Things on the tops of Silverliner IV's

Does anybody know what those things on the front tops of Silverliner IV's are? They're like long rectangular covers or something. They're on both sides of the cars. The Silverliner II's and III's don't have them and the tops of those cars are more rounded as a result. Are these things where the horns are or something?

You can see them quite clearly on this pic:

http://world.nycsubway.org/perl/show?49550

(They're the things above the red marker lights)

If you look at the Silverliner II's for example:

http://www.subwaynut.com/septa/nphil/nphil6.jpg

you'll notice that they're not there.

Anybody know what these things are?

Sorry if this is a stupid post but I've always wondered why the IV's have these things whereas the II's and III's don't.

heres a better view up top

http://images.nycsubway.org/i61000/img_61340.jpg

Dynamic brake grids.

Dynamic brakes save wear and tear on pneumatic brake equipment by turning the motors into generators and dumping the electricity into large banks of resistors located in this case on top of the cars. They get hot, which is why there are intakes for cooling air on them.

I think that he was talking about the air vents in the upper corners of the trains. I believe those feed air to equipment of some sort (not sure what).

I always wondered what they were also . When I was a youngin', I thought thats where the horn was

They do function as air vents for fresh air. They were added in the late '70's.

Can somebody find a picture of a S4 without the vents then?

Matthew Mitchell wrote:Dynamic brakes save wear and tear on pneumatic brake equipment by turning the motors into generators and dumping the electricity into large banks of resistors located in this case on top of the cars. They get hot, which is why there are intakes for cooling air on them.

Of course on a lot of more modern equipment that extra juice is dumped back into the power grid instead of being bled off as heat. IIRC Alstom claims about a 25% recovery ratio in their current product line.

Anyone know if the SL-V's are supposed to have recovery capability?

Yes, they are. The real question is, why are they also going to have brake grids? The ALP-46s don't, any new MUs for NJT might not, and such items tend to remain unused on an AC system, because you're regenerating all the time. FWIW, a lot of newer industrial inverters don't have them either, even when braking's being used (which it isn't always), since the cost of building a regen converter vs a brake unit is pretty much the same now.

You need it on a DC system because DC can't always absorb regen (though I think the Milwaukee's could, and did). AC systems pretty much always can.

R8-They are indeed air scoops. As AEM7 said they were indeed installed in the late 70s. The similar NJT Arrow 2s had them also. Older shots of the Silverliner 4s and Arrow 2s when they were new in the mid 70s show the cars beforehand. MACTRAXX

As of mid- to late 1978, when the photos in John Pawson's book (Delaware Valley Rails) were taken, all the cars photographed had the scoops.

Are the air intakes for cooling the traction motors or to supply cleaner air for HVAC vs. drawing it from under the cars?

Here is a picture from the first Silverliner IV excursion: http://rides.webshots.com/photo/1110530 ... 8960WPygnF. As you can see, there are no vents on the top of the cars.

Nasadowsk wrote:Yes, they are. The real question is, why are they also going to have brake grids? The ALP-46s don't, any new MUs for NJT might not, and such items tend to remain unused on an AC system, because you're regenerating all the time...

...You need it on a DC system because DC can't always absorb regen (though I think the Milwaukee's could, and did). AC systems pretty much always can.

The operative words are "tend" and "pretty much". Based on the NEC power study completed two years ago for Amtrak, receptivity varies based on location, location of other trains, voltage already in the wire, etc. There were always times on just about every train (capable of regeneration) when some of the braking energy had to be bled off as heat instead of being fed back into the wire. So, unless you can always put power back (which you really can't, at least right now), you need grids or some other way of losing the energy.

nickrapak wrote:Here is a picture from the first Silverliner IV excursion: http://rides.webshots.com/photo/1110530 ... 8960WPygnF. As you can see, there are no vents on the top of the cars.

Thanks for the old pic! It's amazing how the lack of these vents caught my eye instantly.

So, does anybody know why these vents weren't installed on the Silverliner II's and III's? Are the vents for the dynamic brakes (which I realize the II's and III's do not have), or for fresh air for the cabins?