The hydraulic results of a series of 21-rod bundle water experiments have been analyzed systematically. Models are established for the prediction of the pressure drop over unblocked bundles, grid spacers, coplanar concentric blockage, coplanar concentric blockage with bypass, noncoplanar concentric blockage, and noncoplanar nonconcentric blockage. The models can be extended to other bundles with similar characteristics. The comparisons of these models with the experimental results agree reasonably well.