Throwing distance for points

[Deleted]

Why do some points appear to need more air and a greater length of time to unlock, switch and lock again?

For example, the trailing points on the e/b line at Bethnal Green throw very rapidly - a quick hiss of air and the thunk of the lock and they're ready. On the other hand, the points at Turnham Green w/b, for example, emit a longer hiss of air and take slightly longer to fully switch.

Is this difference in throw times simply an idiosyncracy of the points themselves, or is it a design feature/flaw?

[piccadillypilot]

theonekea said:

Is this difference in throw times simply an idiosyncracy of the points themselves, or is it a design feature/flaw?

Each train has a slightly different performance, some go like stink and stop on the proverbial tanner whilst others won't pull the skin off a rice pudding and need a week's notice in writing to stop.

Some trainstops go up and down very fast, others take forever (and can catch unwary drivers out).

It's in the nature of mechanical, pneumatic and electrical contraptions that some move more freely than others and the slow ones won't be told otherwise.

[Deleted]

piccadillypilot said:

Some trainstops go up and down very fast, others take forever (and can catch unwary drivers out).

Some are set like that for a reason thought. The outlet from NFDs depot East End comes to mind.

[Deleted]

But a slow trainstop at least has some purpose (IIRC it's called slugging, and uses tubing of a certain length and diameter to increase/decrease air pressure to the trainstop itself). Why would you want to slug a set of points?

[Deleted]

theonekea said:

Why would you want to slug a set of points?

I cant see any reason for it. Have you got a certain set of points in mind, that can be used as an example?

[Deleted]

The ones at Turnham Green, for example - why do they move at the speed that they do, compared to the ones at Bethnal Green?

[Deleted]

Hmmm, possibly the Bethnal Green points are newer? The points on the Jubilee Line extension are all of a different type than the normal LUL points, and are very quiet in operation...
I couldn't imagine any reason why a set of points would be deliberately slowed down!

[q8]

I *think* the throwing distance and speed of points may be in part due to the length of the blades and angle of turnout. A short blade with obviously throw faster than a long one.

I am not techhnically educated enough to explain it in detail but having been a driver and sat at stations like Aldgate East and watched them throw (fast) and Turnham Green (slow) I suspect that the reasons I state may be the cause.

[citysig]

My colleague or someone from the technical department will be able to elaborate further but...

The length of time is normally due to the point equipment installed. The blades will throw just as quick, regardless of length. But certain sites use one type of point lock, and others use a faster type. For example, points at Hammersmith (Met) take ages to throw, but points of a similar length at Edgware Road, go over in a jiffy.

As I said, Harsig, Tom, or one of the AETs will elaborate on the technical science stuff.

[Deleted]

theonekea said:

The ones at Turnham Green, for example - why do they move at the speed that they do, compared to the ones at Bethnal Green?

It might be to do with the fact that (a) the equipment at Bethnal Green is newer than the equipment installed at Turnham Green; or (b) IIRC the points at Bethnal green are electrically operated, compared to the points at Turnham Green are air operated.

[Tom]

On both cases, you'd be wrong.

Bethnal Green is an air site, same as Turnham Green. Electric or EH operation isn't used in section 12 areas of the central line. Likewise, the equipment wasn't changed upon resignalling.

Clamplocks as used at Hammersmith (Met) generally take longer as they need to prove the groundlock has retracted before the points are thrown and are genrally slower to throw as they are damped.

Chairlocks at Turnham Green tend to be faster than Clamplocks but slower than 4 foots (as found at Bethnal Green), mainly because the motor has a larger stroke (9" compared to 8"). Four foots are generally the fastest, and can go over in a second or less. However, this depends on the condition of the track, length of switch, wether or not a supplementary dirve is fitted, etc etc.

[Deleted]

it could mean alot of of reasons but generally if they are slow to throw its either because they have been badly set up or in some cases slugged ( this is done by putting long hoses on them ). the points on the w/b at turnham green are of the chairlock point mechanism design these are generally slower then the normal 4' design. the points on the jle are a 4' design but because they use shallow switches and they have longer turnouts (bigger switches) it takes them longer to throw because of the extra weight involved.

you sure you hear air at bethal green as i thought the points on the central now where either electrical or hydrolic now (soz for the spelling)

the only points which are always slugged abit are the clamplock design (b.r design) as they do not like being throw over with 60 lbs p.s.i so the motor as a damper built into it so the points go over alot smoother

but generally points should still throw even if the air got down to 25 lbs p.s.i but as a set i was working on last night around the hammersmith (dist) i got them working on 18 lbs p.s.i

by the way dont expect the last pic to go into the sidings from hammersmith as i took the set of points out of commission last nite ;D ;D ;D ;D ;D ;D ;D

[Tom]

Air operation was retained at Queensway, Marble Arch, Holborn, Liverpool St and Bethnal Green. The oil used in the Electro Hydraulic unit isn't suitable for use in tunnels, and there's no room for M63s.

[Deleted]

tom said:

Air operation was retained at Queensway, Marble Arch, Holborn, Liverpool St and Bethnal Green. The oil used in the Electro Hydraulic unit isn't suitable for use in tunnels, and there's no room for M63s.

Does a type of electric point exist that will fit in tube tunnels?

[towerman]

They're doing a trial at SMD at the moment of a set of "Surelock" points from WRSL,the mechanism is in the track between the running rails.If successful they will be adopted LUL wide.

[igelkotten]

theonekea said:

Does a type of electric point exist that will fit in tube tunnels?

Of course!

The Paris Metro, to take another tube system with smallish tunnels, uses electric points. And several narrow-gauge mining railways that I know of in Germany uses electrically operated points. And while Stockholm tunnels are bigger than a London tube, our electric point machines would have no problems fitting in a tube tunnel.

[Tom]

They're planning to use Surelocks for the VLU, they just need to be used on a mainline test.

And we did import a Swedish point machine at one stage, but it never got installed. Pity. (looks for a devil smiley)

[igelkotten]

tom said:

They're planning to use Surelocks for the VLU, they just need to be used on a mainline test.

And we did import a Swedish point machine at one stage, but it never got installed. Pity. (looks for a devil smiley)

So, how much overweight are you willing to pay on your next flight...?

[Tom]

Perhaps I should go as baggage and let the point machine take my seat? ;D