Air Brake Issues 101:

[Euclid]

BaltACD

Unfortunately, industrial design is filled with hundreds, if not thousands, of such occurances.

 

These kinds of design problems are indeed common.  They also come in lots of shades of gray.  However, I would not conclude that because there are many design problems in products, the QRB valve problem is typical and acceptable.  In my opinion, the QRB problem stands out as a glaring design defect.  It is not ever close to being typical.  It makes me wonder what happened to common sense when they came up with the idea.

 

The only answer to that question that I can see is that the designers did not recognize the problem until the related elements of the design were already locked in.  So they were blindsided by the linkage problem, but it was too late to change it.  So in true bureaucratic fashion, they produced a complex workaround to override the linkage problem.  The QRB valve was the workaround.

 

I can see how they could have overlooked the problem with the brake linkage, even though one might not expect experts to make such a mistake.  An important objective of such linkage is to have it apply the brakes no matter whether the application is powered by air or by the handbrake mechanism.  This linkage does that just fine.

 

The linkage used on freight cars does it fine too, but there is a difference.  On freight car linkage, if the air is applied and then the handbrake; both power inputs act independently on the brake linkage.  If one releases, the other continues holding.

 

However, with the QRB linkage, if air is applied and then the handbrake, both power inputs act in tandem on the brake linkage.  They depend on each other.  So, if one releases, they both release. 

 

Air can always release inadvertently by leakage, so that is why air is not allowed to be used in securing a train.  For securing a train, handbrakes are the only brake acceptable.   The problem with the QRB valve linkage is that if air is applied before the handbrake, that air is included in a way that makes it part of the securement.  Then if the air leaks off, the handbrake force also relaxes and releases.  So, fundamentally—if the air were applied first—they had air being a part of securement; and that is explicitly against the rules. 

 

That is a fatal flaw in the linkage.  Adding the QRB valve cancels out the fatal flaw, but if the QRB valve should happen to malfunction, the fatal flaw comes back.  And this may easily go undetected.

 

So I think the QRB valve is their best effort to fix the underlying flaw, but I suspect the flaw got included in the first place because they did not immediately recognize it.  I can’t see another explanation.  If there is another explanation, I would like to hear it.  There might be an interesting back story about this QRB valve application.   

 

[Euclid]

Wizlish

 

Euclid

This seems like a lot of confusing rigmarole to assure the safe operation of a safety device as critical as a locomotive handbrake.

 

 

Without IN ANY WAY compromising your opinion that the design of the brake system is fundamentally flawed... I don't see *that* much 'rigmarole' involved with the QRB approach.  Hopefully Randy Stahl will comment specifically on what MMA operating policy calls for with respect to setting locomotive handbrakes, but the actual procedure seems fairly clear:

1) Be aware that the handbrake only applies to one axle of the locomotive, and is only intended as a parking brake for the locomotive itself, not in any sense for a train;

2) If you have to apply the handbrake with the independent applied, be sure to release the QRB valve on any locomotive so equipped -- look at the position of the brake cylinders on the truck if there's any question.

3) Be familiar enough with the QRB valve's function and construction that you know how to actuate it, how to ensure it has released (exhaust air from cylinder, brake shoes on respective axle release), and what to do if it doesn't release (Randy: what's the right set of procedures?)

4) When the QRB valve is fully released, tighten the handbrake again, and inspect the shoes for engagement again.

5) (and I'm adding this as a suggestion, not knowing whether it's part of procedure) -- if you are relying on handbrake to secure a locomotive consist from possible rollaway, release the independent and conduct a roll test after the above procedure with QRB release and retightening of handbrake is complete, to ensure that 'enough handbrake' has indeed been applied.  (This would seem common sense to me!)

How long could it possibly be, even if dog-tired and within minutes of dying on HoS, to flip a valve, listen for the air, check the shoes, and give a few more pumps or turns on the handbrake?

AGREED that this has very, very little to do with the outcome at Lac Megantic except in certain political and legal senses, so let's not go there any more.  

 

 

I believe that it is too much rigmarole, considering the potential for fatal consequences if not performed properly.  Other than that, the procedure itself is not overly complicated.

The procedure calls for listening to make sure compressed air is releasing from the brake cylinder, and looking at the brake cylinder to make sure that the piston is retracted.  If the piston is not retracted and/or no exhausting air is heard, the procedure calls for operating the QRB valve by direct hand manipulation of the operating stem.  In other words, you check to see if the QRB valve is not working, and if it is not working, you attempt to do a special workaround procedure.  If the workaround procedure does not work, you cannot rely on setting the handbrake.

In addition to the rigmarole and what is at stake in terms of safety, there is also the fact that this concern about the operation of the QRB valve is not at all intuitively obvious.   On the contrary, there is a widespread realm of operation in which handbrakes are correctly applied after air has been set, no air will be heard escaping, and the piston will remain extended.  So this very common practice and experience makes these conditions as being normal, and yet in the rare case of the QRB valve system, these conditions are supposed to signal trouble.  I think that is an interesting twist as well.

You mention the purpose of setting locomotive handbrakes as being only for securing the locomotive and not a train.  However, on the MM&A RR, the locomotive hand brakes were allowed as part of the whole train securement.  Granted, we are only talking about one handbrake being available or not.  So it is unlikely that this issue could have been decisive in the runaway cause which required many handbrakes.

But, what is interesting is that two different reasons for applying insufficient handbrakes happened to have converged here with the Lac Megantic wreck.  One was a misunderstanding of the special instructions calling for a number of handbrakes needed; and the other was lack of familiarity with the special instruction pertaining to the proper operation of the QRB Valve.  Both of these information failure modes definitely played a role in the Lac Megantic runaway.