I've never heard of such an arrangement on a North American Mallet or other articulated. I believe it may have been possible to cut out one engine on a Beyer-Garratt.

The problem with your idea is that I can't think of a "mechanical problem" where such an arrangement would be of benefit, except maybe blowing out the cylinder head of one engine. If you drop a rod or the valve gear, you have to get that out of the way first, and if you slip a cylinder ring you'd have to disconnect the main rod........

Agreed. Better to limp home on 3 cylinders than 2.

For this test and clean out, they would have set the locomotive up so the front engine was running "simple". That is, it would get full pressure steam just like the rear engine. Apparently something was not right with the simpling valve because the front engine was not getting any steam. But that's why they run the tests. Take a bunch of items off the punch list and add another item.

Every test brings us closer to the real deal.

During a test of this type, you do not want the valves installed as they would prevent the debris from being blown out of the chambers. The narrator kept saying "pistons" but he was referring to the piston valves. The actual pistons had already been installed, as could be seen by the piston rods connected to the crossheads.

The simpling valve does not allow full boiler pressure to the LP engine, as that would cause the engine to basically run away (owing to the much larger cylinder volume). On the mallets that I have dealt with, there is a pressure reducing valve in line with the simpling valve, and the steam line to the LP engine is only about 2" diameter.

But pistons may not have been installed yet on the rods. Not saying that's true in this case.... If I were going to blow out the steam passages I wouldn't have anything in the cylinders and would blank off the ends of the valve chest. Your mileage may vary, of course........ I got bit in the ass by not having things open once and don't need that experience again.

You're right. Just because I see piston rods in place doesn't mean the pistons are on them. I don't have an opinion one way or the other on their method; just curiosity.

Thanks for the clarification! I knew about the simpling valve but did not realize (or maybe forgot!) that it had to have some kind of a restrictor. Makes perfect sense as the low pressure cylinder uses a much larger volume of steam to produce the same work as the high pressure cylinders.

I was aboard an Australian NSW Class 60 Garrett-hauled train that had a dry pipe failure at one end. It was not possible to isolate the failed end and operate the locomotive using the other end. The whole engine was dead and needed towed in.

Phil Mulligan