The ornamental design for expansion valve, as shown and described.
FIG. 1 is a first perspective view of an expansion valve showing our new design;
FIG. 2 is a second perspective view thereof;
FIG. 3 is a front view thereof;
FIG. 4 is a rear view thereof;
FIG. 5 is a right side view thereof;
FIG. 6 is a left side view thereof;
FIG. 7 is a top view thereof; and,
FIG. 8 is a bottom view thereof.
The dashed broken lines shown in the figures are included for the purpose of illustrating portions of the expansion valve that form no part of the claimed design. The dash-dotted broken lines represent the bounds of the claimed design that form no part of the claimed design.