Steam & Excursion > Power reverse, safety back-up pressure schemes.

As the 1910-era ICC Steam Loco Inspection Rules matured, additions were made to the rules.  
One such addition was the provision for an emergency supply provision for a few cycles of reverser operation, in case of a hypothetical loss of air supply to the power reverse.
There were several approved schemes: a “steam operation” change-over valve, or an isolated/separated tank of compressed air
( localized near the power reverse).

A small air tank, fed from the main reservoir can be used as the back-up supply—— however,  the air supply line must be isolated by using a check valve in the supply line.    The check valve prevents a loss of air in case of a break in the supply line from the main reservoirs.

Most RRs opted for the temporary air tank provision—- mostly because of the possible damage caused by use the steam emergency change over valve.  

Such a provision’s origin is a mystery.  Why did the ICC adopt it, is lost in the mists of time.
Modernized PRR locos, like the K4s, have a clearly visible spare-air tank mounted directly behind the reverse cylinder.
Some tanks were actually part of the PRR’s rear cylinder head of the power reverse.

If the steam back-up scheme were on any loco that I was advising-on, I would strongly recommend the use of an emergency air supply, in place of the steam alternative.   Properly designed, an air-based system would comply with rule requiring alternate
( emergency) pressure supply for the power reverse.

 It seems to me that preserving the steam back-up in today’s world is an anachronism....presumably harkening back to the days when ICC was sensitive to possible cost objections/concerns from RR managements —— mandated by the GVT. on RRs.... so,
they gave RRs the option of a steam-supply provision...  

In today’s world, it doesn’t make any sense to retain that option,  when modern, better ways are allowed ....

W.
 



Edited 2 time(s). Last edit at 04/19/19 15:21 by wcamp1472.

Wes, could a modern loco take advantage of the main reservoir air of a trailing diesel to provide as an emergency back up? Assuming main reservoir air could make it through tenders, aux. tenders, support cars, etc.

Posted from iPhone

Sure.
I would want to verify that different MR pressures were ameliorated to make a unified system, regulated by the leading Steam Loco.

With “light” passenger excursion trains ( under 30 cars...), and modern (car) air brake equipment, most operating excursion steam locos today don’t need a lot of MR air capacity.  With excursion trains, I would also expect virtually zero ‘train line leakage’ —- during the measurement time peroid.

But, you COULD do it.

​W.



Edited 1 time(s). Last edit at 04/19/19 17:17 by wcamp1472.

I recall James Eno (?), DRGW rules instructor telling a small group of us that the unthinkable happened.
A winter lease DMIR articulated decending light engine towards Denver had its main reservoir break off and suddenly there was no air for braking.  The DRGW crew was used to having access to a steam cut-over valve but the DMIR did not have one.  The run-away ended badly at the big ten curve.  He did not mention an emergency air reservoir.
In some book I read the SP had a cab forward break off the main reservoir at the end of the blind tunnel at the stem of the wye at Cascade Summit.  In this case the steam cut-over valve worked as intended.
Since reading that I have looked for that cut-over valve on SP engines, and believe that I have seen it every time.
Corrections requested.

railstiesballast Wrote:
-------------------------------------------------------
> I recall James Eno (?), DRGW rules instructor
> telling a small group of us that the unthinkable
> happened.
> A winter lease DMIR articulated decending light
> engine towards Denver had its main reservoir break
> off and suddenly there was no air for braking. 
> The DRGW crew was used to having access to a steam
> cut-over valve but the DMIR did not have one. 
> The run-away ended badly at the big ten curve. 
> He did not mention an emergency air reservoir.

I wonder if he might have been referring to the "run-away" on the D&RGW with a leased DM&IR 2-8-8-4, because the DM&IR locomotives were not equipped with the standard D&RGW "water brake" system. While the Engineer was trying to use the non-existent "water brake" system, the train got away from him. I'm pretty sure that even the DM&IR M4 Yellowstones had that emergency steam supply valve for the power reverse cylinder.

> In some book I read the SP had a cab forward break
> off the main reservoir at the end of the blind
> tunnel at the stem of the wye at Cascade Summit. 
> In this case the steam cut-over valve worked as
> intended.
> Since reading that I have looked for that cut-over
> valve on SP engines, and believe that I have seen
> it every time.
> Corrections requested.

I recall an instance when someone actually cut in the steam reverse and destroyed the packing cups. They did it because they said they wanted to see what would happen. This occurred thirty minutes before the train was scheduled to depart with four hundred passengers. New packing cups were made, installed, and tested, and the train only left three hours left with the majority of passengers going along for the ride. A backup crew was called, which included my self, to get the train back home without violating HOS. It was an interesting day....

With an integral (spare) air reservoir ( & check valve), a failure in the supply piping, does not affect ( endanger) the pressure in safety reservoir. AND, the engineer does NOT have to find a valve to turn, etc, —— as in the steam back-up schemes.

In case of main reservoir ( system)  total loss of air, you also loose air supply for the loco’s  brake cylinders.  
When operating with a train, the train can be stopped, halting the brake-less engine.  Main reservoir pressure is necessary for proper manipulation of train and loco brakes.  Short of a complete, on-site, repair of the broken element of the air system piping, another loco is the only way out, to move the train, 

if, however, you’re in a ‘light engine’  mode ( no train cars) and a MR air supply failure occurs,  then stopping becomes a bigger challenge.  “Reversing” the drivers is problematic if it produces slipping.....

Slipping produces sparking from the film of liquid metal at the wheel and rail....thus, the drivers are sliding on a thin film of molten steel..   Some locos were equipped with cab-operated brake cylinder cut-out cocks ( for the main drivers).  

On long down-grades, with a light engine, the driver brakes could be  ‘cut-out’ ,  so that the ( shrink-fit) drivers would not overheat and fall off the wheel centers.  With a light engine, that ( driver brakes inoperative)  leaves only the truck brakes ( as equipped) for braking the loco.

The automatic activation feature of the emergency reverser air supply & reservoir is one less thing the engineer has to deal with to take a dangerous situation under control.

Since the emergency steam operation of the power reverse is never operated....that means that there’s years of accumulated rusty water trapped behind the cab operating valve.  When a true emergency occurs, and the valve is opened ( under great struggle?),then that slug of rusty water, first, rushes to the reverser’s piston.  
The ‘hot steam’ aspect does not come into play, since there is no continuous flow to the cylinder.  

 So, continuous  use of the steam for power and the abrasive, hard, crud shot into the cylinder soon ruins the “rubber”( neoprene?) packing cups of the reverser’s piston... which could set-up a path for continuous steam flow through the ruined packing cups, now introducing hotter and hotter steam and the ensuing further ruination of cylinder walls and piston metals rubbing together... 

Always change the existing steam back-up system to an all-air , in the 21st century, there’s no reason to have
to rely on an out-dated scheme.  

Or at least, annually flush and blow out the steam related piping....be sure to disconnect the the cylinder-end of the steam piping, to blow the crud out & into the atmosphere (remember that the steam supply piping and valve are fed from the turret, boiler-top in front of the cab).  

That’s a lot of rusty, rotten pipe to keep cleaned out, if you’re going to rely on it as your safety back-up plan.

Also, if steam equipped, when testing and firing-up the loco, remember to blow-out the piping and the cab valve & keep the steam-supply pipe ‘open’ at the cylinder-end before blowing out the emergency-steam piping scheme.
At flush-out time, you don’t want to blow steam, rust and crap into a healthy reverser cylinder.

​W.
not yet proofed 



Edited 13 time(s). Last edit at 04/20/19 12:45 by wcamp1472.