of the design.

 

[Bikeman78]

This is a good explanation, however they seem to have similar 'flapping' issues as the other Mk3-derived units, so they are not very good at solving that issue. But the idea that this is perhaps an early trial of top-hung doors makes sense. Later units don't have these, so I assume either they decided not to bother for later designs or they figured out how to do it more discreetly.

I think they do help a bit. The doors on the 317s bang when they pass another train. However, if you go on a 150 Cardiff to Shrewsbury, the doors tend to rattle at speed even when not passing another train.

 

[edwin_m]

Am I right in saying the doors on the units in question don't open quite as widely as on later versions that didn't have the "doorstops"?

 

[cjmillsnun]

Am I right in saying the doors on the units in question don't open quite as widely as on later versions that didn't have the "doorstops"?

Originally yes, however I know that SWT altered the doors on their 455s to open fully.