What is a pump
What is a pump?
A pump is a machine that conveys or pressurizes fluid. It transmits the mechanical energy or other external energy of the prime mover to the liquid to increase the liquid energy. The pump is mainly used to transport water, oil, acid and alkali liquid, emulsion, suspending emulsion and liquid metal, and also can transport liquid, gas mixture and liquid containing suspended solids. Pumps can generally be divided into positive displacement pumps, power pumps and other types of pumps according to the working principle. In addition to classification according to working principle, it can also be classified and named according to other methods. For example, it can be divided into electric pump and hydraulic pump according to the driving method; According to the structure, it can be divided into single-stage pump and multi-stage pump; According to the purpose, it can be divided into boiler feed pump and metering pump; According to the nature of the transported liquid, it can be divided into water pump, oil pump and mud pump. According to the shaft structure, it can be divided into linear pump and traditional pump. The water pump can only transport the logistics with fluid as the medium, not solids.
Main classification of pumps
According to the working principle:
1. Positive displacement pump
The working volume is periodically increased and reduced by the movement of the working parts to absorb and discharge the liquid, and the pressure of the liquid can be directly increased by the extrusion of the working parts.
According to the different motion modes of moving parts, it is divided into two categories: reciprocating pump and rotary pump.
According to the structure of moving parts, there are piston pump and plunger pump, gear pump, screw pump, vane pump and water ring pump.
2. Vane pump
Impeller pump is driven by the impeller to rotate the liquid at high speed and transfer the mechanical energy to the transported liquid.
According to the different structural characteristics of the impeller and flow channel of the pump, the impeller type can be divided into:
- 1) Centrifugal pump
- 2) Axial pump
- 3) Mixed flow pump
- 4) Vortex pump
3. Jet pump
The high-speed jet produced by the working fluid ejects the fluid, and then increases the energy of the ejected fluid through momentum exchange.
Pumps can also be divided into:
- 1) Vertical pump
- 2) Horizontal pump
According to the number of suction ports:
- 1) Single suction pump
- 2) Double suction pump
According to the prime mover driving the pump:
- 1) Motor pump
- 2) Steam turbine pump
- 3) Diesel pump
- 4) Pneumatic diaphragm pump
Common types of pumps
Water and type
The promotion of water is very important for human life and production. In ancient times, there were various water lifting appliances, such as chain pumps in Egypt (17th century BC), orange cones in China (17th century BC), windlasses (11th century BC) and waterwheel (1st century BC). More famous is the screw rod invented by Archimedes in the third century BC, which can steadily and continuously lift water to a height of several meters. Its principle is still used by modern screw pumps.
Around 200 BC, the fire pump invented by the ancient Greek craftsman Ctesibius is one of the most primitive piston pumps. It already has the main components of a typical piston pump, but the piston pump developed rapidly only after the emergence of the steam engine.
From 1840 to 1850, Worthington invented the piston pump with the opposite pump cylinder and steam cylinder and the direct action of steam, marking the formation of modern piston pump. From 1851 to 1875, multistage centrifugal pumps with guide vanes were invented one after another, making it possible to develop high head centrifugal pumps. The 19th century is the climax of the development of piston pump. At that time, it has been used in hydraulic press and other machinery. However, with the rapid increase of water demand, since the 1920s, the low-speed piston pump with greatly limited flow has been gradually replaced by the high-speed centrifugal pump and rotary pump. However, in the field of high pressure and small flow, reciprocating pump still occupies a major position, especially diaphragm pump and plunger pump, which have unique advantages and are used more and more.
The emergence of rotary pump is related to the increasing diversification of industrial requirements for liquid transportation. As early as 1588, there were records about the four blade sliding vane pump, and other rotary pumps appeared one after another. However, until the 19th century, the rotary pump still had the disadvantages of large leakage, large wear and low efficiency. At the beginning of the 20th century, people solved the problems of rotor lubrication and sealing, and adopted high-speed motor drive. The rotary pump suitable for high pressure, medium and small flow and various viscous liquids developed rapidly. The type of rotary pump and the types of liquid suitable for delivery are more than other types of pumps.
The idea of using centrifugal force to carry water first appeared in the sketch made by Leonardo da Vinci. In 1689, French physicist Papan invented the volute centrifugal pump with four blade impeller. But closer to the modern centrifugal pump is the so-called Massachusetts pump with radial straight blades, semi open double suction impeller and volute, which appeared in the United States in 1818. From 1851 to 1875, multistage centrifugal pumps with guide vanes were invented one after another, making it possible to develop high head centrifugal pumps.
Although as early as 1754, the Swiss mathematician Euler put forward the basic equation of impeller hydraulic machinery and laid the theoretical foundation for the design of centrifugal pump, its advantages were not brought into full play until the invention of high-speed motor made the centrifugal pump obtain an ideal power source at the end of the 19th century. Based on the theoretical research and practice of many scholars such as Renault in the UK and pflederer in Germany, the efficiency of centrifugal pump has been greatly improved, and its performance range and application field are also expanding day by day. It has become the pump with the widest application and the largest output in modern times.
1. Selection and installation of centrifugal pump
The centrifugal pump shall be selected according to the delivered liquid, check the required performance, analyze the suction and discharge conditions, intermittent operation or continuous operation, etc. Centrifugal pumps shall normally operate at or near the pressure and flow specified by the manufacturer’s design. The following rechecks shall be carried out during pump installation:
- ① The size, position and elevation of the foundation shall meet the design requirements. The anchor bolts must be properly and correctly fixed in the concrete foundation. The machine shall be free of missing parts, damage or corrosion;
- ② According to the characteristics of the medium conveyed by the pump, the materials of main parts, shaft seals and gaskets shall be checked if necessary;
- ③ The leveling and alignment of the pump shall comply with the provisions of the equipment technical documents. If there is no provision, it shall comply with the provisions of the current national standard general code for construction and acceptance of mechanical equipment installation engineering;
- ④ The installation of all pipes and pipe fittings connected to the pump body and the cleaning requirements of lubricating oil pipes shall comply with the provisions of relevant national standards.
2. The use of centrifugal pump and the test run of pump shall meet the following requirements:
- ① The steering of the driving machine shall be the same as that of the pump;
- ② Find out the steering direction of pipeline pump and coaxial pump;
- ③ Each fixed connection part shall be free of looseness, and the specification and quantity of lubricant added to each lubricating part shall comply with the provisions of equipment technical documents;
- ④ The parts with pre lubrication requirements shall be pre lubricated as required;
- ⑤ All indicating instruments and safety protection devices shall be sensitive, accurate and reliable;
- ⑥ The turning gear shall be flexible without abnormalities;
- ⑦ The pump body shall be preheated before the test run of the high-temperature pump, the temperature shall rise evenly, and the temperature rise per hour shall not be greater than 50 ℃; The temperature difference between the pump surface and the process pipeline with working medium inlet shall not be greater than 40 ℃;
- ⑧ A connecting device is set to eliminate the influence of temperature rise, and a bypass connecting device is set to provide cooling water source.
The following points shall be noted during the operation of centrifugal pump:
- ① Do not operate without water, do not adjust the suction population to reduce the displacement, and do not operate under too low flow;
- ② Monitor the operation process, completely prevent the leakage of the stuffing box, and use new packing when replacing the stuffing box;
- ③ Ensure that the mechanical seal has sufficient flushing water flow, and excessive water flow is prohibited for water-cooled bearings;
- ④ Do not use too much lubricant;
- ⑤ Check according to the recommended cycle. Establish operation records, including operation hours, adjustment and replacement of packing, lubricant addition and other maintenance measures and time. The suction and discharge pressure, flow, input power, temperature and vibration of washing solution and bearing of centrifugal pump shall be measured and recorded regularly.
- ⑥ The main engine of the centrifugal pump depends on atmospheric pressure to pump the water at the low place to the high place, and the atmospheric pressure can only support about 10.3M water column at most, so the main engine of the centrifugal pump cannot work 12 meters away from the water surface.
3. Maintenance of centrifugal pump
3.1 Failure analysis of mechanical seal of centrifugal pump
The shutdown of centrifugal pump is mainly caused by the failure of mechanical seal. Most of the failure manifestations are leakage, and the leakage causes are as follows:
- ① The main reasons for the leakage of the sealing surface of the dynamic and static ring are: the flatness and roughness of the end face do not meet the requirements, or the surface is scratched; There is particulate matter between the end faces, resulting in the same operation of both ends; The installation is not in place and the method is incorrect.
- ② The main reasons for the leakage of the compensation ring seal ring are: the gland is deformed and the preload is uneven; Incorrect installation; The quality of sealing ring does not meet the standard; Incorrect seal ring selection.
The actual application results show that the most failed parts of the sealing elements are the end face of the dynamic and static ring, and the cracking of the end face of the static ring of the centrifugal pump is a common failure phenomenon. The main reasons are as follows:
- ① During installation, the clearance between sealing surfaces is too large, and the flushing fluid has no time to take away the heat generated by the friction pair; The flushing fluid leaked from the gap of the sealing surface, resulting in overheating and damage of the end face.
- ② The vaporization and expansion of liquid medium makes the two ends separated by the vaporization and expansion force. When the two sealing surfaces are firmly bonded, the lubricating film is damaged, resulting in overheating of the end surface.
- ③ The lubricity of liquid medium is poor, and the operating pressure is overloaded, so the tracking rotation of the two sealing surfaces is not synchronous. For example, the rotating speed of the high-speed pump is 20445r/min, and the central diameter of the sealing surface is 7cm. After the pump is running, its linear speed is as high as 75m/s. when a sealing surface lags behind and cannot track the rotation, the instantaneous high temperature will cause damage to the sealing surface.
- ④ The sealing flushing liquid orifice or filter screen is blocked, resulting in insufficient water and failure of the mechanical seal.
In addition, the sliding groove on the surface of the sealing surface and the gap in the fitting of the end face lead to the failure of the sealing element. The main reasons are:
- ① The liquid medium is not clean and has small hard particles, which slide onto the sealing surface at a high speed and scratch the end surface and become invalid.
- ② The coaxiality of the pump transmission parts is poor. After the pump is started, the end face is shaken and rubbed once every revolution, and the moving ring running track is not concentric, resulting in end face vaporization, overheating and wear.
- ③ The frequent occurrence of hydraulic characteristics of liquid medium causes the vibration of pump unit, resulting in the dislocation of sealing surface and failure.
The corrosion of liquid medium to sealing elements, stress concentration, coordination of soft and hard materials, erosion, incompatibility between auxiliary seal 0-ring, V-ring, concave ring and liquid medium, deformation, etc. will cause damage and failure of mechanical seal surface. Therefore, the damage form should be comprehensively analyzed to find out the root cause and ensure the long-term operation of mechanical seal.
3.2 Requirements after the centrifugal pump stops running
- ① After the centrifugal pump stops running, close the inlet valve of the pump, and then close the valves of the auxiliary system after the pump cools down.
- ② The shutdown of high-temperature pump shall be carried out according to the provisions of equipment technical documents. After shutdown, turn for half a turn every 20-30min until the pump body temperature drops to 50 ℃.
- ③ When the cryogenic pump is stopped, when there are no special requirements, the pump shall be often filled with liquid; The suction valve and discharge valve shall be kept normally open; For cryogenic pumps with double face mechanical seals, the level controller and the sealing fluid in the pump sealing cavity shall maintain the grouting pressure of the pump.
- ④ For the pump conveying media easy to crystallize, solidify and precipitate, the pump shall be prevented from blocking after stopping the pump, and the pump and pipeline shall be washed with clean water or other media in time.
- ⑤ Discharge the liquid accumulated in the pump to prevent corrosion and frost crack.
3.3 Storage of centrifugal pump
- ① The pump that has not been installed shall be coated with a layer of appropriate antirust agent on the unpainted surface, the oil lubricated bearing shall be filled with appropriate oil, and the grease lubricated bearing shall be filled with only one kind of grease instead of mixed grease.
- ② Pump clean liquid for a short time, flush, suction pipeline, discharge pipeline, pump casing and impeller, and drain the flushing liquid in pump casing, suction pipeline and discharge pipeline.
- ③ Drain the oil from the bearing box, fill it with clean oil, thoroughly clean the grease and fill it with new grease.
- ④ Seal the suction port and discharge port, store the pump in a clean and dry place, protect the motor winding from moisture, and spray the inside of the pump shell with antirust fluid and anti-corrosion fluid.
- ⑤ Rotate the pump shaft once a month to avoid freezing, and lubricate the bearing.
Positive displacement pump relies on the working elements to make reciprocating or rotary motion in the pump cylinder, so that the working volume increases and decreases alternately, so as to realize the suction and discharge of liquid. The positive displacement pump with reciprocating motion of working elements is called reciprocating pump, and the one with rotary motion is called rotary pump. The suction and discharge processes of the former are alternately carried out in the same pump cylinder and controlled by the suction valve and discharge valve; The latter forces the liquid to transfer from the suction side to the discharge side through the rotation of working elements such as gears, screws, leaf rotors or sliding blades.
The flow of positive displacement pump at a certain speed or reciprocating times is certain, which hardly changes with the pressure; The flow and pressure of reciprocating pump have large pulsation, so corresponding pulsation reduction measures need to be taken; Rotary pump generally has no pulsation or only small pulsation; With self-priming capacity, the pump can remove the air in the pipeline and inhale the liquid after starting; When starting the pump, the discharge pipeline valve must be fully opened; Reciprocating pump is suitable for high pressure and small flow; Rotary pump is suitable for medium and small flow and high pressure; The reciprocating pump is suitable for conveying clean liquid or gas-liquid mixture. In general, the efficiency of positive displacement pump is higher than that of power pump.
The mechanical energy is transferred to the liquid by the force of the rapidly rotating impeller on the liquid to increase its kinetic energy and pressure energy, and then most of the kinetic energy is converted into pressure energy through the pump cylinder. Power pump is also known as impeller pump or vane pump. Some power pumps have main impeller and auxiliary impeller, and centrifugal pump is the most common power pump.
There is a limit value for the head generated by the power pump at a certain speed, and the head changes with the flow; Stable operation, continuous transportation, no pulsation of flow and pressure; Generally, there is no self-priming capacity. The pump needs to be filled with liquid or the pipeline needs to be vacuumized before it can start working; Wide range of applicable performance; It is suitable for conveying clean liquid with low viscosity.
Impeller, water pressure chamber and are the two core components of sewage pump. The structure of impeller is divided into four categories: blade type (open and closed), swirl type, channel type, (including single channel and double channel) and spiral centrifugal type. The quality of its performance represents the quality of pump performance. The anti blocking performance, efficiency and cavitation performance of sewage pump are mainly guaranteed by two parts: impeller and water pressure chamber.
Diaphragm pump, also known as control pump, is the main type of actuator. It changes the fluid flow with the help of power operation by receiving the control signal output by the modulation unit. Diaphragm pump is generally composed of actuator and valve. Compressed air is used as the power source to pump and absorb all kinds of corrosive liquids, liquids with particles, high viscosity, volatile, flammable and highly toxic liquids.
Overview of diaphragm pump
Pneumatic diaphragm pump has four materials: plastic, aluminum alloy, cast iron and stainless steel. Electric diaphragm pump has four materials: plastic, aluminum alloy, cast iron and stainless steel. The diaphragm pump adopts nitrile rubber, neoprene, fluororubber, polyvinylidene fluoride and polytetraethylene according to different liquid media. To meet the needs. It is arranged on various special occasions to pump media that cannot be pumped by conventional pumps.
Diaphragm pump category
According to the power used by the actuator, the diaphragm pump can be divided into pneumatic, electric and hydraulic, that is, the pneumatic diaphragm pump with compressed air as the power source, the electric diaphragm pump with electricity as the power source and the electro-hydraulic diaphragm pump with liquid medium (such as oil) pressure as the power.
The function of diaphragm pump in process control is to receive the control signal of regulator or computer, change the flow of regulated medium, and maintain the regulated parameters within the required range, so as to achieve the automation of production process. If the automatic adjustment system is compared with the manual adjustment process, the detection unit is human eyes and the adjustment control unit is human brain, then the execution unit diaphragm pump is human hands and feet. In order to realize the regulation and control of a certain parameter of the process, such as temperature, pressure, flow, liquid level, etc., it is inseparable from the diaphragm pump. Therefore, the correct selection of diaphragm pump is of great significance in process automation.
Other types of pumps refer to a type of pump that transmits energy in another way. For example, the jet pump sucks the fluid to be transported into the pump by relying on the working fluid ejected at high speed, and transfers energy through momentum exchange through the mixing of the two fluids; Water hammer pump uses the energy generated when the flowing water is suddenly braked to raise part of the water pressure to a certain height; Electromagnetic pump is to make the electrified liquid metal flow under the action of electromagnetic force to realize transportation; The gas lift pump sends compressed air or other compressed gas to the bottom layer of the liquid through the pipe to form a lighter gas-liquid mixed fluid, and then presses the mixed fluid up by the pressure of the liquid outside the pipe.
Working principle of pump
The impeller is installed in the pump shell and fastened on the pump shaft, which is directly driven by the motor. There is a liquid suction pipe in the center of the pump housing. The liquid enters the pump through the bottom valve and suction pipe. The liquid discharge port on the pump shell is connected with the discharge pipe.
Before the pump is started, the pump shell is filled with transported liquid; After startup, the impeller rotates at a high speed driven by the shaft, and the liquid between the blades must also rotate with it. Under the action of centrifugal force, the liquid is thrown from the center of the impeller to the outer edge and obtains energy, leaving the outer edge of the impeller at high speed and entering the volute pump housing. In the volute, the liquid decelerates due to the gradual expansion of the flow channel, converts part of the kinetic energy into static pressure energy, and finally flows into the discharge pipe at a higher pressure and is sent to the place where it is needed. When the liquid flows from the center of the impeller to the outer edge, a certain vacuum is formed in the center of the impeller. Since the pressure above the liquid level of the storage tank is greater than the pressure at the inlet of the pump, the liquid is continuously pressed into the impeller. It can be seen that as long as the impeller rotates continuously, the liquid will be sucked in and discharged continuously.
The working principle of linear pump is different from that of any other pump. It adopts magnetic levitation principle and spiral ring hydrodynamics structure to realize fluid propulsion, that is, cancel the shaft, cancel the shaft connection and cancel the shaft sealing structure. After startup, the current is converted into a magnetic field, and the magnetic field force drives the spiral ring to operate, that is, the spiral ring lifts the fluid forward.
Pump performance parameters
It mainly includes flow and head, in addition to shaft power, speed and necessary NPSH. Flow refers to the amount of liquid output through the pump outlet in unit time, generally using volume flow; Head is the energy increment of liquid transported per unit weight from the pump inlet to the outlet. For positive displacement pumps, the energy increment is mainly in the increase of pressure energy, so it is usually expressed by pressure increment instead of head. Pump efficiency is not an independent performance parameter, but can be calculated by other performance parameters, such as flow, head and shaft power. On the contrary, the shaft power can also be obtained when the flow, head and efficiency are known.
There is a certain interdependent relationship between the performance parameters of the pump. Through the test of the pump, the parameter values can be measured and calculated respectively, and drawn into curves. These curves are called the characteristic curve of the pump. Each pump has a specific characteristic curve, which is provided by the pump manufacturer. Generally, the recommended performance range is also indicated on the characteristic curve given by the factory, which is called the working range of the pump.
The actual working point of the pump is determined by the intersection of the pump curve and the pump device characteristic curve. When selecting and using the pump, the working point of the pump shall be within the working range to ensure the economy and safety of operation. In addition, when the same pump delivers liquids with different viscosities, its characteristic curve will also change. Generally, the characteristic curve given by the pump manufacturer mostly refers to the characteristic curve when conveying clean cold water. For power pumps, with the increase of liquid viscosity, the head and efficiency decrease, and the shaft power increases. Therefore, in industry, sometimes the liquid with high viscosity is heated to reduce the viscosity, so as to improve the transmission efficiency.
Application field of pump
In the production of chemical and petroleum departments, raw materials, semi-finished products and finished products are mostly liquids. Making raw materials into semi-finished products and finished products requires complex process. In these processes, pumps play the role of conveying liquid and providing pressure flow of chemical reaction. In addition, pumps are also used to adjust temperature in many devices.
In agricultural production, pump is the main drainage and irrigation machinery. China’s rural area is vast, and a large number of pumps are needed in rural areas every year. Generally speaking, agricultural pumps account for more than half of the total output of pumps.
Pumps are also the most used equipment in the mining and metallurgical industries. The mine needs to be drained by pumps. In the process of beneficiation, smelting and rolling, pumps are needed to supply water.
In the power sector, nuclear power plants need nuclear main pumps, secondary pumps and tertiary pumps, and thermal power plants need a large number of boiler feed pumps, condensate pumps, oil-gas mixed transmission pumps, circulating pumps and ash pumps.
In national defense construction, pumps are needed for the adjustment of aircraft flaps, tail rudders and landing gears, the rotation of warships and tank turrets, and the ups and downs of submarines. High pressure and radioactive liquid, and some require the pump to have no leakage, etc.
In short, whether it is aircraft, rockets, tanks, submarines, drilling, mining, trains, ships, or daily life, pumps are needed everywhere, and pumps are running everywhere. That’s why the pump is listed as a general machinery, which is a major product in the machinery industry.
Electric pump, that is, electrically driven pump. The electric pump is composed of pump body, lifting pipe, pump seat, submersible motor (including cable) and starting protection device. The pump body is the working part of the submersible pump, which is composed of water inlet pipe, diversion shell, check valve, pump shaft, impeller and other parts. There are two ways to fix the impeller on the shaft.
Selection principle of pump
1. Make the type and performance of the selected pump meet the requirements of process parameters such as unit flow, head, pressure, temperature, cavitation flow, suction head, etc.
2. It must meet the requirements of medium characteristics.
- For pumps conveying flammable, explosive, toxic or valuable media, reliable shaft seals or leak free pumps are required, such as magnetic drive pumps, diaphragm pumps and shielded pumps
- For pumps conveying corrosive media, convection parts are required to be made of corrosion-resistant materials.
- For the pump conveying medium containing solid particles, the convection parts shall be made of wear-resistant materials, and the shaft seal shall be washed with clean liquid if necessary.
3. High mechanical reliability, low noise and low vibration.
4. Economically, it is necessary to comprehensively consider that the total cost of equipment cost, operation cost, maintenance cost and management cost is the lowest.
5. The centrifugal pump has the characteristics of high speed, small volume, light weight, high efficiency, large flow, simple structure, no pulsation of infusion, stable performance, easy operation and maintenance.
Therefore, centrifugal pump shall be selected as far as possible except for the following cases:
- a. When there are metering requirements, the metering pump shall be selected.
- b. When the head requirement is very high, the flow is very small and there is no suitable centrifugal pump with small flow and high head, the reciprocating pump can be selected. If the cavitation requirement is not high, the vortex pump can also be selected.
- c. When the head is very low and the flow is very large, axial flow pump and mixed flow pump can be selected.
- d. When the medium viscosity is large (greater than 650 ~ 1000mm2 / s), rotor pump or reciprocating pump (gear pump and screw pump) can be considered.
- e. When the medium gas content is 75%, the flow is small and the viscosity is less than 37.4mm2/s, the vortex pump can be selected.
- f. For occasions with frequent startup or inconvenient pump filling, pumps with self-priming performance shall be selected, such as self-priming centrifugal pump, self-priming vortex pump and pneumatic (electric) diaphragm pump.
Selection basis of pumps
The pump selection basis shall be considered from five aspects according to the process flow and water supply and drainage requirements, namely, liquid delivery capacity, device head, liquid properties, pipeline layout and operation conditions.
- 1. Flow is one of the important performance data of pump selection, which is directly related to the production capacity and transportation capacity of the whole device. If the design institute can calculate the normal, minimum and maximum flow of the pump in the process design. When selecting the pump, it is based on the maximum flow and takes into account the normal flow. When there is no maximum flow, it is usually 1.1 times of the normal flow as the maximum flow.
- 2. The head required by the device system is another important performance data for pump selection. Generally, the head shall be selected after enlarging the margin of 5% – 10%.
- 3. Liquid properties, including liquid medium name, physical properties, chemical properties and other properties. Physical properties include temperature C, density D, viscosity u, solid particle diameter and gas content in the medium, which involves the head of the system, calculation of effective cavitation allowance and type of appropriate pump: chemical properties, mainly referring to the chemical corrosivity and toxicity of liquid medium, It is an important basis for selecting pump material and which type of shaft seal.
- 4. The pipeline layout conditions of the device system refer to the liquid delivery height, liquid delivery distance, liquid delivery direction, some data such as the lowest liquid level on the suction side and the highest liquid level on the discharge side, as well as the pipe specification and its length, material, pipe fitting specification and quantity, so as to calculate the system head and check the NPSH.
- 5. There are many operating conditions, such as liquid operation T, saturated steam force P, suction side pressure PS (absolute), discharge side vessel pressure PZ, altitude, ambient temperature, whether the operation is intermittent or continuous, and whether the pump position is fixed or movable.
Specific operation of pump selection
According to the pump selection principles and basic conditions, the specific operations are as follows:
1. Horizontal, vertical and other types of pumps (pipeline type, submersible type, submerged type, non blocking type, self-priming type, gear type, etc.) shall be selected according to the layout, topographic conditions, water level conditions and operation conditions of the unit.
2. According to the properties of liquid medium, determine whether the clean water pump, hot water pump or oil pump, chemical pump, corrosion-resistant pump or impurity pump, or non clogging pump. The pump installed in the explosion area shall adopt corresponding explosion-proof motor according to the grade of the explosion area.
3. Determine whether to select single suction pump or double suction pump according to the flow; According to the lift, select single-stage pump or multi-stage pump, high-speed pump or low-speed pump (air conditioning pump), and the efficiency of multi-stage pump is lower than that of single-stage pump. If both single-stage pump and multi-stage pump can be used, first select single-stage pump.
4. Determine the specific model of the pump
After determining which series of pumps to select, the specific model can be determined on the type spectrum or series characteristic curve according to the maximum flow (when there is no maximum flow, 1.1 times of the normal flow is usually taken as the maximum flow), and the two main performance parameters of the head amplified by 5% – 10%. The operation is as follows:
Use the pump characteristic curve to find the required flow value on the abscissa and the required head value on the ordinate, and lead the vertical line or horizontal line upward and right respectively from the two values, and the intersection of the two lines just falls on the characteristic curve, then the pump is the pump to be selected, but this ideal situation is generally rare, and the following two situations usually occur:
- The first type: the intersection point is above the characteristic curve, which indicates that the flow meets the requirements, but the head is not enough. At this time, if the head difference is not much, or the difference is about 5%, it can still be selected. If the head difference is much, select the pump with large head. Or try to reduce the resistance loss of the pipeline.
- The second type: the intersection point is below the characteristic curve and within the fan trapezoid range of the pump characteristic curve, this model is preliminarily determined, and then whether to cut the impeller diameter is determined according to the difference in head, if the head difference is very small, do not cut. If the head difference is very large, cut the impeller diameter according to the required Q, H, NS and cutting formula. If the intersection does not fall within the fan trapezoid range, select the pump with smaller head. When selecting the pump, sometimes the production process requirements must be considered and the Q-H characteristic curves of different shapes shall be selected.
5. After the pump model is determined, for the pump or the pump with physical and chemical medium similar to water, it is necessary to go to the relevant product catalogue or sample, and calibrate it according to the performance table or performance curve of the model to see whether the normal working point falls in the priority working area of the pump? Whether the effective NPSH is greater than (NPSH). In turn, NPSH can be used to correct the geometric installation height?
6. For the liquid pump conveying viscosity greater than 20mm2 / S (or density greater than 1000kg / m3), the characteristic curve of the water experimental pump must be converted into the performance curve of the viscosity (or density), especially the suction performance and input power shall be carefully calculated or verified.
7. Determine the number of pumps and standby rate:
- a. Generally, only one pump is used for normal operation, because one large pump is equivalent to two small pumps working in parallel (referring to the same head and flow), and the efficiency of the large pump is higher than that of the small pump. Therefore, from the perspective of energy saving, it is better to choose one large pump instead of two small pumps. However, in case of the following situations, the parallel cooperation of two pumps can be considered: the flow is large, and one pump can not reach this flow.
- b. For large pumps requiring 50% standby rate, two smaller pumps can be changed to work, one for standby (three in total).
- c. For some large pumps, pumps with 70% flow requirements can be selected for parallel operation without standby pumps. When one pump is overhauled, the other pump still undertakes 70% of the transportation in production.
- d. For pumps requiring 24-hour continuous operation, three pumps shall be standby, one for operation, one for standby and one for maintenance.
8. Generally, customers can submit their “basic conditions for pump selection” and our company can select or recommend better pump products. If the design institute has determined the model of the pump when designing the device and equipment, it shall be configured according to the requirements of the design institute.
Pump maintenance management
The pump should be divided into two aspects: electricity and machine. For the machine, you can compare the previous maintenance records. The second is the electrical aspect. We should understand the power of each pump motor and have a certain understanding of its control system.
Development trend of pump
Pump is one of the indispensable and important equipment in enterprises. Affected by working conditions, it often appears corrosion, cavitation, erosion, wear and other phenomena, resulting in equipment failure. Enterprises can only invest a lot of money to buy new pumps, and charge a lot of parts, resulting in a lot of waste of money. The design and manufacture of domestic pumps basically follow the “metal” idea, that is, stainless steel and carbon steel are used as the main pump body materials. In the face of high corrosion and strong scouring environment, high nickel alloy is required, and even excellent corrosion-resistant materials such as titanium, zirconium and tantalum are used. These rare metal materials are expensive and have large price fluctuations, Moreover, the high manufacturing cost and complex manufacturing process lead to the high price of such pumps, generally ranging from tens of thousands to millions, which also leads to the high procurement cost of such pumps. With the development of international advanced pump body research and the application of new material pump body, domestic scientific research institutions learn from the development ideas of pump body research in western developed countries, and a few domestic enterprises and institutions begin to develop inorganic non-metallic materials such as ceramics, FRP, graphite and carbon products, as well as synthetic organic polymer materials such as plastics, glass fiber or carbon fiber reinforced engineering plastics. The development trend of these domestic pumps catered to the international trend, and soon achieved good use results in China.
It is through the effective solution of such detailed problems that the advantages of low production cost and strong competitiveness of European, American, Japanese and Korean enterprises are realized. Domestic enterprises continue to introduce advanced equipment and hire managers with high salaries, but ignore the details of such daily equipment management. They only unilaterally reduce costs by reducing workers’ wages and welfare benefits, resulting in low labor enthusiasm and chaotic management.
Obviously, the use of this kind of material greatly reduces the production cost, does not need to purchase high-value metals, does not need special equipment and professional production, and has good use effect, longer service life and simpler repair. Its great advantages are by no means comparable to traditional pump body materials. The application of new materials for pump body greatly reduces the material cost and maintenance cost of pump body.
Source: China Pipe Fitting Manufacturer – Yaang Pipe Industry (www.epowermetals.com)
(Yaang Pipe Industry is a leading manufacturer and supplier of nickel alloy and stainless steel products, including Super Duplex Stainless Steel Flanges, Stainless Steel Flanges, Stainless Steel Pipe Fittings, Stainless Steel Pipe. Yaang products are widely used in Shipbuilding, Nuclear power, Marine engineering, Petroleum, Chemical, Mining, Sewage treatment, Natural gas and Pressure vessels and other industries.)
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