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Everything posted by Edwin_m

  1. Certainly they should vent on over-pressure - anyone remember the concern about BLEVEs (boiling liquid expanding vapour explosion) back in the 70s? If the tank is exposed to an external heat source, venting of vapour even if it catches fire is probably preferable to the huge explosion (BLEVE closely followed by vapour-air) that could result if it was unvented and eventually failed.
  2. The wheel and track dimensions haven't changed significantly (new track was 3mm narrower for a couple of decades then went back to the traditional 1435mm). But my own theory is that you may be hearing the consequence of modern bogie dynamics. Above a certain speed any rail vehicle will zigzag from side to side as it runs along the track, known as hunting. This was analysed in the 1960s by British Rail Research and to counteract it most trains built from the 1970s onwards have dampers (shock absorbers) that resist the rapid rotation of the bogie that takes place during hunting. These can be seen mounted horizontally outside the bogie frame on many types of rolling stock, with brackets attaching one end to the bogie and the other end to the body. However these have the side-effect that the bogie doesn't line up as exactly with the track on curves, so there is more flange squeal.
  3. Someone mentioned the Digikeijs DR5000 a few posts back. I'm still wiring up but as far as I can tell the EB1s (kept from the previous setup and around 11 years old) are quick enough to cut out before the 5000.
  4. However if it needs replacement of certain parts then there is an opportunity to upgrade to something better at the same time, which will cost a lot less than replacing like for like then upgrading a few years later. It was originally designed for trains of up to 8 cars at up to 100mph, but it is now expected to supply trains with two pans at 125mph, not to mention a far more intensive service in general.
  5. At the time they may have expected it to be in service much more quickly, so they would have had to erect all of it before the degradation became apparent. This might also have reduced the rate of degradation, if it's related to the presence of disel exhaust which will be somewhat less when it goes live. However even if the degradation correlates absolutely with exposure to diesel fumes the fact it's having problems after three years or so means it's unlikely it would have reached its design life.
  6. I can't imagine the amount of water coming into the Channel Tunnel is anywhere near what enters the Severn Tunnel, and it also has the benefit of a modern ventilation system that should clear away any humidity. It also has a traditional contact wire rather than overhead rail, so whever has caused problems under the Severn wouldn't be present.
  7. Going by the sign in the foreground, Down is away from the camera.
  8. I wondered about that as well, hence the bit of my post you didn't quote.
  9. I guess general rises in property and land values, most often seen in the form of house prices, also affect businesses as landlords raise rents in line with the amount they would get for those properties if they sold them on. It seems to me that since IA's death the people who now run the business are treating it as strictly commercial and spinning of or closing anything that was relevant to IA's personal interests but not making that much money.
  10. The box seems very low. If it was higher then the signalman would have had a view over a Down train without having to resort to a mirror. Any reason why it wasn't? I was thinking it might be to view Down tail lights as they went under that bridge, but because of the left hand curve it wouldn't give much extra viewing time.
  11. One reason to put a box at each end of the station rather than in the middle was so the signalmen could observe tail lights on arriving trains. Otherwise they would have had to rely on hand signals from guards or wait until the train departed before they could give out of section. For this reason the two boxes are normally at "NW" and "SE" corners (for a north soute line, rotated appropriately) as at Stockport. Many large stations had a box each end and one or more in the middle to control mid-platform crossovers. Sometimes these boxes only had authority over some of the parallel tracks - both main Nottingham stations had two middle boxes (which can still be seen at Midland, though now used for other purposes).
  12. It's known as a datum plate. The little slider is I think aligned with a line across the top of the rails and there are various figures related to track geometry. Helps to ensure the track is in the correct position especially next to a platform where trains scraping it is a bad idea but so are big gaps for passengers.
  13. Looks like few or no bi-modes will stop south of Kettering. In my experience the ones that do so now are fullest between Bedford and Luton Airport Parkway, so while it means some people have extra changes of train it does even out the loadings for these services. Along with the other issues, a 5-car IET-based unit should have a lot more passenger space than a 5-car 222. I think I read somewhere that these will continue, but I can't imagine them being anything more than units in marginal time that would otherwise be doing nothing. But it seems the longer-distance trains aren't stopping at Luton Airport Parkway.
  14. More recently 12-car formations have run with three pans, although since the introduction of the 700s it's back to two. There seems to be a committed upgrade package for OLE south of Bedford, but I haven't seen any official statement of what this includes.
  15. There are plenty of countries where the de facto commercial capital is separate from the administrative capital, Australia Netherlands and USA for example. This helps to distribute the activity more fairly, as those companies with an interest in being close to government will gravitate to a different place from those serving commercial business. Germany now has its historic capital back, but a lot of government institutions are devolved to other cities such as the federal courts in Karlsruhe (and unlike UK efforts this is the headquarters not just the back office). Regional subsidies tend to develop into a bidding war between regions and I agree the companise thus incentivised tend to leave if the subsidy ends or it is the first office to close if business declines. Better transport links do however represent a more concrete (literally) commitment to long-term development and should reduce costs for business in the regions and also reduce the perceptional barrier if a business can boast of being close in time to central London or other cities.
  16. You're right that both criteria are important. But both depend on the resistance in the bus, droppers and track, and if point (2) is satisfied then point (1) almost always is as well (possible exceptions on very small layouts with high-powered command stations). As someone mentioned above, a 5 amp command station needs the resistance out and back to be less than 3 ohms for the cutout to work, and actually significantly less given that the "short" itself will not be zero resistance. On a quick search, 16/0.2 wire which might be typical for feeds on a DC layout has a resistance of around 3 ohms per 100 metres so would probably be inadequate on a large DCC layout. 2.5mm2 cable reduces this resistance by a factor of about five - though there is still the resistance of the droppers and track to think about.
  17. The resource that modern industries rely on is not coal or ore but brainpower. And the way the economy is set up at present, that all gravitates to the south-east. By making links easier the theory is that people can be based in the north and still visit colleagues, suppliers and clients in the south-east and vice versa, as well as other parts of the north. I would personally like to see little or no season ticket discount on HS2, as an incentive to draw business and activity out of London rather than just increasing the commuter belt. The same effect applies across Europe, that areas close to the centre of activity are more prosperous. Successive UK governments have ignored the regions remote from London and I can't see how losing the small amount of rebalancing the EU has provided can help. Cutting oneself off from the centre of activity either in the UK or in Europe isn't going to revive those industries that depend on resources that have been exhausted or are no longer relevant, and doesn't strike me as a recipe for a more prosperous or better life.
  18. Tell that to the loco I melted (actually thinking about it, it was a driving trailer with lighting). There's an important principle here that just using wire with ampage greater than that of the command station may not be enough, and that the coin test is essential.
  19. Absolutely. Furthermore, as the voltage drop is the resistance multiplied by the current, it can also be minimised by ensuring that the maximum current possible is no more than what is necessary (power districts, circuit breakers, command station current limit).
  20. Absolutely agree. Keep the bus resistance low and make sure the cutout is effective.
  21. I believe this is a misquote. As the error apparently relates more to the MML I have posted the details on that thread:
  22. That looks like a misquote by the IRJ. They say: Following the links through to the actual report it says:
  23. I've never seen that argument put before. It has some logic to it but because the wiring resistance will vary depending on how far the short is from the command station, it would be difficult to apply this principle to a short near the command station without invalidating the protection against short circuits on more distant parts of the layout. You'd be better off inserting a resistor of small ohmage and large wattage in the command station feed and making the rest of the wiring as low resistance as possible. Or just ensuring that the short circuit protection is appropriate to the power demand of the layout, adjusting the command station trip current if possible and using circuit breakers if necessary, and ensuring that the wire is suitable for those currents but more importantly that the whole layout is coin-tested. It's also worth considering what fault current might flow if a train is bridging two power districts when a short circuit happens somewhere.
  24. Perhaps the person quoted in the OP was thinking of (or pondering on) the transformer the pantograph is connected to?
  25. A quick search shows definitions of short circuit involving low resistance, not no resistance. There will always be some resistance. The probem I had was a loco with a plastic chassis where the pickups on the two bogies were linked to the motor by thinnish wires which could probably take about 1 amp. The pickups themselves would also have had some resistance (it wasn't clear from the remains where the heat was coming from). It derailed such that the left hand wheels of one bogie touched the right hand rail while the other bogie stayed on the track. You can't design the internal wiring of a loco to take maximum DCC fault current - particularly as the faul current depends on the command station - so you need to be sure the cutout will work quickly enough to avoid overheating, which is how cables fail if they are used above their rated current. DCC command stations cut out very quickly as long as the trip current is reached.
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