Steam & Excursion > NKP 765 in Black and White - (Part Four)

Here is the fourth and final part of this series of NKP 765 black and whites taken from color images. These are from September 9, 2010 in Medina, Ohio.
1) Full scene.
2) Closer up.
3) Last image of this set.
Bob

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Nice. She is stopped, right?

Yes, she is stopped. She is awaiting a train to clear the tracks ahead.
Bob

Pic 2.....( corrected...ooops)

The steam by the stack is the combined exhaust
from the 2 cross-compound air compressors.

Live steam (for the compressors) from the boiler is taken from 
a large-diameter dry-pipe, supplying boiler steam at the input side of
the superheater header ( which joins and supports all the superheater
steam piping).  The air compressor steam comes out of the smoke box,
just behind tte superheater header, and at the non-pressure side of tube sheet,
at the 12 o'clock position.
(A single superheater pipe is divided into two passes,
thus with Type E superheater units, each unit occupies 4 flues.)
The boiler steam, not yet superheated, from the inlet side ( of the header)  
is piped down to the two compressors mounted above the loco's pilot.

Since, it's heat-saturated steam ( steam at the same temperature as 
the water that boiled it) any decrease  in pressure necessarily creates 
a portion of condensed steam,  as some of the gas-form of steam
turns into the vapor cloud.

The steam in the cross-compound compressors is expanded two 
times --- once in each cylinder.  The lower pressure steam cylinder
is larger diameter to keep the same compressing force as the smaller
piston, which has the higher steam pressure from the boiler.

The twice-expanded steam at the exhaust near the stack is extremely 
wet and about atmospheric temperature --- it's REALLY WET!
The steam separator, next to the smoke stack, has a water drain-pipe leading 
down to the tracks.  The condensed water is cooled off, running onto the 
tracks.

It is crucial for safe train handling, that the loco's boiler pressure 
remains at maximum pressure during the long descent.  
As you may remember from your days at hand-pumping your 
bicycle tires, it's only the last 10% of the stroke where the air is
actually, and firmly compressed.  So, with locos, its the speed at which 
the pistons operate that makes for high air pressures in the Main 
Reservoirs.  

High MR pressure is needed after a brake pipe reduction, and application
of the brake shoes, in order to release and quickly re-charge every trailing car's
AuxiliaryReservoirs.  At a further distance, the engineer might need to
re-apply the train brakes.
Going downhill, you MUST have full boiler steam.

On some other RRs' locos, the air compressor exhaust is piped to the loco cylinder 
exhaust nozzle, beneath the bottom of the smoke stack....
On some engines, the wet air compressor exhaust steam 'washes'  accumulated 
soot and grime from the inside of the smokestack --- making a "dirty rain" that
falls onto surfaces and people.  The exhaust separators on NKP locos ensure
that the condensate 'rain' is water, only.  
Most of the separated water is sent cleanly to the tracks.

We applied a similar separator on sister loco 759, that separated the water 
from the exhaust steam of the reciprocating Hot Water pump of 
the Worthington feedwater system ---pre-heated feed water that was pumped 
to the boiler.  We mounted the 759's water pump exhaust steam separator*,
on the fireman's side of the smokestack, to match the similar location of
the air compressor's exhaust steam separator.

The Lima smoke stack casting was formed with two separate, cast 
Integral passages, where the pump exhausts were factory-applied &
was their original application.  No condensate condensors.

Now, you know.

​W.

(* Our improvised separator for 759, copied to similar dinensions,  contained a more simple,
     internal water-baffle than the original vendors' products. 
     But our separator worked just as effectively.

    One challenge with the original Lima application was that over long periods of sitting 
   idle, with the air compressors cycling every couple of minutes; was that condensate water 
   without a steady flow, tended to accumulate in the exhaust piping leading up to the stack.
   After several hours of accumulation, often an engine was called to duty, and as 
   the air pumps became more active...for the first several minutes it would 
   'rain' rusty water down and around the front of the engine!  Same thing happened with the 
   the recip-water pump  [exhaust]. In today's fan trip duty that would make a LOT of 
   customers very UNHAPPY!  Exhaust-water separators contain & confine the exhausted condensate).



Edited 11 time(s). Last edit at 04/07/24 12:21 by wcamp1472.

Thanks Bob for another excellent series on 765 in black and white.

Larry

I really like that second shot.  Great lighting :-)