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渣漿泵特性曲線的用途
離心泵的實(shí)際特性曲線表明，泵在恒定轉(zhuǎn)速下工作時(shí),對應(yīng)于泵的每一個(gè)流量Q必定相應(yīng)有一個(gè)確定的揚(yáng)程H、功率P、效率η和汽蝕余量[NPSHr]。在實(shí)際中,每條曲線都有其作用。
(1)H-Q曲線是選擇和操作使用泵的主要依據(jù)。因各種泵的結(jié)構(gòu)型式不同,所以H-Q曲線有“陡降”、“平坦”及“駝峰”等形狀。具有平坦形H-Q曲線的離心泵的特點(diǎn)是:在流量變化較大時(shí),揚(yáng)程H變化不大;具有陡降H-Q特性的離心泵正好相反，當(dāng)揚(yáng)程變化較大時(shí)，流量Q變化不大;具有駝峰形H-Q特性的泵，在某一流量范圍(小于峰值流量)內(nèi)，容易產(chǎn)生不穩(wěn)定工況。用戶可根據(jù)工作要求來選擇具有不同特性的離心泵。
對具有平坦或陡降H-Q特性的離心泵，流量Q增大，揚(yáng)程H下降，反之亦然。因此，在離心泵操作中，可以用減小或增大揚(yáng)程H來調(diào)節(jié)流量Q。生產(chǎn)中常采用調(diào)節(jié)泵出口閥門，改變管路阻力損失，進(jìn)而使泵提供的揚(yáng)程H發(fā)生變化，達(dá)到調(diào)節(jié)流量的的。
(2)P-Q曲線是合理選擇原動(dòng)機(jī)功率和正常啟動(dòng)的依據(jù)。通常應(yīng)按所需流量變化范圍中的最大功率，再加上適當(dāng)?shù)陌踩嗔?/span>來確定原動(dòng)機(jī)的功率。應(yīng)確保泵在耗功最小的條件下啟動(dòng)，以降低啟動(dòng)電流保護(hù)電動(dòng)機(jī)。一般當(dāng)Q=0時(shí)，離心泵的功率最小，因此，啟動(dòng)泵時(shí)，應(yīng)關(guān)閉出口調(diào)節(jié)閥門，待泵正常運(yùn)轉(zhuǎn)后，再調(diào)節(jié)到所需流量。渣漿泵
(3)η- Q曲線是確定泵工作經(jīng)濟(jì)性的依據(jù)。離心泵實(shí)際運(yùn)行效率是判斷離心泵運(yùn)行是否經(jīng)濟(jì)的主要指標(biāo),離心泵的工作點(diǎn)如果對應(yīng)的效率較高，即能夠滿足經(jīng)濟(jì)性要求。工程上將泵最高效率點(diǎn)稱為額定點(diǎn)，與該點(diǎn)相對應(yīng)的工況稱為額定工況(即額定流量、額定揚(yáng)程、額定功率),它一般就是泵的設(shè)計(jì)工況。離心泵的設(shè)計(jì)流量按照最高效率點(diǎn)確定,因此，當(dāng)離心泵的實(shí)際流量偏離設(shè)計(jì)流量較多時(shí)，離心泵的效率下降就較多。在實(shí)際工作中，要保證離心泵的工作點(diǎn)能夠接近離心泵效率最高點(diǎn)，泵應(yīng)盡量在高效率區(qū)域工作。為了擴(kuò)大泵的使用范圍,通常規(guī)定:對應(yīng)于最高效率點(diǎn)以下7%的工況范圍為高效工作區(qū)，有些離心泵樣本上只給出高效工作區(qū)內(nèi)的各特性曲線。
(4)NPSHr-Q曲線是檢查泵是否發(fā)生汽蝕的依據(jù)。泵的安裝高度和入口阻力損失等應(yīng)全面考慮，防止泵發(fā)生汽蝕。、
Application of characteristic curve of slurry pump
The actual characteristic curve of centrifugal pump shows that when the pump works at constant speed, each flow Q corresponding to the pump must have a certain head h, power P, efficiency η and NPSHr. In practice, each curve has its own function.
(1) H-Q curve is the main basis for selecting and operating pumps. Because of the different structure types of pumps, H-Q curve has "steep drop", "flat" and "Hump" shapes. The characteristics of the centrifugal pump with flat H-Q curve are as follows: when the flow changes greatly, the head h does not change much; the centrifugal pump with steep drop H-Q characteristics is just the opposite, when the head changes greatly, the flow Q does not change much; the pump with hump H-Q characteristics is easy to produce unstable conditions in a certain flow range (less than the peak flow). The user can choose the centrifugal pump with different characteristics according to the working requirements.
For the centrifugal pump with flat or steep drop H-Q characteristics, flow Q increases, head h decreases, and vice versa. Therefore, in the operation of centrifugal pump, the flow Q can be adjusted by reducing or increasing the head H. In production, the outlet valve of the pump is often adjusted to change the resistance loss of the pipeline, so that the head h provided by the pump changes to adjust the flow.
(2) The P-Q curve is the basis for the reasonable selection of prime mover power and normal start-up. Generally, the power of the prime mover should be determined according to the maximum power in the range of the required flow change and the appropriate safety margin. It shall be ensured that the pump is started under the condition of minimum power consumption to reduce the starting current to protect the motor. Generally, when q = 0, the power of centrifugal pump is the minimum. Therefore, when starting the pump, the outlet regulating valve shall be closed, and after the pump operates normally, the required flow shall be adjusted. Slurry pump
(3) η - Q curve is the basis to determine the economic performance of pump. The actual operation efficiency of centrifugal pump is the main index to judge whether the operation of centrifugal pump is economical. If the corresponding efficiency of the working point of centrifugal pump is high, it can meet the economic requirements. In engineering, the highest efficiency point of pump is called rated point, and the corresponding working condition is called rated working condition (i.e. rated flow, rated head and rated power), which is generally the design working condition of pump. The design flow of centrifugal pump is determined according to the highest efficiency point. Therefore, when the actual flow of centrifugal pump deviates from the design flow more, the efficiency of centrifugal pump will drop more. In practical work, to ensure that the working point of centrifugal pump can be close to the highest efficiency point, the pump should work in the high efficiency area as much as possible. In order to expand the scope of use of the pump, it is generally stipulated that the operating range corresponding to 7% below the highest efficiency point is the high efficiency working area, and some centrifugal pump samples only give the characteristic curves in the high efficiency working area.
(4) Npshr-q curve is the basis of checking whether the pump has cavitation. The installation height and inlet resistance loss of the pump shall be fully considered to prevent cavitation of the pump.
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