The ornamental design for a vacuumpump, as shown and described.
FIG. 1 is a perspective view of a vacuum pump showing our new design;
FIG. 2 is another perspective view;
FIG. 3 is a bottom view;
FIG. 4 is a rear side view;
FIG. 5 is a right side view;
FIG. 6 is a front view; and,
FIG. 7 is a left side view.
The broken line showing of elements shown throughout the drawings is included for the purpose of illustrating environmental matter and forms no part of the claimed design.