No paywall for this story:

https://railfan.com/new-positive-train- ... ific-2816/



Much more at the link.

Great news. Has important implications for other mainline capable locomotives. Here's wishing CPKC a trouble free 3 nation tour.

Ross Rowland

I look forward to learning more details about how this was accomplished. I was watching some videos of the most recent test run and one thing that stands out is that I do not see the PTC antenna array anywhere on the locomotive. I know early on there was a concern that even if you can pull it off, it would ruin the appearance. Seems like a lot of R&D for a locomotive that has rarely, if ever, run without a diesel in the consist.

Did I mis it? How is steam locomotive throttle cut when PTC or any other train control system initiates a penalty brake application?

Not required, just the cab equipment and penalty application.

How do you enforce compliance with a required reduction in speed or a stop signal on a steam locomotive if the PTC system can't close the throttle? I believe that to be incorrect information.
Mike Tillger

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I know that this has been discussed before, but there must be some type of electrically-controlled valve that could be placed before/after the throttle that would close it. Nuclear power plant technology must have developed many of these types of valve. It sure seems simpler than jury-rigging an engine with a diesel helper.

Historically (in the 1920s implementations) the penalty application was on the combined automatic (with independent actuation) and the drivers were 'stalled' from rotating by the brakes.

The more modern version is tied into the reverse, to center the power reverse 'softly' to as near full mid as the combination lever geometry will permit. This is comparatively little steam mass flow and hence little developed horsepower, and the driver brake application will comfortably arrest it. It does not matter substantially what the throttle position is; the steam doesn't get past the valves into the cylinders in substantial amount.

I'm sure there will be some here who think that's not fully possible. I remind you that very effective 'automatic cutoff' relative to exhaust back pressure was practically demonstrated in 1922.

Of course, if the engine has an air throttle, like the Franklin Precision type specified for the PRR T1, modulating the throttle from an electronic system becomes trivial. The same is true if poppet-valve gear is equipped with four Wagner throttles, as Porta specified for the LP cylinders on the ACE3000. But that's essentially gilding the lily as far as PTC "penalty" braking would be concerned. You'd find that sort of thing valuable in commanding and maintaining proportional speed restriction or cruise, of course.

The actual solution is wildly less difficult. Take any of the air assists for throttle application developed in the 1940s, and apply it to the existing linkage for a front-end (or dome) throttle. Use an appropriate balancing return-spring arrangement so that the throttle soft-closes against a dashpot if control-air pressure fails.

Something you do NOT want is some idiot fast-acting valve in the main steamline, to slam closed suddenly or start oscillating from full open to full close while the valve gear is away from center. Keep in mind that top speed in a range of historical locomotives has been at somewhere in the low 40% range.

This brings up an amusing memory from the nuclear-power safety engineering course at Columbia in the early 1980s. Steam is a lousier moderator than either borated feedwater or air, so in a GE BWR you want to avoid any issue with circulation being arrested before the reactor has fully SCRAMmed, or there is still considerable decay heat to be dissipated but no way to vent pressure in the core to let the ECCS water do its job. The Government mandated just this sort of positive, fast-acting valve at the main reactor exit, "to keep from causing a LOCA in case of serious seismic pipe disturbance". If, for some reason, this valve actuated with the reactor at normal criticality, and there was no SCRAM activation (as, for example, might have occurred in a Brown's-Ferry style mass loss-of-control event) the calculation I saw indicated you had 12 seconds to a PEA, which is the innocent-sounding 'prompt excursion accident'. You do not, not, NOT want that. Yet here was the government facilitating it by mandate...

Again some folks delight in making mountains out of mole hills.

I've run a lot of mainline steam miles and can testify that when there's a full service application it matters little where the throttle is....you're gonna stop pronto.

To satisfy the computer on the 614 we rigged the throttle quadrant with a small switch at about the 20% on mark that told the computer that the throttle had been ' closed". That setting allowed sufficient steam to be delivered to the valves/pistons carrying its lubrication oil to keep things lubed until the full stop occurred.

Not complicated. Ross Rowland

In the CFR section covering PTC it really only mentions what PTC must prevent, but never goes into detail of how it must prevent it.

It just says the system must stop be able to stop the train under certain conditions, but HOW to stop the train is not defined.

Even the old Automatic Train Stop regulations only mention penalty brake application and nothing about throttle or power.

These automatic braking systems are not new to Canadian Pacific. Steam locomotives in passenger service into Buffalo, New York had to be fitted with Automatic Train Control (ATC). That included Toronto, Hamilton & Buffalo Railway passenger power.
The ATC pick up "shoe" was mounted on a tender truck. Here is a Brief discussion on it from Ray Kennedy's excellent site Old Time Trains:

http://www.trainweb.org/oldtimetrains/C ... TC_NYC.jpg

Instead of wildly and endlessly speculating how they did it - has anyone considered asking someone in the CP Steam shops, "hey - how did you do it?"

There has to be someone here with contacts, or people that know people. Of course, endless speculation is one of many favorite pastimes here...

The 'easier' way to implement the throttle-control issue is to recognize that a defined drifting-throttle setting ought to be provided on a working locomotive. I believe it is easier to implement feedback from a steamchest-pressure gauge so that slight overpressure is provided at the valves (about 7-15psig) to keep air excluded, prevent cinders and whatnot from being sucked in, and maintain effective cylinder-oil tribology (etc.) This is more effective, less wasteful, and far more positive in operation than kludging a 'throttle position sensor', and it has the additional benefit that arrangements that fully 'stop' the throttle can be provided without affecting drifting, inducing flats on the drivers, and so on.

Part of the reason ATS couldn't be reset except from the ground was to ensure that, in the event a steam-locomotive engineer had been incapacitated, the reverse would be centered and the throttle closed before the valve was reset.