How to calculate impeller cutting for multi-stage centrifugal pumps

Repost: A special cutting method for multi-stage centrifugal pumps – removing the impeller. When the excess head in operation exceeds the head produced by a single stage, the solution is to use one fewer impeller; if the excess head is not equal to the head of a single stage, then the method of cutting the outer diameter of the impeller is employed. The impeller should be removed at the discharge end; if it is removed at the suction end, the resistance on the suction side increases, which can lead to cavitation. Moreover, the inlet of the suction impeller in multi-stage centrifugal pumps is larger, so the first-stage impeller cannot be removed. The intermediate section of a multi-stage pump can also be removed, but in that case the shaft must be replaced. It is also possible to remove only the impellers of the multi-stage pump while keeping the intermediate section; this way, the shaft does not need to be replaced, although the head capacity will decrease. 3.5 Cutting Method for the Outer Diameter of Multi-stage Centrifugal Pumps: When the additional head provided by a multi-stage centrifugal pump is not equal to the head of a single stage, the outer diameter of the impeller is cut (only the impeller blades are cut). When cutting the outer diameter of the impellers in multi-stage centrifugal pumps, it is generally not necessary to cut the impeller of the first stage; instead, the impellers of the subsequent stages are mainly cut. Generally speaking, if the excess head is less than 0.2 times the head of a single stage, it is sufficient to cut only the last impeller, removing the blades from it alone ； If the excess head is less than one single-stage head value but greater than 0.2 times that value, it is advisable to cut the impeller blades after the first stage (in the case of a 2-stage pump, the blades of the first stage should also be cut accordingly, but the extent of cutting should be less than that of the blades of the second stage). Why are only the blades of the impeller cut when modifying a multi-stage centrifugal pump? This is because if the base circle diameter of the guide vanes in such pumps is too large, it will reduce the pump’s efficiency (usually, the D value is about 1–3 cm larger). If the front and rear cover plates are not retained while cutting the impeller, the distance between the outer edge of the impeller and the guide vanes increases, which in turn leads to a decrease in pump efficiency. That’s why, when modifying a multi-stage centrifugal pump’s impeller, only the blades are cut.

Cut it like this? The flow channel of a multi-stage pump is wide in the middle and narrow on the sides, so it’s quite difficult to make it flat

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