Valve cover

The design is the features of shape, pattern and ornament of the portions of the valve cover as shown in solid lines in the drawings. The portions of the valve cover shown in stippled lines do not form part of the design. The respirator shown in stippled lines in FIG. 8 is environment and does not form part of the design.Drawings of the design are included.FIG. 1 is a right top perspective view of a valve cover showing the design;FIG. 2 is a top plan view of the design of FIG. 1;FIG. 3 is a front elevation view of the design of FIG. 1;FIG. 4 is a rear elevation view of the design of FIG. 1;FIG. 5 is a left side elevation view of the design of FIG. 1;FIG. 6 is a bottom plan view of the design of FIG. 1;FIG. 7 is a left bottom perspective view of the design of FIG. 1; andFIG. 8 is a right top perspective view of the design of FIG. 1 and shown attached to a respirator.