D, DG type horizontal boiler feed water centrifugal pump working principle, basic structure, etc.
I. D, DG type horizontal boiler feed water centrifugal pump overview:
D, DG horizontal boiler feed water centrifugal pump has the characteristics of high efficiency, wide performance range, safe and stable operation, low noise, long service life and convenient installation and maintenance. For transporting clean water or other liquids with physicochemical properties similar to water. It can also be used to transport hot water, oil, corrosive or abrasive-containing media by changing the material of the pump's flow-through components, the form of the seal, and adding a cooling system. The product implements JB/T1051-93 "Multi-stage centrifugal pump type and basic parameters" standard.
D, DG type horizontal boiler feed water centrifugal pump is generally driven by the motor, 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. Since the self-priming centrifugal pump is capable of transporting liquid, mainly by the action of centrifugal force, it is called a centrifugal pump.
D, DG horizontal boiler feed water centrifugal pump is the most widely used in chemical production, because it has a wide range of performance (including flow, pressure head and adaptability to the properties of the medium), small size, simple structure, easy operation Outstanding advantages such as uniform flow, low failure, long life, low purchase cost and low operating cost. Therefore, this chapter focuses on the centrifugal pump as a typical example of the application of fluid mechanics.
I. D, DG type horizontal boiler feed water centrifugal pump basic structure and working principle Discuss the basic structure and working principle of the centrifugal pump, it is necessary to firmly buckle the kinetic energy into static pressure energy theme to expand
(1) Basic structure of D, DG horizontal boiler feed water centrifugal pump
D, DG type horizontal boiler feed water centrifugal pump basic components are high-speed rotating impeller and 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.
(II) Working principle of D, DG horizontal boiler feed water centrifugal pump
When the D and DG horizontal boiler feed water centrifugal pump is started, the pump shaft drives the impeller to rotate together at high speed, forcing the pre-filling liquid to rotate between the blades. Under the action of inertial centrifugal force, the liquid is radially outward from the center of the impeller. movement. 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 D and DG horizontal boiler feed water centrifugal pump need to be emphasized that if the pumped liquid is not filled into the pump casing before the centrifugal pump starts, the impeller rotates due to the 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 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 the D, DG horizontal boiler feed water centrifugal pump
1. D, DG type horizontal boiler feed water centrifugal pump impeller The impeller is a key component of the D, DG type horizontal boiler feed water 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. D, DG type horizontal boiler feed water centrifugal pump guide wheel in order to reduce the energy loss caused by the impact of the liquid leaving the impeller directly into the pump casing, sometimes a fixed and bladed device between the impeller and the pump casing Guide wheel. 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 D, DG type horizontal boiler feed water 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.
Centrifugal concept centrifugation is actually the expression of the inertia of an object. For example, water droplets on an umbrella, when the umbrella rotates slowly, the water droplets will follow the umbrella, because the friction between the umbrella and the water droplets acts as a centripetal force to the water droplets. But if the umbrella rotates Speed ​​up, this friction is not enough to make the water droplets move in a circular motion, then the water droplets will move away from the outer edge of the umbrella. Just like pulling a stone with a rope to make a circular motion, if the speed is too fast, the rope will be broken, stone The block will fly out. This is called centrifugation. D, DG horizontal boiler feed water centrifugal pump is designed according to this principle. The high-speed rotating impeller blades drive the water to rotate, and the water is pumped out to achieve the purpose of transportation. There are many kinds of centrifugal pumps. It can be divided into civilian use. And industrial pumps, from the transport medium can be divided into clean water pumps, impurity pumps, corrosion-resistant pumps and so on. Basic structure of centrifugal pump D, DG type horizontal boiler feed water centrifugal pump basic structure is composed of six parts, namely: impeller, pump body, pump shaft, bearing, seal ring, stuffing box
1. The impeller is the core part of the centrifugal pump. It has high output speed and large output force. The blade on the impeller plays a major role. The impeller should pass the static balance test before assembly. The inner and outer surfaces of the impeller are required to be smooth to reduce the frictional loss of water flow.
2, the pump body is also called the pump casing, it is the main body of the pump. It acts as a support and is attached to the bracket on which the bearing is mounted.
3. The function of the pump shaft is to connect the coupling to the motor and transfer the torque of the motor to the impeller, so it is the main component that transmits mechanical energy.
4. The bearing is a member that supports the pump shaft on the pump shaft, and has two kinds of rolling bearings and sliding bearings. Rolling bearings use butter as a lubricant to refuel properly. Generally 2/3 ~ 3 / 4 of the volume will be too much heat, too little and there is noise and heat! The sliding bearing centrifugal pump structure uses a transparent oil as a lubricant and refuels to the oil level line. Too much oil will ooze along the pump shaft and float *, too few bearings will overheat and burn out and cause accidents! During the operation of the pump, the temperature of the bearing is at most 85 degrees and generally runs at about 60 degrees. If it is high, it is necessary to find the cause (whether there are impurities, whether the oil is black or not, whether it is water) and deal with it in time!
5, the seal ring is also known as the leak reduction ring. The gap between the impeller inlet and the pump casing is too large, so that the water in the high pressure zone of the pump flows to the low pressure zone through the gap, which affects the water output of the pump and reduces the efficiency! Too small a gap will cause friction between the impeller and the pump casing. In order to increase the backflow resistance and reduce the internal leakage, and delay the service life of the impeller and the pump casing, a sealing ring is arranged at the joint of the inner edge of the pump casing and the external aid of the impeller, and the gap of the sealing is preferably maintained between 0.25 and 1.10 mm.
6. The stuffing box is mainly composed of packing, water sealing ring, packing tube, packing gland and water sealing tube. The function of the stuffing box is mainly to close the air between the pump casing and the pump shaft, so that the water in the pump does not flow to the outside and the outside air does not enter the pump. Always keep the vacuum inside the pump! When the pump shaft and the packing friction generate heat, the water seals the water to the water seal ring to cool the packing! Keep the pump running properly. Therefore, it is especially important to check the stuffing box during the running inspection of the pump! The packing should be replaced after about 600 hours of operation.
Second, D, DG type horizontal boiler feed water centrifugal pump use:
D, DG horizontal boiler feed water centrifugal pump is suitable for industrial and urban water supply and drainage, high-rise building pressurized water supply, garden sprinkler irrigation, fire booster, long-distance water supply, heating, bathroom and other cold and warm water cycle pressurization and equipment support, etc. For small boiler feed water.
Third, D, DG horizontal boiler feed water centrifugal pump features:
1.D, DG horizontal boiler feed water centrifugal pump advanced hydraulic model, high efficiency, wide range of performance.
2.D, DG horizontal boiler feed water centrifugal pump runs smoothly and has low noise.
3. The shaft seal adopts soft packing seal or mechanical seal. The seal is safe and reliable, the structure is simple, and the maintenance is convenient and quick.
4. The shaft is a full-sealed structure, ensuring that it does not come into contact with the medium, does not rust, and has a long service life.
Fourth, D, DG horizontal boiler feed water centrifugal pump technical parameters:
D, DG horizontal boiler feed water centrifugal pump Flow: 18-108m3 / h;
Head: 19-240m;
Power: 2.2-110KW;
Speed: 1450-2950r/min;
Caliber: φ50-φ125;
Temperature range: ≤105 °C;
Working pressure: ≤3.0Mpa.
Five, D, DG type horizontal boiler feed water centrifugal pump model meaning:
For example: 50D-8×6
D-segment boiler feed water centrifugal pump
50-caliber (mm)
8-single lift (m)
6-level