Several people have mentioned a requirement for a hydraulic ram pump of reasonable efficiency being ... if several consecutive reductions in pipe diameter are used. It should be noted that the sequence of pipes of reducing diameters is merely a "practical method" of approximating the "ideal" of a smooth exponentially decreasing pipe diameter.

Several "hunting horns" incorporate close approximations to the theoretically preferred exponential taper, but I'm at a loss to see an easy way of straightening one out sufficiently to place the large inlet end at sufficient elevation above the smaller end in the supply stream.

Some might suggest that taking a hammer to a selection of such horns to see how "straight" (or maybe they're thinking "flat") they could be made might be a worthwhile undertaking, but I suspect their motivation might be more related to the common uses of such horns rather than the practical improvement of hydraulic devices.

And it seems that those instruments most appropriately nominated to be chucked into a stream seldom incorporate even approximately "smoothly tapered" bores - or even identifiable bores of any kind.

John