In this paper physical models of common rectangular pianokey weirs (PKW) and modified pianokey weirs (MPKW) have been made using PVC plates. Experiments are conducted for a wide range of the hydraulic conditions in order to determine the general flow field and head-discharge curves. Discharge capacity of the pianokey weirs with vertical wall at the upstream end of the outlet keys (UPKW), as an idea to increase the flow depth at the beginning of the key, and also a vertical wall at the downstream end of the inlet key (DPKW), as a technique to modify the flow pattern at the downstream of the weir, are evaluated. Results show that the UPKW performs almost the same as the PKW, while in the DPKW, the vertical wall at the downstream end of the inlet key, results in better distribution of the flow over the side crests and prevents the napes collision at the downstream end of the outlet keys. The improved flow field over the different parts of the DPKW increases the discharge coefficient compared to the PKW. Flow streamlines and 3D water surface maps obtained from numerical simulations, confirm these findings.