In this drawing Leonardo presents a study of a pump, called "galley trumpet". It is designed to pump water out of bilges (the bottoms of boats) here symbolized by a basket. An associated drawing on a different sheet represents a conical valve. When the pump is operated, the valve lifts and opens allowing the water to travel upwards but not in the opposite direction.
Manuscript L, sheet 25 v. 1497-1502 - Manuscript E, sheet 76 r. 1513-1515