The Different Parts of the Centrifugal Pump
Centrifugal pumps are widely used in industrial fluid transfer due to their high efficiency, large flow capacity, and simple structure. Their stable operation relies on the coordinated work of multiple core components, each of which plays a critical role in energy conversion, fluid sealing, and mechanical support. This article systematically elaborates on the classification, structural characteristics, and functional principles of centrifugal pump components to provide a professional reference for equipment maintenance and performance optimization.
1. Casing: The Core of Energy Conversion
The casing is a static pressure-containing component (usually made of cast iron, stainless steel, or alloy materials) that serves two core functions: protecting internal components and converting fluid kinetic energy into pressure energy. Its structural design directly affects the pump’s efficiency and pressure stability.
1.1 Classification by Structure
·Volute Casing
Shaped like a "snail shell," it features a gradually expanding flow channel from the impeller outlet to the discharge port. When the high-velocity fluid (15–30 m/s) thrown out by the impeller enters the volute, the cross-sectional area of the flow channel increases, reducing the fluid velocity (to 2–5 m/s) and converting kinetic energy into static pressure energy. This design is simple to manufacture and is widely used in single-stage centrifugal pumps (e.g., water supply pumps).
·Diffuser Casing
Equipped with a set of fixed guide vanes (diffuser vanes) around the impeller, the diffuser vanes are arranged in a circular array, with their inlets close to the impeller’s outer edge. The fluid flows through the narrow gap between the vanes, and the gradually expanding vane channels achieve more efficient kinetic energy-pressure energy conversion. Diffuser casings are commonly used in multi-stage centrifugal pumps (e.g., boiler feed pumps) because they can evenly distribute fluid to the next stage impeller, reducing energy loss.
Note: The casing’s inner surface finish (Ra ≤ 1.6 μm) and dimensional accuracy directly affect hydraulic loss—rough surfaces increase friction, reducing pump efficiency by 2–5%.
2. Impeller: The "Power Source" of Fluid Conveyance
As the only rotating component in the hydraulic system, the impeller converts mechanical energy (from the motor) into fluid kinetic energy through high-speed rotation (typically 1,500–3,000 rpm). Its structural design determines the pump’s flow rate, head, and anti-cavitation performance.
2.1 Classification by Flow Direction
·Radial Flow Impeller
The fluid enters axially from the impeller center and is thrown radially (perpendicular to the shaft) under centrifugal force. This type of impeller generates high head (up to 200 m per stage) but has a moderate flow rate, making it suitable for high-pressure scenarios (e.g., irrigation pumps, industrial water supply).
·Axial Flow Impeller
The fluid flows parallel to the shaft direction. The impeller blades are similar to propellers, generating large flow rates (up to 10,000 m³/h) but low head (usually <15 m). They are used in low-lift, large-flow applications such as flood control and drainage.
·Mixed Flow Impeller
Combines radial and axial flow characteristics, with a flow direction at a 30–60° angle to the shaft. It balances flow rate and head (head 15–50 m) and is commonly used in agricultural irrigation and urban water supply.
2.2 Classification by Suction Mode
·Single-Suction Impeller
Fluid enters from one side of the impeller center. It has a simple structure but is prone to unbalanced axial thrust, which requires thrust bearings to compensate. It is widely used in small and medium-sized pumps.
·Double-Suction Impeller
Fluid enters from both sides of the impeller, which balances axial thrust and reduces cavitation risk. It has a larger flow capacity (2–3 times that of a single-suction impeller of the same diameter) and is used in large pumps (e.g., circulating water pumps in power plants).
Material Selection Tip: For clean water, cast iron impellers are sufficient; for corrosive media (e.g., seawater), 316 stainless steel is preferred; for abrasive slurries, high-chrome cast iron (Cr27) is used to resist wear.
3. Sealing Components: Preventing Fluid Leakage
Sealing systems prevent fluid in the pump from leaking to the outside (external leakage) and air from entering the pump (internal leakage), which directly affects the pump’s efficiency and operational safety. Common sealing components include:
3.1 Mechanical Seals
A precision sealing device consisting of a rotating ring (connected to the shaft) and a stationary ring (fixed to the casing). The two rings form a dynamic seal through end face contact (pressure 0.1–0.3 MPa) under spring force, with a leakage rate <5 mL/h. It is suitable for high-pressure (up to 40 bar) and high-speed (up to 3,600 rpm) scenarios and is widely used in chemical, pharmaceutical, and other industries with strict sealing requirements.
3.2 Gland Packing (Stuffing Box)
Made of flexible materials (e.g., PTFE, graphite, or asbestos-free fibers) woven into a rope shape, it is wrapped around the shaft sleeve and compressed by a gland to form a seal. The leakage rate is relatively high (50–100 mL/h), but it has good wear resistance and is suitable for low-pressure (≤10 bar) and non-toxic media (e.g., water pumps). It requires regular adjustment of gland pressure to maintain sealing performance.
3.3 Auxiliary Sealing Elements
·Gaskets: Made of rubber, metal, or composite materials, they are used for static sealing between flange connections (e.g., casing split surfaces) to prevent leakage at fixed joints.
·O-Rings: Elastic rubber rings (usually nitrile rubber or EPDM) that deform under pressure to seal gaps between moving and stationary parts (e.g., between the impeller and shaft). They are simple in structure and low in cost, with a service life of 1,000–3,000 hours.
4. Bearing Systems: Ensuring Smooth Rotation
Bearings support the rotating shaft, reduce friction, and maintain the coaxiality of the impeller and casing. Their performance directly affects the pump’s operating stability and service life.
4.1 Classification by Load Type
·Radial Bearings: Bear radial loads (perpendicular to the shaft). Common types include:
·Ball Bearings: Use steel balls to reduce friction, suitable for high speeds (up to 6,000 rpm) and light loads.
·Roller Bearings: Use cylindrical or tapered rollers, suitable for heavy loads (up to 100 kN) and medium speeds.
·Thrust Bearings: Bear axial loads (parallel to the shaft). Common types include:
·Pivot Shoe Bearings: Composed of multiple tilting shoes that automatically adjust to the load, suitable for high axial loads (up to 500 kN) and high speeds, used in large multi-stage pumps.
·Ball Thrust Bearings: Suitable for light axial loads and low speeds.
4.2 Bearing Pedestal
A support structure (cast iron or cast steel) that fixes the bearings and ensures the shaft’s concentricity. It is usually equipped with an oil filling hole, oil level indicator, and cooling water jacket (for high-temperature applications) to maintain proper lubrication and operating temperature (20–60°C).
Maintenance Tip: Bearings should be lubricated with special grease (e.g., lithium-based grease) every 2,000–4,000 hours, and the lubrication amount should be 1/2–2/3 of the bearing cavity to avoid overheating.
5. Auxiliary Components: Monitoring and Auxiliary Functions
·Pressure Gauges: Installed at the pump inlet and outlet to monitor pressure (accuracy class 1.0–2.5). The inlet pressure reflects the anti-cavitation performance, and the outlet pressure indicates the head. Abnormal pressure fluctuations may indicate impeller wear or pipeline blockage.
·Oil Seals: Made of rubber with a metal skeleton, they are installed at the bearing end to prevent lubricating oil from leaking into the pump cavity or external dust from entering the bearing.
·Shaft Sleeve: A cylindrical component sleeved on the shaft, protecting the shaft from wear by the seal and fluid. It is usually made of stainless steel or ceramic and can be replaced after wear, reducing maintenance costs.
6. Conclusion
Each component of a centrifugal pump plays a unique role: the casing and impeller complete energy conversion, the sealing system prevents leakage, the bearing system ensures smooth rotation, and auxiliary components monitor and protect the equipment. Understanding their structural principles and performance characteristics is crucial for optimizing pump efficiency, reducing failure rates, and extending service life.
In practical applications, component selection should be based on working conditions (medium, pressure, temperature) and operational requirements. For example, in corrosive media, choose stainless steel casings and mechanical seals; in high-speed scenarios, use ball bearings with good high-speed performance. Regular inspection and maintenance of key components (e.g., replacing worn impellers, lubricating bearings) can significantly improve the pump’s operational reliability.
