All of that, and, or, like a fixed pitch Scimitar propeller blade. The less fancy the wider the operating range. And vice/versa. The performance requirements of automotive pumps are so minimal that just in the last few years have folks been improving water output vice HP input.

To improve mileage. Smoother scrolls, even machined impeller faces. Unheard  of before now.

 

Lynn E. Hanover

 

Jeff,

To give the short answer, Mazda is turning the impeller in the correct
direction (namely in the direction correlating to the increasing scroll
volume, as depicted in your "Water Pump Pulley 03.jpg").

The long answer is that the impeller blades, oriented as they are, is a
stable, wide operating band style impeller.  To use an aircraft analogy,
this pump has a positive static margin.

Something that's interesting about pumps such as this is that they can
squeeze more efficiency out of the impeller by rotating the blade on the
impeller.  The downside to increasing the efficiency in this manner is
that the operating range is reduced and, similar to reducing the static
margin in an airplane, is that you pay for it in stability.  If a pump
of this design were "flying" at its neutral point, the blades would be
oriented radially from the axis of rotation.  Continuing with the
airplane analogy, if the pump were "flying" with negative static margin,
but also at its most potentially efficient, but also most likely to
cavitate and go unstable, the blades would be mirror-imaged from the
orientation they're in now, but still rotating in the same direction.

I'm sure what I've explained is clear as mud, yes?

Anyway, hope it helps.

Regards,

Cedric Gould