The ornamental design for a valve, as shown and described.
FIG. 1 is a front elevation view of a valve showing the new design;
FIG. 2 is a rear elevation view of the valve of FIG. 1;
FIG. 3 is a left side elevation view of the valve of FIG. 1;
FIG. 4 is an elevation view of the valve of FIG. 1 rotated 120° about its longitudinal axis from the view of FIG. 1;
FIG. 5 is an elevation view of the valve of FIG. 1 rotated 240° about its longitudinal axis from the view of FIG. 1;
FIG. 6 is a right side elevation view of the valve of FIG. 1;
FIG. 7 is a bottom plan view of the valve of FIG. 1; and,
FIG. 8 is a top plan view of the valve of FIG. 1.
The broken lines shown in the figures are included for the purpose of illustrating contextual portions of the valve and form no part of the claimed design.