Steam & Excursion > Little-known fact about Westinghouse Cross-Compound Compressors

The popular Westinghouse CC compressors, in the '30s and '40s were 
available in two capacities: 150 cu. In/ minute and 120 cu. In / per minute.*

Our early advisor on restoring NKP 759, pointed out to me the fact that the 
NKP Berks were spec'd with 8 1/2 - 120 compressors.  The identifying feature 
is the slightly smaller ( diameter) air cylinders   The cykinder head, external sizes 
were the same, only the cylinders were smaller.

The Tee- head bolts that secure the 4 compressor head assemblies are the same size,
but, the 8-1/2 150 model has external  ( individual) recesses that allow the Tee-bolts
to seat squarely are more distinct on the 150's external cylinder-walls, at the cylinder
head.  The 120's air cylinders are smaller, so the bolt recesses in the cylinder-wall 
are less pronounced.

The air-end cylinders differ only slightly in diameters, between the two sizes,
so, it takes a keen eye to spot the difference. 

Functionally, the compressors operate identically, the advantage of the 
120-size is more snappy piston strokes.   Especially if boiler pressure 
droops, a little bit ... The two 120s, applied the  NKP S2 Berks 
supply and make plenty of air.  And they're fitted with the Westinghouse 
dual-pressure 'compressor governors' --- a fancy term to steam-supply 
control valves the start and stop the compressors.

The dual-top governors have two compression springs, with different 
pressure settings.  One is set typically to regulate the maximum air 
pressure at 140 psi,  and a higher setting for 150 psi.

The air line from the engineer's #6ET brake valve feeds the 150 psi 
governor top, and an air line from the Main Reservoir sends pressure
to the 140-psi setting/and control-top

When the engineer, moves the brake handle to
the 'Lap'  position, or 'more-advanced' positions,
the air-line from the brake stand to the 'high pressure'
governor-top --- operates the governor, beyond 
the 'normal' pressure ( which regulates ar the 
140-psi level).  The pressure regulating spring,
in the 150-psi governor-top, keeps the compressors
snappily making air, and building-up MR pressure 
to 150 psi ...

Why?, you ask...

Simple... the movement of the brake handle to
'Lap' ...
      ( "lap" means that trainline air flow, from
           the brake stand is stopped... Air flow 
           has 3 states, only ONE is active at-a-time ..
          > air flows into the train-line
          >  air flows out-of the train-line
           > air flow stops ( and is trapped) in 
           the train-line, we call that position 
            "Lap", as in the control handle is 
              between the two air-flow ports,
               the control-port of the handle
               is blanked-off...   )

Moving the handle to lap generally tells the brake system that the engineer 
is preparing to apply the train brakes...

He does that by making a controlled-release of air from the trainline.
A typical release amount lowers the train-line pressure by 10 psi..
 ( we call the train-line : the " BP" --- 'Brake-Pipe').

The engineer controls a reference-tank --- which actually controls the flow--
and the reference tank regulates the 75-car train's,  entire length BP...
( The reduction of air comes to the engine in waves, from the long BP,
   and the reference-tank  controls the exhausting flow-rates --- all the
   way until the BP pressure is reduced...at a new, lower pressure.
  
   Example: if the running --- 'released' pressure-- is 80PSI, a 10-pound reduction 
   would lower the BP to a steady -but, reduced pressure of 70PSI..

   Once the 70 psi level is reached, ALL air flow out of the BP is 'Lapped' --- and all 
   air flow, into, or out-of the BP is  stopped!).

With no further changes, the train will be braked to a stop...

If,  however, the engineer was obeying a 'slow-order' , he will control the train 
speed at that lower speed-limit... Once the train reaches that lower speed...
he must release the braking; otherwise, the train will be braked to a 🛑 stop.

So, once he reaches that allowed 'rolling speed',  he moves the brake handle 
to the 'Running'  position ---- air now flows from the engine's Main Reservoir,
into the BP ---- However, the MR has been pressured to 150 psi..and now that 
higher available pressure is used to more-quickly supply more compressed-air to more quickly 
release the train's brskes --- at every car...

The air brake system anticipated the coming 'release', and increased MR pressure
in order to have more quantity of compressed air --to ensure a more rapid restoration of the BP,
back to 80 psi....

So.... The 8 1/2 -120 compressors will MORE QUICKLY, super-charge the MR to the150 PSI
than the "8 1/2 -150s" ---- account the 120s run faster;( make more piston strokes)
and make more air at the 150-pesssure setting....when the braking system is anticipating
a coming 'release' command..

So, the NKP crews had very responsive air brakes, with lots of advantages...
Once, he's got the entire train over the 'slow-order',
the engineer can widen on the throttle, and High Ball---
to his destination --- which might be 'home' and a HOT dinner!

​W.


(* Note: The ratings listed “150” & “120” are laboratory conditions when
supplied with specific steam testing pressures and a storage reservoir
of known capacity, and fitted with
an open orifice of specific flow
capacities. They would use a nominal boiler pressure of approximately 225 PSI.

If a specific boiler pressure is different , a commensurate change
in can be expected in the actual
installation’s performance characteristics.

Engines operating at 300 psi, will
have higher capacity, than locos
with lower operating pressures.

Also, compressors using the higher boiler pressure, than the standardized Lab pressures, will
run at faster speeds, against the
standard lab testing orifice.
If lower boiler pressures are used
on specific locos, the operating
speeds will be lower …
Example: PRR K4 class Pacifica
operate on 205psi… so, their compressors have different capacities, than the laboratory
sample).
Not proofed, yet..


              
               




 



Edited 5 time(s). Last edit at 09/18/23 02:54 by wcamp1472.

I'm attempting to make corrections to 'typos'..in the 'air brake' post, above...
but this software won't let me back into the document ..now.

I'll try...later 

It is unresponsive to my attempts to make edits, at times..
Oh, well ..

Wes...

 



Edited 3 time(s). Last edit at 09/17/23 19:58 by wcamp1472.

Still a great post despite the typos. Good luck fixing them.
—Mac

So, did it make sense?
 
I'm open to any suggestions....
I'm trying to avoid the typical 'air brake grammar' .... and the unique terms..

Its like being in a foreign land, once you try to read the original 
Westinghouse hand books..l

​W.

Very interesting.  I had been dealing with some unrelated air brake issues with our 6BL SW7 switcher.  I saw the 8 (gov) pipe info on the automatic brake valve and suspected it had something to do with steam loco air compressors.  You've explained "the rest of the story."  

So GOOD to hear from you, Allen!

I hope you're doing well!

Wes Camp,
Dover, Delaware!

Using 6ET, if you bring the train to a stop and nee to keep brakes set, which position do you use?

Tominde Wrote:
-------------------------------------------------------
> Using 6ET, if you bring the train to a stop and
> nee to keep brakes set, which position do you use?

Just leave the brakes set, i.e. "Lap", instead of going to "Release".

It depends...

A critical need is to get the cars' Auxiliaey Reservoirs fully recharged.--- 
you can only do that by placing the brake handle in it's Running ' position.

If it is a short duration period, you might be able to leave the brakes applied,
and leave the brake handle in 'Lap'..

For Longer duration waiting periods,  I'd recommend applying sufficient numbers of 
hand brakes be firmly applied --- again, the main purpose is to recharge the cars's reservoirs....
which only occurs when BP pressure is brought back up, to the running pressure ---
for freight service it's typically between 70 & 90,psi BP pressure.

Remember, that the increasing levels of stored pressure, slows-down the charging-rate, 
The closer the brake pipe pressure gets to the pressure stored in the Aux. Reservoirs'
the air flow gets slowed --- with growing pressure in the tanks you want to get re-charged,
opposes the intended "charging" pressure.  The goal is to 'equalize' the two pressures:
supply & "stored"...

The first 50 lbs charges-up quickly, --- 50 up to 60 takes longer,
and the last 10 pounds to, say, 70 lbs, is only a 10psi differential.. so that 
last 10 lbs could take 15 to 20 minutes....to get 95% stored pressure.

The brakes don't apply, until the BP drops below the stored 
pressure.... then the sensing-valve moves it's 'metering-valve' to direct
stored air pressure to the brake cylinders....

So, if you're impatient, and your auxiliary Resevoirs are only charged
to 65psi, you have to draw-down the BP to below 65 lbs to get the
brakes to begin re-apply ... but, you need to 'go deeper' if you want to stop!

A couple of repeated applications....and you're out of air --- and 
facing a run-away situation..  Hopefully, the stored-air in the
Emergency Resrevoirs,  can bring the train to a STOP.

​W.

 

HotWater Wrote:
-------------------------------------------------------
> Tominde Wrote:
> --------------------------------------------------
> -----
> > Using 6ET, if you bring the train to a stop and
> > nee to keep brakes set, which position do you
> use?
>
> Just leave the brakes set, i.e. "Lap", instead of
> going to "Release".

As asked, bringing the train to a stop and needing to keep the brakes set, HotWater's answer is correct. 

Wes in his follow up is discussing more the need to recharge the brake pipe after a stop or understanding how if not properly understanding a non-pressure maintaing brake (one that does not make up for brake pipe leakage.... old style #6, #8, #14 etc.) while in braking mode going over the railroad can get you in very serious trouble if you are not watching what is going on. As I posted earlier in the thread, you want to know the leakage in your brake pipe (pounds / minute) , the grades or profile of your railroad and calculate speed and distance while watching the gauges (especially main reservoir). The brake pipe (BP) and main reservoir (MR) will slowly drop as you are in lap as a result of your leakage, which you should know from your Initial Terminal or Class I brake test. I always did a balance of throttle and brake when dropping over a hill and down a grade whereby as air leaked on I could give another notch on the throttle to compensate and keep the speed steady. By understanding the leakage you could figure a location where you could release and recharge and then grab a second bite. Or know when the grade levelled out to make the release. On those old brakes, without retainers or passenger cars set with graduated release, you have to make a full release. It is not like a car just letting up a little on the pedal to reduce the braking effort.

And when you are in the situation where you have stopped with the handle in lap, or handle out position, leakage is still going on in the brake pipe. So you stop, then set a full set and sit. Eventually with the ongoing leakage the air will dump. Always good to set some hand brakes. After the air dumps, then it can bleed off and release the brakes, and if you have ZERO on the brake pipe and no hand brakes .... its off to the races as a runaway. 

I guess it is rather an art form learned from experience. I started on the old style and then went to 24RL and 26L. Any experience with CCBI , CCBII, 26 FastBrake or other more modern stuff has been strictly mechanical, not operating.

 



Edited 2 time(s). Last edit at 09/18/23 13:24 by train1275.

train1275 Wrote:
-------------------------------------------------------
> I guess it is rather an art form learned from
> experience. I started on the old style and then
> went to 24RL and 26L. Any experience with CCBI ,
> CCBII, 26 FastBrake or other more modern stuff has
> been strictly mechanical, not operating.

Indeed it is.  An engineer always has to monitor the brake set on his train.  A brake valve advertised as pressure maintaining can fail.  I saw a bunch of 26L's leak down and also saw one or two CCB's fail too.  Then there are careless or clumsy people that bump into your brake valve.  In the modern era , add to that the big backed swivel seats that will inadvertently bump into your brake valve.  The steam era engineers I learned from would talk about how well their engine and tender brakes would hold most of their trains for recharging.  Not so today with the PSR size trains possibly pulled by only two big widenoses.  Today add to that, officers and dispatchers telling you to stop your train at places no exerienced and prudent engineer would stop at in the past.
 

I have cut out the doubleheading cock on a 26 after making a first service(minimum repuction) and let the leakage do the braking. Also the electroic brakes are as the previous poster said strictly mechcaial with no changing the program. I've also seen them towed trail only for electrinic brake problems.

Sam

I wouldn't brag about "letting leakage" do the braking...

It works in specific situations. but why surrender control?
By cutting-out the brake valve, you add delay in recovering 
control.

​W.


 

wcamp1472 Wrote:
-------------------------------------------------------
> I wouldn't brag about "letting leakage" do the
> braking...
>
> It works in specific situations. but why surrender
> control?
> By cutting-out the brake valve, you add delay in
> recovering 
> control.
Well, sometimes it's the best bet to get over the road if you have a faulty 26L brake valve that's - (1)- not lapping or (2)- got a quick action beyond a certain level of application.  I find it interesting that Trainhand and I learned train handling on the same railroad and sometimes the same division, just a number of years apart.  Evidently those train handling tricks got us both to retirement. 

OK...

My comment was responding as if it was a "common thing.."
In my limited experience, the 26L's I had, worked fine.

YES!
In case of failures---- it's good to know the work-around.
And it's good to ( in controlled situations) 'practice" the technique....

If you're not experienced in the method and how it works --- you're  taking 
your chances.   So, several times, with different trains, practicing the 
technique gives you confidence --- so when a 'real' situation arises, you're prepared.

Experience is a great teacher...
Thank you for the explanation and the hint about the ways a 26 can FAIL.
Having proven 'work-arounds' , is ALWAYS a good idea.

Greatly appreciated !

​W.

( I had purposely left out the discussion about 'leakage'...yet, its vital 
   to have it 'quantified', and knowing how each train behaves.
  So knowing the real leakage rate,  before departure is key.
    I'll discuss the 'leakage' problem,  later...

   One time, during the Rock's 'directed-carrier' status, 
    I had an entirely 'new train' of more than 100 brand-new, loaded,
    covered hoppers to get from Silvis to Des Moines, Ia...
    All new brakes, ABDX valves, all new 'shoes, all new hoses --- and 
    NO measurable leakage !  That was a TIGHT !!  train..

    It handled like a DREAM...very quick response, and very fast
    'releases' --- it handled like a 10-car train!
     Once, you climb out of the Mississippi River valley, up & through
     Davenport, Ia--- it's virtually FLAT all the way to Des Moines!).


 



Edited 1 time(s). Last edit at 09/19/23 09:13 by wcamp1472.

26L and the modern Buck Rogers stuff is all I ever operated. Putting the cut out to “Pass” will cure a leaky 26L and I have used the feed valve more times than I ever wanted to.

Now I can’t even teach any of the tricks to the new firemen. PTC and the electronica have killed the old ways.

Regards

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