Axially Split Casings Pump
Regardless of the arrangement of the stages in the casing, it is necessary to connect the successive stages of a multistage pump. In the low and medium pressure and capacity ranges, these interstage passages are cast integrally with the casing proper (see Figures 18 and 19). As the pressures and capacities increase, the desire to maintain as small a casing diameter as possible, coupled with the necessity of avoiding sudden changes in the velocity or the direction of the flow, leads to the use of external interstage passages cast separately from the pump casing. They are formed in the shape of a loop, bolted or welded to the casing proper (see Figure 20).