1、泵的基本知识Pump Essentials一、概述I. Overview 通常把提升液体、输送液体或使液体增加压力，即把原动的机械能变为液体能量的机器统称为泵。泵的用途各不相同，根据原理可分为三大类：1.容积泵，2.叶片泵，3.其他类型的泵。In general terms, a pump refers to a machine that transports or delivers liquid or increases the liquid pressure, i.e. converting the original mechanical energy into liquid energy
2、. A pump can be used for different purposes. It can be divided into three categories according to the principle: 1. Positive displacement pump, 2. Vane pump, 3. other types of pump. 容积泵利用工作容积周期性变化来输送液体，例如：活塞泵、柱塞泵、隔膜泵、齿轮泵、滑板泵、螺杆泵等。叶片泵利用叶片和液体相互作用来输送液体，例如：离心泵、混流泵、轴流泵、旋涡泵等。Positive displacement pump del
3、ivers the liquid based on the periodic changes in the working volume, for example, piston pump, plunger pump, diaphragm pump, gear pump, slide-vane pump, screw pump, etc. Vane pump delivers the liquid by relying on vane-liquid interactions, for example, centrifugal pump, mixed flow pump, axial flow
4、pump, peripheral pump, etc. 电厂水系统用的泵一般是离心泵、混流泵和轴流泵，容积泵多用于油系统。The water system of the power plant usually adopts the centrifugal pump, mixed flow pump and axial flow pump. Positive displacement pumps are often used in the oil system. 二、离心泵II. Centrifugal Pump 离心泵依靠旋转叶轮对液体的作用把原动机的机械能传递给液体。由于离心泵的作用，液体从
5、叶轮进口流向出口的过程中，其速度能和压力都能得到增加，被叶轮排出的液体经过压出室，大部分速度能转换成压力能，然后沿排出管路输送出去，这时叶轮进口处因液体的排出而形成真空或低压，吸水池中的液体在液面压力( 大气压) 的作用下，被压入叶轮的进口，于是旋转着的叶轮就连续不断地吸入和排出液体。The centrifugal pump transfers the mechanical energy of the prime motor to the liquid by relying on the effect of the rotating impeller on the liquid. By vir
6、tue of the centrifugal pump, the velocity energy and pressure energy of the liquid can be increased as it flows from the impeller inlet to the outlet. The liquid discharged by the impeller flows through the delivery chamber, while most of the velocity energy is converted into pressure energy and is
7、then fed out along the discharge pipeline. At this time, vacuum or low pressure is formed at the impeller inlet due to the discharge of the liquid. The liquid in the sump is pressed into the impeller inlet under the effect of liquid level pressure (atmospheric pressure), allowing the rotating impell
8、er to continuously suction and discharge the liquid. 1.离心泵的特点1. Characteristics of centrifugal pump其特点为：转速高、体积小、重量轻、效率高、流量大、结构简单、性能平稳、容易操作和维修；其不足是：起动前泵内要灌满液体、液体精度对泵性能影响大、只能用于精度近似于水的液体、流量适用范围：5-20000 立方米/时，扬程范围在 3-2800 米。Characteristics: high speed, small size, light weight, high efficiency, large fl
9、ow, simple structure, steady performance, easy operation and maintenance; Deficiencies: the pump needs to be filled with liquid before startup, liquid accuracy has greater impact on the pump performance, only applicable to liquid whose accuracy is close to water, the range of limit is 3-2,800m when
10、the scope of application of flow is within 5-20,000m3/h. 2.分类2. Classification离心泵按其结构形式分为：立式泵和卧式泵。立式泵的特点为：占地面积少，建筑投入小，安装方便，缺点为：重心高，不适合无固定底脚场合运行。卧式泵特点：适用场合广泛，重心低，稳定性好，缺点为：占地面积大，建筑投入大，体积大，重量重。The centrifugal pump is divided into vertical type and horizontal type according to its structural style. Char
11、acteristics of vertical pump: less floor space, small construction investment, easy installation; Deficiencies: high center of gravity, not suitable for operation in occasions without fixed footing. Characteristics of horizontal pump: wide range of application, low center of gravity, good stability;
12、 Deficiencies: large floor space, large construction investment, large volume, heavy weight. 按扬程流量的要求并根据叶轮结构组成级数分为：It is divided into the followings according to the lift and flow requirements and the composition series of the impeller structure: 单级单吸泵：泵有一只叶轮，叶轮上一个吸入口，一般流量范围为：5.5-300m2/h，H在 8-150 米，
13、流量小，扬程低；Single-stage single-suction pump: one impeller on which there is a suction inlet, general flow range between 5.5-300m2/h, H between 8-150m, small flow and low lift; 单级双吸泵：泵为一只叶轮，叶轮上二个吸入口。流量 Q 在 120-20000 m2/h，扬程 H在 10-110 米，流量大，扬程低；Single-stage double-suction pump: one impeller on which ther
14、e are two suction inlets, flow Q between 120-20,000m2/h, lift H between 10-110m, large flow and low lift; 单吸多级泵：泵为多个叶轮，第一个叶轮的排出室接着第二个叶轮吸入口，以此类推。Single-suction multi-stage pump: multiple impellers, the delivery chamber of the first impeller connected to the suction inlet of the second impeller, and s
15、o on.三、轴流泵III. Axial Flow Pump 水泵运行中对水做机械功，这些功大部分转化为水的压力能，但也有少部分转化为水的内能使水的温度升高，当通过泵的水流量较大时，水温升高很有限，但水量较小时水温升高过大，将引起水泵的汽蚀。所以水泵一般设有最小流量再循环，以协调用户用水量与水泵要求的最小流量间的矛盾。While in operation, the pump does mechanical work on the water. Most of the work is converted into water pressure energy, but a small portio
16、n is converted into internal energy of water resulting in water temperature rise. When a large water flow passes through the pump, water temperature rise can be very limited. However, water temperature rise will be significant when the water flow is small, causing pump cavitation. Therefore, the pum
17、p is capable of minimum flow recirculation to coordinate the conflicts between users water demand and the required minimum flow of the pump. 叶片泵尤其是离心泵和轴流泵启动时需要很大的启动力矩，小流量的小型泵可带负荷启动，大型离心泵启动前一般关闭其出口阀，泵启动后再缓慢开启向用户供水。水泵正常运行中，应监视其出口压力、流量、电机电流、轴承温度等参数，并在现场对泵组振动、壳体温度等进行检查。较大的水泵还有其它设施，如轴端冷却密封水、润滑油、电机冷却系统等，运
18、行中也要进行监视和检查，启动前要启动这些辅助系统和设备。水泵停运时，由于其出口管道存有大量的水，停泵时系统水倒流会使泵倒转，泵倒转会对泵造成推力轴承的损坏、叶片松动、动静摩擦等故障，所以叶片泵出口都装有逆止阀，保护水泵。The vane pump, especially the centrifugal pump and axial flow pump, requires a large starting torque. Small pumps of small flow can be started with load, but large centrifugal pumps should n
19、ot be started until its outlet valve is closed. After the pump is started, it should be slowly opened to supply water to the user. When the pump is in normal operation, it is necessary to monitor its outlet pressure, flow, motor current, bearing temperature and other parameters. On-site inspection o
20、f pump unit vibration, housing temperature, etc. is also needed. Larger pumps are also provided with other facilities, such as shaft end cooling seal water, lubricating oil, motor cooling system, etc. which should also be subject to monitoring and inspection during runtime. These auxiliary systems a
21、nd devices should be first started before the pump is initiated. During pump outage, a lot of water is accumulated in the outlet pipe and backflow of system water will invert the pump. Inversion of the pump will cause damages to the pump thrust bearing, loosening of vane, dynamic friction and other
22、faults. Therefore, a check valve is mounted at each outlet of the vane pump to protect the pump. 四、汽蚀IV. Cavitation液体在一定温度下，降低压力至该温度下的汽化压力时液体便产生汽泡，把这种产生气泡的现象称为汽蚀。汽蚀时产生的气泡流动到高压处时，其体积减小以致破灭。这种由于压力上升气泡消失在液体中的现象称为汽蚀溃灭。Steam bubbles will come out of the liquid at a certain temperature when the liquid pre
23、ssure drops to the vapor pressure at this temperature. Such phenomenon of bubble generation is called cavitation. When the bubble generated in cavitation flows to a higher pressure, its volume is reduced resulting in burst. Such phenomenon of bubble disappearing in the liquid due to pressure rise is
24、 called cavitation collapse. 泵在运转中，若其通流部分的局部区域(通常是叶轮叶片进口稍后的某处) 因为某种原因，抽送液体的绝对压力降低到当时温度下的液体汽化压力时，液体便在该处开始汽化，产生大量蒸汽，形成气泡。当含有大量气泡的液体向前进入叶轮内的高压区时，气泡周围的高压液体致使气泡急剧地缩小以至破裂。在气泡凝结破裂的同时，液体质点以很高的速度填充空穴，在此瞬间产生很强烈的水击作用，并以很高的冲击频率打击金属表面，其冲击应力可达几百至几千个大气压，冲击频率可达每秒几万次，严重时会将壁厚击穿。While the pump is in operation, if the
25、absolute pressure of the pumped liquid is reduced to the liquid vapor pressure at the current temperature in the local area of its flow path (usually somewhere slightly behind the impeller vane inlet) due to some reason, the liquid starts to vaporize at this location and generate a large amount of s
26、team, hence of the formation of bubbles. When the liquid containing a large amount of bubbles flows forward into the high pressure zone within the impeller, the high pressure liquid around the bubbles will make them rapidly narrow and even rupture. At the same time of bubble condensation and rupture
27、, the mass point of the liquid fills the cavities at a high speed. At this instant, strong water hammer will generate and strike the metal surface at a high impact frequency. The impact stress can be up to hundreds to thousands of atmospheric pressures. The impact frequency can be up to tens of thou
28、sands of times per second and breakdown of the wall thickness may result in a serious case. 泵发生汽蚀的条件是由泵本身和吸入装置两方面决定的。因此，研究汽蚀发生的条件，应从泵本身和吸入装置双方来考虑，泵汽蚀的基本关系式为The condition for pump cavitation is determined by the pump itself and the suction device. Therefore, the study on cavitation conditions should
29、take into account the pump itself and the suction device. The basic relation of pump cavitation is as follows: NPSHcNPSHrNPSHNPSHaNPSHa=NPSHr(NPSHc)泵开始汽蚀NPSHa=NPSHr (NPSHc) pump cavitation startsNPSHa NPSHaNPSHr(NPSHc)泵无汽蚀NPSHa NPSHaNPSHr (NPSHc) no pump cavitation式中 NPSHa装置汽蚀余量又叫有效汽蚀余量，越大越不易汽蚀；Here
30、into, NPSHa refers to the net positive suction head of the device, also known as the effective net positive suction head. The greater the NPSHa is, the less likely cavitation is going to happen; NPSHr泵汽蚀余量，又叫必需的汽蚀余量或泵进口动压降，越小抗汽蚀性能越好；NPSHr refers to the net positive suction head of the pump, also kno
31、wn as the essential net positive suction head or the pump inlet dynamic pressure drop. The greater the NPSHr is, the better the cavitation resistance will be; NPSHc临界汽蚀余量，是指对应泵性能下降一定值的汽蚀余量；NPSHc refers to the critical net positive suction head that corresponds to a certain value of pump performance
32、degradation; NPSH许用汽蚀余量，是确定泵使用条件用的汽蚀余量，通常取NPSH=(1.11.5)NPSHc。NPSH refers to the allowable net positive suction head that determines the conditions of pump use, which is usually NPSH = (1.11.5) NPSHc. 欲防止发生汽蚀必须提高装置汽蚀余量，使装置汽蚀余量必需的汽蚀余量。NPSHa must be improved in order to prevent cavitation, so that NPSH
33、a is NPSHr. 防止发生汽蚀的措施如下：The following measures are to prevent cavitation: 1.减小几何吸上高度 hg(或增加几何倒灌高度 )；1. Reduce the geometric suction lift hg (or increase the geometric intrusion height); 2.减小吸入损失 hc，为此可以设法增加管径，尽量减小管路长度，弯头和附件等2. Reduce suction loss hc. To achieve this purpose, try to increase the pipe
34、 diameter and minimize pipe length, elbow and accessories; 3.防止长时间在大流量下运行；3. Prevent long-term operation at a large flow; 4.在同样转速和流量下，采用双吸泵，因减小进口流速、泵不易发生汽蚀；4. Double-suction pump at the same speed and flow is not prone to cavitation due to reduced inlet flow velocity; 5.泵发生汽蚀时，应把流量调小或降速运行；5. In case
35、 of pump cavitation, reduce the flow or operate at a reduced flow; 6.泵吸水池的情况对泵汽蚀有重要影响；6. Conditions in the pump sump have great impact on pump cavitation; 7.对于在苛刻条件下运行的泵，为避免汽蚀破坏，可使用耐汽蚀材料。7. When the pump is run in harsh conditions, cavitation-resistant materials should be used to avoid cavitation damage.
