Impeller Pumps Casing Construction
In the open- or semi open impeller pump, the impeller rotates within close clearance of the pump casing or suction cover. If the intended service is abrasive, a side plate is mounted within the casing to provide a renewable close-clearance guide to the liquid flow ing through the impeller (refer to Figure 12). One of the advantages of using side plates is that abrasion-resistant material, such as stainless steel, can be used for the impeller and side plate, while the casing itself may be of a less costly material. Although double suction, semiopen-impeller pumps are seldom used today, they were common in the past and were generally made with side plates.
In order to maintain pump efficiency, a close running clearance is required between the front unshrouded face of the open or semi open impeller and the casing, suction cover, or side plate. Pump designs provide either jack screws or shims to adjust the position of the thrust bearing housing (and, as a result, the axial position of the shaft and impeller) relative to the bearing frame.