It is a single-stage, horizontal, radially split volute pump. The casing is supported by footing, and has a single-stage radial impeller. The bearing bracket, the shaft, the stuffing box and the impeller form a mounting unit module. Pumps of different specifications are completely interchangable, saving the storage cost of spare parts. Besides, the unit module consisting of the bearing frame, the shaft, the stuffing box and the impeller can be removed without removing the pipes and the motor by removing the removable coupling. The shaft seal is stuffing box seal or mechanical seal, and provided with a cooling, flushing or sealing fluid system.