Centrifugal pump concept

Centrifugal centrifugal pump concept is actually the performance of objects inertia, such as water droplets on the umbrella, when the umbrella slowly turns, the water droplets will follow the umbrella rotation, it is because the friction between the umbrella and the water droplets as the centripetal force to the water droplets. But if the umbrella rotates faster, the friction is not enough to make the water drop in circular motion, then the water drop will move away from the umbrella toward the outer edge, just as a rope pulls the stone to make a circular motion. If it is too fast, the rope will Disconnected, the rocks will fly out. This is called Centrifugal.
Centrifugal pump is designed according to this principle, high-speed rotation of the impeller blades to rotate the water, the water thrown, so as to achieve the purpose of delivery.
There are a variety of centrifugal pumps, from the use can be divided into civilian and industrial pumps; from the transmission medium can be divided into clean pump impurities pump corrosion-resistant pumps.
Centrifugal pump basic structure The basic structure of the centrifugal pump is composed of six parts, namely: impeller, pump body, pump shaft, bearings, seal ring, stuffing box.
1, the impeller is the core part of the centrifugal pump, it is high speed output power, the blades on the impeller 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!
Centrifugal pump structure is the use of transparent oil lubricants, refueling to the oil level line. Too much oil to bleed along the pump shaft and drift *, too little bearing but also overheating and burn accident! In the process of running the pump bearing temperature up to 85 ℃ generally run at 60 degrees, if high, we must find out the reasons (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.
Centrifugal pump works Centrifugal pump principle of work 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) caused by 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 side vertical centrifugal pump.
Impeller is installed in the pump housing 2, and fastened on the pump shaft 3, the pump shaft directly driven by the motor. The pump housing has a liquid suction 4 and suction pipe 5 connected. The liquid enters the pump through the bottom valve 6 and the suction tube. The liquid discharge port 8 in the pump housing is connected to the discharge pipe 9. Before starting the centrifugal pump, the pump housing is filled with liquid being transported; after starting, the impeller is driven by the shaft to rotate at a high speed, and the liquid between the blades must also rotate along with it. Under the action of centrifugal force, liquid is thrown from the center of the impeller to the outer edge and gains energy, leaving the outer edge of the impeller to enter the scroll casing at a high speed. In the volute, the liquid due to the gradual expansion of the slowing down, but also part of the kinetic energy into static pressure, and finally to a higher pressure into the discharge pipe, to the required place. When the liquid flows from the impeller center to the outer edge, a certain vacuum is formed in the center of the impeller. Since the pressure above the liquid level in the sump is greater than the pressure at the inlet of the pump, the liquid is continuously pressed into the impeller. Visible, as long as the impeller constantly rotating, the liquid will be continuously inhaled and discharged.
Barrage Phenomena When there is air in the pump housing, there is less centrifugal force due to the much lower density of the air than the density of the liquid. Thus, the tank above the liquid level and the pump inlet pressure difference is not enough to the tank liquid into the pump pressure, that is, centrifugal pump no self-absorption capacity, so that the centrifugal pump can not deliver liquid, this phenomenon is called the phenomenon of gas tied . In order to fill the pump with liquid, a bottom valve with strainer is usually installed at the bottom of the suction pipe. The bottom valve is a check valve. The strainer prevents solid matter from entering the pump to damage the impeller or impede the normal operation of the pump.
The role of the impeller is to transfer the mechanical energy of the prime mover directly to the liquid, in order to increase the hydrostatic pressure and kinetic energy of the liquid, mainly to increase the static pressure energy. Impellers generally have 6 to 12 blades after bending. Impeller has open, semi-closed and closed three. The open impeller has no cover plate on both sides of the blade, which is simple in manufacture and convenient in cleaning. It is suitable for conveying materials containing a large amount of suspended matter, which has low efficiency and low pressure of liquid to be transported. The semi-closed impeller has no cover on the suction inlet side Plate, and on the other side of the cover, suitable for conveying easily sediment or particles containing materials, the efficiency is lower; closed impeller impeller on both sides of the blade has a front and rear cover, high efficiency, suitable for the delivery of impurities Clean liquid. Most of the centrifugal pump impeller for such. Impeller has a single suction and double suction two suction method. There is a water inlet is a single suction, you can double from the water inlet on both sides.
The role is to seal the impeller in a certain space, so that the role of the impeller suction and out of the liquid. Pump casing made of spiral shape, it is also known as the volute. Due to the gradual enlargement of the cross-sectional area of ​​the flow passage, the high-speed liquid thrown out from the impeller gradually reduces the flow velocity and effectively converts part of the kinetic energy into static pressure energy. Pump housing not only brings together the liquid thrown by the impeller, but also an energy conversion device.
The function of the shaft sealing device is to prevent the liquid in the pump casing from leaking out of the shaft or outside air into the pump casing.
Common shaft seal packing seal and mechanical seal two.
Fillers are generally impregnated with oil or asbestos rope coated with graphite. The main purpose of the mechanical seal is to achieve the purpose of sealing by the relative movement between the moving ring mounted on the shaft and the stationary ring fixed on the pump casing.
Centrifugal pump flow components Introduction Centrifugal pump flow 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.
According to the direction of the liquid flow 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.
Classification by inhalation 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).
According to the form of cover classification Impeller by cover form is divided into three categories:
(1) closed impeller.
(2) open impeller.
One closed impeller is widely used, the aforementioned single suction impeller double suction impeller belongs to this form.
Centrifugal pump type a, according to the number of working impeller to classify 1, single-stage pump: that is, there is only one impeller on the pump shaft.
2, multi-stage pump: that is, there are two or more than two impellers on the pump shaft, and the total lift of the pump is the sum of the lift produced by n impellers.
Second, according to the classification of working pressure 1, low-pressure pump: pressure less than 100 meters of water column;
2, the pressure pump: pressure in the water column between 100 ~ 650 meters;
3, high-pressure pump: pressure higher than 650 meters water column.
Third, according to the classification of the impeller water way 1, one side into the water pump: also known as single suction pump, that is, only one inlet on the impeller;
2, bilateral water pump: also known as double suction pump, that is, both sides of the impeller has a water inlet. Its flow rate is double that of a single suction pump, which can be approximated as two single-suction pump impellers placed back-to-back together.
Fourth, according to the pump shell combined with the type of seam 1, the level of open pump: that is, through the axis of the horizontal plane with a joint seam.
2, the vertical joint pump: that is, the junction plane and the axis of the vertical.
Fifth, according to the pump shaft position to classify 1, horizontal pump: pump shaft is located in horizontal position.
2, vertical pump: pump shaft is located in the vertical position.
Six, according to the impeller out of the way to the pressure chamber out of the classification 1, volute pump: water from the impeller, directly into the pump shell with a spiral shape.
2, guide vane pump: water from the impeller out into the guide vane set outside it, and then into the next level or into the outlet pipe.
Usually we say that a pump is a multistage pump, which means how much the impeller. According to other structural features, it may be horizontal pump, vertical joint surface pumps, vane pumps, high pressure pumps, single-inlet pumps and so on. So according to different, the name is not the same. In addition, the classification can also be used according to the purpose, such as pumps, pumps, condensate pumps, ash pump, circulating pump, etc. Types of types Centrifugal pump features Vertical cylinder pump import and export takeover In the upper part of the same height, Layer shell, the inner shell by the rotor, guide vanes and other components, the outer shell for the import diversion channel, the liquid inhalation from the bottom.
ISG life to the pump, pump life, residential pumps, domestic water supply and drainage equipment, according to IS, IR centrifugal pump performance parameters and the unique combination of vertical pump design, and in strict accordance with the requirements of ISO2858 to set up wine production, using domestic high-quality hydraulic Model design, is the ideal next-generation horizontal pump products. The product will be used carbide mechanical seal. Applications: ISW pump for industrial and urban water supply and drainage, such as high-rise building pressurized water, garden sprinkler, fire pressurization, long distance transmission, HVAC refrigeration cycle, bathroom booster and equipment, the use of temperature does not exceed 85 ℃. ISWR type pump is widely used in: boilers, boilers, water heating, transportation and city heating system in metallurgy, chemical industry, textile, paper making, and guesthouses, etc. The operating temperature of SGWR type does not exceed 120 ℃.
Centrifugal pump installation height that suction Cheng choose a centrifugal pump key installation technology Centrifugal pump pipe installation technology is the key to determine the centrifugal pump installation height that suction stroke. This height refers to the vertical distance from the surface of the water source to the centerline of the centrifugal pump impeller. It is not confused with the allowable suction height. The allowable vacuum height indicated on the pump manual or nameplate means the vacuum value on the water inlet section of the pump, But also at 1 standard atmospheric pressure, the water temperature of 20 ℃, the test was measured and determined. It does not consider the condition of the water flow after the water supply pipe is matched. The pump installation height should be allowed to suck vacuum height deducted after the head of the suction pipe loss, the remaining part of the value, it is necessary to overcome the actual terrain water absorption height. Pump installation height can not exceed the calculated value, otherwise, the centrifugal pump will not pump water. In addition, the impact of the calculated value is the size of the suction pipe lift loss lift, it is appropriate to use the shortest pipe layout, and try to install less elbow and other accessories, but also consider the appropriate with some larger diameter pipes to reduce the flow rate within the pipe.
It should be noted that the pipeline centrifugal pump installation site elevation and water temperature is different from the test conditions, such as the local elevation of 300 meters or more than the water temperature is pumping water, the calculated value to be amended. That is, the atmospheric pressure at different altitude and the saturated steam pressure above 20 ℃. However, when the water temperature is below 20 ℃, the saturated steam pressure is negligible.
From the pipeline installation technology, water pipes require strict sealing, can not leak, leaking, otherwise it will undermine the centrifugal pump inlet at the vacuum, so that the centrifugal pump to reduce the amount of water, even in serious pumping can not come to the water. Therefore, we should conscientiously do the work of the interface of the pipeline to ensure the construction quality of pipeline connection.
Second, the installation of centrifugal pump height Hg Allowable vacuum suction height Hs refers to the pressure at the pump entrance p1 allows the maximum degree of vacuum.
The actual allowable suction height, Hs, is not a value calculated according to the equation, but a value determined experimentally by the pump manufacturer, which is attached to the pump sample for user investigation. It should be noted that the value of Hs given in the pump sample is the value of water used as working medium, operating conditions of 20 ℃ and pressure of 1.013 × 105Pa, when the operating conditions and working medium are different, need to be converted.
1 transport of water, but the operating conditions and experimental conditions are different, according to the following conversion Hs1 = Hs + Ha-10.33 - Hυ-0.24
2 Conveying Other Liquids When the condition of the liquid being transported and the villain is different from the experimental conditions, two-step conversion is required: the first step will be Hs1 detected in the pump sample according to the above formula; and the second step will convert Hs1 into Hs
2 NPSH Δh
For the oil pump, the calculation of the installation height is calculated using the cavitation allowance Δh, that is, the degree of vacuum that the pump allows to suction the liquid, that is, the allowable installation height of the pump, in meters. Naphthenic residual amount Δh by the pump in the sample, its value is also measured with 20 ℃ water. If you transfer other liquids, also need to be corrected, detailed investigation of the books.
Stroke = standard atmospheric pressure (10.33 meters) - NPSH - safe amount (0.5 meters)
Standard atmospheric pressure pipeline pressure can be 10.33 meters in height.
For example: a pump required NPSH is 4.0 meters, suction Δh?
Solution: Δh = 10.33-4.0-0.5 = 5.83 m From the safety point of view, the actual pump installation height should be less than the calculated value. When the calculated value of Hg is negative, it indicates that the suction port of the pump should be below the level of the tank.
Example 2-3 A centrifugal pump from the sample was allowed to suction on the vacuum height Hs = 5.7m. It is known that the total resistance of the suction line is 1.5 mH2O and the local atmospheric pressure is 9.81 × 10 4 Pa. The dynamic head of liquid in the suction line is negligible. Try to calculate
1 transport 20 ℃ water centrifugal pump installation;
2 instead of conveying 80 ℃ water centrifugal pump installation height.
Solution: 1 delivery of 20 ℃ water pump installation height is known: Hs = 5.7m
Hf0-1 = 1.5m
u12 / 2g≈0
The local atmospheric pressure is 9.81 × 104Pa, basically in line with the experimental conditions of the pump factory, so the installation height of the pump Hg = 5.7-0-1.5 = 4.2m.
2 When the delivery of 80 ℃ water pump installation height When the water delivery 80 ℃, can not be directly used in the pump sample Hs value to calculate the installation height, according to the following formula for Hs when the line conversion, that Hs1 = Hs + Ha-10.33 - Hυ-0.24
Ha = 9.81 × 104Pa ~ 10mH2O is known, the saturation vapor pressure of water at 80 ℃ is 47.4kPa.
Hv = 47.4 × 103 Pa = 4.83 mH2O
Hs1 = 5.7 + 10-10.33-4.83 + 0.24 = 0.78m
Hs1 value into the type to obtain the installation height Hg = Hs1-Hf0-1 = 0.78-1.5 = -0.72m
Hg is negative, indicating that the pump should be installed below the tank level, at least 0.72 m below the liquid level
Single-stage double-suction centrifugal pump single-stage double-suction centrifugal pump is a new type of high efficiency energy-saving pump. Under the same energy-using conditions, its operating efficiency can be increased by nearly 20%
1. Compact structure, beautiful appearance, good stability, easy to install.
2. Smooth and optimized design of the double suction impeller to reduce the axial force to a minimum, and has excellent hydraulic properties of the leaf, and after precision casting, the pump casing and the surface of the impeller Extreme Brilliance has significant anti-cavitation And high efficiency.
3 bearing selection SKF and NSK bearings to ensure smooth operation, low noise, long service life.
4. Seal selection BURGMANN mechanical seal or packing seal. 8000 hours to ensure operation without leakage.
5. Installation form Assembly without adjustment, according to the site conditions. Discrete or horizontal installation.
6. The installation of self-priming device, can automatically absorb water, that does not need to install the end of the valve, no vacuum pump, no backfill, the pump can start.
] To extend the service life of centrifugal pumps 1, the choice and installation of centrifugal pumps Centrifugal pumps should be selected in accordance with the delivery of liquid, and check the required performance, analysis of pumping, discharge conditions, is intermittent operation or continuous operation. Centrifugal pumps should normally be operated at or near the pressure and flow rates specified by the manufacturer's design. The pump should be installed for the following review:
① The basic size, location and elevation should meet the design requirements. The anchor bolts must be properly and correctly fixed on the concrete foundation. The machine should not be missing, damaged or corroded.
② According to the characteristics of the pump transmission medium, if necessary, check the main parts, shaft seals and gasket material;
③ Pump leveling, find work should be consistent with the provisions of technical documents, if there is no provision, should be consistent with the existing national standards, "Machinery and Equipment Installation Engineering Construction and Acceptance of Common Specifications" requirement;
④ All connected with the pump pipe, pipe fittings and oil pipe cleaning requirements should be consistent with the relevant national standards.
2, the use of centrifugal pump test run pump should meet the following requirements:
① drive the steering should be the same with the pump steering;
② identify the pipeline pump and coaxial pump steering;
 '¢ the fixed connection should be no loose parts, the lubricating parts filling lubricant specifications and quantity should be consistent with the provisions of technical documents;
④ pre-lubrication requirements of the site should be pre-lubricated;
⑤ all indicating instruments, safety devices should be sensitive, accurate and reliable;
⑥ crank should be flexible, no abnormalities;
⑦ high temperature pump should be preheated before the test run, the temperature should rise evenly, the temperature rise per hour should not exceed 50 ℃; pump surface with the working medium inlet process pipe temperature difference should not exceed 40 ℃;
⑧ set to eliminate the impact of temperature rise of the connection device, set the bypass connection device to provide cooling water.
Centrifugal pump operation should note the following:
① prohibit anhydrous operation, do not adjust the suction port to reduce emissions, prohibit the operation of low flow;
② monitor the operation of the process, completely prevent packing box leakage, replace the packing box with a new filler;
③ to ensure that mechanical seals have a full flush of water, water-cooled bearings prohibit the use of excessive water flow;
④ lubricant do not use too much;
⑤ according to the recommended cycle of inspection. Establish operating records including operating hours, packing adjustments and replacements, adding lubricants and other maintenance measures and times. Centrifugal pump suction and discharge pressure, flow, input power, lotion and bearing temperature and vibration conditions should be measured regularly recorded.
⑥ Centrifugal pump host is relying on the atmospheric pressure will be low water pumping to a height, while the atmospheric pressure can only support about 10.3m of water column, so the host of centrifugal pumps leave the water 12 meters can not work.
3, centrifugal pump maintenance 3.1, centrifugal pump mechanical seal failure analysis Centrifugal pump shutdown is caused mainly by the failure of the mechanical seal. The failure of the performance of most of the leaks, leaks for the following reasons:
① static and dynamic ring seal surface leakage, mainly due to: face flatness, roughness does not meet the requirements, or scratches the surface; between the end of the particulate matter, resulting in both ends can not be the same run; installation is not in place, the way is not correct.
② compensation ring seal leakage, mainly due to: gland deformation, uneven pre-tightening; installation is not correct; seal quality does not meet the standards; seal selection wrong.
The actual use of the results show that the seal failure of the most parts of the dynamic and static end of the ring, the centrifugal pump seal, static ring end face cracking is a common failure phenomenon, the main reasons are:
① installation seal surface clearance is too large, too late to take away the flushing liquid generated by friction heat; flushing fluid leak from the gap in the sealing surface, resulting in overheating and damage to the end.
② vaporization of liquid medium expansion, so that the two ends by the expansion of vaporization and separation, when the two sealing surface force fit, the destruction of the lubricating film resulting in the end surface overheating.
③ liquid medium lubrication is poor, combined with the operating pressure overload, two sealing surface tracking rotation is not synchronized. For example, high-speed pump speed of 20445r / min, the center of the sealing surface diameter of 7cm, pump speed after the line up to 75m / s, when there is a sealing surface can not track the hysteresis rotation, instantaneous sealing surface damage caused by high temperature.
④ seal flushing fluid orifice or filter blockage, resulting in insufficient water, so that machine seal failure.
In addition, the sealing surface of the surface of the sliding groove, the end face of the gap caused by seal failure, mainly due to:
① liquid medium is not clean, there are tiny hard particles, with a very high speed sliding sealing surface, the end surface scratches and failure.
② poor coaxial pump drive parts, the pump is turned on each revolution after a week was shaking the friction end, moving the ring trajectory is not the same heart, resulting in end vaporization, overheating wear.
③ frequent occurrence of hydraulic properties of liquid medium caused pump vibration, resulting in seal surface dislocation and failure.
Liquid medium on the sealing element corrosion, stress concentration, with hard and soft materials, erosion, auxiliary seal 0-ring, V-ring, concave ring and the liquid medium is not compatible, deformation and so will cause mechanical seal surface damage failure, so Damage to the form of a comprehensive analysis to identify the root causes, to ensure long-term mechanical seal operation.
3.2, Centrifugal pump requirements after stopping operation ① Centrifugal pump should stop running after the population of the valve valve, and then turn off the pump after the cooling system of the auxiliary valve.
② high-temperature pump should be stopped according to the provisions of technical documents, after parking should be partial 20 -30 30min half a turn until the pump temperature dropped to 50 ℃ so far.
③ cryogenic pump parking, when no special requirements, the pump should always be filled with liquid; suction valve and the discharge valve should be kept normally open state; the use of double-end mechanical seal of the cryogenic pump, liquid level controller and seal the liquid seal chamber The pump grouting pressure should be maintained.
④ transport easy to crystallize, easy to coagulate, easy precipitation and other media pump, stop the pump should be blocked, and timely flush with water or other media pumps and pipes. ⑤ discharge liquid stored in the pump to prevent corrosion and cracking.
3.3, the preservation of centrifugal pump ① not yet installed on the unpainted pump surface should be coated with a suitable rust inhibitor, lubricated bearings should be filled with the appropriate oil, grease-lubricated bearings should only be filled A grease, do not use mixed grease.
② a short time pump clean liquid, flushing, suction lines, discharge lines, pump housing and impeller, side by side net pump housing, suction lines and discharge lines in the flushing fluid.
③ drain the oil bearing box, then add clean oil, thoroughly clean the grease and then fill the new grease.
④ The suction port and exhaust port sealed up, the pump stored in a clean, dry place, to protect the motor windings from damp, with anti-rust liquid and anti-cavitation spray pump housing inside.
⑤ pump shaft rotation once a month to avoid freezing, and lubrication of bearings.
Centrifugal pump working principle Centrifugal pump main flow components are suction chamber, impeller and pressure chamber. The water suction chamber is located in front of the water inlet of the impeller and functions as a guide for the liquid to the impeller. The water pressure chamber mainly has three forms of a spiral water pressure chamber (volute type), guide vanes and space guide vanes. The impeller is the most The important working element is the heart of the overcurrent part, which consists of the cover and the middle leaf.
Centrifugal pump work before the pump filled with liquid, and then start the centrifugal pump, the impeller rotates quickly, impeller blades drive liquid rotation, the liquid rotates by inertia to the outer edge of the impeller flow, at the same time the impeller sucked liquid from the suction chamber, at the same time In this process, the liquid in the impeller flows around the flow vane, and the liquid acts a lift on the vane in the flow around the flow. In turn, the vane acts on the liquid with a force equal to and opposite to the lift force, So that the liquid energy out of the impeller, then the kinetic energy and pressure of liquid are increased.
Centrifugal pumps depend on the action of the rotating impeller on the liquid to transfer the mechanical energy of the prime mover to the liquid. As the role of centrifugal pump fluid from the impeller inlet to the outlet of the process, its speed and pressure energy can be increased by the impeller discharge liquid through the pressure chamber, most of the speed can be converted into pressure energy, and then along the discharge line Out, at this time, the impeller inlet due to the discharge of liquid to form a vacuum or low pressure, the liquid in the suction tank under the surface pressure (atmospheric pressure) is pressed into the impeller inlet, so the rotating impeller continuous Inhale and discharge liquid.
Centrifugal pump is not the main reason for the water Centrifugal pump with its simple structure, easy maintenance, high efficiency and become the most widely used in agriculture, a pump, but also because of mention of the water is troublesome. Now on the water to mention the reasons for this accident to be analyzed.
There is air in the water inlet pipe and pump body. (1) Some users do not fill enough water before starting the pump. It appears that the water has overflowed from the vent hole, but the air is completely discharged without rotating the pump shaft, causing a little air to still remain in the water inlet pipe or the pump body in.
(2) In case of contact with the water pump, the horizontal section of the water inlet pipe should be descended 0.5% or more to the reverse water flow direction. Up tilt, the intake pipe will remain in the air, reducing the vacuum hose and pump, affecting water absorption.
(3) The long-term use of the pump packing has been worn or the packing pressure is too loose. As a result, a large amount of water is ejected from the gap between the packing and the pump shaft sleeve. As a result, external air enters the pump from these gaps and affects the water supply.
(4) The water inlet pipe is corroded due to long-term diving, and the surface of the water pipe is continuously declining. When the water holes are exposed, the air enters the water inlet pipe from the hole.
(5) cracks in the inlet pipe cracks, inlet pipe and pump connections appear a small gap, are likely to make the air into the inlet pipe.
Pump speed is too low (1) Human factors. A considerable part of the user due to the original motor damage, it is coupled with another motor-driven, resulting in less traffic, head pumping low-pumping consequences.
(2) belt wear. There are many large pump away from the belt, because of long-term use, belt wear and loose, there slipping, reducing the pump speed.
(3) improper installation. Two pulley center distance is too small or two axes are not parallel, tight belt mounted to the top, resulting in the wrapping angle is too small, the two pulley diameter calculation error and coupling shaft pump two eccentric eccentricity will cause the pump Speed ​​changes.
(4) the pump itself mechanical failure. Loosening of the impeller and the shaft of the pump shaft or the deformation and bending of the shaft of the pump cause the impeller to move more, directly friction with the pump body, or bearing damage, which may reduce the pump speed.
(5) Power engine maintenance does not record. The motor burned due to the winding, and loss of magnetism, the maintenance of the winding turns, diameter, wiring methods change, or maintenance failure is not completely ruled out factors will make the pump speed change.
Suction too much Some deep water, some water peripheral potential is relatively flat, while ignoring the pump allowable suction, resulting in little or no absorption of water absorption results. To know the pump suction port to establish a degree of vacuum is limited, the absolute vacuum suction is about 10 meters high water column, and the pump can not establish an absolute vacuum. The degree of vacuum is too large, easy to gasify the pump, work on the pump negative. Each centrifugal pump has its maximum allowable suction, usually between 3 to 8.5 meters, not only when installing the pump is easy and convenient.
Water flow into and out of the pipe resistance loss is too large Some users measure the reservoir or water tower to the water source vertical distance slightly less than the pump head, but to mention a small amount of water or mention the water. The reason is often too long pipe, pipe bend more water pipe resistance loss is too large. The reason is often too long pipe, pipe bend more water pipe resistance loss is too large. Under normal circumstances, 90-degree bend pipe bending resistance than the 120-degree bend, each 90-degree elbow head loss of about 0.5 to 1 meter, 20-meter pipe resistance can make head loss of about 1 meter. In addition, some users are also free to pump into and out of pipe diameter, these have some impact on the lift.
Other factors (1) at the end of the valve can not be opened. Pump is usually set aside too long time, the bottom valve gasket was sticky, no gasket at the end of the valve may rust.
(2) the bottom valve filter is clogged; or the bottom valve causes the clogging of the filter in the sludge layer.
(3) impeller wear serious. Impeller blades worn by long-term use, affecting the pump performance.
(4) Gate valve or check valve failure or blockage will result in reduced flow pumping not on the water.
(5) drain pipe leakage will also affect the amount of water.
Centrifugal pump flow components Centrifugal pump flow 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 of centrifugal pump cavitation and solution phenomenon:
1, sewage pump, the use of temperature around 80 ℃, pump pressure rose to normal after the pump outlet pump normal pressure,
About 10 minutes rapid decline in pump pressure, accompanied by noise, vibration, cavitation occurs Check the sewage station valve closed,
2 material pump material about 90 degrees easy to gasification of organic matter 3 · Unscrew the centrifugal pump body of the diversion plug, perfusion water (or pulp).
4 · Shut off the outlet valve and outlet pressure gauges and import vacuum gauge.
5. Jog the motor to see if the motor is turning properly.
6. Turn on the motor. When the centrifugal pump is operating normally, open the outlet pressure gauge and the inlet vacuum pump as it shows an appropriate pressure. Gradually open the gate valve and check the motor load.
7. Try to control the flow and lift of the centrifugal pump within the range indicated on the plate to ensure that the centrifugal pump operates at its highest efficiency for maximum energy savings.
8 · Centrifugal pump operation, the bearing temperature can not exceed the ambient temperature 35 ℃, the maximum temperature not exceeding 80 ℃.
9. If you find a clear water pump abnormal sound should stop immediately check the reasons.
10. Centrifugal pump to stop using, first close the gate valve, gauge, and then stop the motor.
11 · Centrifugal pump in the first month of work, after 100 hours to replace the oil, every 500 hours after the oil change time.
12 · Regularly adjust the packing gland to ensure that the dripping inside the packing room is normal (as droplet leakage is appropriate).
13. Regularly check the wear and tear of the sleeve, wear and tear should be promptly replaced after larger.
14 · Centrifugal pump in the winter season, after parking, you need to unscrew the lower part of the pump drain plug to the media to the net. Prevent cracking.
15. Long-term deactivation of the centrifugal pump, the pump required to open all, dry the water, the rotating parts and joints coated with grease installed properly protect the centrifugal pump main performance parameters and characteristic curve:
1, Note:
The main performance parameters indicated on the nameplate of the centrifugal pump are the values ​​measured under the highest efficiency conditions with water at 20 ° C.
2, the performance parameters (see pump characteristics curve)
Flow Q, head H, shaft power N and efficiency η (volume loss, hydraulic loss and mechanical loss)
Understand and master the meaning of the curves in the characteristic curve and the conditions of use Pay attention to the range of the highest efficiency zone (η = 92% ηmax) and use 3, the centrifugal pump characteristic curve conversion density change:
Fluid density changes only affect pump shaft power;
Viscosity changes:
Fluid viscosity increases, the energy loss of fluid in the pump increases, the pump head, flow, efficiency are decreased, while the shaft power increases.
Speed ​​changes:
Speed ​​changes in less than 20%, the pump characteristic parameters to meet than the set v Impeller diameter changes:
Cutting within 10%, the pump's characteristic parameters to meet the cutting law.
Preparation of Centrifugal Pump Before Startup a. Check the name, model, main performance and filling quantity of the lubricating oil before the start of centrifugal pump to meet the requirements of technical documents;
Bearing lubrication system, sealing system and cooling system is intact, the bearing oil, water is smooth;
Drive the pump rotor 1 ~ 2 turn, check the rotor for friction or stuck phenomenon;
In the vicinity of the coupling or belt guard, etc., whether there is interference with rotation of debris;
Pump, bearing, motor foundation anchor bolts are loose;
Pump work system valves or ancillary devices should be in the pump load minimum position, should close the exit control valve;
Point pump to see whether the impeller steering steering with the design, if inconsistent, impeller must completely stop turning, adjust the motor wiring, before starting.
b. Centrifugal pump water pump Before start-up, the pump housing and suction pipe must be filled with water, because of the presence of air, the suction port vacuum can not be formed and maintained.
c. Centrifugal Pumps Centrifugal pumps for transporting hot liquids, such as boiler feed pumps for power plants, must be warmed up before starting. This is because when the feed water pump is started, the high-temperature feed water flows through the pump, causing the temperature of the pump body to rise quickly from room temperature to 100-200 ° C, which causes the temperature difference between the inside and outside of the pump and between the components. If there is not enough Heat transfer time and appropriate measures to control the temperature rise will cause uneven expansion of the pump around, resulting in deformation of the various parts of the pump, wear, vibration and axle suspension accidents.

This article Keywords: centrifugal pump

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Design specifications
Main dimensions
Main dimensions of spherical bearings are in accordance with the international standards ISO 6124/1.
Designation
Designation of standard spherical bearings is specified in the dimension tables and consists of type designation and dimension. Non-standard designation (radial clearance, sealing, dimension differences) are designated according to the standard STN 02 04608.

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