On page 86-87 of the latest Trains magazine, there is a picture of D & H GP-38-2 # 7312 exiting Belden Tunnel. My question is about the tunnel portal. Is that big square metal thing over the tunnel portal a door? Is it lowered during the winter to keep out snow? Living in the south, I've never seen that before.
Thanks,
George
Yes to all your questions, George. Sort of anyway. Snow is one reason for the door but so is wind in some cases. Many tunnels have the doors for wind control rather than snow. But in all honesty, in the 50 or so years around here, I've never seen the doors actually closed at Belden Hill. Have seen pictures of doors closed on the west end of Hoosac Tunnel on the B&M and Moffat Tunnel on the old Rio Grande though...and those were for wind or air flow.
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Do you know if the tunnel is equipped with exhaust fans?
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I don't believe so...the tunnel is short and traffic is light.
henry6Many tunnels have the doors for wind control rather than snow.
SP tried doors on several tunnels, just at the uphill end; the door was to stay closed until just before an upgrade train reached it, so air wouldn't be pistoned out of the tunnel ahead of the train.
It is a door. The differences in facings are because of extensive enlarging of the tunnel in the 70's.
Why would wind need to be controlled?
The East Broad Top had problems with seeping water freezing on the tracks & causing trains to derail. they installed doors on the east ends (only) of their two tunnels in order to stop the wind from blowing through, and that solved the problem.
Tunnels can actually become wind tunnels, funneling moving air at higher velocity than through open air. Having a door at the entrance of the common direction of wind will still the air movement inside the tunnel for trains coming opposite to that wind. In some tunnels, the longer ones like Hoosac and Moffat for instance, those doors may stay shut until the train approaches them...in the signal circuitry of course. Wind also cools the air and may cause extensive freezing, worse than without wind.
ACYThe East Broad Top had problems with seeping water freezing on the tracks & causing trains to derail. they installed doors on the east ends (only) of their two tunnels in order to stop the wind from blowing through, and that solved the problem.
Wind through a tunnel can be actually be beneficial. Ventilation is required to clear out the exhaust fumes from diesel and, in earlier days, steam locomotives. Cooler air also helps the diesel's cooling systems - the hot air above the train created the "tunnel motor" variant of the SD40 and SD45 models. Longer tunnels often required expensive fans to artificially create wind.
The problem with natural ventilation appears during winter. Many tunnels have ground water seeping through the walls. This occurs year round since most of the tunnel length is well below the frost line. A constant inflow of cold air will cause the seepage to freeze and build up. Large icicles develop from the crown, on the tunnel walls the ice flow can get over a foot thick, and as others mentioned, you certainly don't want it over the rails.
I don't know anything about this particular tunnel but suspect the door may have been for winter time use. Stopping the flow of air will allow the surrounding rock or earth to keep the tunnel interior warm enough to prevent ice build up. Ice has long been a common problem in Canadian tunnels. Trying to seal off the seepage has at best just reduced the flow; insulating the water from the cold air has been more effective.
John
narig01Just a couple of comments. That looks a little small to be a door. It would not cover the portal. Also no visible hardware to lower it. Looking at the pic the coloration on the portal is different then the retaining wall to the right of the locomotive. Could the tunnel portal been damaged at some point and repaired. The other thought is maybe maybe there was a slide and the metal is a barrier to prevent a repeat. The area above the portal is devoid of trees.Rgds IGN
Johnny
I also read that the doors on Hoosac and Moffat tunnels also assisted the fans in directing the smoke (both steam and diesel) out of the path of the locomotives and trains (especially passenger) so the train crews and passengers would not be asphyxiated in the long tunnels. It also helped the locomotive crew see ahead of the train.
Trains on the EBT would slow or stop before the tunnels to pull a rope that operated a switch to open the doors on the tunnels. The crew on the caboose would pull the cord after the exited the tunnels to close the doors.
Without a door, the air blown by the fans would just flow back through the adjacent portal rather than through a long tunnel to the far end. It may not be immediately obvious, but a mile long column of air has a fair bit of inertia and pressure is needed to get it moving. Without a door to seal the near end it is near impossible to generate the pressure. Most tunnels that had fans also had doors by the fan house.
There are vent shafts at strategic locations in most tunnels. Belden HIll has one. Hoosac I think, two. For instance.
Don't know about the Belden Tunnel, but the Moffatt Tunnel has a blower house adjacent to the east portal. That door is always closed unless there's a train passing through it.
Someone mentioned air 'pistoning' out of a tunnel portal ahead of a train. Due to the speeds involved, this is a serious problem on several Shinkansen routes. The Japanese answer? Extended portals with carefully calculated vent openings, rather like muzzle brake-silencers for artillery.
Chuck
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