In the multi-stage volute pump, two spacer plates unequal pressure stage, there remain some leakage losses, depending on the arrangement of the structure, at both sides of the pressure level may be spaced one, two to three, the differential pressure level, the pressure bulkhead on the left for the two right pressure bulkhead for the three. The more relevant series, the leakage between the spacer will be more severe punishment.
In a segmented multi-stage pump, there are also interstage leakage. But between this and the previously mentioned different level of leakage – in part because it does not pass through the impeller liquid leakage, it does not belong to the volume loss. Here, the pressure difference between the level before and after the interval board, by supercharging effect vane impeller and diffuser section backlash pumping action (the equivalent of a centrifugal impeller) caused. Under the influence of pressure, the leakage of liquid along the board slot into the top grade interval stage impeller backlash, and by the guide vanes, ABM leaves (suction vanes) flows back into the gap between the level, repeat the process. Although inter-segment multi-stage pump leakage level does not belong to volume loss, so it flows back and forth, it is to consume the power consumed. In addition, the part of the liquid through the guide vanes, the vanes can cause the throat to reduce the effective cross section (ie, liquid leakage took up part of the cross-section), so here the flow rate will increase, causing additional hydraulic losses. According to the book “centrifugal pump design basis” : A multi-stage pump station at a flow rate of 20 l / s, there is a gap between the level reduction of 0.75 mm to 0.25 mm, the inter-stage leakage reduce the amount of q 0.7 l / s, due to the q decrease, so that the flow through the vanes is reduced, reducing the flow rate of the guide vane throat, reducing the hydraulic losses vanes, and because q reducing the impeller vanes and side gap relative velocity of the liquid is reduced , thus reducing the friction loss of the impeller disc, so the pump efficiency is increased about 5%.