Self-priming centrifugal pump working principle and classification

Post Time: 2024-01-27 22:30:25

Self-priming centrifugal pump so can send the water out is due to the role of centrifugal force. Water pump before work, the pump body and inlet pipe must be full of water line into a vacuum state, when the impeller rotates quickly, the vane prompts the water to rotate quickly, rotating water in the centrifugal force under the action of the impeller to fly away from the pump, the pump is thrown out of the water, the impeller’s center part of the formation of the vacuum area. Water pump water under the action of atmospheric pressure (or water pressure) through the pipe network pressed into the inlet pipe. This cycle does not stop, it can realize continuous pumping. It is worth mentioning here: self-priming centrifugal pumps must be filled with water to the pump casing before starting, otherwise it will cause the pump body heating, vibration, water output reduction, damage to the pump (referred to as “cavitation”) resulting in equipment accidents!

Basic structure

The basic structure of the self-priming centrifugal pump is composed of six parts, respectively, impeller, pump body, pump shaft, bearings, sealing ring, stuffing box.

1, the impeller is the core part of the self-priming centrifugal pump, it is a high speed, high output, the impeller on the vane and play a major role, the impeller should be assembled through the static balance test. The inner and outer surfaces of the impeller should be smooth to reduce the friction loss of the water flow.

2, the pump body, also known as the pump shell, it is the main body of the pump. Play a supporting fixed role, and with the installation of bearing bracket connection.

3, the role of the pump shaft is through the coupling and motor connection, the motor’s pitch to the impeller, so it is the main part of the transfer of mechanical energy.

4、Bearings are the components supporting the pump shaft, and there are two kinds of bearings: rolling bearings and plain bearings. Rolling bearings use butter as a lubricant refueling should be appropriate generally 2/3 ~ 3/4 of the volume of too much will heat, too little and have a sound and heat! Sliding bearings use transparent oil as lubricant, refueling to the oil level line. Too much oil to seep out along the pump shaft and drift cheap, too little bearing and overheating burned out causing accidents! In the process of pump operation bearing temperature up to 85 degrees in general running at about 60 degrees, if high to find the cause (whether impurities, oil is black, whether water) and timely processing!

5, sealing ring also known as leakage reduction ring. Impeller inlet and pump casing gap between the pump will cause the pump high-pressure area of the water flow through this gap to the low-pressure area, affecting the pump’s water output, reduced efficiency! Too small a gap will cause the impeller and pump casing friction wear. In order to increase the reflux resistance to reduce internal leakage, delay the impeller and the pump casing of the service life, in the pump casing and the impeller outer edge of the combination of external assistance with a sealing ring, sealing the gap to maintain in the 0.25 ~ 1.10mm appropriate.

6, the stuffing box mainly consists of packing, water sealing ring, packing cylinder, packing gland, water sealing tube. The role of the stuffing box is mainly to close the gap between the pump casing and the pump shaft, do not allow the pump water flow does not flow to the outside and do not allow the outside air into the pump. Always keep the vacuum inside the pump! When the pump shaft and packing friction heat generated by the water seal pipe water to the water seal ring to make the packing cool! Maintain the normal operation of the pump. So in the pump running inspection process of the packing box inspection is particularly important to pay attention to! In the operation of 600 hours or so to replace the packing.

Overflow parts

Self-priming centrifugal pumps have three parts of overflow parts: suction chamber, impeller, and press-out chamber. The impeller room is the core of the pump and also the core of the flow parts. The pump works on the liquid through the impeller to increase its energy. Impeller according to the direction of liquid outflow is divided into three categories:

(1) runoff impeller (centrifugal impeller) liquid is along the direction perpendicular to the axis out of the impeller.

(2) oblique flow impeller (mixed flow impeller) liquid is along the axis of the direction of inclination out of the impeller.

(3) Axial impeller liquid flows in a direction parallel to the axis.

Classification of impeller

Impellers are classified into two types according to the way of suction:

(1) single suction impeller (that is, the impeller from one side of the liquid inhalation).

(2) double suction impeller (that is, the impeller from both sides of the liquid inhalation).

The impeller is divided into three categories according to the form of cover:

(1) closed impeller.

(2) open impeller.

(3) Semi-open impeller.


One of the closed impeller is widely used, the aforementioned single suction impeller double suction impeller belongs to this form.

There are many types of self-priming centrifugal pumps, and the following classification methods are common 1 according to the impeller suction mode: single suction self-priming centrifugal pumps double suction self-priming centrifugal pumps. 2 according to the number of impeller points: single-stage self-priming centrifugal pumps

According to the impeller structure: open impeller self-priming centrifugal pump half-open impeller self-priming centrifugal pump closed impeller self-priming centrifugal pump. 4 according to the working pressure: low-pressure self-priming centrifugal pump medium-pressure self-priming centrifugal pump high-pressure self-priming centrifugal pump side of the vertical self-priming centrifugal pump.

Performance Parameters

Water pump performance parameters such as flow Q head H shaft power N speed n efficiency η between the existence of a certain relationship. The relationship between the value of their quantitative changes in the curve to indicate that this curve is called the performance curve of the pump.

Pump performance parameters of the mutual relations and mutual constraints: first of all, the pump’s top speed as a prerequisite.

Pump performance curve mainly has three curves: flow – head curve, flow – power curve, flow – efficiency curve.

Flow – head characteristic curve

A, flow – head characteristic curve

It is the basic performance curve of self-priming centrifugal pump. Than the rotational speed of less than 80 self-priming centrifugal pump with rising and falling characteristics (both the middle of the bulge, both sides of the downward curve), called hump performance curve. Than the rotational speed of 80 to 150 between the self-priming centrifugal pump has a flat performance curve. Than the number of revolutions in 150 or more self-priming centrifugal pumps have a steep decline in the performance curve. Generally speaking, when the flow rate is small, the head is high, and with the increase of the flow rate the head gradually decreases.

Flow – power curve

B、Flow-power curve

Shaft power is increased with the flow, when the flow Q = 0, the corresponding shaft power is not equal to zero, but for a certain value (about 60% of normal operation). This power is mainly consumed in mechanical losses. At this time the pump is full of water, if a long time running, it will lead to rising temperatures inside the pump, pump casing, bearings will heat up, and in serious cases, the pump body may be thermally deformed, which we call “stuffy head”, at this time the head is the maximum, when the outlet valve is gradually opened, the flow rate will gradually increase, and the axial power is also slowly increasing.

Flow rate – efficiency curve

C、Flow-efficiency curve

Its curve like the shape of a hill, when the flow rate is zero, the efficiency is equal to zero, with the flow rate increases, the efficiency also gradually increased, but increased to a certain value after the efficiency will decline, the efficiency of a maximum value, in the highest efficiency point near the efficiency of the higher, this area is known as the high-efficiency zone.

Safe operation and efficiency

The above four aspects of self-priming centrifugal pump structure, principle of operation, after the characteristic curve, how to reasonably configure the motor pump power, is to ensure the safe operation of the pump, high-quality water supply, reduce production costs of the key to the reasonable configuration of the pump power, play the best pump working area of the safe operation of the water supply in my plant, the actual situation, enough to illustrate the importance of the reasonable configuration of the equipment, reliability and economy. 

1, the importance of reasonable allocation of machine and pump equipment. The main task of the water plant is to ensure that the city’s people’s production and living water, the South Plant was the maximum daily water supply of 900,000 tons of water, water inlet and outlet to meet the pressure of the region, but with the relocation of municipal relocation of water users, the water supply is decreasing, with the improvement of people’s quality of life, the demand for water quality is getting higher and higher, the ex-factory water up to 0.3NTU, how to ensure high-quality water supply, the enterprise has adopted a series of measures (a) adjust the reasonable configuration of the machine and pump equipment, the implementation of the best combination of man and machine. (b) increase scientific and technological innovation, invested a lot of money to transform the original backward water purification equipment. (C) investing funds, remodeling old equipment, old pipe network, improve hydraulic conditions, installation of static mixer and so on. (D) installation of forty meters, the use of modern monitoring systems, the whole process of water quality monitoring and control to ensure quality water. These measures fully illustrate the importance of machine pump equipment and water purification equipment reasonable configuration.  

2, machine pump equipment for safe operation of reliability. In order to ensure the safe operation of machine and pump equipment, enterprise management of machine and pump equipment more standardized, a major overhaul every year, once a month, the second level of maintenance, once a day, the first level of maintenance system, these ISO9002 quality management, is to ensure that the safe operation of machine and pump equipment and the measures, in order to ensure the reliability of the safe operation of the technical qualities of the operation of the workers’ training to improve the implementation of safe operating procedures should be In order to ensure the reliability of safe operation, the training and improvement of the technical quality of the operators and the implementation of the safety operation procedures should be strictly implemented. 

3, machine and pump equipment for safe operation of the economy. A talk about economy is the cost of water production enterprises, including electricity, alum, chlorine, ammonia, to the safest mode of operation, the best scheduling mode, the lowest cost of water production, to control the economic activities of enterprises to improve economic efficiency, in this regard, the enterprise has accumulated some experience. Such as: the safest way of operation, Shanghai’s urban water supply network is interoperable, there is a company center dispatch office to control the water supply pressure in the region, too high easily caused by bursting the pipe to the people, the country caused by the loss of property, the water pressure is too low, affecting part of the user’s water use, resulting in a bad image of the enterprise. Therefore, during the daytime to maintain the pressure of the region is about 30-35 kPa, and at night the pressure of the region is maintained at less than 30 kPa. According to the requirements of the pipe network pressure, high head machine pumps are opened during the daytime, and the combination of high and low head is opened at night, which effectively controls the pressure of the water from the factory and ensures the water consumption of the regional pipe network and the high buildings of the hotels, and the use of these optimal machine-pump combinations not only saves the power consumption but also reasonably controls the pressure, and these methods ensure the economy of the safe operation of machine-pump equipments.


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