There are many varieties of centrifugal pumps. Although the structures of various types of pumps are different, the main components are basically the same.
The main components of the centrifugal pump include: impeller, pump shaft, pump casing, pump seat, packing box (shaft seal device), leakage reduction ring, bearing seat, etc.
Impeller
Impeller is the work of centrifugal pump parts, rely on its high-speed rotation of the liquid to do work and realize the delivery of liquid, is an important part of the centrifugal pump.
The impeller is generally composed of three parts: wheel, blade and cover. The cover plate of the impeller is divided into the front cover plate and the rear cover plate. The cover plate on the side of the impeller mouth is called the front cover plate, and the cover plate on the other side is called the rear cover plate.
When the centrifugal pump is started, the pump shaft drives the impeller to make high-speed rotation together, forcing the pre-filled 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 periphery.
The liquid obtains energy during the movement of the impeller, the static pressure energy increases, and the flow rate increases. When the liquid leaves the impeller and enters the pump shell, it is decelerated due to the gradual expansion of the flow passage in the shell, and part of the kinetic energy is converted into static pressure energy, and finally flows into the discharge pipeline along the tangential direction.
According to the structure, the impeller can be divided into the following three types.
(1) closed impeller impeller on both sides of the cover, cover between 4 to 6 blades, closed impeller with high efficiency, wide application, suitable for conveying clean liquid without solid particles and fibers.
(2) The open impeller has no cover on both sides of the blade, which is suitable for conveying liquids containing a large amount of suspended solids, with low efficiency and low liquid pressure.
(3) semi-open impeller impeller only after the cover, it is suitable for conveying easy precipitation or suspended solids containing liquid, its efficiency between open and closed impeller.
Pump shaft
The main function of the pump shaft of the centrifugal pump is to transmit power, and the supporting impeller is kept in the working position for normal operation. One end of it is connected to the motor shaft through a coupling, and the other end supports the impeller for rotation. The shaft is equipped with bearings, axial seals and other parts.
Common materials for the pump shaft are carbon steel and stainless steel.
The impeller and the shaft are connected by keys. Since this connection method can only transmit torque and cannot fix the axial position of the impeller, the shaft sleeve and lock nut are also used in the water pump to fix the axial position of the impeller.
After the impeller is axially positioned with the lock nut and the shaft sleeve, in order to prevent the lock nut from returning, the water pump should be prevented from reversing, especially for the initial installation of the water pump or the water pump after disassembly and maintenance, the steering inspection should be carried out according to the regulations to ensure that the steering is consistent with the regulations.
Shaft sleeve
The role of the shaft sleeve is to protect the pump shaft, so that the friction between the packing and the pump shaft is transformed into the friction between the packing and the shaft sleeve, so the shaft sleeve is a wear-prone part of the centrifugal pump.
The surface of the shaft sleeve can also be treated by carburizing, nitriding, chrome plating and spraying, and the surface roughness is generally required to reach Ra3.2 ~ Ra0.8μm. It can reduce the friction coefficient and increase the service life.
Bearing
The bearings function to support the weight and bearing force of the rotor. Rolling bearings are mostly used in centrifugal pumps. The outer ring and bearing seat hole are made of base shaft system, and the inner ring and rotating shaft are made of base hole system. The matching category standard has recommend values and can be selected according to specific conditions. Bearings are generally lubricated with grease and lubricating oil.
stuffing box
When the pump shaft passes out of the pump casing, there is a gap between the shaft and the casing.
In the single suction centrifugal pump, if the part does not use the shaft seal device, the high pressure water in the pump casing will leak out in large quantities.
Packing box is commonly used as a shaft seal device. The packing box is composed of 5 parts: shaft envelope, packing, water seal pipe, water seal ring and packing gland.
volute
Volute refers to the impeller outlet to the next impeller inlet or to the pump outlet pipe cross-sectional area gradually increased between the spiral flow. The flow channel is gradually expanded, and the outlet is a diffusion tube. After the liquid flows out of the impeller, its flow rate can be gently reduced, so that a large part of the kinetic energy is converted into static pressure energy.
The advantages of the volute are easy to manufacture, wide area, and small change in the efficiency of the pump after turning the impeller.
The disadvantage is that the volute shape is asymmetrical, and the pressure acting on the rotor radial direction is uneven when using a single volute, which is easy to bend the shaft. Therefore, in the multistage pump, only the first and last sections use the volute while the guide wheel device is used in the middle section.
The material of the volute is generally cast iron. The volute of the anti-corrosion pump is made of stainless steel or other anti-corrosion materials, such as plastic glass steel. Multi-stage pump due to the pressure is larger, the material strength requirements are higher, the volute is generally made of cast steel.
Guide wheel
The guide wheel is a fixed disc with forward guide vanes wrapped around the outer edge of the impeller on the front side. These guide vanes form a divergent flow channel, and the back side has reverse guide vanes that lead the liquid to the next impeller population. After the liquid is thrown out from the impeller, it enters the guide wheel smoothly and continues to flow outward along the positive guide vane, the speed gradually decreases, and most of the kinetic energy is converted into static pressure energy.
The radial unilateral clearance between the impeller and the guide vane is about 1mm. If the gap is too large, the efficiency will be reduced; if the gap is too small, it will cause vibration and noise. Compared with the volute, the pump casing of the segmented multi-stage centrifugal pump using the guide wheel is easy to manufacture, and the efficiency of energy transfer is also higher. But the installation and maintenance is more difficult than the volute.
Seal ring
In order to reduce internal leakage and protect the pump casing, a removable sealing ring is installed on the casing corresponding to the inlet of the impeller.
The radial clearance between the inner hole of the sealing ring and the outer circle of the impeller is generally between 0.1 and 0.2mm.
After the seal ring is worn, the radial gap increases, the pump discharge volume decreases, and the efficiency decreases. When the seal gap exceeds the specified value, it should be replaced in time.
There are three types of seal ring structure.
Flat ring type, simple structure, convenient manufacture, but poor sealing effect.
Right-angle type sealing ring, liquid leakage through a 90 ° channel, the sealing effect is better than the flat ring type, widely used.
Labyrinth seal ring, the sealing effect is good, but the structure is complex, difficult to manufacture, the general centrifugal pump is rarely used.