The ornamental design for a meteringpump, as shown and described.
FIG. 1 is a front view of a metering pump showing our new design;
FIG. 2 is a back view thereof;
FIG. 3 is a top view thereof;
FIG. 4 is a bottom view thereof;
FIG. 5 is a right side view thereof; and,
FIG. 6 is a left side view thereof.
The broken lines shown in the drawings are included for the purpose of illustrating portions of the metering pump that form no part of the claimed design.