Centrifugal pump is composed of many parts, the following single-stage single-suction centrifugal pump , for example, to discuss the role of major components, materials and composition.
First, the impeller
Impeller, also known as the work wheel or runner, its role is to pass the mechanical energy of the power machine is pumped by the liquid, the flow through the impeller to increase energy. In the choice of impeller material, in addition to taking into account the centrifugal force under the mechanical strength, but also consider the material wear and corrosion resistance. At present, the impeller is made of cast iron, cast steel and bronze.
According to the structure of the impeller is divided into single suction and double suction two. Single-suction impeller It absorbs water on one side, the front and rear covers of the impeller are asymmetrical. Single suction impeller for single suction centrifugal pump. Double-suction impeller suction water on both sides of it, symmetrical impeller cover, double suction centrifugal pump with double suction impeller, this pump flow, can automatically balance the axial force.
Impeller according to the situation of its cover is divided into closed, open and semi-open three forms. Impeller with two covers, called closed impeller. Between the cover is equipped with 6 to 12 backward curved impeller, only the blade without the cover of the impeller is called open impeller, half open and open less t wheel leaves, usually only 2 to 5, Both impellers are less efficient than enclosed impellers and are suitable for draining or liquids containing large amounts of solid particles
Second, pump shaft
The role of the pump shaft is to support and drive the impeller rotation, the energy transfer to the impeller impeller. Requires the pump shaft end straight and has sufficient strength, stiffness, so as to avoid pump operation due to the bending of the shaft caused by the impeller swinging impeller and the pump shell phase damage and damage. The shaft is generally made of carbon steel or stainless steel. One end of the pump shaft with a flat key and fixed to the impeller impeller, the rotation, the impeller in the tightening state; in large and medium-sized pump, the axial position of the impeller and sleeve and tight nut to locate the nut. Coupling the other end of the shaft
Third, the pump casing
Centrifugal pump casing is contained and liquid-containing spiral volute, which consists of a pump cover and snail body. Pump cover for the pump suction chamber, its role is to minimize the loss of water in the water pipe leading to the impeller. According to the structure of the suction chamber can be divided into straight cone suction chamber, annular suction chamber and semi-spiral suction chamber. Snail body by the snail chamber and diffusion cone composition. The main function of the flash chamber is to collect the water flow thrown by the impeller and to maintain the water flow rate in the volute chamber constant with the increase of its cross section to reduce the head loss. After the water is discharged from the snail chamber, it flows into the pressure tube through the diffuser cone. Diffusion cone for Zan we reduce the speed of water flow, the kinetic energy of the water is converted to pressure energy.
The pump shell into and out of the flange at the flange each have a hole for measuring the pump inlet and outlet pressure of the vacuum gauge and pressure gauge. The top of the pump housing is provided with irrigation (or suction) holes to allow water to be filled or pumped out of the pump housing before the pump is started. The bottom of the pump casing is provided with a water drain hole to drain the water from the pump after stopping the pump to prevent freezing in winter. The bottom of the pump casing is provided with a bolt hole for fixing the foundation. In addition to fixing the pump bolt hole, the other screw holes in the pump operation is temporarily not in use, need to wear with a trace of the tattoo plug.
In the above parts, the impeller and the pump shaft are the rotating parts of the centrifugal pump, and the pump housing is the fixed part. There are three junctions between the two: the shaft seal assembly between the pump shaft and the pump housing, the leakage ring at the seams between the impeller and the pump housing inner wall, and the bearing at the rotational connection between the pump shaft and the pump housing.
Fourth, shaft seal device
If the pump shaft passes through the pump housing, there must be a gap between the rotating pump shaft and the fixed pump housing. If no high pressure water flows out from the impeller, a large amount of high pressure water will flow out through this gap. If the pressure at the clearance is vacuum , Air will enter the pump from there. Therefore, the shaft seal must be set.
There are many forms of shaft seal , the most commonly used vane pump is a packing seal. It consists of the backing ring, packing, water seal ring, packing gland and other components, commonly used filler is soaked in oil, asbestos impregnated graphite rope. In recent years, a variety of high temperature resistant, wear-resistant and corrosion-resistant new filler, such as carbon fiber, stainless steel fiber and synthetic resin fiber woven into the filler. In order to improve the sealing effect, the filler is generally made of rectangular section. Packing the degree of compaction, with a nut on the gland to adjust. If the pressure is too tight, the mechanical wear of the pump shaft and packing increases, the mechanical loss also increases. In severe cases, the water in the production pipe can drip out through the packing gap, which is appropriate. At present, some centrifugal pumps use rubber ring seals, mechanical seals and other types of shaft seal devices.
Fifth, leakage ring
There is a gap between the outer edge of the centrifugal pump impeller inlet and the inner edge of the pump cover. The gap is the interface of high and low pressure water, the gap is too large, high pressure water from the impeller through this gap leakage back to the impeller inlet side, reducing the pump out of water, reducing the efficiency of the pump bar. But the gap is too small, it will cause mechanical wear and tear. Therefore, in order to prolong the service life of the impeller and the pump cover, usually a metal mouth ring is mounted on the pump cover at the ten-day gap or on the pump cover and the impeller. The mouth ring is called a leak-reducing ring and the other of the leak-ring A role is used to bearing mill, in operation, this part of the friction is inevitable, when the friction occurred too long, simply replace the leak ring without causing the impeller and pump cover scrapped. Therefore, the leakage ring, also known as bearing ring, is a wearing parts.
Six, bearing
Bearings are housed in the housing to support the weight of the rotating part and to withstand axial and radial loads during operation of the rotating part and to reduce the frictional force of the rotating shaft. Bearing is divided into two types of rolling bearings and plain bearings. Single-stage single-suction centrifugal pumps usually single-row radial ball bearings, which consists of outer ring, inner ring, rolling body and cage composition. The inner ring is mounted on the journal and rotates with the shaft. Raceway on the outer ring, when the relative rotation of the inner and outer rings, rolling rolling along the raceway, the cage is the role of the rolling body evenly separated. Bearings with thin oil or dry oil lubrication.
Seven, coupling
The coupling connects the pump to the shaft of the power machine to rotate together and transmit the torque. Coupling, also known as "back" wheel, both rigid and flexible. Rigid coupling is actually the connection of two circular flanges, which for the pump shaft and power shaft do not mind, there is no room for adjustment in the connection and operation. Therefore, the installation of high precision, more for vertical units.
Cylindrical pin couplings consist of coupling halves, cylindrical pins, retaining rings, and elastic rings made of rubber or leather, allowing a small deformation during operation and compensating for small displacements between the two axes.
The claw-shaped flexible coupling consists of two claw couplings and a star-shaped elastic block made of rubber, which has the advantages of simple structure, convenient installation and small transmission torque, and is suitable for small horizontal units
Eight. Axial force balance device
Single-stage single-suction centrifugal pump operation, due to the area of ​​the front and rear cover of the impeller is not the same pump work, the pressure on both sides of the call for the call is not equal, in the impeller to produce a population-oriented axial force △ P axis In addition to moving the impeller towards the inlet, it also causes vibration, wear and increased bearing loads. Therefore, we must try to balance the axial force. For single-stage single-suction centrifugal pumps, it is generally taken to open the balance hole near the hub of the impeller rear cover and to install a leakage ring on the rear cover. After the high pressure to reduce the leakage ring, the pressure drop, and through the balance hole back to the impeller inlet, so that the impeller pressure close to the front and rear covers, thus eliminating most of the axial force, a small part of the axial force is not eliminated Bear by the bearing. This method has the advantage of simple structure, the disadvantage is the pump efficiency has decreased. In addition, the impeller can also be added at the back cover plate method to balance the role of the impeller on both sides of the pressure tends to balance. For multi-stage pump generally used in the final impeller balance wheel or balance drum, or take symmetrical arrangement of the impeller to eliminate axial force.
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