I've asked this question before, but now I'm old and feeble and cannot locate the answer?
The question is about the Mallet and Vauclain compound steam engines.
Cross compound engines were always in sync because they work from one side to the other.
Articulated, tandem compounds is where my understanding falls apart.
The engines found there get out of sync to reasons such as a loss of traction on one engine or the other.
How then can the steam be expanded the second time as all compounds do? Railroads went to single expansion fairly quickly as engines were shopped.
So. How does the high pressure and low pressure cylinders expand, if out of sync? Seems it would blow out the cylinder fronts.
I think the Chiel answered the first time.
Any help short of finding a mechanical engineer?
The Chiel2015-11-19T05:07:07Z
I can't readily find a precise answer, but I would not have thought that the circumstances that you describe would lead to burst cylinder covers. Cylinder relief valves became a common fitting on locomotives of all types to guard against damage to the cylinders if the locomotive should 'prime', or 'hydraulicise' - that is, water being carried over into the cylinders. On a compound locomotive, these valves would serve to release any excess pressure. On the larger articulated Garrets, Mallets etc. the receiver pipe between the high and low-pressure engines had a considerable volume, and would be capable of absorbing the additional pressure caused by wheel-slip on the high-pressure engine. I don't know for sure, but perhaps the receiver pipes were also fitted with safety valves. A further consideration is that, when a conventional locomotive 'slips', the exhaust is relatively free. In a compound, the exhaust enters the receiver. Wheel-slip would cause the receiver pressure to rise, which would result in back-pressure on the HP pistons, and I would have though that this would counter the worst 'slipping'. If you want an excellent book on compound locomotives, I would recommend "Compound Locomotives - an International Survey" by the late J.T. van Riemsdijk, published in the UK by Pendragon Books/Atlantic Transport Publishers, 1994. John van Riemsdijk was latterly the Keeper of Mechanical Engineering at the Science Museum in London, and I had the great pleasure of working with him on some of his books about 30 years ago.