First, the overview of the direct vertical centrifugal pump:
The direct-connected vertical centrifugal pump is a high-performance product designed by the company to adopt the IS-type centrifugal pump performance parameters and in strict accordance with the international standard ISO2858 and the latest national standard JB/T6787.2-93. It is an alternative to the IS-type centrifugal pump and the ISG-type pipeline. Ideal for conventional pumps such as centrifugal pumps. Flow range: 33.6-720m3/h, head range: 16-125m, divided into basic type, split type, A, B cutting type and other 200 specifications. According to the flow medium and temperature, the material of the over-flow part and the appropriate structure are designed and manufactured into the series of ISZR, ISZF and other products with the same type of performance parameters, instead of the conventional centrifugal pump used in all occasions.
The direct-coupled vertical centrifugal pump is generally driven by an electric motor, and the pump body and the suction line are filled with liquid before starting the pump. When the impeller rotates at a high speed, the impeller drives the liquid between the blades to rotate. Due to the centrifugal force, the liquid is swept from the center of the impeller to the outer edge of the impeller (the flow rate can be increased to 15-25 m/s), and the kinetic energy is also increased. When the liquid enters the pump casing, the flow velocity gradually decreases as the flow path in the volute casing is gradually reduced, and a part of the kinetic energy is converted into static pressure energy, so that the liquid flows out along the discharge port with a higher pressure. At the same time, the center of the impeller forms a certain vacuum due to the liquid being pumped out, and the pressure Pa at the liquid level is higher than the center of the impeller. Therefore, the liquid in the suction line enters the pump under the pressure difference. The impeller rotates continuously, and the liquid is continuously sucked in and out. Because the direct-coupled vertical centrifugal pump can transport liquid, mainly relying on the centrifugal force, it is called a direct-coupled vertical centrifugal pump.
Direct-coupled vertical centrifugal pumps are the most widely used in chemical production because of their wide range of properties (including flow, pressure head and adaptability to media properties), small size, simple structure, easy operation, and uniform flow. Outstanding advantages such as low failure, long life, low purchase and operating costs. Therefore, this chapter focuses on the centrifugal pump as a typical example of the application of fluid mechanics.
(1) The basic structure of the direct vertical centrifugal pump
The basic components of a direct-coupled vertical centrifugal pump are a high-speed rotating impeller and a fixed snail-shaped pump casing. An impeller having a plurality of (usually 4 to 12) back-curved blades is fastened to the pump shaft and is driven by the motor to rotate at a high speed with the pump shaft. The impeller is a component that directly works on the liquid in the pump and is an energy supply device for the centrifugal pump. The suction port in the center of the pump casing is connected to the suction pipe, and the bottom of the suction pipe is provided with a one-way bottom valve. The discharge port on the side of the pump casing is connected to a discharge line equipped with a regulating valve.
(2) Working principle of direct vertical centrifugal pump
When the direct-coupled vertical centrifugal pump is started, the pump shaft drives the impeller to rotate at a high speed, forcing the pre-filling liquid to rotate between the blades. Under the action of inertial centrifugal force, the liquid moves radially from the center of the impeller to the outer circumference. The liquid gains energy during the movement through the impeller, the static pressure energy increases, and the flow rate increases. When the liquid leaves the impeller and enters the pump casing, some of the kinetic energy is converted into static pressure energy due to the gradual expansion of the flow passage in the casing, and finally flows into the discharge pipe tangentially. Therefore, the volute pump casing is not only a component that collects the liquid flowing from the impeller, but also a transducing device. When the liquid is from the center of the impeller to the outer circumference, the center of the impeller forms a low pressure zone, and the liquid is sucked into the center of the impeller under the action of the total potential energy difference between the liquid level of the sump and the center of the impeller. The liquid is continuously sucked in and discharged by the continuous operation of the impeller. The mechanical energy obtained by the liquid in the centrifugal pump ultimately manifests as an increase in static pressure energy.
[Animation] The basic structure and working principle of the direct-coupled vertical centrifugal pump need to be emphasized that if the liquid to be delivered is not filled into the pump casing before the direct-coupled vertical centrifugal pump is started, the impeller rotates due to low air density. The resulting centrifugal force is small, and the central region of the impeller is insufficient to form a low pressure of the liquid in the suction sump, so that the liquid cannot be delivered although the direct-coupled vertical centrifugal pump is activated. This indicates that the centrifugal pump has no self-priming ability, which is called air binding. The suction line is equipped with a one-way bottom valve to prevent the liquid poured into the pump casing from flowing out of the casing before starting. Air is trapped from the suction line into the pump casing.
(3) Impellers and other components of direct-connected vertical centrifugal pumps
1. The impeller of a direct-connected vertical centrifugal pump is a key component of a direct-coupled vertical centrifugal pump.
(1) According to its mechanical structure, it can be divided into three types: closed type, semi-closed type and open type. Closed impellers are suitable for conveying cleaning fluids; semi-closed and open impellers are suitable for conveying suspensions containing solid particles, which are inefficient. When the closed and semi-closed impellers are in operation, a part of the high-pressure liquid leaving the impeller can leak into the cavity between the impeller and the pump casing. Since the pressure at the liquid suction port on the front side of the impeller is low, the liquid acts on the front and rear of the impeller. The pressure on the sides is not equal, and an axial thrust directed to the suction side of the impeller is generated. This force pushes the impeller to move toward the suction side, causing friction at the contact between the impeller and the pump casing, causing vibration of the pump in severe cases and damaging the normal operation of the pump. Drilling a number of small holes in the rear cover of the impeller reduces the pressure difference across the impeller, thereby reducing the adverse effects of axial thrust, but at the same time reducing the efficiency of the pump. These small holes are called balance holes.
(2) According to different liquid absorption methods, the impeller can be divided into single suction type and double suction type. The single suction type impeller has a simple structure, and the liquid can only be sucked from one side. The double suction impeller can simultaneously draw liquid symmetrically from both sides of the impeller, which not only has a large liquid absorption capacity, but also substantially eliminates the axial thrust.
(3) According to the geometry on the blade on the impeller, the blade can be divided into three types: back bend, radial and forward bend. Because the back bend blade is beneficial to the conversion of kinetic energy of liquid into static pressure energy, it is widely used.
2. Guide wheel of a direct-connected vertical centrifugal pump In order to reduce the energy loss caused by the impact when the liquid leaving the impeller directly enters the pump casing, a fixed and vaned guide wheel is sometimes arranged between the impeller and the pump casing. The vanes in the guide wheel gradually turn the liquid entering the pump casing and the flow passage continuously expands, so that part of the kinetic energy is effectively converted into static pressure energy. Multistage centrifugal pumps are usually equipped with guide wheels. The snail-shaped pump casing, the back-bending blade on the impeller and the guide wheel can all improve the conversion rate of kinetic energy to static pressure energy, so they can all be regarded as energy-transfer devices.
3. Shaft seal device The pump casing is fixed due to the rotation of the pump shaft, and there must be a certain gap at the contact between the shaft and the pump casing. In order to avoid leakage of high pressure liquid in the pump along the gap or to prevent outside air from entering the pump from the opposite direction, a shaft seal device must be provided. The shaft seal of the centrifugal pump has a stuffing box and a mechanical (end) seal. The stuffing box is used to seal the pump shaft through the annular gap of the pump casing, and a soft packing (such as oil-impregnated or graphite-coated asbestos rope) is placed therein. The mechanical seal consists of a moving ring mounted on the rotating shaft and another stationary ring fixed to the pump casing. The end faces of the two rings are relatively rotated by the spring force to act as a seal. Mechanical seals are suitable for applications where the seal is high, such as the transport of acids, bases, flammable, explosive and toxic liquids. When the centrifugal pump is started, the pump shaft drives the impeller to rotate at a high speed, forcing the pre-filling liquid to rotate between the blades. Under the action of the inertial centrifugal force, the liquid moves radially from the center of the impeller to the outer circumference. The liquid gains energy during the movement through the impeller, the static pressure energy increases, and the flow rate increases. When the liquid leaves the impeller and enters the centrifugal pump casing, some of the kinetic energy is converted into static pressure energy due to the gradual expansion of the flow passage in the casing, and finally flows into the discharge pipe tangentially. Therefore, the volute pump casing is not only a component that collects the liquid flowing from the impeller, but also a transducing device. When the liquid is from the center of the impeller to the outer circumference, the center of the impeller forms a low pressure zone, and the liquid is sucked into the center of the impeller under the action of the total potential energy difference between the liquid level of the sump and the center of the impeller. The liquid is continuously sucked in and discharged by the continuous operation of the impeller. The mechanical energy obtained by the liquid in the centrifugal pump ultimately manifests as an increase in static pressure energy. The role of the impeller is to transfer the mechanical energy of the prime mover directly to the liquid to increase the static pressure and kinetic energy of the liquid (mainly increasing the static pressure energy).
1. Impeller The role of the impeller is to transfer the mechanical energy of the prime mover directly to the liquid to increase the static pressure and kinetic energy of the liquid (mainly increasing the static pressure energy). The impeller has three types: open type, semi-closed type and closed type. The open impeller has no cover on both sides of the blade, which is simple to manufacture and convenient to clean. It is suitable for conveying materials containing a large amount of suspended solids. The efficiency is low and the liquid pressure is not high. The semi-closed impeller has no cover on the suction side. The plate has a cover plate on the other side, which is suitable for conveying materials that are easy to precipitate or contain particles, and the efficiency is also low; the closed impeller has a front and rear cover plate on both sides of the blade, and the efficiency is high, and is suitable for conveying impurities. Cleaning liquid.
The general centrifugal pump impeller is mostly of this type.
2. Pump casing The function is to close the impeller in a certain space so that the liquid can be sucked in and out by the action of the impeller. The centrifugal pump casing is often made into a volute shape, so it is also called a volute. Since the cross-sectional area of ​​the flow passage is gradually enlarged, the high-speed liquid drawn from the periphery of the impeller gradually reduces the flow velocity, so that part of the kinetic energy is effectively converted into static pressure energy. The pump casing not only collects the liquid that is pumped out by the impeller, but is also an energy conversion device.
Second, the product introduction of the direct vertical centrifugal pump:
1. ISZ direct-connected horizontal single-stage centrifugal clean water pump for conveying clean water and physical and chemical properties, similar to other liquids used for clean water, suitable for industrial and urban water supply and drainage, high-rise building pressurized water supply, garden sprinkler irrigation, fire protection Pressurization, long-distance transportation, HVAC, refrigeration cycle, bathroom and other pressurization and equipment matching, the use temperature T is not higher than 80 degrees Celsius.
2, IRZ direct-connected horizontal single-stage centrifugal hot water pump is widely used in: metallurgy, chemical, textile, paper, and hotel hotels and other boiler hot water pressurization, transportation, and urban heating system, the use temperature T is not higher than 120 degrees Celsius.
3. IHZ horizontal chemical pump centrifugal pump for conveying liquids without solid particles and corrosive and viscosity close to water. It is suitable for: petroleum, chemical, metallurgy, electric power, paper, food, pharmaceutical and synthetic fiber sectors. The temperature is -20 ~ +120 degrees Celsius.
4, IYZ horizontal oil pump for the delivery of gasoline, kerosene, diesel and other oil products or flammable and explosive liquid, the temperature of the medium to be transported is -20 ~ +120 degrees Celsius.
5. IRZ, IHZ, IYZ performance parameters, installation dimensions, and performance curves are the same as ISZ.
Third, the characteristics of the direct vertical centrifugal pump:
1. The structure is compact, the volume is small, the appearance is beautiful, the center of gravity of the vertical structure is low and the center of gravity coincides with the center of the pump foot, which enhances the operating life and stability of the pump.
2, easy to install, the import and export diameter is on the same center line, can be directly installed in any part of the pipeline like a valve. The motor and protective cover can also be used outdoors. The pump has mounting feet for stable pump installation.
3, the operation is stable, the noise is low, the concentricity is high, the motor adopts low-noise bearing, the pump blade has a good dynamic and static balance, and the operation has no vibration, which changes the use environment.
4. No leakage, the shaft seal is sealed with hard alloy and silicon carbide and other wear-resistant materials. It not only solves the serious leakage problem of the centrifugal pump packing seal, but also has a long service life, ensuring clean and tidy operation.
5, convenient maintenance: do not need to remove the pipe, just remove the pump cover nut, take out the motor and transmission components for maintenance.
6. Its unique structure and perfect design not only reduce the pump room area, improve the space, but also greatly reduce the capital investment.
Fourth, the main purpose of the direct vertical centrifugal pump:
1. Direct-connected vertical centrifugal pump for conveying clean water and other liquids with physical properties similar to clean water. Use medium temperature below 80 °C, suitable for industrial and urban water supply and drainage, high-rise building pressurized water, garden sprinkler irrigation, fire booster, long-distance water delivery, heating bathroom and other cold and warm water circulation pressurization and equipment support.
2, vertical direct-coupled hot water circulation pump, suitable for energy, metallurgical wood processing, chemical textile papermaking and hotel bathroom hotel and other boiler hot water pressurized circulation and urban heating system circulation pump, the use temperature is below 120 °C.
3. Corrosion-resistant centrifugal pump for conveying liquids containing no solid particles and having corrosive viscosity similar to water. It is suitable for petrochemical, metallurgical power, paper, food, pharmaceutical and other departments, and the use temperature does not exceed 120 °C.
Five, direct joint vertical centrifugal pump product specifications:
1.5KW direct-connected centrifugal pump model: BL-type direct-coupled centrifugal pump Yuhuan centrifugal pump, IZ (BL) type pump is a single-stage direct-connected centrifugal pump for conveying clean water or other liquids with physical and chemical properties similar to clean water. Use, the temperature is not higher than 80 °C. The pump has the advantages of small shape, light weight, simple structure, low noise, convenient assembly and disassembly, and the like. The shaft seal adopts mechanical seal and good sealing performance. Applicable to factories, mines, urban water supply and drainage, high-rise building pressurized water supply and farmland irrigation.
Six, the working conditions of the direct vertical centrifugal pump:
Head (m): 3.2-125
Flow rate (m3/h): 7.5--1440
Power (HP): 0.75-335
Speed ​​(r/min): 1480/2900
Cavitation allowance (m): 2-7.2
Efficiency (%): 27-85
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