Why do subway trains "hiss" at their first and last stop?

[Yofi]

Hi there, this is my first post here so I apologize if there's anything I did wrong.

 

Anyway, I have been curious about this ever since I moved to the city last year. I live near the terminus of a train, and I've noticed that every time a train enters or leaves the station, it lets out a very loud hiss after it brakes. It sounds like a large burst of air. I've been paying attention at other stations and it seems that trains on other lines do this at their first and last stop as well, but I've never heard it at intermediary stops. What causes them to make that noise?

 

Thanks!

[SevenEleven]

The loud hiss is the air dumping out from the system, when the emergency brakes are applied:

 

 

[Yofi]

The loud hiss is the air dumping out from the system, when the emergency brakes are applied:

 

 

 

Thanks, that's interesting. Is there a reason that they always use their emergency brakes at the first and last stop? Do they need to empty the air at the beginning and end of each route maybe?

[INDman]

To remove your brake handle (on cars so equipped) or remove your MC key, you need to place the brakes into emergency.

[SevenEleven]

Thanks, that's interesting. Is there a reason that they always use their emergency brakes at the first and last stop? Do they need to empty the air at the beginning and end of each route maybe?

Which hiss are you referring to for the beginning? Can you find a video of it?

[TripleRTO]

Which hiss are you referring to for the beginning? Can you find a video of it?

We dump when coming into the terminal from the layup too, it that's what he meant.

[S78 via Hylan]

Just to throw some out there:

The does it at Utica Av, the at Euclid on the Manhattan bound platform and I think the at 179 St.

[Missabassie]

It could also be called a parking brake. I say that because with all the japanese train vids I watch, it seems like their trains lack this feature.

[Fresh Pond]

It could also be called a parking brake. I say that because with all the japanese train vids I watch, it seems like their trains lack this feature.

Well trains already have a parking brake (handbrake on non-NTT trains) in addition to the regular emergency brakes

[Ethan777]

What about fogging at the terminus?

[Kamen Rider]

Thanks, that's interesting. Is there a reason that they always use their emergency brakes at the first and last stop? Do they need to empty the air at the beginning and end of each route maybe?

 

Most times at terminals, even if you're just walking to the other end and taking the same train out again, you're not at the controls. You can't leave a train sitting without the air brakes set to emergency (the term is "dump"), since so long as there is pressure in the system somewhere, the brakes could slip off. 

 

The brakes work on positive air pressure to keep them off, and release of pressure to apply them. When the train air brakes are applied on-route, a certain amount of air is let out of the system. (newer cars use their air brakes only at the end of the braking cycle, instead reversed the power flow of their traction motors to bleed off forward momentum) When the emergency brake is triggered, the system is vented to "one Atmosphere", which means equal to the outside air pressure ("one 'atmosphere" is the air pressure, from the air's own weight, at sea level. since New York is at sea level...). This is to make absolute sure the train does not move. 

 

The hissing you hear of the trains about to leave is probably the compressor recharging the brake system.

 

What about fogging at the terminus?

???

[realizm]

What about fogging at the terminus?

You meant 'fogging' in the sense of fumigating trains at the terminus - the escorting out of commuters out of the trains at the terminal before the train crews can proceed with turn-around or going to the yards?

 

If thats what you meant: I believe T/Os and C/Rs are responsible for clearing the train from car to car to car before proceeding OOS to then yard, lay-up or for turn-around. Dont quote me on this but according to the rulebooks I have heard this must be done in 30 seconds from the layman knowledge on this that I have. Better for an MTA employee to clarify this for you, but thats what I understand about fumigation of trains.

[SubwayGuy]

What's posted above is not entirely true, and there are numerous mistakes in some of the comments.

Stop. Let's keep it simple for the guy.
 
INDman is 100% correct when he writes that the train needs to be placed in emergency so the train operator can remove their tools from the train, and leave the train "secured" for the next train operator who will take that train.
 
This is what you experience occuring at the last stop.
 
At the first stop, depending on the location, the train may be coming out of the relay. A relay is a move made beyond the station to bring the train back into the station on the proper track (ie a southbound train leaves the station on the southbound track, goes into the relay, and when it comes out, it is on the northbound track). This is the case with the C at 168 St. or Euclid Ave., the 4 at Utica Ave., the 6 at Parkchester (NOT the trains originating from Pelham, just the Parkchester trains), etc.
 
Now, regarding how the emergency brake actually works, if you've read and understand all this, and are curious how brakes on most modern trains work (R32 model through R-68/A models), you can read this post I wrote on the subject a few years back. Focus specifically on the part about the "brake pipe" and emergency brake. You don't need to know this info, it's just here for you if you want to / to correct some of the wrong information posted earlier in the thread so you don't go off believing it.

 

One more thing - If you've gone and read that link: new tech trains (R142-R188) use a system that functionally works the same as described in the post, however mechanically they are very different as there is no straight air pipe on new tech equipment, rather a computer on board the train directs all brake requests.

[SubwayGuy]

You meant 'fogging' in the sense of fumigating trains at the terminus - the escorting out of commuters out of the trains at the terminal before the train crews can proceed with turn-around or going to the yards?

 

If thats what you meant: I believe T/Os and C/Rs are responsible for clearing the train from car to car to car before proceeding OOS to then yard, lay-up or for turn-around. Dont quote me on this but according to the rulebooks I have heard this must be done in 30 seconds from the layman knowledge on this that I have. Better for an MTA employee to clarify this for you, but thats what I understand about fumigation of trains.

 

There is no limit to the amount of time allotted to "clean out" a train of passengers when it is going to relay or go to the yard. Generally it takes 2-3 minutes at most. However, any issues during the process are to be called in immediately so dispatchers are aware that they may have to work around a delay and request police, for example if there is a homeless person refusing to move, or a sick person who is unconcscious, anything like that.

[realizm]

There is no limit to the amount of time allotted to "clean out" a train of passengers when it is going to relay or go to the yard. Generally it takes 2-3 minutes at most. However, any issues during the process are to be called in immediately so dispatchers are aware that they may have to work around a delay and request police, for example if there is a homeless person refusing to move, or a sick person who is unconcscious, anything like that.

 

OK got it now. Thanks for the clarification.