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It Turns Out That You Are Like This Centrifugal Pump

Dec 21, 2019

There are many types of centrifugal pumps. Although the structures of various types of pumps are different, the main parts are basically the same.

The main components of a centrifugal pump include: impeller, pump shaft, pump casing, pump base, stuffing box (shaft seal device), leakage reducing ring, bearing base, etc.

impeller

The impeller is a work part of a centrifugal pump. It relies on its high-speed rotation to perform work on the liquid to achieve liquid transfer. It is an important part of a centrifugal pump.

The impeller is generally composed of three parts: the wheel, the blade and the cover plate. The cover of the impeller is divided into a front cover and a rear cover. The cover on the impeller mouth side is called the front cover, and the cover on the other side is called the rear cover.

When the centrifugal pump is started, the pump shaft drives the impeller to rotate at high speed together, forcing the liquid filled between the blades to rotate in advance. Under the action of inertia centrifugal force, the liquid moves radially from the center of the impeller to the outer periphery.

During the movement of the liquid through the impeller, energy is obtained, the static pressure energy is increased, and the flow velocity is increased. When the liquid leaves the impeller and enters the pump casing, the flow path in the casing gradually expands and decelerates. Part of the kinetic energy is converted into static pressure energy, and finally flows into the discharge pipe in a tangential direction.

According to the structure, the impeller can be divided into the following three types

(1) The closed impeller has cover plates on both sides of the impeller. There are 4-6 blades between the cover plates. The closed impeller has higher efficiency and is the most widely used. It is suitable for conveying clean liquids without solid particles and fibers.

(2) The open impeller has no cover plates on both sides of the blade, which is suitable for conveying liquid containing a large amount of suspended matter, the efficiency is low, and the pressure of the liquid is not high.

(3) Semi-open impeller This impeller has only a rear cover. It is suitable for conveying liquids that are easy to settle or contain suspended solids. Its efficiency is between open and closed impellers.

Pump shaft

The main role of the pump shaft of the centrifugal pump is to transmit power, and the supporting impeller is maintained in the working position for normal operation. One end is connected to the motor shaft through a coupling, and the other end supports the impeller for rotational movement. The shaft is equipped with components such as bearings and axial seals.

Common materials for pump shafts are carbon steel and stainless steel.

The impeller and the shaft are connected by a key. Because this connection method can only transmit torque and cannot fix the axial position of the impeller, a shaft sleeve and a lock nut are also used to fix the axial position of the impeller in the pump.

After the impeller uses the lock nut and the shaft sleeve to be positioned axially, in order to prevent the lock nut from being withdrawn, the water pump must be prevented from reversing. Especially, the newly installed water pump or the water pump after disassembly and repair must be steered in accordance with regulations to ensure that the steering is in accordance with the regulations. Consistent.

Sleeve

The function of the shaft sleeve is to protect the pump shaft, so that the friction between the packing and the pump shaft is converted into the friction between the packing and the shaft sleeve. Therefore, the shaft sleeve is an easy-wearing part of the centrifugal pump.

The surface of the shaft sleeve can also be treated by carburizing, nitriding, chrome plating, spraying and other treatment methods. The surface roughness is generally required to reach Ra3.2μm-Ra0.8μm. Can reduce friction coefficient and improve service life.

Bearing

Bearings support the weight and bearing force of the rotor. Centrifugal pumps often use rolling bearings. The outer ring and bearing seat holes are made of the basic shaft system, and the inner ring and the shaft are made of the base hole system. There are recommended values in accordance with the national standards of the category, which can be selected according to specific conditions. Bearings are generally lubricated with grease and 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 there is no shaft sealing device in this part, the high-pressure water in the pump casing will leak to the outside.

Stuffing box is a commonly used shaft sealing device. The stuffing box is composed of 5 parts: shaft sleeve, packing, water-sealing tube, water-sealing ring and packing gland.

Volute

A volute refers to a spiral flow channel with a gradually increasing cross-sectional area from the impeller outlet to the next impeller inlet or to the pump's outlet tube. Its flow channel is gradually enlarged, and the outlet is a diffused tube. After the liquid flows out of the impeller, its flow rate can be gradually reduced, so that a large part of the kinetic energy is converted into static pressure energy.

The volute has the advantages of convenient manufacturing, wide high-efficiency zone, and small change in the efficiency of the pump after turning the impeller.

The disadvantage is that the shape of the volute is asymmetrical. When a single volute is used, the pressure acting on the radial direction of the rotor is uneven, and it is easy to bend the shaft. Device.

The material of the volute is generally cast iron. The volute of the anticorrosive pump is made of stainless steel or other anticorrosive materials, such as plastic fiberglass. Multi-stage pumps require high material strength due to the high pressure, and their volutes are generally made of cast steel.

Guide wheel

The guide wheel is a fixed disc with front guide vanes wrapped around the outer edge of the impeller on the front. These guide vanes form a diffused flow channel, and on the back there are reverse guide vanes that guide the liquid to the next stage impeller population. . After the liquid is thrown from the impeller, it gently enters the guide wheel and continues to flow outward along the leading vane. The speed gradually decreases, and most of the kinetic energy is converted into static pressure energy.

The radial single-sided gap between the impeller and the guide vane is about lmm. If the gap is too large, the efficiency will decrease; if the gap is too small, it will cause vibration and noise. Compared with the volute, the pump housing of the segmented multistage centrifugal pump using the guide wheel is easier to manufacture and the efficiency of energy conversion is higher. However, installation and maintenance are more difficult than volutes.

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 impeller inlet.

The radial clearance between the inner ring of the seal ring and the outer circle of the impeller is generally between 0.1-0.2mm.

After the seal ring is worn, the radial clearance increases, the pump discharge volume decreases, and the efficiency decreases. When the seal clearance exceeds the specified value, it should be replaced in time.

There are three types of seal ring structure.

Flat ring type, simple structure, easy manufacture, but poor sealing effect.

The right-angle type seal ring passes a 90 ° channel when liquid leaks, and the sealing effect is better than that of the flat ring type, which is widely used.

Labyrinth seal ring, good sealing effect, but complex structure, difficult to manufacture, rarely used in general centrifugal pumps