The difference between a standard ball valve and a full-port ball valve is the size of the ball and bore in relation to the nominal pipe size of the valve. For example, the bore size in a 3/4 inch full port ball valve is 3/4 inch in diameter, while the bore diameter in a standard ball valve is 1/2 inch in diameter. Ball sizes are in proportion to bore sizes. The 1/2 inch diameter is the nominal size of the next smaller pipe. Full port bore size equals pipe size-standard port bore size is the next smaller pipe size. The flow coefficient is a measure of the resistance to flow of a given part of a fluid system. It is sued to calculate the length of straight pipe equivalent to an elbow or valve. The flow coefficient for a full-port valve is almost as low as that of straight pipe so it provides minimal resistance to flow and thus creates only a small pressure drop. The standard port ball valve has a higher flow coefficient and therefore causes a larger pressure drop for a given flow.
