Deleted
Deleted Member
Posts: 0
|
Post by Deleted on Mar 5, 2014 7:19:41 GMT
I think you will also find that swing plug doors take longer to open and close therefore the cumulative effect on an Underground line of this could have a negative impact on the total service.
|
|
|
|
Post by tomek on Mar 5, 2014 9:24:57 GMT
I think it depends on the design. Swing plug doors are often slower than regular ones, however between 2 types of swing plug doors, you can see considerable variation in opening and closing times. I live in France and here almost all the RER rolling stock uses swing plug doors. The new double deck stock on the RER A have very very slow doors (especially the opening times), but on the RER D the doors can open pretty fast, and close even quicker than 1972 stock doors.
|
|
|
|
Post by melikepie on Mar 5, 2014 9:44:57 GMT
People are often complaining about the heat on the tube. There are plans to have air conditioning on all trains eventually. Seeing as it seems plug doors you say are to maintain the heat and pressure in the trains, wouldn't installation of both be pointless?
|
|
class411
Operations: Normal
Posts: 2,747 
|
Post by class411 on Mar 5, 2014 12:11:56 GMT
People are often complaining about the heat on the tube. There are plans to have air conditioning on all trains eventually. Seeing as it seems plug doors you say are to maintain the heat and pressure in the trains, wouldn't installation of both be pointless? Quite the reverse. If you have air-con it is imperative that you avoid air ingress from sources that bypass the air-con unit. Obviously this isn't much of an issue as far as doors are concerned since, for example, both S7's and Electrostars have air-con and one does not have plug doors whilst the other does. |
|
class411
Operations: Normal
Posts: 2,747
|
Post by class411 on Mar 5, 2014 12:17:09 GMT
I think it depends on the design. Swing plug doors are often slower than regular ones, however between 2 types of swing plug doors, you can see considerable variation in opening and closing times. I live in France and here almost all the RER rolling stock uses swing plug doors. The new double deck stock on the RER A have very very slow doors (especially the opening times), but on the RER D the doors can open pretty fast, and close even quicker than 1972 stock doors. All this talk of opening/closing times is a complete red herring. A door has to move its entire opening width - at least a couple of feet - in an acceptable time frame. A couple of inches extra aren't going to make much difference. Certainly nothing an engineering tweek couldn't handle. It was obviously a matter of balancing cost v desirability with possible consideration for the safety elf. |
|
Chris M
Global Moderator
Forum Quizmaster
Always happy to receive quiz ideas and pictures by email or PM
Posts: 19,773
|
Post by Chris M on Mar 5, 2014 13:16:16 GMT
Actually a couple of inches can make a difference on a metro style service when your total dwell time is measured in seconds.
Compare the single leaf doors on the D stock with the double leaves on the other stocks. Single leaf doors being slow were one of the reasons that the 83 stock were retired.
Slide plug doors need to make two movements - out and then sideways. The first movement takes time (say 2-3 seconds) that is wasted from the perspective of allowing people to enter and exit the train, and due to gauge clearance and not hitting people standing on the platform you cannot start to open them until the train is stationary, unlike sliding doors where they can safely be starting to open as the train comes to a halt. You then have an extra 2-3 seconds on the closing movement. That's four to six extra seconds every stop, which is 8-12 percent of a 50-second stop.
|
|
|
|
Post by whistlekiller2000 on Mar 5, 2014 13:54:13 GMT
|
|
class411
Operations: Normal
Posts: 2,747
|
Post by class411 on Mar 5, 2014 17:24:22 GMT
Actually a couple of inches can make a difference on a metro style service when your total dwell time is measured in seconds. Compare the single leaf doors on the D stock with the double leaves on the other stocks. Single leaf doors being slow were one of the reasons that the 83 stock were retired. Slide plug doors need to make two movements - out and then sideways. The first movement takes time (say 2-3 seconds) that is wasted from the perspective of allowing people to enter and exit the train, and due to gauge clearance and not hitting people standing on the platform you cannot start to open them until the train is stationary, unlike sliding doors where they can safely be starting to open as the train comes to a halt. You then have an extra 2-3 seconds on the closing movement. That's four to six extra seconds every stop, which is 8-12 percent of a 50-second stop. I said it wouldn't make much difference, not that it wouldn't make any. But I think you estimate for 2-3 seconds for the in/outward motion is waaay too much. In any case, as I keep pointing out, all this applies to plug doors operating either as mainline trains or trams or current stock with an extra motion added on. Which is why it's a red herring. If it were deemed necessary an engineering fix would no doubt be found. |
|
|
|
Post by domh245 on Mar 5, 2014 18:40:56 GMT
Actually a couple of inches can make a difference on a metro style service when your total dwell time is measured in seconds. Compare the single leaf doors on the D stock with the double leaves on the other stocks. Single leaf doors being slow were one of the reasons that the 83 stock were retired. Slide plug doors need to make two movements - out and then sideways. The first movement takes time (say 2-3 seconds) that is wasted from the perspective of allowing people to enter and exit the train, and due to gauge clearance and not hitting people standing on the platform you cannot start to open them until the train is stationary, unlike sliding doors where they can safely be starting to open as the train comes to a halt. You then have an extra 2-3 seconds on the closing movement. That's four to six extra seconds every stop, which is 8-12 percent of a 50-second stop. I said it wouldn't make much difference, not that it wouldn't make any. But I think you estimate for 2-3 seconds for the in/outward motion is waaay too much. In any case, as I keep pointing out, all this applies to plug doors operating either as mainline trains or trams or current stock with an extra motion added on. Which is why it's a red herring. If it were deemed necessary an engineering fix would no doubt be found. Sorry, but I don't quite follow, what you mean by an extra motion added on, the whole point of a plug door is that it sits flush with the surface, and this cannot be done with any less than 2 movements, the sliding close, and moving to be flush. Mainline stock and Trams have this 2 stage system. How you would make the doors close flush without more than 2 stages is beyond me. You could do a bus system where the door swings out, but that would be problematic. You could have a system where the doors are on a roller which pivots out from the middle, before sliding open, but even that has 2 stages. As for the extra time, I reckon that it is nearer to 2 seconds per stop (ie 1 second to pop open, 1 second to go flush) and looking at a train running from Uxbridge to Cockfosters (amongst the first viable options for a possible plug door tube) the total time added on just by the door moving in and out is: 82 seconds, and during the rush, this could go as high as 120 because of the door repeatedly cycling because of people stood in the doorway. Adding 2 minutes to each trains journey would severely limit the number of trains through the core area, even if you are just running from Rayners Lane to Arnos Grove, it is still over a minute added. It may not seem like much at each station, but by the time you have run a train in service for an entire day going between Uxbridge and Cockfosters (say about 20 trips as a guesstimate) that is almost an extra 3 quarters of an hour. |
|
class411
Operations: Normal
Posts: 2,747
|
Post by class411 on Mar 5, 2014 19:06:30 GMT
Firstly, I would point out that I'm not trying to make a case for plug doors. All I'm saying is that people are being extremely blinkered when the repetitively make a case against them on the basis of doors they have seen operating on things other than underground trains. If they were thought to be necessary an engineering solution would most likely be found. I said it wouldn't make much difference, not that it wouldn't make any. But I think you estimate for 2-3 seconds for the in/outward motion is waaay too much. In any case, as I keep pointing out, all this applies to plug doors operating either as mainline trains or trams or current stock with an extra motion added on. Which is why it's a red herring. If it were deemed necessary an engineering fix would no doubt be found. Sorry, but I don't quite follow, what you mean by an extra motion added on Evidently not. What I mean is that one should not limit one's thinking to a picture of a current underground door mechanism with a completely separate motion appended at right angles. Actually, it can. Look at any number of motor vehicles where a door slides closed in a single, fluid, movement. However, I'm not a door engineer so I have have no idea if that particular type of mechanism could be scaled to something like a train. I just have confidence that it's not a problem that is insurmountable by committed engineers. You are just repeating what many others have done. Working out why it wouldn't work based on a mechanism that is slower than current underground door mechanisms. I don't think anyone has disputed that this would lead to increased dwell times. But if a faster system was engineered the problem would disappear. |
|
|
|
Post by domh245 on Mar 5, 2014 19:35:20 GMT
Actually, it can. Look at any number of motor vehicles where a door slides closed in a single, fluid, movement. However, I'm not a door engineer so I have have no idea if that particular type of mechanism could be scaled to something like a train. Thinking about vehicles with those sliding doors (I assume you mean van style doors) they have two movements, they slide from their open position and then pivot in whilst still going towards the closed position, it seems fluid, but you can still identify the separate movements. The other type of door that you might be talking about are coach style doors (or even doors like on the class 442) but those could be even more problematic, as these would take up more space on the inside, as well as the fact that the doors would swing out as they do. You also mention that the designers could speed up the mechanism, but that would still cause a lot of problems with the maintenance, making something operate faster would lead to a heightened need for maintenance I'm not trying to argue that it couldn't be done, but it would be very difficult for them to do, and you would probably have to come to some compromise against some of the operating factors. |
|
Chris M
Global Moderator
Forum Quizmaster
Always happy to receive quiz ideas and pictures by email or PM
Posts: 19,773
|
Post by Chris M on Mar 5, 2014 21:36:29 GMT
The only way you could possibly have a plug door operate as fast as a sliding door would be for the two movements to operate entirely in parallel. I'm not an engineer, but I'm struggling to imagine how that could be done without wedge-shaped doors and bodysides, which would probably be more complex and possibly more expensive to manufacture and maintain. Almost certainly there would be issues of structural strength that would need to be worked out and maybe around.
But why would anyone spend any R&D money on this when sliding doors exist as a proven product?
|
|
|
|
Post by andypurk on Mar 5, 2014 21:37:02 GMT
I doubt that the problems with sliding-plug doors are as severe as some people imagine. The MF01 stock in Paris has sliding plug doors and they don't seem noticeable slower than pure sliding doors. There is also no real sign of two phases to the door closing, the runners mean that the door moves at the constant speed and for the last little bit curve in so the doors finish up flush with the body. There are plenty of videos showing the doors opening and closing available on line. Likewise many trams have sliding plug doors which don't seem to operate any slower than pure sliding doors.
Also, the doors being described are really sliding-plug, not swing-plug. Swing plug doors also have a single motion, but it is based on a rotating mechanism to open and close the door, and can be seen on the the class 442 mainline units. These are really too slow for metro use and take up a lot of space on the outside of the coach when opening or closing.
|
|
class411
Operations: Normal
Posts: 2,747
|
Post by class411 on Mar 6, 2014 8:50:17 GMT
Actually, it can. Look at any number of motor vehicles where a door slides closed in a single, fluid, movement. However, I'm not a door engineer so I have have no idea if that particular type of mechanism could be scaled to something like a train. Thinking about vehicles with those sliding doors (I assume you mean van style doors) they have two movements, they slide from their open position and then pivot in whilst still going towards the closed position, it seems fluid, but you can still identify the separate movements. No, the particular instance I'm thinking of is one of those small cars that have a back like a bus. Near where I live there is a hill and a woman parks such a car there. I have several times seen her get out and the slope of the hill causes the door to slide shut and plug in. It's quite amusing as it looks as if the door is powered. It's all done by the path of the track. As I said, I'm not a door engineer, but I would assume that one of the major problems train door designers have is that the mechanism must be proof against interference by any and all passenger detritus. Hence you could not simply translate a car/van door to a train. The only way you could possibly have a plug door operate as fast as a sliding door would be for the two movements to operate entirely in parallel. I'm not an engineer, but I'm struggling to imagine how that could be done without wedge-shaped doors and bodysides, which would probably be more complex and possibly more expensive to manufacture and maintain. Almost certainly there would be issues of structural strength that would need to be worked out and maybe around. Of course it would be a more complex (and hence more expensive) mechanism. That goes without saying. Because they decided they were necessary. I have been saying al along that the reason they don't have plug doors is because they are not needed for the application, not because the engineers would be unable to come up with a workable design for them. |
|
rincew1nd
Administrator
Junior Under-wizzard of quiz
Posts: 10,286
|
Post by rincew1nd on Mar 6, 2014 21:46:47 GMT
|
|
|
|
Post by 100andthirty on Mar 7, 2014 20:37:08 GMT
There are three types of power doors in general use. Sliding doors, Swing plug and sliding plug. Of all the designs swing plug doors are the rarest. The place where you see them most is on road coaches (eg National Express) where the door opens outwards and then swings round to a position by the front wheel in a smooth arc. Sliding plug doors are what you see on most modern trains (Class 375/7, class 350/450, Pendolino, Voyager/Meridian. They effectively have the door on a sliding mechanism and it's the sliding mechanism that pops out of the bodyside when the doors are unlocked (when closing the Desiro satisfying clunk on closing. Class 350/450 doors are slow, Class 375/7 are much faster.
Sliding doors simply slide back and forth although on the Hitachi HS1 trains, once closed the doors are moved outwards slightly to engage with seals (draught proofing resistance to pressure pulses).
On tube trains, it's the shape of the doors, having door mechanisms in a very small roof and worries about trains being foul to gauge if doors jam open that prevents their use even before thinking about performance issues.
|
|
|
|
Post by maxym on Mar 9, 2014 21:33:46 GMT
Yeah, well that's what I meant: a double-plug door. Like what Chiltern Railways (Bombardier-built) trains have. That open and close quickly.  Turned out to be an interesting discussion. Thanks all. |
|
|
|
Post by maxym on Mar 9, 2014 21:35:24 GMT
To the Quizmaster, you're not comparing like with like - a four-car train v a seven-car one. If you compared an S7 to a notional 12-car class 450 the figures would be different... And you have to be careful with that sort of argument: for maximum reliability you'd want one set of doors (or even one door, D stock-style), or even a one-car train. The point about frequency of stops is well made though. To the crusty, that Siemens for you. As I suggested earlier, Bombardier do rapid opening and closing really well. I was actually comparing a 7-car S stock with a train composed of 2 4-car 450 units because I was comparing real-world operations. I don't have access to any set working details for any operator, but if anyone does it would be interesting to get a comparison of the typical daily workload of the door sets. One other thing that I neglected to mention is headways and flexibility. A delay of 2 minutes on the Underground is far more significant in terms of reliability of the service than the same delay would be almost everywhere on the mainline network. The mainline network also has a significantly greater number of places a failed train can be worked around or put out of the way than the Underground does. Sorry, Quizmaster. You did say a 2x4-car SWT set, which I overlooked. Apologies. |
|
