泵歸屬于動力機械的一種，動力機械就是指以液體為作業物質和動能媒介的工業設備。

　　動力機械依據能量傳遞的方位不一樣，可分成傳動裝置(水輪發電機組、汽輪發電機)和工作機(泵、離心風機、制冷壓縮機)。泵歸屬于工作機，即消耗能量的機械設備。

　　泵的歸類：

　　1)原理可分成又分為葉輪式、容積式和其他方式。

　　①葉子式泵，借助旋轉的葉輪對液體的驅動力功效，把動能持續地傳達給液體，使液體的機械能(為主導)和壓力能**，接著根據壓出來室將動能轉換為壓力能，又可分成離心水泵、混流泵、部位流泵和漩渦泵等。

　?、谌莘e式泵，借助寬容液體的密封性工作空間容量的周期性變化，把動能周期性地傳送給液體，使液體的負擔**至將液體強制排出來，依據工作中元器件的運動形式又可分成往復泵和旋轉泵。

　?、燮渌愋偷谋?，以別的方式傳遞能量。如射流泵依賴快速噴涌的工作中液體將需運輸的液體吸進泵后攪拌，開展動量矩互換以傳遞能量;水錘泵運用制動系統時流動性中的一部分水被升至一定相對高度傳遞能量;磁力驅動泵是使插電的合金在磁場力功效下形成流動性而達到運輸。此外，泵也可按運輸液體的特性、推動方式、構造、應用領域等開展歸類。

　　2)按工作中葉輪數量來歸類：

　?、賳渭壉茫杭丛诒幂S上只有一個葉輪。

　　②多級離心泵：即在泵軸上面有2個或兩個以上的葉輪，這時候泵的總揚程為n個葉輪造成的揚程之和。

　　3)按壓力來歸類：

　?、俚蛪罕茫汗ぷ鲏毫π∮?00米水柱;

　?、谥袎罕茫汗ぷ鲏毫υ?00～650米水柱中間;

　?、鄹邏?a href="https://www.www.t6961.cn/pump/">水泵：工作壓力高過650米水柱。

　　4)按葉輪滲水方法來歸類：

　　①一側滲水式泵：又叫單吸泵，即葉輪上只有一個進水管;

　　②兩側滲水式泵：又叫雙吸泵，即葉輪兩邊都是有一個進水管。它流量比單吸式泵大一倍，能夠類似看作是二個單吸泵葉輪背對背地放到了一起。

　　5)按泵殼融合縫方式來種類：

　?、偎疁手虚_啟式泵：即在根據樞軸線的水準表面開有融合縫。

　?、谪Q直結合面泵：即結合面與重心線相豎直。

　　6)按泵軸部位來種類：

　?、倥P式泵：泵軸坐落于水平位置。

　?、诹⑹奖茫罕幂S坐落于豎直部位。

　　7)按葉輪出去的水引到壓出來室的形式歸類：

　?、贉u殼泵：水從葉輪出去后，直接進入具備螺旋形態的泵殼。

　?、跀U壓器泵：水從葉輪出去后，進到它外邊設定的擴壓器，以后進下一級或注入出入口管。(常用于多級離心泵和混流泵)

　　泵的實際操作基本原理、結構：

　　由多個彎折的葉子構成的葉輪放置具備渦殼安全通道的泵殼以內。葉輪擰緊于泵軸上，泵軸與電機相接，可由電機推動轉動。吸進口坐落于泵殼中間與吸進管道相接，請在吸進管底端裝一止回閥。泵殼的側面為排出入口，與流出管道相接，配有調節閥門。

　　離心水泵往往能運輸液體，主要是借助高速運轉葉輪所造成的向心力，因而稱之為離心水泵。

　　離心水泵的工作過程：

　　開泵前，先往泵內注滿要傳送的液體。

　　開泵后，泵軸推動葉輪一起高速運轉造成向心力。液體在這里功效下，從葉輪核心被拋到葉輪外圍，工作壓力提高，并且以很高的速率注入泵殼。在泵殼中因為過流道的不斷擴大，液體的流動速度緩減，使絕大多數機械能轉換為壓力能。*終液體以較高的負壓強從排出入口注入排出來管路。泵里的液體被拋出去后，葉輪的核心形成了真空泵，在液位氣體壓強(大氣壓力)與泵內壓力(負壓力)的壓力差的作用下，液體便經吸進管道進到泵內，彌補了被清除液體的部位。

　　離心水泵啟動時，假如泵殼內存有氣體，因為空氣的密度遠小于液體的相對密度，葉輪轉動所造成的向心力不大，葉輪核心處發生的低電壓不能導致吸上液體所必須的真空值，那樣，離心水泵就沒法作業。以便使起動前泵內充斥著液體，在吸進管路底端裝一止回閥。除此之外，在離心水泵的出入口管道上也裝一調節閥門，用以開停機和調節流量。

　　基本上構件和結構：

　　1)葉輪：將電動機的機械動能發送給液體,使液體的機械能逐步提高。

　　2)泵殼：匯聚液體，作導出來液體的安全通道;

　　使液體的動能產生變換，一部分能量轉化為壓力能。

　　3)水泵密封設備：為了避免髙壓液體從泵殼內沿軸的四周而漏出來，或是外部氣體漏入泵殼內。

　　旋轉密封和機封的較為：

　　壓力和密封性：

　　旋轉密封水泵：較大壓力4-5bar.(規范規格型號)

　　機封水泵：

　　水泵較大壓力<10bar時：不平衡機封(規范)

　　水泵較大壓力>10bar時：均衡機封(額定電流與封口的構造有關系)

　　總流量、揚程、總負壓、摩阻、水泵特性曲線圖、運行圖、并聯運行、系統軟件摩擦阻力曲線圖、幾臺水泵并接的壓力線條、壓力、水泵承受壓力、壓力<較大壓力(PN)、

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

　　留意：假如葉輪孔徑更改或水泵轉速比更改，NPSH將產生變化。

　　舉例說明：

　　總流量200l/s,揚程37.5m，采用水泵型號規格ASP200B，葉輪孔徑360mm，轉速比1450RPM，高效率87%工作狀況點電機功率84.5kW。

　　假如轉速比變成1000RPM，依據類似基本定律這時總流量和揚程及輸出功率為是多少?

　　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。

　　水泵電機功率測算：

　　挑選電機時要了解：安全性能，水泵每臺運作與并聯運行。

　　鉆削基本定律：

　　計算方式：

　　從零點與已經知道較大葉輪孔徑點交叉，計算方法。

　　D=規定的工作部位葉輪孔徑;D1=已經知道葉輪孔徑;

　　H=規定的工作部位的揚程;

　　H1=從零點與D1孔徑曲線圖相交點處揚程。

　　型號選擇根據：

　　我們要挑選什么樣的泵，必須什么標準根據?

　　水泵總流量;運作水泵數量及預留水泵數量;

　　水泵揚程;水泵吸進口工作壓力;

　　水泵總數;供應范疇;

　　供電系統標準(工作頻率,工作電壓…);

　　是不是裝有變頻式機器設備;

　　物質種類(如：冷水or乙二醇?冷凍水?冷卻循環水?河流?海面?…);物質環境溫度。

　　盡量依照買家需要的主要參數、形式、原材料等型號選擇，別的的解決方案可作為挑選。

　　假如買家對水泵的轉數和噪聲要求不高，那樣充分考慮揚程、總流量、NPSH值達到的情況下挑選***的和高速旋轉的泵的種類。

　　挑選的水泵應在高效率區范圍之內工作中。

　　型號選擇時留意設計方案揚程與現實運作揚程差別，能夠適度調整(下降)設計方案揚程值，至水泵的高效率點，那樣更安全。

　　泵的型號選擇：

　　1、物質的特點：物質名字、相對密度、黏度、腐蝕、毒副作用等。

　　a.物質名字：冷水、廢水、原油等。當物質含氣量>75%時，**是采用齒輪油泵或是磁力泵。

　　b.相對密度：

　　離心式泵的流量與相對密度不相干;離心水泵的揚程與相對密度不相干;離心水泵的高效率不隨相對密度更改;

　　當相對密度≠1000Kg/m3時，電機的效率應當為一般輸出功率與物質相對性冷水密度比的相乘，防止電機負載超流。

　　c.黏度：物質的黏度對泵的特性影響很大，黏度過過大時，泵的拉力(揚程)減少，總流量減少，高效率降低，泵的電機功率擴大。

　　當黏度**時，泵的揚程曲線圖降低，**工作狀況的揚程和總流量均隨著降低，而輸出功率則也隨之升高，因此高效率減少。一般樣版上的參數均為運輸冷水時的特性，當運輸黏性物質時要開展計算。

　　d.腐蝕：物質有浸蝕時，選用耐腐蝕性能好的原材料。

　　e.毒副作用：考慮到密封方式，可選用干氣密封等。

　　2、物質中常含液體的顆粒物孔徑、成分是多少。依據顆粒物孔徑、成分是多少，可選用采用單流道、雙流道、多過流道方式的葉輪。顆粒物成分>60%時，考慮到選用液下渣漿泵。

　　3、物質環境溫度：(℃)持續高溫物質需考慮到橡膠密封件的選取及原料的線膨脹系數。物質環境溫度稍低時，考慮到選用超低溫潤滑脂和超低溫電機。

　　4、所必須的總流量(Q)

　　a、假如生產工藝流程中已得出*少、正常的、**流量，應按**流量考慮到。

　　b、假如生產工藝流程中只得出正常的總流量，應考慮到留出一定的容量。

　　c、假如基本數據只給氣體流量，應轉換成體積流量。

　　5、揚程：水泵的揚程大概為打水相對高度的1.15～1.2倍(應用于補水泵只得出系統圖必須測算揚程的情況)。如碰到只得出*少總流量、**流量及相對應的揚程，應盡量按大流量挑選。

　　由于：

　　a、高揚程的泵用以低揚程，便會發生總流量太大，造成電機超重，若長期運作，電機溫度升高，乃至損壞電機。

　　b、小流量泵在大流量下運行時，會造成氣蝕，泵長期氣蝕，危害水泵過電流構件的使用壽命。

　　泵的并接：

　　1.兩部泵的吸進、排出來管路同樣—管路特性曲線圖同樣;

　　2.兩部泵的流量、拉力同樣—泵的特性曲線圖同樣;3.針對“泵”的特性曲線圖，同一拉力下，兩部并接泵的流量相當于并接中每臺泵的二倍;(留意：針對單位重量的液體，在各泵中得到的能量轉換是相同的。)4.并接后流量擴大，但小于原單獨的每臺泵流量的二倍。

　　泵的串連：

　　1.兩部泵的流量、拉力同樣—泵的特性曲線圖同樣;2.針對“泵”的特性曲線圖，同一總流量下，兩部串連泵的拉力相當于并接中每臺泵的二倍;(留意：穿過兩部泵的流量是一致的。)

　　3.串連后流量、總拉力擴大，但拉力小于原單獨的每臺泵壓頭的二倍。

　　泵的汽蝕：

　　1、汽蝕產生：泵在運行中，輸送藥液的絕壓減少到那時候環境溫度下的該液態氣化工作壓力時，溶液便在該處逐漸氣化，產生汽泡，當帶有很多汽泡的藥液流到離心葉輪里的髙壓區的時候，小氣泡周邊的髙壓液態導致汽泡大幅度地減小以致裂開。在汽泡裂開的與此同時，液態簡諧運動以很高的速率添充空化，在這里一瞬間造成很明顯的水錘功效，并且以很高的沖擊性工作頻率嚴厲打擊金屬表層，沖擊性地應力可以達到好幾百至幾千個大氣壓力，沖擊性工作頻率可以達到每秒鐘幾萬元次，比較嚴重的時候會將壁穿透。

　　2.汽蝕的傷害：

　　a、離心葉輪上留有嚴厲打擊狀的坑;干擾離心葉輪的使用期限。

　　b、機器設備造成震動。

　　c、**噪聲。

　　d、輕度的汽蝕只能導致水泵高效率或水泵揚程的減少。低比轉速比泵;隨汽蝕性能降低顯著，高比轉速比泵，當汽蝕做到一定程度時，性能逐漸降低。

　　e、比較嚴重的汽蝕會發生很強的噪聲，并減少水泵的運用壽。

　　f、估計而言，損害較大占設計方案水泵揚程的3%。

　　g、針對多級別水泵,汽蝕只會對**級離心葉輪產生影響。

　　3、泵汽蝕的主要表達式為：

　　NPSHc≤NPSHr≤[NPSH]≤NPSHa

　　式中：NPSHa—設備汽蝕余量又叫合理汽蝕余量，就是指在現場標準下的汽蝕余量。它可也依據體系的設計圖計算出來，越大越不容易汽蝕;

　　NPSHr—泵汽蝕余量，又叫必不可少的汽蝕余量，就是指水泵的一個特性數據信息，這是由水泵生產商給予的。該標值在水泵的性能數據圖表中早已被標記出去，越小型泵抗汽蝕性能就越好;

　　NPSHc—臨界值汽蝕余量，就是指相匹配泵性能降低一定值的汽蝕量;

　　[NPSH]—允許汽蝕余量，是明確泵使用條件用的汽蝕余量。

　　為保證系統的安全運行：

　　具體汽蝕余量值(NPSHa)一定要高過設計方案汽蝕余量值(NPSHr)。即：NPSHa>NPSHr。

　　5.具體汽蝕余量(NPSHa)的計算公式：

　　NPSHa=(Hz-Hf)+(Hp–Hvp)

　　在其中：

　　Hp=水泵入口液態表層的絕壓(m)

　　Hz=液態間距水泵軸線的靜態數據落差(m)

　　注：針對立柱式水泵以**級離心葉輪的軸線為標準。

　　Hf=管路系統軟件入口磨擦和通道損害包含氣體壓力頭。(m)

　　Hvp=在水泵操作溫度下的液態蒸汽壓力。(m)

　　假如NPSHA標值不大，提議挑選：更高一些規格的水泵或轉速比變慢一些的水泵。

　　4、避免汽蝕的對策

　　避免泵產生汽蝕從兩方面考慮到，即擴大NPSHa和減少NPSHr，常見的下面幾個方式。

　　a、減少幾何圖形吸上相對高度hg(或增多幾何圖形倒流相對高度);

　　△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、**管經，盡可能減少管路長短，彎管和配件等;

　　c、盡可能調小流量，避免泵長期在大流量下運作;

　　d、在一樣轉速比和總流量下，選用雙吸泵，因減少進口的流動速度、泵不容易產生汽蝕;

　　e、加誘發輪或**離心葉輪進口的處的光滑度。

　　f、針對在嚴苛標準下運作的泵，為防止汽蝕毀壞，可使用耐汽蝕原材料。

　　普遍及應注意的情況：

　　1、電動機的挑選：電動機的選用要留出一定的安全性容量。

　　2、離心水泵啟動時要關掉出入口閥，混流泵啟動時要開啟出入口閥。

　　因離心水泵啟動時，泵的出入口管路內還水少，因而還不會有管路摩擦阻力和**高度阻力，在泵起動后，泵揚程很低，總流量非常大，這時泵電動機(電機功率)導出非常大(據泵性能曲線圖)，非常容易超重，便會使泵的電動機及路線毀壞，因而啟動時要關掉出入口閥，才可以使泵正常運行。

　　離心水泵在零流量時，電機功率為額定值工作狀況下電機功率的30%～90%。

　　混流泵在零流量時，電機功率為額定值工作狀況下電機功率的140%～200%。

　　因此混流泵要開閥運行。

　　3、泵運行前要檢查泵軸健身運動是否正常，是不是有卡住想像。啟動電動機，看運行方位是否正確。

　　4、泵組裝時，泵進出口貿易管路上不可以載重。泵軸對中要在灌滿水的標準下實現。

　　5、污水潛水泵長期性無需時，應清潔并吊起來放置自然通風干躁處，留意防寒。若放置水里，每15天*少運行30min(不可以拋光)，以檢測其作用和適應能力。

　　確定機封使用壽命長度的關鍵環節：

　　水泵設計方案(軸是不是偏位，滾動軸承負荷和帶座軸承的同軸度…)

　　組裝(軸對中是不是維持…)

　　工作部位(是不是在高效率區，當在能延長機封使用壽命)

　　表層原材料(合適物質，碳碳復合材料、鈷合金)

　　密封性潤化(潤化不太好可減少密封性使用壽命)

　　運用場所(要是在持續高溫、髙壓場所,密封性使用壽命減少)

　　滾動軸承：

　　確定軸承壽命長度的關鍵環節：

　　滾動軸承載荷在設計方案點;

　　水泵是不是在高效率區工作中(在高效率區工作中能延長軸承壽命);

　　組裝/水泵軸對中/泵室;

　　由汽蝕或其他軟件緣故造成水泵震動將減少軸承壽命。

　　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.

　?、?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.

　?、?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.

　?、?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.

　?、?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:

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

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

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

　　4) Classified by impeller water seepage method:

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

　?、?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:

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

　?、?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.

　?、?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:

　?、?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.