Key words: Centrifugal pump Construction principle Property practice
Pump in tap water production line is widely used, variety specifications. Its classification methods are also different, according to their working principle can be divided into three categories: vane pumps, positive displacement pumps, other types of pumps. Most of the use in our plant is a single-stage double-suction centrifugal pump, a vane pump, the pump is due to the work of high-speed rotation of the impeller vane to spin the liquid, the liquid to obtain centrifugal force to complete the pump So the pump is called a centrifugal pump.
Centrifugal pumps are used in a wide variety of applications in many sectors of the national economy. In the water supply system is almost an indispensable device, if the water pipe network as the body's vascular system, then the centrifugal pump is to send blood to the heart. As the centrifugal pump is an important equipment, and its operation to consume a lot of power! In order to rationally and economically select and use water pumps to ensure water supply to the waterworks, we must understand the working principle and basic performance of the centrifugal pumps.
First, the basic structure of the centrifugal pump is composed of six parts
The basic structure of the centrifugal pump is composed of six parts are the impeller, pump body, pump shaft, bearings, seal rings, stuffing box.
1, the impeller is the core part of the centrifugal pump, its speed is high, the impeller blades play a major role in the impeller assembly before static balance experiment. The inner and outer surfaces of the impeller require smoothness to reduce the frictional loss of water flow.
2, also known as the pump casing, it is the main pump. To support the role of fixed, and with the bearing bracket to connect.
3, the role of the pump shaft is connected by a coupling and motor, the motor torque to the impeller, so it is the main component of mechanical energy transfer.
4, the bearing is set on the pump shaft supporting the pump shaft components, there are two types of rolling bearings and plain bearings. Rolling bearings using butter as a lubricant to the appropriate general size of 2/3 ~ 3/4 Too much heat, too little sound and fever! Sliding bearings are used as a transparent oil lubricant, refueling to the oil level line. Too much oil to bleed along the pump shaft and cheap, too little bearing but also overheating and burn accident! In the process of running the pump bearing temperature up to 85 degrees generally run at 60 degrees, if high, we must find out the reason (whether impurities, whether the oil is black, whether the water) and timely treatment!
5, seal ring, also known as leakage ring. The gap between the impeller inlet and the pump casing is too large, causing the water in the high-pressure area of the pump to flow to the low-pressure area through this gap, affecting the output of the pump and reducing the efficiency. The gap is too small will cause the impeller and the pump shell friction wear. In order to increase the backflow resistance to reduce internal leakage, delay the service life of the impeller and the pump housing, the inner edge of the pump housing and the impeller is provided with a sealing ring at the joint of the outer support, and the sealed clearance is maintained at between 0.25 and 1.10mm.
6, stuffing box mainly by the filler, water seal ring, packing tube, packing gland, water seal tube. The purpose of the stuffing box is to close the gap between the pump housing and the pump shaft so that the water inside the pump does not flow outside and the outside air does not enter the pump. Always keep the pump vacuum! When the pump shaft friction with the filler to generate heat will depend on the water seal to live in the water seal ring so that the filler cooling! Maintain the normal operation of the pump. Therefore, during the inspection of the pump running inspection of stuffing box is a special note! Filler needs to be replaced after about 600 hours of operation.
Second, the over-current components of the centrifugal pump
Centrifugal pump over-current components are: suction chamber, impeller, pressure chamber three parts. The impeller chamber is the heart of the pump and the heart of the flow component. Pump through the impeller on the liquid work, to increase its energy. Impeller according to the direction of the liquid is divided into three categories:
(1) Radial impeller (centrifugal impeller) Liquid flows out of the impeller in a direction perpendicular to the axis.
(2) Diagonal impeller (Francis impeller) The liquid flows out of the impeller in a direction inclined to the axis.
(3) Axial impeller The direction of liquid flow parallel to the axis.
Impeller by inhalation is divided into two categories:
(1) Single-suction impeller (ie impeller sucks liquid from one side).
(2) double suction impeller (ie impeller suction fluid from both sides).
Impeller by the cover form is divided into three categories:
(1) closed impeller.
(2) open impeller.
(3) Semi-open impeller.
One closed impeller is widely used, the aforementioned single suction impeller double suction impeller belongs to this form.
Third, the working principle of centrifugal pumps
The working principle of centrifugal pump is: centrifugal pump so water can be sent out due to the role of centrifugal force. Pump before work, the pump body and the inlet pipe must be filled with water into a vacuum state, when the impeller is rapidly rotating, the blade to promote rapid rotation of water, rotating water from the impeller in the centrifugal force of the fly, the pump After the water is thrown out, the central part of the impeller forms a vacuum area. Suwon's water pressure in the air pressure (or water pressure) under pressure through the pipe into the water pipe. This endless cycle, you can achieve continuous pumping. It is worth mentioning that: before starting the pump must be filled with water to the pump casing before starting, otherwise it will cause the pump body heat, vibration, reduce the amount of water, causing damage to the pump (referred to as "cavitation") Cause equipment accident!
Many types of centrifugal pumps, classification methods are common in the following ways 1 by the impeller inhalation points: single suction centrifugal pump double suction centrifugal pump. 2 according to the number of impeller points: single-stage centrifugal pump multistage centrifugal pump. 3 according to the structure of the impeller: open impeller centrifugal pump semi-open impeller centrifugal pump closed impeller centrifugal pump. 4 according to the working pressure points: low pressure centrifugal pump medium pressure centrifugal pump high pressure centrifugal pump. 5 points by the pump shaft position: horizontal centrifugal pump side vertical centrifugal pump.
Fourth, the following centrifugal pump introduces several important performance curves.
Pump performance parameters such as flow Q head H-axis power N speed η efficiency between the existence of a certain relationship. The relationship between the magnitude of their changes is represented by a curve, which is called the performance curve of the pump.
Pump performance parameters between the mutual changes and mutual constraints: first of all the top speed of the pump as a prerequisite.
Pump performance curve has three main curves: flow - lift curve, flow - power curve, flow - efficiency curve.
A, flow - lift characteristic curve
It is the basic performance curve of a centrifugal pump. Than the speed of less than 80 centrifugal pump has the characteristics of rising and falling (both in the middle convex, both sides of the bend), said the hump performance curve. Centrifugal pumps with speeds greater than 80 to 150 have flat performance curves. Centrifugal pumps with specific rotations above 150 have sharp drop performance curves. In general, when the flow is small, the lift is high, and as the flow increases, the lift gradually decreases.
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 by mechanical losses. At this time the pump is full of water, if the long run, will lead to continuous temperature rise in the pump, the pump housing, bearings will be heated, may cause severe thermal deformation of the pump body, we call "stuffy head" at this time The maximum lift, when the valve is gradually opened, the flow will gradually increase, the shaft power is also slowly increasing.
C, flow - efficiency curve
Its curve resembles the shape of a hill. When the flow rate is zero, the efficiency is also equal to zero. As the flow rate increases, the efficiency also gradually increases. However, when the flow rate increases to a certain value, the efficiency decreases, and the efficiency has a highest value. At the highest efficiency Near the point, the efficiency is relatively high, this area is called the high efficiency area.
Five, a reasonable allocation, safe operation, high-quality water supply
The above four aspects of the centrifugal pump to understand the structure, working principle, characteristic curve, how to rationally configure the power of the motor pump is to ensure the safe operation of pumps, water supply, reduce production costs, the key to rational allocation of pump power to play the best pump The safe operation of the work area, the actual situation of our factory water supply, sufficient description of the importance of the rational allocation of equipment, reliability and economy.
1, the importance of reasonable configuration of pump equipment. The main task of the water plant is to ensure that the people of the city's production and domestic water supply, the original maximum daily water supply of South Plant 900,000 tons, influent, effluent to meet the pressure in the region, but the last ten years, with the relocation of municipalities, large water users As the quality of life of the people is getting higher and higher, the demand for water quality is getting higher and higher, and the factory water reaches 0.3 NTU. How to ensure the quality of water supply, the company has adopted a series of measures: (a) Adjusting the reasonableness of the pump equipment Configuration, the implementation of the best combination of man-machine. (B) To increase scientific and technological innovation and devote substantial funds to reforming the original outdated water purification equipment. (C) Funds invested, renovation of old equipment, old pipe networks, improvement of hydraulic conditions, installation of static mixers, etc. (D) The installation of forty meters, the use of modern monitoring system, the whole process of water quality monitoring and control, to ensure that quality water. These measures fully demonstrate the importance of rational allocation of pump and water purification equipment.
2, pump equipment, safe operation of the reliability. In order to ensure the safe operation of pump equipment, equipment companies more standardized management of pump equipment, major maintenance once a year, the monthly secondary maintenance, once-daily maintenance system, these ISO9002 quality management is to ensure that the pump equipment Safe operation of the various measures, in order to ensure the safe operation of the reliability of the technical quality of workers operating training, improvement, the implementation of safety procedures should be strictly enforced, the implementation of these safe operation system is to ensure the reliability of pump operation The guarantee.
3, the safe operation of pump equipment economy. When it comes to economy, it is the cost of making water for enterprises, including electricity, alum, chlorine and ammonia. It is necessary to control the economic activities of enterprises and raise the economy in the safest mode of operation, the optimal mode of operation and the lowest cost of water system Benefit, in this area enterprises have accumulated some experience. Such as: the safest mode of operation, Shanghai's urban water supply network is interoperable, the company's central dispatch room to control the pressure of water supply in the region, too high likely to cause squibs, to the people, the country caused property damage, water pressure is too low, Affect some users of water, resulting in a bad corporate image. Therefore, the pressure during the day to maintain the region is 30-35 kPa, nighttime pressure stays below 30 kPa. According to the requirements of pipe network pressure, high-lift pump open during the day and high-lift and low-lift combination at night effectively control the pressure of the factory water to ensure the water supply of the regional pipe network and the hotel's tall buildings. By adopting these best pump combinations, Not only saving power consumption, but also reasonably control the pressure, these methods to ensure the safe operation of pump equipment economy.
With the continuous development of science and technology, the degree of modernization of pumps has been continuously improved, reducing many man-made management operations. Mostly now using computer monitoring of automatic mode of operation, which also raised the operator's own quality requirements. Because of a pump abnormal situation will affect the entire water supply network, with serious consequences. After several years of practical work and theoretical study, the learned knowledge can be applied to practical work, and the water distribution and scheduling can be reasonably arranged. Utilizing the characteristics of each pump to reach the maximum output of the pump with the least power, Best operating condition And to be safe, high quality, low consumption of water supply.
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