The inducer has much higher cavitation resistance than the centrifugal impeller, so a pre-inducer (ie, an inducer in front of the primary impeller) is widely used in some pumps requiring high cavitation performance.
Why does the induction wheel have much higher cavitation resistance than the centrifugal impeller? This is because in the centrifugal impeller, the liquid into the blade head, the direction to a sharp turn, the flow rate to be increased, so the pressure should be reduced, which is prone to cavitation, the vapor and liquid separation; the birth of cavitation After centrifugal impeller can not limit its development, because the liquid in the impeller flow direction is along the role of centrifugal force direction, the liquid in the centrifugal force, thrown out at high speed, thus increasing the separation of gas and liquid , But this is not the case in the induction wheel. First, the liquid is less prone to cavitation when it enters the induction wheel without turning and the dynamic pressure drop is lower; cavitation occurs (mainly at the rim of the entrance because of this At the relative maximum speed), the bubble will immediately be subject to two aspects of the attack: on the one hand, due to the outer edge of the bubble along the axial flow to the high pressure area, the pressure immediately condensation; the other hand, the role of the centrifugal pump, The liquid at the hub rushed to the outer edge of the induction wheel, also making the bubble pressure condensation.
Induction wheel is actually an axial impeller, but it compared with the general axial flow pump, has the following characteristics:
1, the ratio of the outer diameter of the impeller and the hub is small;
2, fewer leaves;
3, blade placement angle is small;
4, cascade density L / t big.
When the inducer wheel and centrifugal pump impeller work together, inducer produced lift the centrifugal impeller pressure.
Induced wheel-type flat and curved with two kinds. Flat-leaf type, the blade entrance and exit angle is equal, also known as pitch induction wheel. The inducing wheel with camber leaf type, the import placement angle is small, the export resettlement angle, that is β1 <β2, known as the pitch induction wheel. The first leaf type is often seen in cylindrical induction wheels. The second type is often seen in conical induction wheels. Compared with the conical induction wheel, the latter induction wheel is better, which has the advantages of high efficiency, good anti-cavitation performance (stable operation due to large outlet angle, conical shape and favorable re-condensation of bubbles) No noise.
General induction wheel:
The aspect ratio hi / dt = 0.3 ~ 0.4 {dt = (d + d1t) / 2};
Number of leaves Z = 2-3;
Cascade density L / t ≈ 1.5 (L is the cascade length, t is the cascade spacing);
Rounded blade inlet edge R = 0.32d;
Hub and rim profile, cylindrical or 15 ° taper.
In the power plant, inducer more used in the new unit of the condensate pump, due to the induction wheel, the pump can increase the number of revolutions, and thus in the same flow and head, the impeller diameter can be greatly reduced or reduce the number of stages, Condensate pump structure to miniaturization and simplification.