Brakes and doors

[Deleted]

The S-stock trains are a real improvement on the previous A stock, which were really showing their age, but in my view they are marred two niggles.

Why do the doors make so much noise? There is a loud bang when they open, and are only slightly quieter when closing. They seem much noisier that any other tube or even national rail stock.

Also, in recent days I've noticed that the brakes on some trains squeal just before they come to a halt. I first noticed it on 21049/21050, but others also seem to have a similar problem.

Still, no compressor noise. That's a bonus. I can sit anywhere in the train now, rather than in the end or centre cars with drivers cabs. And I don't have to work out where to stand on the platform to make sure I can step staright onto the right cars.

[Deleted]

If you want squeaky brakes, try the 2009 stock. Quite a few units seem to have chronic squeaky brakes - maybe something to do with the pads Bombardier are using?

As for the doors, they look rather vicious on the S stock. The noises too - wouldn't want to get shut in one. Getting whacked in the head by a door on an 09 isn't much fun, let alone getting jammed between the doors!

[jardine01]

Probally the newness of the train come a few years i bet the doors will settle down a bit with wear and tear so they will probally open and close a bit more smoother. I cant understand why these trains have squeeky brakes the pads should not be worn down yet?

[tecchy]

Pads don't have to wear down to squeak or not squeak. Its the material. For example, on the 1992 Stock, you cannot change more than 51% of the brakes on a train. The brake pads are lined with a surface protector which must be worn through before the brake pad becomes thoroughly effective.

The new pads often squeak, but when they wear down they are better (or worse)

Water, heat, material and pressure types can all effect how much a trains brakes squeak.

[phillw48]

Squeaking brakes are caused by the leading edge of the brake pads trying to 'dig in' to the disc or drum according to the type of brakes fitted. This is more prevalent on new brakes because the leading edge is 'sharp' but the squealing should diminish as the pads wear. At one time it was usual to file a 'chamfer' (a slight curve) onto the leading edge but this does not appear to be done anymore.

[Deleted]

Chamfering the edges of the pads also helps stop cracking when they first start to wear too..

[mcmaddog]

I'd have thought noisy doors are useful in discouraging PAX from putting their hands in the way of them closing. The snap the Capitalstars and S Stock have seems a pretty good deterant.

[a60]

I think C69/77 Stock takes the biscuit for squeaky brakes.

[causton]

Sept 6, 2011 8:58:40 GMT mcmaddog said:

I'd have thought noisy doors are useful in discouraging PAX from putting their hands in the way of them closing. The snap the Capitalstars and S Stock have seems a pretty good deterant.

Oh indeed, I've certainly thought "I wouldn't want to mess with them" on the S stock! The Capitalstars don't seem as vicious though...

[Deleted]

I've noticed also the S stock doors all open one after another, any reason for this

[uzairjubilee]

Sept 17, 2011 23:56:36 GMT @ianmcqueen94 said:

I've noticed also the S stock doors all open one after another, any reason for this

I've also noticed this. All the doors are not completely in sync.

[Deleted]

Today whilst waiting for an A stock home, I saw an S stock close its doors and there was this sound as if rubber and plastic were rubbing together coming from one door when it closed

[Deleted]

I'm wondering if the loud 'clunk' when the doors shut occurs because the doors are forming a tighter seal, to prevent the loss of all that nice cool air from the aircon system.
Older stock doors only need to keep passengers from falling out rather than holding air in as well.

[plasmid]

Older stock doors like the 67ts are allowed to open whilst the train is braking due to the force of gravity to allow cool air in and allow passengers to fall out.

Older stock doors like the 92ts are allowed to have a 1inch gap between the door and the body of the train to allow air in to cool the passengers, make a loud noise when air gushes through it and slow down the train due to poor aerodynamic design. They also make a loud bang where they smash against the body of the car when they reach a ventilation point.

I've seen the videos of the S stock on YouTube and besides the noise I don't see any issues with them.

As for the brakes on the S stock...378's don't squeal as bad (I don't think) so the only thing I can think of is that the S stock is designed for a lower speed and TFL require a higher braking rate for their stock which may affect the type of pads they use etc.

[chrisvandenkieboom]

Or do the squeaky brakes also have something to do with the fact that regenerative braking can't be introduced yet until the entire subsurface network (at least the Circle) is on the S stock?

[Deleted]

plasmid I'm sure doors on the 67ts etc arnt designed to let cool air in, or to let passengers 'fall out'

Also I really dont think that the small amount of air that seeps through the doors on a 92ts slows the train down

[chrisvandenkieboom]

Sept 18, 2011 17:51:16 GMT @bronzeonion said:

plasmid I'm sure doors on the 67ts etc arnt designed to let cool air in, or to let passengers 'fall out'

Also I really dont think that the small amount of air that seeps through the doors on a 92ts slows the train down

But the fact that the doors are sticking out does cause a little more air friction...

[tecchy]

Sept 18, 2011 17:55:57 GMT chrisvandenkieboom said:

Sept 18, 2011 17:51:16 GMT @bronzeonion said:

plasmid I'm sure doors on the 67ts etc arnt designed to let cool air in, or to let passengers 'fall out'

Also I really dont think that the small amount of air that seeps through the doors on a 92ts slows the train down

But the fact that the doors are sticking out does cause a little more air friction...

That is very negligible! You could argue that the 'flat' front on tube trains causes air friction. But having like the front of a TGV would, remove the piston effect...

[plasmid]

Sept 18, 2011 17:51:16 GMT @bronzeonion said:

plasmid I'm sure doors on the 67ts etc arnt designed to let cool air in, or to let passengers 'fall out'

Also I really dont think that the small amount of air that seeps through the doors on a 92ts slows the train down

Board a 92ts Eastbound from Liverpool Street and tell me the same thing again. With 32 Double Doors per train.

It's got to be at least 1 or 2 measly mph...though as chrisvandenkieboom said it's probably the front end of the train causing most of the friction.

I didn't say the 67ts let cool air in...that was for the 92ts. Best place to get a breeze on a busy train if your not near the front or rear.

67ts doors open slightly when the train brakes hard and then slam back shut...the force of gravity.

[chrisvandenkieboom]

Sept 18, 2011 19:11:34 GMT plasmid said:

Sept 18, 2011 17:51:16 GMT @bronzeonion said:

plasmid I'm sure doors on the 67ts etc arnt designed to let cool air in, or to let passengers 'fall out'

Also I really dont think that the small amount of air that seeps through the doors on a 92ts slows the train down

Board a 92ts Eastbound from Liverpool Street and tell me the same thing again. With 32 Double Doors per train.

It's got to be at least 1 or 2 measly mph...though as chrisvandenkieboom said it's probably the front end of the train causing most of the friction.

I didn't say the 67ts let cool air in...that was for the 92ts. Best place to get a breeze on a busy train if your not near the front or rear.

67ts doors open slightly when the train brakes hard and then slam back shut...the force of gravity.

Even in the underground wind tunnelstubes? Will be useful information when the handrails are sweaty and no place to move (aka rush hour)

[norbitonflyer]

Sept 18, 2011 17:51:16 GMT @bronzeonion said:

plasmid I'm sure doors on the 67ts etc arnt designed to let cool air in, or to let passengers 'fall out'

nick0323's original comments was, I trust, facetious - nobody thinks trains are really designed to let people fall out.

Sept 18, 2011 19:11:34 GMT plasmid said:

67ts doors open slightly when the train brakes hard and then slam back shut...the force of gravity.

That's not gravity - unless the doors are moving downwards! It's conservation of momentum - a small amount of resilence (slack) in the mvchanism allows the door to move slightly as the train body starts to slow down before the door catches up. The same phenomenon that causes any loose objects (or passengers) to be urged towards the front of the train as it decelerates.

The flat fronts are not only space-effecient, but are probably best at moving air around in a confined tunnel, where most of the air has to be pushed forward as, unlike surface transport, there ius little room to pass it round. A wedge shaped nose would result it extremely high pressures at the apex of the resulting wedge-shaped volume of air, potentially damaging the cab roof and/or tunnel roof.

Incidentally, i read that the pointy nose of HSTs, TGVs, and the rest actually have more effect on the aerodynamics at the rear of the train, smoothing the airflow behind it and reducing the partial vacuum trying to hold the train back.

Trains, by virtue of their low frontal area to volume ratio, are very aerodynamic anyway.

[tecchy]

Sept 18, 2011 19:11:34 GMT plasmid said:

Sept 18, 2011 17:51:16 GMT @bronzeonion said:

plasmid I'm sure doors on the 67ts etc arnt designed to let cool air in, or to let passengers 'fall out'

Also I really dont think that the small amount of air that seeps through the doors on a 92ts slows the train down

Board a 92ts Eastbound from Liverpool Street and tell me the same thing again. With 32 Double Doors per train.

It's got to be at least 1 or 2 measly mph...though as chrisvandenkieboom said it's probably the front end of the train causing most of the friction.

I didn't say the 67ts let cool air in...that was for the 92ts. Best place to get a breeze on a busy train if your not near the front or rear.

67ts doors open slightly when the train brakes hard and then slam back shut...the force of gravity.

That is not the force of gravity. Gravity is force which acts downward upon an object. Gravity is the force which is putting most of the 'weight' of the door on the top runner. The force of the train slowing down (say x newton metres) on the door against the door engine is equal to or greater than the force of the spring arm door engine (on the 92's for example its around 35psi).

[Deleted]

Sept 18, 2011 20:25:30 GMT @tecchy said:

That is not the force of gravity. Gravity is force which acts downward upon an object. Gravity is the force which is putting most of the 'weight' of the door on the top runner. The force of the train slowing down (say x newton metres) on the door against the door engine is equal to or greater than the force of the spring arm door engine (on the 92's for example its around 35psi).

If you are being picky, torque is measured in newton metres, force is measured in newtons.

What happens when a train brakes is that a door is continuing to move forward with respect to the train (due to its momentum), applying a force to the door gear of roughly (mass of door x train acceleration) - friction force in the runners.

With the old pushback systems, the force applied by the door overcomes the pushback spring slightly, which is why you see the gapping under very heavy braking or motoring.

S Stock and 09 Stock doors are over centre locked in place, and have no pushback mechanism, which is why they do not gap when braking. Early pushback versions of 09 doors did gap very slightly at the end of a stop. It is very difficult to have a pushback system where you meet the pushback forces, light enough so a passenger caught in the door can get free, and heavy enough for them not to move under heavy braking. This is mainly due to the fact that externally hung doors, by their nature are fairly heavy.

[tecchy]

My mistake! I am so used to the words newton metres, i never usually write them without each other. But in this case yes Newtons!

I do not believe the 09s had 'push back' even in the trail trains (as were gonna call it that!) I assume you mean push back like on the old 67's where you could push the spring arm door back about 3-4 so inches?

[Deleted]

Sept 19, 2011 22:35:25 GMT @tecchy said:

My mistake! I am so used to the words newton metres, i never usually write them without each other. But in this case yes Newtons!

I do not believe the 09s had 'push back' even in the trail trains (as were gonna call it that!) I assume you mean push back like on the old 67's where you could push the spring arm door back about 3-4 so inches?

Yes the same as 67 TS had (think I could move them about 3"). Train 1 definitely had pushback doors, and Train 2 did for a few months before it was fitted with sensitive edges prior to it entering its limited passenger service operation.