渣浆泵的主要零部件
一、叶轮
    叶轮是离心泵中传递能量的主要部件。对叶轮的主要要求是:单级叶轮能给予液体较大的理论扬程，以便在达到高扬程时采用较少的级数，使机器结构紧凑，叶轮的效率较高，抗汽血性能好以及性能曲线形状满足工艺生产要求等。下面分析与这些要求有关的叶轮结构形式和几何参数等。
    离心泵的叶轮大多数为后弯叶片型叶轮，只有高速部分流泵和旋涡泵等采用径向叶片叶轮。常用的后弯叶轮的叶片数一般在6~12 片之间。比转速在60~250之间的泵，叶片常为6片,低比转速泵可取9片,高比转速泵可为4~5片。通常,增加叶片数可以改善液体流动情况,适当提高泵的扬程;但叶片数增加后又会使叶片摩擦损失变大，使流道通流面积变小，从而会降低效率，容易导致汽蚀。反之,若叶片数过少，每个叶片的负荷增加,对液体的导流作用减小，又会使泵的扬程下降。
    离心泵叶轮的叶片形状有两类:圆柱面状叶片和扭曲叶片。石油储运工程用离心泵的比转速小于90的，般都采用圆柱面状叶片它垂直于叶轮前后盖板制造较容易。对比转速大于90的泵，常采用扭曲叶片。
    后弯叶片型叶轮叶片的出口叶片角P2A和进口叶片角B人对泵的性能有重要的影响。叶片出口叶片角B:u一般是在15-~40°之间石消储运工程用为泵为20-30。比转述较低的泵，选择较大的B2.可以增加扬程.减小直径D2,，从而减少圆盘摩擦损失,提高泵的效率;但增大Bax时，在相同流量下增加叶轮出口速度C:压液室的水力损失增加尤其是非设计流量下冲击规时规，在以使H-Q性能曲线出现驼峰。此外必校时，叶道中液流相对速度w2更小，使流动扩散损失越严重，因此，为获得平坦下降的性能曲线，不宜选过大的总间，

叶轮进口角 就是在叶片入口处，叶片工作面的切线(严路地说应该是在流面上叶片骨线的切线)与圆周切线间的夹角，通常是接设计流量下波流进叶道时绝对速度c1的方向角来定的。当流量偏离设计流量时，进口液流角p与叶片进口角队间的差记。为了提高泵的抗汽蚀性能，一般采用正冲角Ap(3°~10)。因为正冲角能增大叶片进口角，减小叶片的弯曲，从而增加叶片进口过流面积，降低叶片进口处的C1和w1;另一方面,采用正冲角时，在非设计流量下,液体在叶片非工作面形成旋涡，由于这里是低压,旋涡不易向高压区扩散，因而旋涡是稳定的,对汽蚀影响较小。综上所述,叶片进口角应在18°~-25°范围内。
    就离心泵叶轮的结构形式来看,可分为闭式.半开式和开式三种,如图1- 58所示。
    闭式叶轮具有盖板和轮盘，流道是封闲的，如图1-58(a)所示。这种时轮水力效率较高，适用于高扬程，输送洁净的液体，半开式叶轮只有轮盘。流道是半开启的:如图，运用于输送含固体颗粒和杂质的液体，它的叶片和轮盘可由整块锻件铣制成一个整体。强度较高，且制造较容易;开式叶轮既无盖板，又无轮盘，流道完全敞开，如图1 58(c)所示，常用来输送浆状或糊状液体。离心泵叶轮还分为单吸式和双吸式两种,单吸式构造简单，液体从叶轮一侧被吸入;双吸式叶轮,如图1- 58(d)所示,构造比较复杂，液体从叶轮两侧吸入。显然，双吸式具有较大的吸液能力,抗汽蚀性能较好，而且基本上可以消除轴向力,适用于流量较大的情况。
    另外，闭式叶轮和半开式叶轮后盖板与泵壳之间的缝隙内，液体的压力较入口侧高，这便产生了指向叶轮吸入口方向的轴向推力，使叶轮向吸入口窜动，引起叶轮与泵壳接胜处磨损。严重时造成渣浆泵振动。为此，可在后盖板上钻几个小孔，称为平衡孔，让一部分高压液体漏到低压区，降低叶轮两侧的压力差。这种方法虽然他便，但由于液体通过平衡孔短路回流，增加了内泄漏量，因而降低了泵的效率。

Main parts of slurry pump

I. impeller

Impeller is the main part of centrifugal pump to transfer energy. The main requirements for impellers are: the single-stage impellers can give a larger theoretical lift of liquid, so as to adopt less stages when reaching the high lift, so as to make the machine structure compact, the efficiency of impellers is high, the resistance to steam blood is good, and the performance curve shape can meet the production requirements. The impeller structure and geometric parameters related to these requirements are analyzed below.

Most of the impellers of centrifugal pumps are backward curved impeller, only high-speed partial flow pump and vortex pump adopt radial impeller. The commonly used number of blades of backward curved impeller is generally between 6 and 12. For pumps with specific speed between 60-250, the blades are usually 6 pieces, 9 pieces for low specific speed pumps and 4-5 pieces for high specific speed pumps. Generally, increasing the number of blades can improve the flow of liquid and increase the head of pump properly; however, increasing the number of blades will increase the friction loss of blades and reduce the flow passage area, which will reduce the efficiency and easily lead to cavitation. On the contrary, if the number of blades is too small, the load of each blade will increase, the diversion effect on the liquid will decrease, and the head of the pump will decrease.

There are two types of blade shapes of centrifugal pump impeller: cylindrical surface blade and twisted blade. When the specific speed of centrifugal pump used in petroleum storage and transportation engineering is less than 90, it is easy to use cylindrical blade which is perpendicular to the front and back cover plate of impeller. Compared with the pump whose speed is more than 90, the twisted blade is often used.

The outlet blade angle P2a and the inlet blade angle B of the backward curved blade type impeller blade have an important influence on the performance of the pump. The blade angle B: u at the blade outlet is generally 20-30 for the stone elimination storage and transportation project between 15-40 °. Compared with the pump with lower rotation, the larger B2 can increase the lift and reduce the diameter D2, so as to reduce the disc friction loss and improve the efficiency of the pump; but when Bax is increased, the impeller outlet speed C is increased under the same flow rate; the hydraulic loss of the pressure chamber is increased, especially the impact gauge under the non design flow rate, so as to make the H-Q performance curve appear hump. In addition, when it has to be calibrated, the relative velocity W2 of the liquid flow in the blade channel is smaller, which makes the flow diffusion loss more serious. Therefore, in order to obtain a flat decline performance curve, it is not suitable to select a large total chamber,

The impeller inlet angle is the angle between the tangent line of the blade working surface (strictly speaking, it should be the tangent line of the blade bone line on the flow surface) and the tangent line of the circumference, which is usually determined by the direction angle of the absolute velocity C1 when the wave flows into the blade channel under the design flow. When the flow deviates from the design flow, the difference between the inlet flow angle P and the blade inlet angle is recorded. In order to improve the anti cavitation performance of the pump, the positive impact angle AP (3 ° ~ 10) is generally used. Because the positive impact angle can increase the inlet angle of the blade and reduce the bending of the blade, thus increasing the flow area at the inlet of the blade and reducing the C1 and W1 at the inlet of the blade; on the other hand, when the positive impact angle is adopted, under the non design flow rate, the liquid forms a vortex on the non working surface of the blade. Because it is low pressure, the vortex is not easy to spread to the high pressure area, so the vortex is stable and has little impact on cavitation. To sum up, the blade inlet angle should be in the range of 18 ° - 25 °.

According to the structure of centrifugal pump impeller, it can be divided into closed, semi open and open, as shown in figure 1-58.

The closed impeller has a cover plate and a disc, and the flow channel is sealed, as shown in Fig. 1-58 (a). This kind of impeller has high hydraulic efficiency, which is suitable for high lift and conveying clean liquid. The semi open impeller has only a disc. The runner is half open: as shown in the figure, it is used to transport liquid containing solid particles and impurities. Its blades and wheels can be milled into a whole by a whole forging. It has high strength and is easy to manufacture; the open impeller has neither cover plate nor disc, and the flow channel is completely open, as shown in Figure 158 (c), which is commonly used to transport slurry or paste liquid. The impeller of centrifugal pump is also divided into single suction and double suction. The single suction structure is simple, and the liquid is drawn in from one side of the impeller; the double suction impeller, as shown in figure 1-58 (d), has complex structure, and the liquid is drawn in from both sides of the impeller. Obviously, the double suction type has a larger suction capacity, better anti cavitation performance, and can basically eliminate the axial force, which is suitable for the case of large flow.

In addition, in the gap between the rear cover plate of closed impeller and semi open impeller and the pump housing, the liquid pressure is higher than that of the inlet side, which produces the axial thrust pointing to the suction port of the impeller, makes the impeller move towards the suction port, and causes the abrasion at the junction of the impeller and the pump housing. In serious cases, it will cause vibration of slurry pump. Therefore, several small holes can be drilled on the back cover plate, called balance holes, to let part of the high-pressure liquid leak into the low-pressure area, reducing the pressure difference on both sides of the impeller. Although this method is convenient, because the liquid is short circuited through the balance hole, the internal leakage is increased, so the efficiency of the pump is reduced.