The concept of impeller:
The impeller refers to both the disc with moving blades, which is a component of the impulse turbine rotor, and the general term for the disc and the rotating blades installed on it. The impellers are commonly cast or welded, and the material is selected according to the working medium.
Main function:
The impeller converts the mechanical energy of the prime mover into the static and dynamic pressure energy of the working fluid.
Classification
According to the blade form, it can be divided into three types: open impeller, closed impeller, and semi open impeller.
The closed impeller consists of front and rear cover plates and blades;
A semi open impeller consists of blades and a rear cover plate;
Open impellers only have blades and a partial rear cover plate or no rear cover plate.
The semi open and open impellers in blade type impellers are easy to cast and can transport media containing certain solid particles. However, due to the erosion of the flow channel by solid particles, the working efficiency of the pump will be reduced.
Closed impellers have high operating efficiency and can run smoothly for a long time. The axial thrust of the pump is small, but closed impellers are not easy to transport sewage media containing large particles or long fibers.
According to the working mode, it is divided into single suction impeller and double suction impeller.
Single suction impeller refers to the impeller sucking liquid from one side.
Double suction impeller refers to the impeller that sucks in liquid from both sides and has excellent anti cavitation performance.
According to structure, there are four types: channel type (single channel, double channel), blade type (closed, open), spiral centrifugal type, and swirl type.
1. Flow channel impeller:
The flow channel impeller is a curved flow channel from the inlet to the outlet, which is suitable for conveying liquids containing large particle impurities or long fibers. Because this type of impeller has excellent anti clogging performance. But its drawback is that its anti cavitation performance is weaker than other forms.
2. Blade type impeller:
The semi open and open impellers in blade type impellers are easy to cast and maintain, as well as clean impurities that may clog during transportation. However, its drawbacks lie in the increased gap between the inner wall of the pressurized water chamber and the blades due to the erosion of solid particles during transportation, which reduces the operating efficiency of the water pump. Moreover, the increased gap disrupts the stability of the liquid flow in the channel, causing the pump to vibrate. This type of impeller is not easy to transport media containing large particles and long fibers. The enclosed impeller has high operating efficiency and can run smoothly for a long time. The axial thrust of the pump is small, but the enclosed impeller is prone to entanglement and difficult to transport sewage media containing large particles or long fibers.
3. Spiral centrifugal impeller:
The spiral centrifugal impeller has twisted blades and extends axially from the suction port on a conical hub body. When the liquid being transported flows through the blades, it does not collide with any part of the pump, so there is no damage to the water pump. At the same time, there is no destructive effect on the liquid being transported. Due to the propulsion effect of the spiral, the passage of suspended particles is strong. Therefore, pumps using this type of impeller are suitable for pumping media containing large particles and long fibers.
4. Swirl impeller:
The swirl type impeller has all or part of the impeller retracted into the pressure chamber flow channel, and has good anti clogging performance. The particles flow in the water pressure chamber and are propelled by the vortex generated by the rotation of the impeller. The suspended particles themselves do not generate energy, but exchange energy with the liquid in the flow channel. During the flow process, suspended particles or long fibers do not come into contact with the worn blades. The situation of excessive blade wear is relatively mild, and there is no increase in gaps due to abrasion. It is suitable for pumping media containing large particles and long fibers.
Main geometric parameters
Dj: Inlet diameter of impeller;
D1: Blade inlet diameter;
Dh: impeller hub diameter;
B1: Leaf inlet width;
β 1: Leaf inlet angle;
D2: Outer diameter of impeller;
B2: Width of impeller outlet;
β 2: Leaf exit angle;
Φ: blade wrap angle;
Z: Number of leaves.
The geometric parameters of the impeller inlet have a significant impact on cavitation performance, while the geometric parameters of the impeller outlet have a significant impact on performance (H, Q), both of which have an impact on pump efficiency.
6 common problems and solutions for impellers
1, Casting defects
1. Fault manifestation: inclusions in the flow channel; Succulent; Not smooth; trachoma; crackle; Shrinkage and looseness, etc.
2. Treatment method: Grinding, welding and other methods can be carried out according to the actual situation. If the problem is serious, it needs to be scrapped and recast.
2, Abrasion and abrasion
1. Fault performance: The figure shows the abrasion of the process pump impeller cast from gray cast iron by water containing a small amount of cement foam within five years. The abrasion problem is more caused by the designer's improper selection of materials or pump type, or the process medium is polluted.
2. Solution: Change the impeller material; Change the design scheme and modify the pump type; Check the process medium.
3, Cavitation
1. Fault manifestation: Improper design scheme; The installation position is too high; Improper selection of materials, etc.
2. Solution: Lower the installation position; Change materials that are more resistant to cavitation; Redesign the pump type, etc.
4, Mouth Ring Lock
1. Fault manifestation: The design clearance is too small; The hardness difference between the front and rear mouth rings is less than 50HBW; There are solid particles in the gap between the mouth rings; Deformation of the mouth ring, etc.
2. Solution: Increase the design gap; Replace the material of the mouth ring; Check the process medium; Replace with a new mouth ring, etc.
5, Fracture
1. Fault manifestation: caused by cavitation, corrosion, and abrasion; Poor quality of castings leading to; Caused by water hammer.
2. Solution: Replace the impeller with a new one.
6, Corrosion
1. Fault manifestation: Improper material selection.
2. Solution: Replace the impeller with a new one and use corrosion-resistant and wear-resistant materials; Coating of corrosion-resistant layer on impeller; Spray coating of corrosion-resistant layer on impeller.
