Working principle and basic structure of self-priming centrifugal pump

Working principle and basic structure of self-priming centrifugal pump

1. The basic structure of the self-priming centrifugal pump is composed of six parts
The basic structure of self-priming centrifugal pump is composed of six parts: impeller, pump body, pump shaft, bearing, sealing ring and stuffing box.
1. The impeller is the core part of the self-priming centrifugal pump. Its rotating speed is higher than the output. The blades on the impeller play a major role. The impeller must pass the static balance experiment before assembly. The inner and outer surfaces of the impeller are required to be smooth to reduce the frictional loss of water flow.
2. The pump body is also called pump casing, it is the main body of the pump. It plays the role of supporting and fixing, and is connected with the bracket where the bearing is installed.
3. The role of the pump shaft is to connect the motor with the coupling and transfer the torque of the motor to the impeller, so it is the main component to transfer mechanical energy.
4. The bearing is a member that is sleeved on the pump shaft to support the pump shaft. There are two types of rolling bearings and sliding bearings. Rolling bearings should be properly lubricated with butter as a lubricant. Generally 2/3 to 3/4 of the volume will generate heat, too little will make noise and heat! The plain bearing uses transparent oil as lubricant, add oil to the oil level line. Too much oil should seep along the pump shaft and drift, and too little bearing should be overheated and burned out to cause an accident! During the operation of the pump, the temperature of the bearing is superior to 85 degrees. Generally, it runs at about 60 degrees. If it is high, it is necessary to find the cause (whether there are impurities, whether the oil is black, and whether it is water) and handle it in time!
5. Sealing ring is also called leakage reduction ring. If the gap between the impeller inlet and the pump casing is too large, the water in the high-pressure area of ​​the pump will flow to the low-pressure area through this gap, affecting the output of the pump and reducing the efficiency! If the clearance is too small, it will cause friction between the impeller and the pump casing and cause wear. In order to increase the backflow resistance, reduce the internal leakage, and delay the service life of the impeller and the pump casing, a seal ring is installed at the joint of the pump casing inner edge and the impeller external assistance, and the sealing gap should be kept between 0.25 and 1.10 mm.
6. The stuffing box is mainly composed of packing, water seal ring, packing cylinder, packing gland, and water seal pipe. The purpose of the stuffing box is mainly to close the gap between the pump casing and the pump shaft, so that the water flow in the pump does not flow to the outside and the outside air does not enter the pump. Always keep the vacuum inside the pump! When the friction between the pump shaft and the packing generates heat, it is necessary to rely on the water seal pipe to hold the water into the water seal ring to cool the packing! Keep the pump running normally. Therefore, special attention should be paid to the inspection of the stuffing box during the tour inspection of the pump operation! The filler should be replaced after about 600 hours of operation.
2. Overflow parts of self-priming centrifugal pump
The self-priming centrifugal pump has three parts: the suction chamber, the impeller, and the pressure chamber. The impeller chamber is the core of the pump and the core of the flow components. The pump's work on the liquid through the impeller increases its energy. The impeller is divided into three categories according to the direction of liquid outflow:
(1) Radial impeller (centrifugal impeller) The liquid flows out of the impeller in a direction perpendicular to the axis.
(2) Oblique flow impeller (mixed flow impeller) The liquid flows out of the impeller along the direction of the inclined axis.
(3) The flow direction of the axial impeller is parallel to the axis.
Impeller is divided into two categories according to the way of inhalation:
(1) Single suction impeller (that is, the impeller sucks liquid from one side).
(2) Double suction impeller (that is, the impeller draws liquid from both sides).
Impeller is divided into three types according to the cover plate form:
(1) Closed impeller.
(2) Open impeller.
(3) Semi-open impeller.
Among them, the closed type impeller is widely used. The aforementioned single suction impeller and double suction impeller belong to this form.
3. Working principle of self-priming centrifugal pump
The working principle of the self-priming centrifugal pump is that the self-priming centrifugal pump can send water out because of the centrifugal force. Before the pump works, the pump body and the inlet pipe must be filled with water to form a vacuum state. When the impeller rotates quickly, the blades prompt the water to rotate quickly. The rotating water flies out of the impeller under the action of centrifugal force After the water is thrown out, the central part of the impeller forms a vacuum area. Under the action of atmospheric pressure (or water pressure), the water of the water source is pressed into the inlet pipe through the pipe network. In this way, continuous pumping can be achieved. It is worth mentioning here: before starting the self-priming centrifugal pump, it must be filled with water in the pump casing before it can start, otherwise it will cause the pump body to generate heat, vibration, reduced water output, and damage to the pump (referred to as "cavitation" ") Cause equipment accidents!
There are many types of self-priming centrifugal pumps. The common classification methods are as follows: 1 According to the impeller suction method: single-suction self-priming centrifugal pump Double-suction self-priming centrifugal pump. 2According to the number of impellers: single-stage self-priming centrifugal pump
Multi-stage self-priming centrifugal pump. 3According to the structure of the impeller: open type impeller self-priming centrifugal pump semi-open type impeller self-priming centrifugal pump closed type impeller self-priming centrifugal pump. 4 According to working pressure: low-pressure self-priming centrifugal pump, medium-pressure self-priming centrifugal pump, high-pressure self-priming centrifugal pump, vertical self-priming centrifugal pump.
Fourth, the following introduces several important performance curves of self-priming centrifugal pumps.
There is a certain relationship between the performance parameters of the water pump such as flow rate Q head H axis power N speed n efficiency η. The relationship between the changes in magnitude between them is represented by a curve, which is called the performance curve of the pump.
The mutual change relationship and mutual restriction between the performance parameters of the water pump: First, the pre-top speed of the water pump is the prerequisite.
The pump performance curve has three main curves: flow-head curve, flow-power curve, flow-efficiency curve.
A 、 Flow-head characteristic curve
It is the basic performance curve of self-priming centrifugal pump. Self-priming centrifugal pumps with a specific speed of less than 80 have the characteristics of rising and falling (both convex in the middle and curved on both sides), which is called the hump performance curve. Self-priming centrifugal pumps with a specific speed between 80 and 150 have a flat performance curve. Self-priming centrifugal pumps with a specific rotation speed above 150 have a steep drop performance curve. Generally speaking, when the flow rate is small, the head is high, and the head gradually decreases as the flow rate increases.
B 、 Flow-power curve
The shaft power is increased with the flow rate. When the flow rate Q = 0, the corresponding shaft power is not equal to zero, but 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 it runs for a long time, it will cause the temperature in the pump to continue to rise, the pump casing and bearings will heat up, and in serious cases, the pump body may be thermally deformed. The head is a superior large value. When the outlet valve is gradually opened, the flow rate will gradually increase, and the shaft power will also increase slowly.
C 、 Flow-efficiency curve
Its curve is like the shape of a mountain. When the flow rate is zero, the efficiency is equal to zero. As the flow rate increases, the efficiency also gradually increases, but after increasing to a certain value, the efficiency decreases. The efficiency has a superior high value. Near the high efficiency point, the efficiency is relatively high. This area is called the high efficiency area.
V. Reasonable configuration, safe operation, high-quality water supply
After understanding the structure, working principle and characteristic curve of the self-priming centrifugal pump, how to reasonably configure the power of the motor water pump is the key to ensure the safe operation of the water pump, high-quality water supply, and reduce production costs. The safe operation of the superior and good work area and the actual situation of the water supply of our plant have fully explained the importance, reliability and economy of the reasonable configuration of the equipment.
1. The importance of reasonable configuration of the pump equipment. The main task of the water plant is to ensure the production and living water of the people in the city. The south plant used to have a superior daily large water supply of 900,000 tons. The inflow and outflow can meet the regional pressure, but it has been superior for nearly ten years. With the migration of large households, the amount of water supply is decreasing. With the improvement of people ’s quality of life, the demand for water quality is getting higher and higher. The factory water reaches 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 pump equipment, and implement a superior combination of man and machine. (B) Increase technological innovation and invest a lot of money to transform the original backward water purification equipment. (C) Invest funds, renovate old equipment, old pipe network, improve hydraulic conditions, install static mixers, etc. (D) Install forty meters and use a modern monitoring system to monitor and control the entire process of water quality to ensure high-quality water. These measures fully illustrate the importance of reasonable configuration of pump equipment and water purification equipment.
2. The reliability of the safe operation of the pump equipment. In order to ensure the safe operation of the pump equipment, the company has more standardized management of the pump equipment. The annual overhaul, the monthly secondary maintenance, and the daily primary maintenance system. These ISO9002 quality management are to ensure the pump equipment In order to ensure the reliability of safe operation, the training and improvement of the technical qualities of the operating workers and the implementation of safe operation regulations must be strictly implemented. The implementation of these safe operation systems is to ensure the reliability of the operation of the pump equipment Guarantee.
3. Economical efficiency of the safe operation of the pump equipment. When it comes to economics, the cost of water production by enterprises, including electricity, alum, chlorine, and ammonia, must be controlled by superior and safe operation methods, superior and good dispatching modes, and superior low water production costs to control the economic activities of enterprises. Economic benefits, companies have accumulated some experience in this regard. Such as: superior and safe operation mode, Shanghai's urban water supply network is inter-connected, and there is a company's central dispatch room to control the water supply pressure in the area. If the pressure is too high, it will easily cause pipe explosion, cause property damage to the people and the country, and the water pressure will be too low. Affect the water consumption of some users and cause a bad image of the enterprise. Therefore, the pressure in the area during the day is about 30-35 kPa, and the pressure in the night area is kept below 30 kPa. According to the requirements of the pipe network pressure, the high-lift pump is turned on during the day and the combination of high and low head is turned on at night, which effectively controls the factory water pressure and ensures the water consumption of the regional pipe network and the high-rise buildings of the hotel. It not only saves power consumption, but also controls the pressure reasonably. These methods ensure the economy of the safe operation of the pump equipment.
With the continuous development of science and technology, the modernization of water pumps has also continued to improve, reducing many man-made management operations. Most of the computer-controlled automatic operation modes are now used, which puts forward higher requirements for the operator's own quality. Because the abnormal condition of a water pump will affect the entire network of water supply systems, causing serious consequences. After several years of practical work and theoretical study, apply the knowledge learned to practical work, reasonably arrange the distribution and scheduling of water volume, use the characteristics of each pump to use superior and small power to achieve superior water output of the pump , To achieve superior and good operating conditions. And to achieve safe, high-quality, low-consumption water supply!

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