I used the underground extensively for the first half of my life. I recall often sitting waiting fo departure at East Finchley on sunny days, with the doors open for some time.
During that time a device (engine or motor) beneath the floor would start up, run for a while and then stop. What was it doing?
I?ve always assumed it?s a compressor charging air tanks for the doors and maybe the brakes too.
Tim
me too
Probably maintaining the compressed air in the brake system resevoirs. Needs enough pressure in there to move the brakes off the wheels.
Vacuum pump to allow the brakes to be taken off.
Have a look for the pressure gauge it's under one of the seats. Interesting viewing, if you have little else to be bored doing.
When I was young with an inventive imagination, I used to think it was spinning some kind of flywheel...
... but, nah - that would never work :)
Must have confused with another system. Compressed air!
Replacing the compressed air (for the brakes and door pistons) that was leaking somewhere.
me three
pumping up the hydraulics for the braking system, or in some very rare cases the air for air brakes. It used to happen on the old suburban electric rolling stock on British Railways too. What I never figured out is why the Underground trains were so much lower than the normal trains or why they went for a central rail for power instead of a side rail or pantograph. Brian
Yes as I say, both systems were used on different stock. It always sounded like it was very crude.
Some doors were obviously air powered but some were almost silent so I assume some kind of hydraulics were used. They seemed to be the ones with the silver outside with the kind of bulls eye markings under a layer of plastic. Most of the old red ones used air, most definitely and were bloody noisy inside as the had open windows permanently. I also remember those naff escalators where the hand rail seems to have been travelling too fast or too slow which could make you start to lean a bit. Brian
Wimbledon Station was another place to hear this as it was the end of the District line and they tended to leave the doors open there.
Brian
A video which might as well just be an audio track, brian
Plus the ticket machines that looked like overgrown flip-top kitchen bins
All very exciting for a young visitor to London ...
I think the clue is "underground" ...
So they could fit into the size of tunnel they could build for the deep level lines. The rolling stock for the earlier cut and cover lines, like the Metropolitan Line, have larger carriages.
or why they went for a central rail for power instead
They use a four rail system. Two running rails and two power rails. Power on the outer rail, furthest from the platform, with return on the centre rail. No room for overhead power.
Well you couldn't really have overhead wires in the "tube"! (though the new Elizabeth Line does/will; the tunnels are much bigger.) Since the older deep underground tunnels are lined with cast iron which the running rails are bolted too, it was found that using them as an electrical return caused corrosion and sparking, so it has a central line as the return. The cut-and-cover lines have the same system as they share lines with the deep trains in some places.
The first lines were cut and cover (and originally used steam locos, with the exhaust being fed through the water tanks to condense and clean it up).
The later (deeper) lines had to be tunnelled out. They used a tunnelling shield that allowed men to dig through gaps in the shield, then screw-jacks to move it forward a few feet, lined the tunnel behind and then carried on digging - similar to how many tunnels are dug today, except that boring machines use powered cutting heads, hydraulic rams and automatically lift pre-formed concrete panels into place (or spray shotcrete).
The deep lines were lined with curved cast-iron panels, that bolted to each other and formed a full circle for strength (and, I think, water-tightness). Being hand dug, they were necessarily small and being circular, forced the use of even lower railway stock, with heavily curved roofs.
As for power. They used a four rail system, with power supplied via the side rail and returned via the centre rail. This meant that the running rails could be firmly bolted to the tunnel floor, but no current flowed through them (preventing electrolytic corrosion problems for the tunnel liners) and possibly, where tube stock shared overground lines with other railway stock, full track-circuiting for signalling train detection would also allow rail-break detection, with none of the problems that using one of the running rails as the power return causes.
and, from Wimbledon to West Putney, they share track with what used to be Southern Railways. They may in other places, but I've been on that bit of line. When you realise thatb you are in a tunnel on your commute from Wimbledon to Clapaham Junction, you know something's not quite normal.
As a child, I seem to remember that the metropolitan tube trains (bigger carriages?) seemed to make a lot more compressor noise.
Andrew
Going down the drain from Waterloo to Bank was the best. They used to have yellow painted lines marking where the carriage doors would stop, so the bowler hatted gents could form orderly queues.
Also remember the combined coat and bowler hat hooks on all the southern region carriages.
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