against the flaplike member as it pivots away from the flow
and the downward movement of the float are particularly
effective in quickly closing the flaplike member and trapping a column of liquid in the tube. The weight of the float and water
column hold the flaplike member in a closed position until the
liquid resumes a higher level, whereupon it is snapped to an
open position by the upward force of the water against the float.