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Steam & Excursion > Screw reverser on the NYC Hudsons

Date: 03/14/23 22:02
Screw reverser on the NYC Hudsons
Author: ApproachCircuit

Wonder old pictures on Flicker show hogger and fireman inside the cab of 5400 series Hudsons. Screw Reverse.
Johnson Bar was stone age-good on a goat for switching but not much else.
Long Live the Screw Reverse!
Johnson Bar was installed and its linkage because it was cheaper'
Screw Reverse required more engineering and total cost to carrier.

Date: 03/14/23 23:20
Re: Screw reverser on the NYC Hudsons
Author: wcamp1472

An early application was on PRR E-6 Atlantic, 4-4-2, about 1912.
I believe that the K4 class and L1 class early production 
models were screw reverse equipped.

Power reverse mechanisms were not commercially produced 
until about the1920s.  These were lever-operated, compressed air powered
pistons, with 'self-locking', trapped, compressed air maintaining the selected 

The engineer has  a short lever and a curved quadrant, with gear teeth to
lock the lever at various positions.  The lever, when centered, allows the
moving parts of the drive wheels' valve gears to have the spool vslve
at its shortest travel distance..... meaning that the spool valve still opens
the steam admission ports...powering the pistons....
as the wheels go-round-and-round

With conventional 'radial' valve gears  ( Walschaert or Baker)  the 
valve is always opened by the two bars that connect the piston's
crosshead to the valve stem's crosshead.  When the piston is at either 
end of its travel the two links : a vertical bar = 'combination lever",
and its crosshead connector = the 'Union' link wil have the admission
ports opened and admitting steam..... if the throttle is opened..

The width of the openining, when measured at the dead-centers 
( piston at the cylinder heads) will have the valve port open by
1/2" , or so.  The lead ( say: 'leed') is designed on the builders's construction drawings.
As the valve gear pins and bushings wear, over time, the slop reduces the amount
of travel of the spool valve, at the ports... they open later & to a lesser amount.

In operation, a centered reverse lever still allows port openings.::::
once underway, it's possible for the loco to power down the tracks...
with the reverse lever 'on center'..

The valve closes at later periods, as the engineer adjusts the power reverse
for different power conditions.  The eccentric crank on the Main driver and
the curved Walschaert link operate the radius rod, whose front end is
connected at the valve's crosshead over the power cylinders.

The engineer can control the valve's closing-point, from a maximum duration of boiler 
steam, of 85% of the piston stroke down to the fixed-dimension of the valve Leed.

The quadrant & lever operated reverse schemes allow the first strokes to
set the loco in either forward operation or reverse operation.
Once underway the valve events are symmetrical.

The early Screw Reverse gears were manually cranked, with the centered
position being the mid-point of the screws' length.  It was a pain in the engineer's 
butt when making numerous couplings and uncouplings --  he has to manually
crank the follower-block from full forward postion to full reverese position.

Making couplings, and testing that the knuckles are locked meant that the engineer
had to make 4 complete screw reversals --- more if the coupler knuckle pin failed to lock!

Franklin Ry. Supply company marketed an air powered reversing mechanism that was 
a powered assist device so that it was easier to complete the full-stroke movements
durung coupling moves.
The Franklin Precision Screw Reverse 

It was easier, but still required the engineer to manually make every single 
turn of the reverse wheel when making couplings and testing the 'lock' ...
.It still wears-out your arm if used in freight service, or there's a lot of
switching/coupling moves.    ( I think it's like 20- turns, lock-to-lock).

Common on Canadian engines was a manual screw reverse shaft, wiith
a sprocket & chain around the shaft.  a conventional 'air-motor' (for
operating drilling/polishing tools)  was  securely mounted & used to spin
the reverse shaft.

The engineer had a two-position, center-off, stubby air-valve lever to operate
the air motor.   A roller-chain connected the air-motor's shaft ( small gear)
to the larger gear mounted on the reverse shaft.  
That made life simpler for the hog-head.

In the 'States, different RRs added such air motor/chain-and-sprockets to
the reverse shafts of the Franklin Screw-reverse.  
Life became easier.

invariably, these chain-drive arrangements were non-standard, and applied
by various shops, as locos were undergoing 'classified repairs' --- more extensive 
than daily/monthly inspections..  No two applications were alike, in construction 

So, if you were an engineer ---- if you had a loco with an unmodified
Franklin Screw reverse, it was going to be a long day, and sore right arm!

NKP Berks were  built with the Franklin Precision loco screw reverse,---  
and later in life, many were replaced by lever operated power reverse
with conventional compressed air cylinder & small Johnson bar. 

So, there were variants when it came to power-operated, screw reverse
mechanisms: from full-manual, to Franklin Precision cylinders, to chain-drive, and 
hybrid combinations of chain/ air-motors.

SAFETY WARNING : With air motor/ chain-drives modifications  it's important
to remove any manual-wheel crank handles from the powered, spinning wheel&shaft.

Engineers can get nasty bruises and broken forearms...if they get hit
by the spinning wheel and it's protruding crank handle. 
Make sure to remove any crank handles, if modifying screw reversers
( with powered shaft-drives) on locos that are modified.


It's dark out..I'll proof-it,  later 

Edited 6 time(s). Last edit at 03/17/23 11:35 by wcamp1472.

Date: 03/15/23 10:57
Re: Screw reverser on the NYC Hudsons
Author: timz

> inside the cab of 5400 series Hudsons. Screw Reverse.

Meaning no power reverse? On late NY Central Hudsons?

Date: 03/15/23 12:44
Re: Screw reverser on the NYC Hudsons
Author: wcamp1472


[ edit: With Screw reverse schemes,
there are two distinct ways to
change valve travel settings:
Full-manual operation using the
Mechanical advantage of the
screw device OR a Power-assisted
scheme; i.e. Franklin Precision Reverse.

In either case the screw
shaft must be still turned by the
engineer to its new setting....
The power assist of the Franklin
device makes it way-easier to
change settings —- but you still
gotta' do the cranking… )

The Hudsons used the Franklin Precision ( screw) Reverse ----
in which, air-powered actuating piston controls the loco's valve gear
positions.   The screw-wheel, in the cab, is spun manually ---
the loco's valve gears ( R & L sides) are re-positioned by pressurized
air acting on the cykider's piston, from the MR.  As the piston moves,
it re-centers the pilot valve shutting-off the air --- at the new setting.

Manual-input is what determines the movement of the power reverse
operations.  The System works by the engineer manually turning the
control wheel.  That simultaneously moves an air pressure, port-valve down
at the reverse cylinder.

The port-valve allows compressed air to push the power piston & the valve gear
in the direction selected.  Once the air piston moves to the chosen, advanced position,
it closes it's own port--- and locks the piston with compressed air on
both sides --- securely stable.

Its a very clever system, and works flawlessly ...But in 'switching service',
so much manual cranking can get tiring back in those days of the 16-hour law.

Powered Shaft Mod.
The air motor/ sprocket, roller-chain modification allows the majority of the spinning
to be completed by the air motor,( controlled by a stubby, 3--way, air control lever)
and fine tuning can still be accomplished manually and at will.  
The air-motor saves the enginner from having to do ALL the cranking..

As I've said, some extant Franklin Precision reverse systems have an added
'overlay' of air motor/ chain drive ---- to reduce engineer arm-fatigue.


The term "Franklin Precision screw reverse" applies only to their
   air-assisted screw reverse cylinder model). 

Edited 11 time(s). Last edit at 03/17/23 08:58 by wcamp1472.

Date: 03/15/23 15:39
Re: Screw reverser on the NYC Hudsons
Author: Notch7

wcamp1472 Wrote:
> Engineers can get nasty bruises and broken
> forearms...if they get hit
> by the spinning wheel and it's protruding crank
> handle. 

Yes the handle on the CP-SOU 2839's wheel whacked my kneecap pretty hard.  Thankfully I was still a young railfan-engineer, and the thrill of running a Royal Hudson overuled the knee pain.  I found a way to fold the handle down as I remember.  The power wheel came in handy because I had to switch a cut of freight with the 2839 to get out the coal conveyor car  to recoal the tender.

Date: 03/15/23 16:08
Re: Screw reverser on the NYC Hudsons
Author: wcamp1472

The voice of experience!

The engine he's describing is equipped with roller-chain, and
2 sprockets ( larger one on the reverse shaft).  There is no 
air cylinder on a typical Canadian installation.

There is a forward/reverse, center-off, control valve that spins 
the air motor & shaft.  An ingenious, economical solution to
screw-reverse equipped locos.

Handling freight cars can be a frustrating task --- if you're involved with
many changes in direction.... A lever operated air valve makes ALL
the difference.

I think Michigan's ex-PM 1225, 2-8-4, has a Franklin Precision Reverse
cylinder; but, I don't know if it has been fitted with a 'chain drive' mod.

ex-C&O 2839, 2-8-4,  has a Franklin Precision Reverse, from when it
was built.  For a while 2839 provided power for Sou/N&W excursions,
and I visited it at a service stop when at Manassas, Va., mid-1980s.  
I seem to remember an added "air motor & chain drive" for the shaft,
mounted on the side of the firebox, engineer's side.



Edited 7 time(s). Last edit at 03/17/23 08:53 by wcamp1472.

Date: 03/15/23 18:44
Re: Screw reverser on the NYC Hudsons
Author: flyingfred

I ran the PM 1225 in an engineer for an hour program many years ago. That was my first experience running and firing a coal fired mainline engine so I had nothing to compare to at the time. I sort of got used to the constant cranking of the reverser as it was a forward and reverse operation. Since that time I have run engines with a power reverse cylinder on a Jonson bar so I can appreciate what a pain a screw reverser can be in a switching operation. When in constant motion on a mainline, I can appreciate the more finite control of the screw reverser.


Date: 03/15/23 18:50
Re: Screw reverser on the NYC Hudsons
Author: wcamp1472

Thank you for your first-hand experiences, Fred.


Edited 1 time(s). Last edit at 03/15/23 18:50 by wcamp1472.

Date: 03/17/23 10:31
Re: Screw reverser on the NYC Hudsons
Author: kurtarmbruster

Thanks all for this great information!

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