A seal to prevent fluid transfer using double diameters to provide a tighter seal is disclosed. The double diameter seal has a body with a first diameter containing an upper contact area and a second diameter forming a lower contact point. A notch extends into the body between the upper contact area and the lower contact point for a predetermined distance to form a transition point. In use, the first diameter is dimensioned to place a portion of the length of the upper contact area in sliding engagement adjacent to a length of the first surface. The second diameter dimensioned to place the lower contact point contacting an angled second surface of a valve.