The ornamental design for a diaphragmpump, as shown and described.
FIG. 1 shows a front view of a diaphragm pump showing my new design;
FIG. 2 shows a rear view thereof;
FIG. 3 shows a right side view thereof;
FIG. 4 shows a left side view thereof;
FIG. 5 shows a top view thereof;
FIG. 6 shows a bottom view thereof;
FIG. 7 shows a bottom, front and right side perspective view thereof; and,
FIG. 8 shows a top, rear and left side perspective view thereof.
The broken lines in FIGS. 2, 5, 6 and 8 are included for the purpose of illustrating portions of the claimed design that form no part of the claimed design.