Centrifugal pump impellers can be divided into three types: closed type, semi-open type and open type. The closed impellers has wheel covers and discs on both ends of the blade, and the blade channel section is closed, as shown in Figure 1(a). Cleaner liquid; the semi-open impellers only has a wheel disc without a front cover, and the flow channel is semi-open; as shown in Figure 1(b), it is suitable for conveying liquid containing impurities, and the hydraulic efficiency of the pump is low; The impellers has neither the front cover nor the rear cover of the disc, and the flow channel is completely open, as shown in Figure 1(c), and is often used to transport slurry-like viscous media. Centrifugal pump impellers are also divided into single-suction and double-suction impellers. Double-suction impellers are shown in Figure 1(d). They are suitable for large flow rates, and have better cavitation resistance and can basically eliminate axial force.
Most of the impellers of centrifugal pumps are backward curved blade impellers, and the number of blades of backward curved blade impellers is generally 6 to 12 pieces. Usually, the increase of the number of blades can change the flow of the liquid, which can correspondingly increase the lift of the pump, but it also increases the friction loss of the liquid in the pump, reduces the efficiency, and is prone to cavitation; if the number of blades is too small, the load of each blade increases, The reduction of the diversion effect on the liquid will also reduce the head of the pump.
(a)Back curved blades
(c)Forward curved blades
Under the same impellers structure and size, the forward curved blade impellers has larger blade curvature and shorter blade passage, and the cross-sectional area of the blade passage increases rapidly, as shown in Figure 3, so the fluid is prone to boundary layer separation , so the efficiency is lower, while the backward curved blade impellers are the opposite, the efficiency is higher, and the radial blade impellers are between the two.
(a)Backward curved blade impellers
(b)Backward curved blade impellers
βA1——Blade inlet installation angle;
βA2——Blade outlet installation angle