Rotary tides

Fig. iO. Velocity vectors recorded for successive 20-min time intervals by a current meter 2 m above the bottom near the geometrical center of Long Island Sound. The rotary character of the tide and the net drift of bottom water due to the estuarine circulation are shown. 

A key part of a rotary piston pump is the slide valve, and especially the inlet sleeve within it. One end of the slide valve (a cylinder or tube) is continually completely open to the work chamber the other end continually contacts (tides upon) the moving rotary piston. 

---