Do you know centrifugal water pump?

Detailed introduction of centrifugal water pump

I. Basic structure and composition

Centrifugal water pump is a mechanical equipment that uses centrifugal force to transport liquid from low to high. It is widely used in agricultural irrigation, industrial water supply, building drainage and other fields. Its core components include impeller, pump casing, pump shaft, bearing and sealing device.

Impeller

The impeller is the core component of the centrifugal pump, responsible for converting mechanical energy into kinetic energy of the liquid. Impellers are divided into three types: closed, open and semi-open. Closed impellers are efficient and suitable for clean water; open impellers allow particles to pass through and are suitable for liquids containing impurities; semi-open impellers are between the two. The impeller material is usually cast iron, stainless steel or bronze, and the specific choice depends on the corrosiveness and temperature of the liquid.

Pump casing

The pump casing is the outer shell that wraps the impeller, usually designed in the shape of a volute, which can convert the kinetic energy of the liquid thrown out by the impeller into pressure energy. The diffusion angle of the pump casing is designed to be 8°-12° to ensure maximum energy conversion efficiency.

Pump shaft and bearing

The pump shaft connects the motor and impeller to transmit power. The bearing supports the pump shaft and reduces friction loss. Bearing types include rolling bearings and sliding bearings. The former is suitable for high-speed operation, while the latter is suitable for heavy-load scenarios.

Sealing device

The sealing device prevents liquid leakage. Common types include mechanical seals and packing seals. Mechanical seals are suitable for high-pressure or corrosive liquids. Packing seals are low-cost but require regular maintenance.

2. Working principle

The working principle of centrifugal water pumps is based on centrifugal force and kinetic energy conversion. When the motor drives the impeller to rotate at high speed, the liquid is thrown from the center of the impeller to the edge and gains kinetic energy. Subsequently, the liquid enters the volute channel of the pump casing, and the kinetic energy is gradually converted into pressure energy and finally discharged from the outlet.

Centrifugal force

The centrifugal force generated by the rotation of the impeller causes the liquid to gain speed and form a high-pressure area. The liquid flows from the center of the impeller to the edge, and the pressure gradually increases.

Kinetic energy conversion

After the liquid enters the pump casing, the diffusion design of the volute reduces the flow rate and converts kinetic energy into pressure energy, thereby realizing the delivery of the liquid.

Cavitation prevention

Cavitation is a common problem of centrifugal pumps, which occurs when the pressure in the pump is lower than the saturated vapor pressure of the liquid. To avoid cavitation, it is necessary to ensure that the installation height and suction conditions of the pump meet the design requirements.

3. Main classification

Centrifugal water pumps can be divided into many types according to their structure and working characteristics. The common classifications are as follows:

By the number of stages

A single-stage pump has only one impeller, with a simple structure, suitable for medium and low head scenarios. A multi-stage pump has multiple impellers connected in series, suitable for high head requirements, such as deep well water extraction or high-pressure water supply.

By installation method

Horizontal pumps occupy a large area and are easy to maintain, and are often used in industrial scenarios. Vertical pumps save space and are suitable for wells or small areas.

By suction method

Single-suction pumps suck liquid from one side of the impeller and have a simple structure. Double-suction pumps suck liquid from both sides of the impeller, with large flow and small vibration, suitable for large water supply systems.

4. Key performance parameters

Head (H)

Head is the height to which the water pump lifts the liquid, in meters. Vertical height, pipeline friction loss and outlet pressure requirements must be considered when selecting.

Flow rate (Q)

Flow rate is the volume of liquid delivered by the pump per unit time, in cubic meters per hour or liters per second. When selecting a pump, the flow rate range must be determined according to actual needs.

Efficiency (η)

Efficiency is the ratio of the pump's output power to its input power. The efficiency of a high-efficiency pump can reach 85%-92%. When selecting a pump, try to choose a high-efficiency working point.

Shaft power (P)

Shaft power is the power required for the pump to operate, calculated as: P = (liquid density × gravitational acceleration × flow × head) / (3.6 × 10⁶ × efficiency).

Required NPSHr

NPSHr is the minimum suction pressure required for the pump to operate normally. When selecting a pump, ensure that the actual available NPSHa is greater than NPSHr.

V. Application scenarios

Agricultural irrigation

Centrifugal pumps are widely used in farmland irrigation, especially in low-head and high-flow scenarios. For example, a single-stage centrifugal pump can be used to extract river or lake water, and can be used with a drip irrigation system to achieve efficient and water-saving irrigation.

Industrial circulating water

In industrial production, centrifugal pumps are used in cooling water circulation, boiler water supply and other scenarios. Multistage centrifugal pumps are suitable for high-lift requirements, such as high-pressure boiler water supply.

Building water supply

Vertical pipeline pumps are often used in high-rise building water supply systems, saving machine room space while meeting high-lift requirements.

Municipal drainage

Double-suction pumps are suitable for municipal drainage systems and can handle large flows of rainwater or sewage to ensure smooth urban drainage.

VI. Installation and maintenance

Installation steps

When installing a centrifugal pump, ensure that the foundation is stable and the pump shaft is aligned with the motor shaft. The suction line should be as short and straight as possible to avoid the formation of air pockets. Fill the pump with liquid before starting for the first time to prevent cavitation.

Daily maintenance

Check the vibration, noise and leakage of the pump daily. Perform bearing lubrication and seal inspections every month. Perform a comprehensive overhaul once a year, including impeller wear detection and shaft alignment calibration.

VII. Advantages and limitations

Advantages

Centrifugal pumps have a simple structure, easy maintenance, smooth operation and a wide range of applications. Whether it is clean water or corrosive liquids, centrifugal pumps can deliver them efficiently.

Limitations

Centrifugal pumps need to be primed before starting, and cannot be self-priming. In addition, centrifugal pumps are sensitive to liquid viscosity and have low efficiency for high-viscosity liquids.

VIII. Selection Guide

Clear Requirements

Before selecting, parameters such as liquid properties, flow, head, and temperature must be clarified. For example, cast iron can be selected when conveying clean water, and stainless steel can be selected when conveying corrosive liquids.

Matching Parameters

Select the efficient working point according to the flow-head curve to ensure that the pump operates within the optimal efficiency range.

Special Requirements

For high-temperature liquids, high-temperature resistant seals must be selected; for sand-containing water, wear-resistant materials or open impellers must be selected.

IX. Common Faults and Treatments

Insufficient flow

Possible causes are impeller blockage or air leakage in the suction pipe. The solution is to clean the impeller or tighten the flange.

Abnormal vibration

Possible causes are shaft misalignment or bearing damage. The solution is to re-center the shaft or replace the bearing.

Seal leakage

Possible causes are aging of the mechanical seal or wear of the sleeve. The solution is to replace the seal or sleeve.

10. Summary

Centrifugal water pumps are efficient and reliable liquid conveying equipment, widely used in agriculture, industry, construction and municipal fields. Through reasonable selection, correct installation and regular maintenance, the service life of the water pump can be significantly extended and the operating efficiency can be improved. For scenes requiring large flow, medium and low head, centrifugal pumps are an ideal choice; when self-priming or handling high-viscosity liquids is required, other pump types need to be considered.