Vacuum breaker for valve stem packing
FIG. 1 is a top plan view of a vacuum breaker for valve  stem packing showing our new design; 
     FIG. 2 is a bottom plan view thereof; 
     FIG. 3 is a perspective cross sectional view  taken on line 3--3 of FIG. 1; and 
     FIG. 4 is an exploded perspective view thereof.