SEMI-OPEN IMPELLER S035
The semi-open impeller looks like an open impeller but there is a shroud on one side of the vanes.
In some designs the impeller is designed to run with a close clearance to the pump back plate. This puts the shroud on the opposite side of the vanes requiring a “flow through” design.
Most Duriron (Flowserve) brand impellers are made this way.