I. Working Principle of the Impeller: The Secret of Energy Conversion
The basic principle of a centrifugal pump is not complicated: The motor drives the impeller to rotate at high speed, and the liquid between the blades rotates along with it. Under the action of centrifugal force, the liquid is thrown to the outer edge and gains speed and pressure; then the liquid slows down and is pressurized along the volute flow channel, and finally is discharged from the pump body. At the same time, a low-pressure area forms in the center of the impeller, and new liquid is sucked in to form a continuous flow.
During this process, the impeller undertakes three tasks:
Transmitting torque: Passing the rotational power of the shaft to the liquid
Doing work to accelerate: Giving the liquid sufficient kinetic energy
Guiding flow direction: Controlling the flow direction of the liquid through the blade shape
It is precisely this "rotation → acceleration → guidance" triad function that makes the impeller the most crucial part in pump design.
II. Main Classification of the Impeller: Form Determines Function
According to the structural form, common centrifugal pump impellers can be divided into three categories:
1. Closed impeller
Structure: A curved blade is sandwiched between the front and rear cover plates, forming a closed flow channel
Characteristics: The highest efficiency, up to 85% - 92%; but the flow channel is narrow, prone to clogging
Application: Water pumps, boiler feed water pumps, chemical process pumps
Representative scenario: The secondary pressure station of the water treatment plant
2. Open impeller
Structure: Only the blades and the rear cover plate (or without a cover plate), with the blades completely exposed
Characteristics: The flow channel is wide, less prone to clogging; but the efficiency is lower (about 65% - 75%), and the blade root is prone to wear
Application: Sewage pumps, pulp pumps, conveying media with solid particles
Representative scenario: Submersible pumps of the inlet pump station in the sewage treatment plant
3. Semi-open impeller
Structure: There is a rear cover plate but no front cover plate, with one side of the blades open
Characteristics: It is between the closed and open types, balancing efficiency and flow capacity
Application: Slurry pumps, media with a small amount of impurities
Representative scenario: Sludge return pumps
In addition, according to the suction method, it can be divided into single suction type (liquid enters from one side) and double suction type (liquid enters from both sides, with self-balancing axial force), the latter is often used in large flow scenarios.
III. Material Selection: "Armor" for Different Media
The working environment of the impeller varies greatly, and the choice of material is of utmost importance:
Cast iron / ductile iron: Low cost, easy to process, suitable for clear water and weakly corrosive media. However, it has limited corrosion resistance and is not suitable for acidic or alkaline environments.
Stainless steel (304/316/dual phase steel): Strong corrosion resistance. 316L is especially suitable for environments with chloride ions. Widely used in seawater desalination, medicine, and food industries.
High-chromium alloy: High hardness (HRC above 55), excellent wear resistance. The preferred material for slurry pumps and desulfurization pumps.
Bronze / aluminum bronze: Resistant to seawater corrosion, no sparks, suitable for marine pumps and flammable and explosive environments.
Engineering plastics / fluoroplastics: Such as polypropylene, PVDF, PTFE, resistant to strong acids and strong alkalis, but with low strength, suitable for small-scale chemical pumps.
Ceramics / carbon fiber composite materials: Emerging high-end materials, combining ultra-high wear resistance and chemical inertness. Currently mainly used in special working conditions.
Selection rule: Use iron for clear water, steel for sewage, alloy for sediment, plastic for strong acids.
