Sheet metal casing for multistage pump and method for manufacturing the same

A sheet metal casing for multistage pump which consists a plurality of pump casings serially mounted on a rotationable spindle, the pump casing includes a casing, an impeller and a vane, the casing comprising;

• an outer shell engaged with an inner shell;
• an annular outer shell made by integral forming including at least, starting from one end thereof, a front end ring approximately normal to the spindle and extending outward, a step positioning ring having one end thereof connecting with the front end ring, an outer shell surface extending nearly parallel with the spindle and a positioning end connecting with an end of the outer shell surface and extending toward the spindle;
• an inner shell fixedly located in the outer shell and housed the vane therein, including at least, starting from an end adjacent the front end ring, an inner ring approximately normal to the spindle and extending outward, an inner shell surface approximately parallel with the spindle, and a step positioning end connection with inner shell surface at one end thereof, the step positioning end forming a holding space with the outer shell surface;
• and
• wherein the front end ring has a first front end bent parallel with the spindle and extending forward, the inner end has a second front end bent parallel with the spindle and extending forward, the first and second front ends form a gap therebetwen mating with an inlet of the impeller for sealing the impeller.