I claim the ornamental design for a valve assembly, as shown and described.
FIG. 1 is a front right perspective view of the claimed design;
FIG. 2 is a bottom left 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 broken lines formed by equal length dashes shown in the figures are for the purpose of illustrating portions of the valve assembly that form no part of the claimed design. The broken lines formed by unequal length dashes (i.e., dash-dot) shown in the figures are for the purpose of defining bounds of the claimed design.