泵归属于动力机械的一种，动力机械就是指以液体为作业物质和动能媒介的工业设备。

　　动力机械依据能量传递的方位不一样，可分成传动装置(水轮发电机组、汽轮发电机)和工作机(泵、离心风机、制冷压缩机)。泵归属于工作机，即消耗能量的机械设备。

　　泵的归类：

　　1)原理可分成又分为叶轮式、容积式和其他方式。

　　①叶子式泵，借助旋转的叶轮对液体的驱动力功效，把动能持续地传达给液体，使液体的机械能(为主导)和压力能**，接着根据压出来室将动能转换为压力能，又可分成离心水泵、混流泵、部位流泵和漩涡泵等。

　　②容积式泵，借助宽容液体的密封性工作空间容量的周期性变化，把动能周期性地传送给液体，使液体的负担**至将液体强制排出来，依据工作中元器件的运动形式又可分成往复泵和旋转泵。

　　③其他类型的泵，以别的方式传递能量。如射流泵依赖快速喷涌的工作中液体将需运输的液体吸进泵后搅拌，开展动量矩互换以传递能量;水锤泵运用制动系统时流动性中的一部分水被升至一定相对高度传递能量;磁力驱动泵是使插电的合金在磁场力功效下形成流动性而达到运输。此外，泵也可按运输液体的特性、推动方式、构造、应用领域等开展归类。

　　2)按工作中叶轮数量来归类：

　　①单级泵：即在泵轴上只有一个叶轮。

　　②多级离心泵：即在泵轴上面有2个或两个以上的叶轮，这时候泵的总扬程为n个叶轮造成的扬程之和。

　　3)按压力来归类：

　　①低压泵：工作压力小于100米水柱;

　　②中压泵：工作压力在100～650米水柱中间;

　　③高压水泵：工作压力高过650米水柱。

　　4)按叶轮渗水方法来归类：

　　①一侧渗水式泵：又叫单吸泵，即叶轮上只有一个进水管;

　　②两侧渗水式泵：又叫双吸泵，即叶轮两边都是有一个进水管。它流量比单吸式泵大一倍，能够类似看作是二个单吸泵叶轮背对背地放到了一起。

　　5)按泵壳融合缝方式来种类：

　　①水准中开启式泵：即在根据枢轴线的水准表面开有融合缝。

　　②竖直结合面泵：即结合面与重心线相竖直。

　　6)按泵轴部位来种类：

　　①卧式泵：泵轴坐落于水平位置。

　　②立式泵：泵轴坐落于竖直部位。

　　7)按叶轮出去的水引到压出来室的形式归类：

　　①涡壳泵：水从叶轮出去后，直接进入具备螺旋形态的泵壳。

　　②扩压器泵：水从叶轮出去后，进到它外边设定的扩压器，以后进下一级或注入出入口管。(常用于多级离心泵和混流泵)

　　泵的实际操作基本原理、结构：

　　由多个弯折的叶子构成的叶轮放置具备涡壳安全通道的泵壳以内。叶轮拧紧于泵轴上，泵轴与电机相接，可由电机推动转动。吸进口坐落于泵壳中间与吸进管道相接，请在吸进管底端装一止回阀。泵壳的侧面为排出入口，与流出管道相接，配有调节阀门。

　　离心水泵往往能运输液体，主要是借助高速运转叶轮所造成的向心力，因而称之为离心水泵。

　　离心水泵的工作过程：

　　开泵前，先往泵内注满要传送的液体。

　　开泵后，泵轴推动叶轮一起高速运转造成向心力。液体在这里功效下，从叶轮核心被抛到叶轮外围，工作压力提高，并且以很高的速率注入泵壳。在泵壳中因为过流道的不断扩大，液体的流动速度缓减，使绝大多数机械能转换为压力能。*终液体以较高的负压强从排出入口注入排出来管路。泵里的液体被抛出去后，叶轮的核心形成了真空泵，在液位气体压强(大气压力)与泵内压力(负压力)的压力差的作用下，液体便经吸进管道进到泵内，弥补了被清除液体的部位。

　　离心水泵启动时，假如泵壳内存有气体，因为空气的密度远小于液体的相对密度，叶轮转动所造成的向心力不大，叶轮核心处发生的低电压不能导致吸上液体所必须的真空值，那样，离心水泵就没法作业。以便使起动前泵内充斥着液体，在吸进管路底端装一止回阀。除此之外，在离心水泵的出入口管道上也装一调节阀门，用以开停机和调节流量。

　　基本上构件和结构：

　　1)叶轮：将电动机的机械动能发送给液体,使液体的机械能逐步提高。

　　2)泵壳：汇聚液体，作导出来液体的安全通道;

　　使液体的动能产生变换，一部分能量转化为压力能。

　　3)水泵密封设备：为了避免髙压液体从泵壳内沿轴的四周而漏出来，或是外部气体漏入泵壳内。

　　旋转密封和机封的较为：

　　压力和密封性：

　　旋转密封水泵：较大压力4-5bar.(规范规格型号)

　　机封水泵：

　　水泵较大压力<10bar时：不平衡机封(规范)

　　水泵较大压力>10bar时：均衡机封(额定电流与封口的构造有关系)

　　总流量、扬程、总负压、摩阻、水泵特性曲线图、运行图、并联运行、系统软件摩擦阻力曲线图、几台水泵并接的压力线条、压力、水泵承受压力、压力<较大压力(PN)、

　　类似基本定律、Q1/Q2=N1/N2，H1/H2=(N1/N2)2，P1/P2=(N1/N2)3。

　　留意：假如叶轮孔径更改或水泵转速比更改，NPSH将产生变化。

　　举例说明：

　　总流量200l/s,扬程37.5m，采用水泵型号规格ASP200B，叶轮孔径360mm，转速比1450RPM，高效率87%工作状况点电机功率84.5kW。

　　假如转速比变成1000RPM，依据类似基本定律这时总流量和扬程及输出功率为是多少?

　　N1=1450RPM，N2=1000RPM;

　　Q1=200l/s，Q2=Q1×N2/N1=200×1000/1450=138l/s

　　H1=37.5m，H2=H1×(N2/N1)2=37.5×(1000/1450)2=17.8m

　　P1=84.5kW，P2=P1×(N2/N1)3=84.5×(1000/1450)3=27.7kW。

　　水泵电机功率测算：

　　挑选电机时要了解：安全性能，水泵每台运作与并联运行。

　　钻削基本定律：

　　计算方式：

　　从零点与已经知道较大叶轮孔径点交叉，计算方法。

　　D=规定的工作部位叶轮孔径;D1=已经知道叶轮孔径;

　　H=规定的工作部位的扬程;

　　H1=从零点与D1孔径曲线图相交点处扬程。

　　型号选择根据：

　　我们要挑选什么样的泵，必须什么标准根据?

　　水泵总流量;运作水泵数量及预留水泵数量;

　　水泵扬程;水泵吸进口工作压力;

　　水泵总数;供应范畴;

　　供电系统标准(工作频率,工作电压…);

　　是不是装有变频式机器设备;

　　物质种类(如：冷水or乙二醇?冷冻水?冷却循环水?河流?海面?…);物质环境温度。

　　尽量依照买家需要的主要参数、形式、原材料等型号选择，别的的解决方案可作为挑选。

　　假如买家对水泵的转数和噪声要求不高，那样充分考虑扬程、总流量、NPSH值达到的情况下挑选***的和高速旋转的泵的种类。

　　挑选的水泵应在高效率区范围之内工作中。

　　型号选择时留意设计方案扬程与现实运作扬程差别，能够适度调整(下降)设计方案扬程值，至水泵的高效率点，那样更安全。

　　泵的型号选择：

　　1、物质的特点：物质名字、相对密度、黏度、腐蚀、毒副作用等。

　　a.物质名字：冷水、废水、原油等。当物质含气量>75%时，**是采用齿轮油泵或是磁力泵。

　　b.相对密度：

　　离心式泵的流量与相对密度不相干;离心水泵的扬程与相对密度不相干;离心水泵的高效率不随相对密度更改;

　　当相对密度≠1000Kg/m3时，电机的效率应当为一般输出功率与物质相对性冷水密度比的相乘，防止电机负载超流。

　　c.黏度：物质的黏度对泵的特性影响很大，黏度过过大时，泵的拉力(扬程)减少，总流量减少，高效率降低，泵的电机功率扩大。

　　当黏度**时，泵的扬程曲线图降低，**工作状况的扬程和总流量均随着降低，而输出功率则也随之升高，因此高效率减少。一般样版上的参数均为运输冷水时的特性，当运输黏性物质时要开展计算。

　　d.腐蚀：物质有浸蚀时，选用耐腐蚀性能好的原材料。

　　e.毒副作用：考虑到密封方式，可选用干气密封等。

　　2、物质中常含液体的颗粒物孔径、成分是多少。依据颗粒物孔径、成分是多少，可选用采用单流道、双流道、多过流道方式的叶轮。颗粒物成分>60%时，考虑到选用液下渣浆泵。

　　3、物质环境温度：(℃)持续高温物质需考虑到橡胶密封件的选取及原料的线膨胀系数。物质环境温度稍低时，考虑到选用超低温润滑脂和超低温电机。

　　4、所必须的总流量(Q)

　　a、假如生产工艺流程中已得出*少、正常的、**流量，应按**流量考虑到。

　　b、假如生产工艺流程中只得出正常的总流量，应考虑到留出一定的容量。

　　c、假如基本数据只给气体流量，应转换成体积流量。

　　5、扬程：水泵的扬程大概为打水相对高度的1.15～1.2倍(应用于补水泵只得出系统图必须测算扬程的情况)。如碰到只得出*少总流量、**流量及相对应的扬程，应尽量按大流量挑选。

　　由于：

　　a、高扬程的泵用以低扬程，便会发生总流量太大，造成电机超重，若长期运作，电机温度升高，乃至损坏电机。

　　b、小流量泵在大流量下运行时，会造成气蚀，泵长期气蚀，危害水泵过电流构件的使用寿命。

　　泵的并接：

　　1.两部泵的吸进、排出来管路同样—管路特性曲线图同样;

　　2.两部泵的流量、拉力同样—泵的特性曲线图同样;3.针对“泵”的特性曲线图，同一拉力下，两部并接泵的流量相当于并接中每台泵的二倍;(留意：针对单位重量的液体，在各泵中得到的能量转换是相同的。)4.并接后流量扩大，但小于原单独的每台泵流量的二倍。

　　泵的串连：

　　1.两部泵的流量、拉力同样—泵的特性曲线图同样;2.针对“泵”的特性曲线图，同一总流量下，两部串连泵的拉力相当于并接中每台泵的二倍;(留意：穿过两部泵的流量是一致的。)

　　3.串连后流量、总拉力扩大，但拉力小于原单独的每台泵压头的二倍。

　　泵的汽蚀：

　　1、汽蚀产生：泵在运行中，输送药液的绝压减少到那时候环境温度下的该液态气化工作压力时，溶液便在该处逐渐气化，产生汽泡，当带有很多汽泡的药液流到离心叶轮里的髙压区的时候，小气泡周边的髙压液态导致汽泡大幅度地减小以致裂开。在汽泡裂开的与此同时，液态简谐运动以很高的速率添充空化，在这里一瞬间造成很明显的水锤功效，并且以很高的冲击性工作频率严厉打击金属表层，冲击性地应力可以达到好几百至几千个大气压力，冲击性工作频率可以达到每秒钟几万元次，比较严重的时候会将壁穿透。

　　2.汽蚀的伤害：

　　a、离心叶轮上留有严厉打击状的坑;干扰离心叶轮的使用期限。

　　b、机器设备造成震动。

　　c、**噪声。

　　d、轻度的汽蚀只能导致水泵高效率或水泵扬程的减少。低比转速比泵;随汽蚀性能降低显著，高比转速比泵，当汽蚀做到一定程度时，性能逐渐降低。

　　e、比较严重的汽蚀会发生很强的噪声，并减少水泵的运用寿。

　　f、估计而言，损害较大占设计方案水泵扬程的3%。

　　g、针对多级别水泵,汽蚀只会对**级离心叶轮产生影响。

　　3、泵汽蚀的主要表达式为：

　　NPSHc≤NPSHr≤[NPSH]≤NPSHa

　　式中：NPSHa—设备汽蚀余量又叫合理汽蚀余量，就是指在现场标准下的汽蚀余量。它可也依据体系的设计图计算出来，越大越不容易汽蚀;

　　NPSHr—泵汽蚀余量，又叫必不可少的汽蚀余量，就是指水泵的一个特性数据信息，这是由水泵生产商给予的。该标值在水泵的性能数据图表中早已被标记出去，越小型泵抗汽蚀性能就越好;

　　NPSHc—临界值汽蚀余量，就是指相匹配泵性能降低一定值的汽蚀量;

　　[NPSH]—允许汽蚀余量，是明确泵使用条件用的汽蚀余量。

　　为保证系统的安全运行：

　　具体汽蚀余量值(NPSHa)一定要高过设计方案汽蚀余量值(NPSHr)。即：NPSHa>NPSHr。

　　5.具体汽蚀余量(NPSHa)的计算公式：

　　NPSHa=(Hz-Hf)+(Hp–Hvp)

　　在其中：

　　Hp=水泵入口液态表层的绝压(m)

　　Hz=液态间距水泵轴线的静态数据落差(m)

　　注：针对立柱式水泵以**级离心叶轮的轴线为标准。

　　Hf=管路系统软件入口磨擦和通道损害包含气体压力头。(m)

　　Hvp=在水泵操作温度下的液态蒸汽压力。(m)

　　假如NPSHA标值不大，提议挑选：更高一些规格的水泵或转速比变慢一些的水泵。

　　4、避免汽蚀的对策

　　避免泵产生汽蚀从两方面考虑到，即扩大NPSHa和减少NPSHr，常见的下面几个方式。

　　a、减少几何图形吸上相对高度hg(或增多几何图形倒流相对高度);

　　△h=10m-NPSH-∑h

　　∑h：管路摩擦阻力，也叫安全性能，取：0.5～1.0m水柱

　　△h：吸程

　　b、**管经，尽可能减少管路长短，弯管和配件等;

　　c、尽可能调小流量，避免泵长期在大流量下运作;

　　d、在一样转速比和总流量下，选用双吸泵，因减少进口的流动速度、泵不容易产生汽蚀;

　　e、加诱发轮或**离心叶轮进口的处的光滑度。

　　f、针对在严苛标准下运作的泵，为防止汽蚀毁坏，可使用耐汽蚀原材料。

　　普遍及应注意的情况：

　　1、电动机的挑选：电动机的选用要留出一定的安全性容量。

　　2、离心水泵启动时要关掉出入口阀，混流泵启动时要开启出入口阀。

　　因离心水泵启动时，泵的出入口管路内还水少，因而还不会有管路摩擦阻力和**高度阻力，在泵起动后，泵扬程很低，总流量非常大，这时泵电动机(电机功率)导出非常大(据泵性能曲线图)，非常容易超重，便会使泵的电动机及路线毁坏，因而启动时要关掉出入口阀，才可以使泵正常运行。

　　离心水泵在零流量时，电机功率为额定值工作状况下电机功率的30%～90%。

　　混流泵在零流量时，电机功率为额定值工作状况下电机功率的140%～200%。

　　因此混流泵要开阀运行。

　　3、泵运行前要检查泵轴健身运动是否正常，是不是有卡住想像。启动电动机，看运行方位是否正确。

　　4、泵组装时，泵进出口贸易管路上不可以载重。泵轴对中要在灌满水的标准下实现。

　　5、污水潜水泵长期性无需时，应清洁并吊起来放置自然通风干躁处，留意防寒。若放置水里，每15天*少运行30min(不可以抛光)，以检测其作用和适应能力。

　　确定机封使用寿命长度的关键环节：

　　水泵设计方案(轴是不是偏位，滚动轴承负荷和带座轴承的同轴度…)

　　组装(轴对中是不是维持…)

　　工作部位(是不是在高效率区，当在能延长机封使用寿命)

　　表层原材料(合适物质，碳碳复合材料、钴合金)

　　密封性润化(润化不太好可减少密封性使用寿命)

　　运用场所(要是在持续高温、髙压场所,密封性使用寿命减少)

　　滚动轴承：

　　确定轴承寿命长度的关键环节：

　　滚动轴承载荷在设计方案点;

　　水泵是不是在高效率区工作中(在高效率区工作中能延长轴承寿命);

　　组装/水泵轴对中/泵室;

　　由汽蚀或其他软件缘故造成水泵震动将减少轴承寿命。

　　Pump belongs to a kind of power machinery, which refers to the industrial equipment with liquid as the working material and kinetic energy medium.

　　Power machinery can be divided into transmission devices (water turbine generator set and steam turbine generator) and working machines (pumps, centrifugal fans and refrigeration compressors) according to the different directions of energy transmission. The pump belongs to the working machine, that is, the mechanical equipment that consumes energy.

　　Pump classification:

　　1) The principle can be divided into impeller type, volumetric type and other modes.

　　① With the help of the driving force effect of the rotating impeller on the liquid, the leaf pump continuously transmits the kinetic energy to the liquid, so as to increase the mechanical energy (dominant) and pressure energy of the liquid, and then converts the kinetic energy into pressure energy according to the pressure chamber, which can be divided into centrifugal pump, mixed flow pump, partial flow pump and vortex pump.

　　② Positive displacement pump, with the help of tolerating the periodic change of the capacity of the liquid sealing workspace, periodically transmits the kinetic energy to the liquid, so that the burden of the liquid is increased to the forced discharge of the liquid. According to the movement form of the components in the work, it can be divided into reciprocating pump and rotary pump.

　　③ Other types of pumps transmit energy in other ways. For example, the jet pump relies on the liquid in the fast gushing operation to suck the liquid to be transported into the pump and stir it, and carry out momentum moment exchange to transfer energy; When the water hammer pump uses the braking system, part of the water in the fluidity is raised to a certain relative height to transmit energy; Magnetic drive pump is used to make the plug-in alloy flow under the effect of magnetic force to achieve transportation. In addition, pumps can also be classified according to the characteristics, driving mode, structure, application field, etc. of the transported liquid.

　　2) Classified according to the number of impellers in operation:

　　① Single stage pump: that is, there is only one impeller on the pump shaft.

　　② Multistage centrifugal pump: that is, there are 2 or more impellers on the pump shaft. At this time, the total head of the pump is the sum of the heads caused by N impellers.

　　3) Classified by pressure:

　　① Low pressure pump: the working pressure is less than 100m water column;

　　② Medium pressure pump: the working pressure is in the middle of 100 ~ 650 m water column;

　　③ High pressure water pump: the working pressure is higher than 650m water column.

　　4) Classified by impeller water seepage method:

　　① One side seepage pump: also known as single suction pump, that is, there is only one water inlet pipe on the impeller;

　　② Two side seepage pump: also called double suction pump, that is, there is a water inlet pipe on both sides of the impeller. Its flow is twice as large as that of a single suction pump, which can be regarded as two single suction pump impellers put together back to back.

　　5) Type according to the mode of pump casing fusion joint:

　　① Horizontal middle open pump: namely, there is a fusion joint on the horizontal surface according to the pivot axis.

　　② Vertical joint surface pump: that is, the joint surface is vertical to the center of gravity line.

　　6) Type according to pump shaft position:

　　① Horizontal pump: the pump shaft is located in a horizontal position.

　　② Vertical pump: the pump shaft is located in the vertical position.

　　7) Classified according to the way that the water from the impeller is led to the pressure chamber:

　　① Volute pump: after water goes out from the impeller, it directly enters the pump shell with spiral shape.

　　② Diffuser pump: after water goes out from the impeller, it enters the diffuser set outside it, and then enters the next stage or injects into the inlet and outlet pipe. (commonly used for multistage centrifugal pumps and mixed flow pumps)

　　Basic principle and structure of actual operation of pump:

　　The impeller composed of a plurality of bent leaves is placed in the pump casing with the safe passage of the volute. The impeller is screwed on the pump shaft, which is connected with the motor and can be driven to rotate by the motor. The suction inlet is located in the middle of the pump casing and connected with the suction pipe. Please install a check valve at the bottom of the suction pipe. The side of the pump casing is the discharge inlet, which is connected with the discharge pipe and is equipped with a regulating valve.

　　Centrifugal pumps are often able to transport liquids, mainly with the help of centripetal force caused by high-speed running impellers, so they are called centrifugal pumps.

　　Working process of centrifugal water pump:

　　Before starting the pump, fill the pump with the liquid to be transmitted.

　　After starting the pump, the pump shaft pushes the impeller to run at a high speed, causing centripetal force. Under this effect, the liquid is thrown from the impeller core to the impeller periphery, the working pressure is increased, and the liquid is injected into the pump casing at a very high rate. In the pump casing, due to the continuous expansion of the flow passage, the flow speed of the liquid slows down, so that most of the mechanical energy is converted into pressure energy. Finally, the liquid is injected into the discharge pipeline from the discharge inlet with a high negative pressure. After the liquid in the pump is thrown out, the core of the impeller forms a vacuum pump. Under the action of the pressure difference between the liquid level gas pressure (atmospheric pressure) and the pressure in the pump (negative pressure), the liquid will be sucked into the pump through the suction pipe, making up for the part where the liquid is removed.

　　When the centrifugal water pump is started, if there is gas in the pump shell, because the density of air is far less than the relative density of liquid, the centripetal force caused by the rotation of the impeller is not large, and the low voltage at the core of the impeller can not lead to the vacuum value necessary for absorbing liquid, so the centrifugal water pump can not work. In order to fill the pump with liquid before starting, install a check valve at the bottom of the suction pipeline. In addition, a regulating valve is also installed on the inlet and outlet pipes of the centrifugal water pump to start, stop and regulate the flow.

　　Basic components and structures:

　　1) Impeller: sends the mechanical kinetic energy of the motor to the liquid to gradually increase the mechanical energy of the liquid.

　　2) Pump casing: collect the liquid and act as a safe channel for the liquid;

　　The kinetic energy of the liquid is transformed, and part of the energy is converted into pressure energy.

　　3) Water pump sealing equipment: to prevent high-pressure liquid from leaking out from the pump casing along the circumference of the shaft, or external gas from leaking into the pump casing.

　　Comparison between rotary seal and mechanical seal:

　　Pressure and tightness:

　　Rotary seal water pump: high pressure 4-5bar (specification and model)

　　Mechanical seal water pump:

　　When the pump pressure is larger than 10bar: unbalanced mechanical seal (specification)

　　When the pump pressure is larger than 10bar: equalize the mechanical seal (the rated current is related to the seal structure)

　　Total flow, head, total negative pressure, friction resistance, pump characteristic curve, operation diagram, parallel operation, system software friction resistance curve, pressure line connected by several pumps in parallel, pressure, pump bearing pressure, pressure < large pressure (PN)

　　Similar to the basic law, q1/q2=n1/n2, h1/h2= (n1/n2) 2, p1/p2= (n1/n2) 3.

　　Note: if the impeller diameter changes or the pump speed ratio changes, NPSH will change.

　　Examples:

　　The total flow is 200l/s, the lift is 37.5m, the model and specification of the water pump asp200b are adopted, the impeller diameter is 360mm, the speed ratio is 1450rpm, the high efficiency is 87%, and the motor power at the operating point is 84.5kw.

　　If the speed ratio becomes 1000rpm, what is the total flow, head and output power according to similar basic laws?

　　N1=1450RPM，N2=1000RPM;

　　Q1=200l/s，Q2=Q1 × N2/N1=200 × 1000/1450=138l/s

　　H1=37.5m，H2=H1 × (N2/N1)2=37.5 × (1000/1450)2=17.8m

　　P1=84.5kW，P2=P1 × (N2/N1)3=84.5 × (1000/1450)3=27.7kW。

　　Calculation of pump motor power:

　　When selecting the motor, it is necessary to understand: safety performance, operation and parallel operation of each pump.

　　Basic drilling Law:

　　Calculation method:

　　The calculation method is based on the intersection between the zero point and the known point of larger impeller diameter.

　　D= impeller diameter at the specified working position; D1= impeller diameter is known;

　　H= lift of specified working part;

　　H1= lift from the intersection of zero point and D1 aperture curve.

　　Model selection based on:

　　What kind of pumps should we choose and what standards should we follow?

　　Total flow of water pump; Number of operating water pumps and reserved water pumps;

　　Pump lift; Working pressure at suction inlet of water pump;

　　Total number of pumps; Scope of supply;

　　Power supply system standard (operating frequency, operating voltage...);

　　Whether the frequency conversion machine equipment is installed;

　　Type of substance (e.g. cold water or ethylene glycol? Chilled water? Cooling circulating water? River? Sea surface?...); Material ambient temperature.

　　Try to select according to the main parameters, forms, raw materials and other models required by the buyer, and other solutions can be selected.

　　If the buyer does not have high requirements for the number of revolutions and noise of the water pump, the cheapest and high-speed rotating pump shall be selected under the condition that the head, total flow and NPSH value are fully considered.

　　The selected water pump shall operate within the high efficiency zone.

　　When selecting the model, pay attention to the difference between the design scheme head and the actual operation head, and properly adjust (reduce) the design scheme head value to the high efficiency point of the pump, which is safer.

　　Pump model selection:

　　1. Characteristics of the substance: substance name, relative density, viscosity, corrosion, toxic and side effects, etc.

　　a. Material name: cold water, waste water, crude oil, etc. When the air content of the material is more than 75%, it is better to use gear oil pump or magnetic pump.

　　b. Relative density:

　　The flow of centrifugal pump is irrelevant to the relative density; The head of centrifugal pump is irrelevant to the relative density; The high efficiency of centrifugal pump does not change with the relative density;

　　When the relative density is ≠ 1000kg/m3, the efficiency of the motor shall be the multiplication of the general output power and the density ratio of the relative cold water of the material, so as to prevent the overload of the motor load.

　　c. Viscosity: the viscosity of the material has a great impact on the characteristics of the pump. If the viscosity is too large, the pull (head) of the pump will be reduced, the total flow will be reduced, the high efficiency will be reduced, and the motor power of the pump will be expanded.

　　When the viscosity increases, the head curve of the pump decreases, the head and total flow under the best working conditions decrease, and the output power also increases, so the high efficiency decreases. Generally, the parameters on the sample plate are the characteristics when transporting cold water, and the calculation shall be carried out when transporting viscous substances.

　　d. Corrosion: raw materials with good corrosion resistance shall be selected when the material is corroded.

　　e. Toxic and side effects: considering the sealing method, dry gas sealing can be selected.

　　2. What is the pore size and composition of liquid particles in a substance. According to the particle diameter and composition, the impeller with single passage, double passage and multiple passage can be selected. When the particle composition is >60%, the submerged slurry pump shall be selected.

　　3. Material ambient temperature: (℃) the selection of rubber seals and the linear expansion coefficient of raw materials shall be taken into account for materials with continuous high temperature. When the ambient temperature of the material is slightly lower, ultra-low temperature grease and ultra-low temperature motor shall be considered.

　　4. Total flow required (q)

　　a. If the minimum, normal and maximum flow has been obtained in the production process, the maximum flow shall be considered.

　　b. If only the normal total flow is obtained in the production process, a certain capacity shall be reserved.

　　c. If the basic data only give gas flow, it should be converted to volume flow.

　　5. Lift: the lift of the water pump is about 1.15 ~ 1.2 times of the relative height of pumping water (it is applied to the case that the lift must be calculated only when the system diagram of the make-up pump is obtained). If only the minimum total flow, the maximum flow and the corresponding head are obtained, the large flow shall be selected as far as possible.

　　because:

　　a. If the pump with high head is used for low head, the total flow will be too large, causing the motor to be overweight. If it operates for a long time, the motor temperature will rise, and even damage the motor.

　　b. When a small flow pump operates at a large flow, it will cause cavitation, which will damage the service life of the over-current components of the pump for a long time.

　　Parallel connection of pump:

　　1. the suction and discharge pipelines of the two pumps are the same - the pipeline characteristic curve is the same;

　　2. the flow and tension of the two pumps are the same - the characteristic curve of the pump is the same; 3. according to the characteristic curve of "pump", under the same tension, the flow of two parallel connected pumps is equal to twice that of each pump in parallel connection; (Note: for the liquid per unit weight, the energy conversion obtained in each pump is the same.) 4. after parallel connection, the flow is expanded, but it is less than twice the flow of each pump.

　　Serial connection of pumps:

　　1. the flow and tension of the two pumps are the same - the characteristic curve of the pump is the same; 2. according to the characteristic curve of "pump", under the same total flow, the pull of two series connected pumps is equivalent to twice of that of each pump in parallel connection; (Note: the flow through the two pumps is the same.)

　　3. after the series connection, the flow and total tension are expanded, but the tension is less than twice of the original pressure head of each pump.

　　Cavitation of pump:

　　1. Cavitation: during the operation of the pump, when the absolute pressure of the conveyed chemical solution is reduced to the liquid gasification working pressure under the ambient temperature at that time, the solution will be gradually gasified there to produce bubbles. When the chemical solution with many bubbles flows to the high-pressure area in the centrifugal impeller, the high-pressure liquid around the small bubble will cause the bubbles to be greatly reduced and cracked. At the same time of the bubble cracking, the liquid simple harmonic motion adds cavitation at a very high rate, causing obvious water hammer effect in an instant, and severely attacks the metal surface with a high impact working frequency. The impact ground stress can reach hundreds to thousands of atmospheric pressure, and the impact working frequency can reach tens of thousands of yuan per second. In serious cases, the wall will be penetrated.

　　2. cavitation damage:

　　a. The centrifugal impeller is provided with a severely striking pit; Interfere with the service life of the centrifugal impeller.

　　b. Vibration caused by machinery and equipment.

　　c. Raise the noise.

　　d. Slight cavitation can only lead to the high efficiency of the pump or the reduction of the pump head. Low specific speed ratio pump; With the significant reduction of cavitation performance, the performance of high specific speed ratio pump will gradually decrease when cavitation reaches a certain degree.

　　e. Severe cavitation will produce strong noise and reduce the service life of the water pump.

　　f. It is estimated that the damage is relatively large, accounting for 3% of the pump lift in the design scheme.

　　g. For multi-stage pumps, cavitation will only affect the first stage centrifugal impeller.

　　3. The main expression of pump cavitation is:

　　NPSHc≤NPSHr≤[NPSH]≤NPSHa

　　Where: npsha - Equipment NPSH, also known as reasonable NPSH, refers to the NPSH under the site standard. It can also be calculated according to the design drawing of the system, and the larger it is, the less likely it is to cavitation;

　　NPSHr - pump NPSH, also known as essential NPSH, refers to a characteristic data information of the pump, which is given by the pump manufacturer. This standard value has already been marked out in the performance data chart of the pump. The smaller the pump, the better the anti cavitation performance;

　　Npshc - critical NPSH, which refers to the amount of cavitation that reduces the performance of the matching pump by a certain value;

　　[npsh] - allowable NPSH, which is the NPSH used to specify the service conditions of the pump.

　　To ensure the safe operation of the system:

　　The specific npsha value must be higher than the NPSHr value in the design scheme. Namely: npsha>npshr.

　　5. specific npsha calculation formula:

　　NPSHa=(Hz-Hf)+(Hp–Hvp)

　　In which:

　　Hp= absolute pressure of liquid surface at pump inlet (m)

　　Hz= static data drop between liquid and pump axis (m)

　　Note: for column pump, the axis of the first stage centrifugal impeller is taken as the standard.

　　Hf= pipeline system software inlet friction and channel damage include gas pressure head. (m)

　　Hvp= liquid vapor pressure at pump operating temperature. (m)

　　If the npsha standard value is not large, it is suggested to select a pump with higher specification or a pump with slower speed.

　　4. Countermeasures to avoid cavitation

　　To avoid cavitation of the pump, consider two aspects, namely, expanding npsha and reducing NPSHr. The following methods are common.

　　a. Reduce the relative height Hg of geometric drawing (or increase the relative height of geometric drawing backflow);

　　△h=10m-NPSH-∑h

　　Σ H: pipeline friction resistance, also known as safety performance, taken as 0.5 ~ 1.0m water column

　　△ H: suction lift

　　b. The length of the riser shall be reduced as much as possible, including bends and fittings;

　　c. Reduce the flow as much as possible to avoid long-term operation of the pump under large flow;

　　d. Under the same speed ratio and total flow, the double suction pump is selected, because the flow speed at the inlet is reduced, the pump is not easy to produce cavitation;

　　e. Add inducer or improve the smoothness of the inlet of centrifugal impeller.

　　f. For pumps operating under strict standards, cavitation resistant raw materials can be used to prevent cavitation damage.

　　General and noteworthy conditions:

　　1. Selection of motor: a certain safety capacity shall be reserved for the selection of motor.

　　2. The inlet and outlet valves shall be closed when the centrifugal water pump is started, and the inlet and outlet valves shall be opened when the mixed flow pump is started.

　　When the centrifugal water pump is started, there is less water in the inlet and outlet pipelines of the pump, so there will be no pipeline friction resistance and lifting height resistance. After the pump is started, the pump head is very low and the total flow is very large. At this time, the pump motor (motor power) is very large (according to the pump performance curve). It is very easy to be overweight, which will destroy the pump motor and route. Therefore, the inlet and outlet valves should be closed during the start-up to make the pump operate normally.

　　When the centrifugal water pump is at zero flow, the motor power is 30% ~ 90% of the motor power under the rated working condition.

　　When the mixed flow pump is at zero flow, the motor power is 140% ~ 200% of the motor power under rated operating conditions.

　　Therefore, the valve of the mixed flow pump shall be opened for operation.

　　3. Before running the pump, check whether the fitness exercise of the pump shaft is normal and whether it is stuck. Start the motor and check whether the running direction is correct.

　　4. When the pump is assembled, the import and export trade pipeline of the pump shall not be loaded. The pump shaft alignment shall be realized under the standard of full water filling.

　　5. When the sewage submersible pump is not needed for a long time, it should be cleaned and hoisted to place in a dry place with natural ventilation, and pay attention to cold protection. If it is placed in water, it shall be operated for at least 30min every 15 days (polishing is not allowed) to test its function and adaptability.

　　Key links for determining the service life length of mechanical seal:

　　Design scheme of water pump (whether the shaft is offset, the load of rolling bearing and the coaxiality of bearing with seat...)

　　Assembly (whether shaft alignment is maintained...)

　　Working position (whether it is in the high efficiency area, which can prolong the service life of the mechanical seal)

　　Surface raw materials (suitable substances, carbon carbon composites, cobalt alloys)

　　Sealing lubrication (poor lubrication can reduce the service life of sealing)

　　Application site (in case of continuous high temperature and high pressure, the service life of sealing property will be reduced)

　　Rolling bearing:

　　Key links for determining bearing life length:

　　The load of rolling bearing is at the design point;

　　Whether the water pump is working in the high efficiency zone (the bearing life can be prolonged in the high efficiency zone);

　　Assembly / pump shaft alignment / pump room;

　　Pump vibration caused by cavitation or other software will reduce bearing life.