Steam & Excursion > PM 1225 question…

Is the PM 1225, 2-8-4, the only operating  U.S. loco that is 
equipped with the Franklin 'Precision' screw-reverse for setting
the valve gear?

The NKP Berks were all built with the Franklin, air-operated "screw-reverse" operating 
cylinder.   The engineer had a large, aluminum operator's-wheel in front of his knees..

The screw reverse, late in the life of Berks, was a pain in the right arm, when 
used in service with a lot of car couplings and uncouplings..

Especially, if you had a 'missed-coupling'   ----- where the first  attempt at getting the
knuckles to lock, missed...

You had to crank the screw reverse wheel all the way to full ' reverse', then pull the couplers apart.
Then, crank the screw reverse to the full opposite setting, and move again, to attempt the get the
knuckles to 'lock'.      You, then,  had to 'test' that the 'pin dropped': you had to crank the
screw reverse all the way to the opposite setting, than give a tug with the throttle...  
Hopefully, the coupling was 'tight'...
Then, in order to release the pressure on the knuckles, you had to fully 'crank & reverse'
the engine 2-more times...

What is it, about 20 full-turns, 'lock-to-lock'?
A full day of handing freight cars, wiith a screw-reverse equipped engine,
could quickly  'wear-out' a fella's right arm, by 9 AM!...

Its no-wonder that the NKP had fitted lever-operated, "power reversers" on many of their locos,
near the end of steam...

​W.

 



Edited 7 time(s). Last edit at 11/29/22 11:35 by wcamp1472.

Here's what Wes is talking about... That screw is clearly visible, and yeah, I always thought that would quickly become a pain in the ass.

Note: This was shot in 2010, when the 1225 was undergoing boiler inspection work.



Edited 1 time(s). Last edit at 11/29/22 11:43 by jkh2cpu.

---

Some of CP'S hudsons had a power screw reverse.  That thing would really speed to either full reverse or forward and you had better not have your hand in it,  I could also be used manually.
 

Yes, the Canadians routinely rigged up a conventional 'tool-like' 
'air-motor', with a roller-chain & sprockets over the reverse's drive shaft. 

It was controlled by a two-position, center-off, operating lever. 
The aluminum 'drive wheel' did NOT have a crank handle. 
There was a fixed, indicator scale with a traveling pointer to 
locate the centered valve gear. 

And, yes, you could manually turn the shaft's wheel by hand....for fine-tuning 
the setting.  A very sensible solution. 

If it was me, I'd add a similar,  'air-drive' solution to 1225. 
Its simple enough.. 

Thanks for the picture. 

W. 

(I'd also up-grade that brake stand with a newer 26-NL engineer's brake valve to control  
  an upgraded 6NR Distributing valve, under the cab floor.  Look it up ). 
 
 



Edited 1 time(s). Last edit at 11/29/22 13:17 by wcamp1472.

C&O 2716 still has its Franklin Power reverse. I think it was Bill Purdie who fitted the air motor to it, if I remember right.
NKP's operating conditions for the 700's where such that they would, and did, handle through freights but they also were required to make setouts and pickups quite often, so NKP had an ongoing program to replace the Franklin reverse with the Alco Type G or H Power reverse. According to NKP drawings, S & S1 class engines were to get the Type G reverse while the S2 & S3 engines were to get the Type H, which had a 2" larger cylinder than the type G. 

Jim Kreider



Edited 1 time(s). Last edit at 11/29/22 13:39 by jimeng.

You're right..!!

I remember seeing the 2716, SOU excursion, when it paused at,
Manassas, Virginia, 1980s(?).

Power-assist for screw reverse:  I remember seeing the drive motor, chain and sprockets, mounted near the firebox..

Thanks for reminding me.

​W.



Edited 2 time(s). Last edit at 11/29/22 16:27 by wcamp1472.

tomstp Wrote:
-------------------------------------------------------
> Some of CP'S hudsons had a power screw reverse. 
> That thing would really speed to either full
> reverse or forward and you had better not have
> your hand in it,  I could also be used manually.

That is what the Royal Hudson 2839 had when I ran it some on the Southern long ago.  I learned not to have my kneecap near the manual handle when using power reverse.  I think I found a way to fold the manual handle down.

In regular passenger service, the screw reverse is so good for fine tuning the cutoff.  You want 28, not 30%, you got it.  Do it right and your fireman will love you.  So will the bean counters.

Tominde Wrote:
-------------------------------------------------------
> In regular passenger service, the screw reverse is
> so good for fine tuning the cutoff.  You want 28,
> not 30%, you got it.  Do it right and your
> fireman will love you.  So will the bean
> counters.

Are you saying that an Engineer couldn't do that with the Alco Power Reverse "stick" quadrant? I know for a fact that all those nice fine notch teeth on the power reverse quadrant of SP 4449, UP 844, UP 3985, and NKP 765 work just fine at "fine tuning" the valve cut-off.

My guess is that ALL early applications of Walschaert valve gears 
were manual, screw-reverse equipped.

By 'early' I'm talking between 1905 and 1925, before reliable, lever-operated,
'air cylinder types' became reliable and produced in great enough numbers.
The 'power reversers' product-development occurred at about the same pace
as the evolution of reliable coal stokers.

The first, moderately, reliable stoker was Standard's "Duplex stoker".
It consisted of a screw conveyor from tender-to-loco, with two 
angled, elevator screws up each side of the backhead fire-door.
It was crude at best,

The improved variant was the Standard "B" stoker.... it used the screw conveyor 
from the tender, to a point under the cab floor, than used a angled tube ( no -screw),
up to the fire-door.   It took up a lot of cab-floor, and made occasional hand-firing,
a near impossibility. 

Standard moved the elevator tube to just inside the fire door, and raised over
the grates.  That version became very popular, and marketed as the MB stoker,
"Modified-B" stoker.  used successfully for locos up to UP's  4000-class locos.

MBs were handi-capped because the "steam distribution head"  --- the 
5 jets-array--- was above the column of coal from the conveyor.  
That lead to the jets blowing the fine, crushed coal forward, under the brick-arch,
and the larger lumps congregated at the rear corner of the grate, nearest the engineer's
knees.

The steam jets blow over-top of the coal 'column' and the heavier-coal rarely gets directly 
into the path of the steam jets.

Standard improved the MB , and marketed the "HT" stoker, after about 1936...
The HT, uses an angled elevator tube and internal screw, through the cab floor,
and through the back-head, under the 'Butterfly' firedoors...

The coal falls onto a flat, cast iron, 'firing-table'....  it has low, deflecting vanes to direct
the coal fuel across the entire grate area.  The steam jets are just above the firing table,
and the coal column is above the jets, and the coal falls more directly into the 
path of the steam jets.  Lighter coal particles get blow around easily, and the heavier
coal chunks fall more directly into the path of the steam-jets.   The heavier chunks,
get more evenly distributed across the firebed, than in the case of the MB stokers.

Modern, firebeds and grates are heavily dependent on the free-flow of air through 
the 'bed', but the air volume and velocity is strongest at the rear 30% of the grate.
The air flow through the remaining 70% is a much lower rate and quantity...

When firing, the back areas of tte grare, wihich has the highest velocities, burns coal
at a much faster rate than the front 70%..... as the bare area looses heat and fire,

 Cold air, at greater velocity comes into the firebox---- cooling-off & dropping firebox temps...
the novice fireman,runs the stroker delivery screw faster ---- but, that doesn't help,
when the fire is OUT on that back grare area ---- resulting in cold air in the firebox &
great clouds of black, unburned coal..

Also, modern firebox grates and air velocities are designed to properly function
with 100% of the designed-load behind the tender.   That is the condition that the
greatest heat is needed, and the greatest air-flow.  

The ideal fuel ratio, by weight, is 16:1,  oxygen to carbon.  
Since, nitrogen comprises 72% of air's volume, and oxygen about 16%--
--- you need a lot of cubic feet of aur to burn even 1lb of coal.... remember,
the 16:1 ratio is by 'weight', and the O2 component is only 16% of the volume.

So, with a light train , as in the typical excursions, and a large grate --- designed
for maximum performance, you'll soon be in trouble.   The reduced draft, from the
lighter train, makes it hard to effectively fire the coal bed, since you can't get a draft
that comes close to the original "design parameters...". The poor 4014 will never see
it's designed trailing load .... a huge grate, and 10-cars, or so,  don't work together,
very well... grare area is inconsequential statistic, when considering oil burners...
But, great volume also affects the oil-flame, too.  The oil burner makes the oil flane
a very intense, localized, high temperature 'hot spot' ---- that hot spot on similar,
high performance locomotives led to more frequent firebox replacement periods...
bolt thread-wear and excessive cracking of firebox sheets in tte lower 4 corners.

A smaller engine, like a 4-6-2, and the like, will burn a much better fire, 
at closer to it's designed capacity and speeds ..( whether coal, or oil fired).

​W.

not proofed, yet





 



Edited 2 time(s). Last edit at 12/04/22 11:14 by wcamp1472.

HotWater Wrote:
-------------------------------------------------------
> Tominde Wrote:
> --------------------------------------------------
> -----
> > In regular passenger service, the screw reverse
> is
> > so good for fine tuning the cutoff.  You want
> 28,
> > not 30%, you got it.  Do it right and your
> > fireman will love you.  So will the bean
> > counters.
>
> Are you saying that an Engineer couldn't do that
> with the Alco Power Reverse "stick" quadrant? I
> know for a fact that all those nice fine notch
> teeth on the power reverse quadrant of SP 4449, UP
> 844, UP 3985, and NKP 765 work just fine at "fine
> tuning" the valve cut-off.

I think what Tominde is alluding to is the fact that the design of the Franklin Precision Power Reverse provided an “infinitely variable” cutoff position compared to the individual position settings available of the reverse lever on a notched quadrant (or “stick” as you call it). Kind of like comparing an analog system to a digital system. I think however that it boiled down to kind of “nit-picking” in the practical world, and as you say, the fine notch settings worked just fine. 
Jim Kreider  
 

Remember, too, that most late manufactured locos ere fitted with 
very precise control throttles.  The problem with a single, large diameter,
lifting-disc, or dome-throttle, was that it is an 'all-or-nothing' design.... the control-range
of lifting the valve open was about 1/4" of lift.... once opened that far, the throttle
wss no longer an effective flow-control device..... full flow was inevitable.

Later loco designs, used a row of 5 or 6 individual 'poppet' valves', each sequentially opened,
according to the engineer's setting of the throttle lever.  A half-open throttle would be like 3 -poppets
lifted, 2 or 3 closed..

Yes, each individual poppet went fully open, when lifted, but the port-hole was 
a small, limited area... what controlled the steam flow was the number of smaller ports 
that the engineer opened, and NOT the 'lift'  that each valve was opened.

So, steam flow to the cylinders is a combination of throttle opening + the steam pressure 
delivered at the spool valve..  That pressure is also dependent on driver RPMs, as well as
throttle opening.  

On front end throttle equipped locos, the throttle is AFTER. the superheater piping,
so that the flow-rate through the superheater is slowed, with fewer throttle valves opened...
the "slowed-flow"  increases the 'dwell-time' of the heat-saturated* steam in the path of the 
flames from the firebox.  The longer the dwell-time, the hotter the superheat....
The more-dense, heat-saturated steam is expanded, as the steam temperature increases ...
thus, more steam exits the hot superheater, than goes into the units .  The 'colder' steam
increases in volume, as it becomes superheated..

We talk about the amount of superheat  in terms of the heat added,  like +200, + 250, etc.  
So, you'd add the heat-saturated steam temperature  of, say, 400 degree steam, plus amount of
superheat, to get steam temperatures at the pistons.

Its very common, when cruising, to have the valve gear set for 'early cutoff', and have 700-degree
steam in the cylinders, with 100-psi at the spool vakve....  I've seen the NKP 759 powering 80-
freight cars, up the Potomac River-grade, to Cumberland, Md., with the reverse lever near 'center'
and the throttle half-closed!  

We had full boiler pressure, a white-hot fire,  the stoker turning very slowly, and the
water pump lazily pumping...but  our speed was held to about 45-mph, as limited by the rule-book...
( rock-slide territory, + slide-fence signals...).  Otherwise, we coulda' been doing better than 60-per!

[ And, yes, I had asked the crew why were going so slowly...
  . "Rock Slide territory", I was quickly told..    Oooops! ]

You don't need a wide-open throttle to get beneficial pressure against the piston-face,
all the way down it's stroke..  You still can have superheated steam out the stack.

So, when it comes to steam flow-control, the need for precise settings of the screw reverse
is mitigated by the combination of reduced throttle setting, & the valve gear's early cut-off setting.  
The two settings, together, control the steam pressure at the piston-face.

'Stick' vs. screw  becomes inconsequential, if you have a 'front-end' throttle for
steam flow-control.

​W.
 
(* Heat-saturated steam is steam in contact with & above the boiling water that produced it.
    They are both at the same temperature, Steam has absorbed 8-times the number
     of  BTUs as it took to get to the boiling point.

    Adding more heat to the water only increases the water temperature ,
    boiling more water;  but, you can't raise the steam temperature above the
    temperature of the water, by raising the fire's intensity.  
    You just make steam faster.

   The steam is 'heat-saturated'.    Steam is the gaseous state of water, it is 'dry', 
   with no moisture.

   By removing and rerouting the steam into HOT superheater piping, you can raise 
   the steam-flow's temperature.    The pressure remains the same, so the steam molecules 
   become more active in their vibrations, separating the molecules..... thus, more steam
   volume exits the units --- at a hotter temperature.   You're not raising the pressure --- as 
   soon as you close the throttle, the safety valve lifts! )

 



Edited 4 time(s). Last edit at 12/02/22 00:55 by wcamp1472.

C&O 2716

---

CP 5468 at Revelstoke.

---

NKP 765 got the Alco Type G in the 1955 shopping and I think the 755 did also. All of the other NKP Berkshire survivors still have the Franklin hand crank wheel reverser: 757, 759, 763, 779.

After diesels started arriving, the 765 would sometimes get assigned to the "Argos Turn" and other switch runs. The Alco Type G made it a lot easier and faster on the engineer.

Confirmation or correction of the Type G conversions is welcome.

Posted from Android

757, 759, and 765 all have the Alco Type H power reverse which had a 2" larger cylinder than the Type G. 
Jim Kreider

759 has the Alco, Lever-operated power reverse.
HICo ran that engine from 1968 to 1972...

I don't know about the others on your list. but remove NKP 759.

​W.
CMO, HICo.



Edited 1 time(s). Last edit at 12/04/22 11:02 by wcamp1472.