Interesting. I did a Google image search, and the only thing they could come up with was a "Churchill Tank"; i.e. a WWII military tank. I don't even have a W.A.G., but I don't think it is a water pump, especially for a mining operations, nor do I think it is designed to handle a piston. Seems right behind the opening the thing narrows, so the opening either doesn't go much farther, or it changes shape drastically.
If form follows function, I would focus on the wheel on the far left. I would guess that is the functional part of the thing, but I can't imagine what it would be designed to do. The thing is not in good focus, so detail is lacking, but it doesn't have a lot of piping, attachments, etc. so maybe it's not too complicated.
I suppose it could be designed to process materials of some sort...like a rock crusher...with the material going into the opening and coming our around the wheel. In that case, it more than likely would we lying on its side as we see it on the RR car.