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多級(jí)串聯(lián)渣漿泵的葉輪平衡怎么
(1)對(duì)稱布置葉輪。
如圖1-69所示,對(duì)稱布置葉輪適用于級(jí)數(shù)為偶數(shù),若級(jí)數(shù)為奇數(shù)，則第一級(jí)可采用雙吸葉輪。由于多級(jí)泵各級(jí)漏損不同，各級(jí)輪轂大小不同，故葉輪對(duì)稱布置不能完全平衡軸向力，仍有一部分軸向力需由軸承來(lái)承受。這種平衡方法的優(yōu)點(diǎn)是不增大容積損失，缺點(diǎn)是泵體結(jié)構(gòu)較復(fù)雜。它多應(yīng)用于單吸兩級(jí)懸臂泵和蝸殼式多級(jí)泵上。
(2)采用平衡鼓。圖1- 70是平衡鼓的示意圖，裝在末級(jí)葉輪之后。平衡鼓后面為平衡室,通過(guò)平衡管與第I級(jí)葉輪的吸入室相通。因此,平衡鼓前面的壓力接近于末級(jí)葉輪的排出壓力，而平衡鼓后面的壓力等于吸入室中的壓力與平衡管中阻力之和。這樣就產(chǎn)生了平衡鼓前后的壓力差，以平衡泵的軸向力。平衡鼓外緣與泵體上平衡套間的間隙很小，為0.2~
0.3mm。由于泵的工況經(jīng)常變化，平衡鼓的平衡狀態(tài)要受到影響，仍需止推軸承承受剩余的軸向力。
(3)采用自動(dòng)平衡盤(pán)。自動(dòng)平衡盤(pán)在離心泵中習(xí)慣簡(jiǎn)稱為平衡盤(pán).其優(yōu)點(diǎn)是在不同工況下可自動(dòng)平衡全部軸向力，故廣泛用于多級(jí)分段式離心泵中，其結(jié)構(gòu)如圖1-71所示。它結(jié)構(gòu)上的特點(diǎn)是除了輪轂(或軸套)與泵體之間有一個(gè)徑向間隙b外，平衡盤(pán)端面與泵體間還有一個(gè)軸向間隙bo，平衡盤(pán)后面是與泵吸入口相通的平衡室。徑向間蹤b前的液體壓力是末級(jí)葉輪普面的壓力p，液體流過(guò)徑向間院b后壓力降到p,徑向間院的壓力降為:
△p1=p-p
液體流過(guò)軸向間家b0后壓力再下降到p0，軸向間隙兩端的壓力降為，
Ap2=p- Pu
這樣,在平衡盤(pán)上作用一個(gè)平衡力，其方向與軸向力相反。
自動(dòng)平衡低工作原理如下:當(dāng)軸向?yàn)榇笥谄胶饬r(shí):轉(zhuǎn)子向左移動(dòng)、軸向間隙b0減小，流過(guò)該間隙的阻力系數(shù)增大。當(dāng)然整個(gè)平衡裝置的總阻力系數(shù)也隨之而增大，但△p并不改變，可見(jiàn)泄漏量q減少.結(jié)果是△p1，減小而△p2增大,從而增大了平衡力。轉(zhuǎn)子不斷向左移動(dòng)，平衡力不斷增加,到某一位置，平衡力和軸向力相等而達(dá)到平衡。
同理，當(dāng)軸向力小于平衡力時(shí),轉(zhuǎn)子將向右移動(dòng),b0增大, △p2減小，平衡力變小。當(dāng)轉(zhuǎn)子移動(dòng)到一定位置時(shí)，平衡力也減小到與軸向力相等而重新達(dá)到平衡。所以裝有平衡盤(pán)裝置的離心泵一般不配止推軸承。
(4)采用平衡盤(pán)與平衡鼓組合的平衡裝置。由于平衡鼓可以平衡50% -80%的軸向力，這祥就減輕了渣漿泵平衡盤(pán)的負(fù)荷，從而可采用較大的軸向間隙，避免因轉(zhuǎn)子審動(dòng)而引起平衡盤(pán)與泵休的摩擦。實(shí)踐證明，這種平衡裝置用于大容量，高參數(shù)的分段式多級(jí)須中效果良好，
How to balance the impeller of multistage series slurry pump
(1) Arrange impellers symmetrically.
As shown in figure 1-69, impeller with symmetrical arrangement is suitable for even number of stages. If the stage is odd, double suction impeller can be used for the first stage. Due to the different leakage and hub sizes of different stages of multistage pump, the impeller symmetrical arrangement can not completely balance the axial force, there is still a part of the axial force to be borne by the bearing. The advantage of this balance method is not to increase the volume loss, but the disadvantage is that the structure of the pump body is complex. It is mainly used in single suction two-stage Cantilever Pump and volute type multistage pump.
(2) Use balance drum. Figure 1-70 is a schematic diagram of the balancing drum, installed behind the last stage impeller. The balance chamber is behind the balance drum, which is connected with the suction chamber of the stage I impeller through the balance pipe. Therefore, the pressure in front of the balance drum is close to the discharge pressure of the last stage impeller, while the pressure behind the balance drum is equal to the sum of the pressure in the suction chamber and the resistance in the balance pipe. This creates a pressure difference before and after the balance drum to balance the axial force of the pump. The gap between the outer edge of the balance drum and the balance sleeve on the pump body is very small, which is 0.2~
0.3mm. Due to the frequent changes of pump working conditions, the balance state of balance drum will be affected, and the thrust bearing is still required to bear the remaining axial force.
(3) Automatic balancing plate is adopted. In centrifugal pumps, the automatic balancing disk is commonly referred to as the balancing disk. Its advantage is that it can automatically balance all axial forces under different working conditions, so it is widely used in multistage segmented centrifugal pumps. Its structure is shown in Figure 1-71. Its structure is characterized by a radial clearance B between the hub (or shaft sleeve) and the pump body, and an axial clearance Bo between the end face of the balance plate and the pump body. Behind the balance plate is the balance chamber which is connected with the suction port of the pump. The liquid pressure before the radial trace B is the pressure P on the general surface of the last stage impeller. After the liquid flows through the radial chamber B, the pressure drops to P. the pressure drop of the radial chamber is as follows:
Delta p1=p-p
After the liquid flows through the axial gap, the pressure drops to P0, and the pressure at both ends of the axial gap drops to,
Ap2=p- Pu
In this way, a balance force is applied on the balance plate, and its direction is opposite to the axial force.
The principle of auto balance is as follows: when the axial direction is greater than the balance force, the rotor moves to the left, the axial clearance B0 decreases, and the resistance coefficient through the clearance increases. Of course, the total resistance coefficient of the whole balancing device also increases, but △ P does not change, so the leakage Q decreases. As a result, △ P1 decreases, while △ P2 increases, thus increasing the balancing force. The rotor moves to the left continuously, and the balance force increases continuously. When it reaches a certain position, the balance force and the axial force are equal and reach balance.
Similarly, when the axial force is less than the balance force, the rotor will move to the right, B0 increases, △ P2 decreases, and the balance force decreases. When the rotor moves to a certain position, the balance force is reduced to the same as the axial force, and the balance is achieved again. Therefore, the centrifugal pump equipped with balance plate device is generally not equipped with thrust bearing.
(4) The balance device is composed of balance plate and balance drum. Since the balance drum can balance 50% - 80% of the axial force, it can reduce the load of the balance plate, so a large axial clearance can be used to avoid the friction between the balance plate and the pump due to the rotor movement. It has been proved that this kind of balancing device has a good effect in large capacity and high parameter segmented multistage whiskers,
