【導(dǎo)讀】空，不斷吸引更多的流體進入泵的葉輪附近，這樣由葉輪的旋轉(zhuǎn)來完成液體的進出。等的一系列問題。從而幫助我們加深對離心泵的理解。泵的提出，最先是用于轉(zhuǎn)移或壓縮液體和氣體的設(shè)備。在所有泵中，我們一步步采。取措施來防止氣蝕，氣蝕將減少流量并且破壞泵的結(jié)構(gòu)。用來處理氣體和蒸汽的泵稱為。氣體壓縮機，研究流體的運動的科學(xué)稱為流體力學(xué)。到一萬磅每平方英尺。日常生活中，泵是很多見的，有用于在魚池和噴泉使水循環(huán)和向。水中充氣的電泵，還有用于從住宅處把水引走的污水泵。不會因為碎片而堵塞。在這些區(qū)域里，早期的泵是為了將水一桶一桶的從水源或河渠。古希臘的發(fā)明家和數(shù)學(xué)家阿基米德被認為是公元前3世紀首先提出螺。之后，古希臘發(fā)明家發(fā)明了第一個提水泵。的狀態(tài)是漸進的，對于中間狀態(tài)，設(shè)備可稱為混流泵。葉輪由一系列弧形葉片組成，因此能使液體的流動盡可能平穩(wěn)。

　　

【正文】 perature of the liquid rises, raising the vapor pressure such that it bees equal to or greater than the operating pressure at the liquid surface. For example, if water at room temperature (about 77 176。F) is kept in a closed container and the system pressure is reduced to its vapor pressure (about psia), the water quickly changes to a vapor. Also, if the operating pressure is to remain constant at about psia and the temperature is allowed to rise above 77 176。F, then the water quickly changes to a vapor. Just like in a closed container, vaporization of the liquid can occur in centrifugal pumps when the local static pressure reduces below that of the vapor pressure of the liquid at the pumping temperature. Step Two, Growth of bubbles Unless there is no change in the operating conditions, new bubbles continue to form and old bubbles grow in size. The bubbles then get carried in the liquid as it flows from the impeller eye to the impeller exit tip along the vane trailing edge. Due to impeller rotating action, the bubbles attain very high velocity and eventually reach the regions of high pressure within the impeller where they start collapsing. The life cycle of a bubble has been estimated to be in the order of seconds。 Step Three, Collapse of bubbles， As the vapor bubbles move along the impeller vanes, the pressure around the bubbles begins to increase until a point is reached where the pressure on the outside of the bubble is greater than the pressure inside the bubble. The bubble collapses. The process is not an explosion but rather an implosion (inward bursting). Hundreds of bubbles collapse at approximately the same point on each impeller vane. Bubbles collapse nonsymmetrically such that the surrounding liquid rushes to fill the void forming a liquid microjet. The micro jet subsequently ruptures the bubble with such force that a hammering action occurs. Bubble collapse pressures greater than 1 GPa (145x106 psi) have been reported. The highly localized hammering effect can pit the pump impeller. The pitting effect is Collapse of a Vapor Bubble 18 illustrated schematically in this the figure. After the bubble collapses, a shock wave emanates outward from the point of collapse. This shock wave is what we actually hear and what we call cavitation. The implosion of bubbles and emanation of shock waves (red color) . In nutshell, the mechanism of cavitation is all about formation, growth and collapse of bubbles inside the liquid being pumped. But how can the knowledge of mechanism of cavitation can really help in troubleshooting a cavitation problem. The concept of mechanism can help in identifying the type of bubbles and the cause of their formation and collapse. (5)Solution and Remedies： For vaporization problems (cavitation) ( cure vaporization problems you must either increase the suction head, lower the fluid temperature, or decrease the . Required. We shall look at each possibility: 1).Increase the suction head: ?Raise the liquid level in the tank ? Raise the tank ? Put the pump in a pit ? Reduce the piping losses. These losses occur for a variety of reasons that include : 1. The system was designed incorrectly. There are too many fittings and/or the piping is too small in diameter. 2. A pipe liner has collapsed. 3. Solids have built up on the inside of the pipe. 4. The suction pipe collapsed when it was run over by a heavy vehicle. 5. A suction strainer is clogged. 6. Be sure the tank vent is open and not obstructed. Vents can freeze in cold weather 7. Something is stuck in the pipe, It either grew there or was left during the last time the system was opened . Maybe a check valve is broken and the seat is stuck in the pipe. 8. The inside of the pipe, or a fitting has corroded. 19 9. A bigger pump has been installed and the existing system has too much loss for the increased capacity. 10. A globe valve was used to replace a gate valve. 11. A heating jacket has frozen and collapsed the pipe. 12. A gasket is protruding into the piping. 13. The pump speed has increased. ? Install a booster pump ? Pressurize the tank 2) lower the fluid temperature ? Injecting a small amount of cooler fluid at the suction is often practical. ? Insulate the piping from the sun39。s rays. ? Be careful of discharge recirculation lines, they can heat up the suction fluid. 3) reduce the . Required ? Use a double suction pump. This can reduce the . by as much as 27% or in some cases it will allow you to raise the pump speed by 41% ? Use a lower speed pump ? Use a pump with a larger impeller eye opening. ? If possible install an Inducer. These inducers can cut . by almost 50%. ? Use several smaller pumps. Three half capacity pumps can be cheaper than one large pump plus a spare. This will also conserve energy at lighter loads. (2. For suction cavitation: 1. Remove debris from suction line. 2. Move pump closer to source tank/sump 3. Increase suction line diameter. 4. Decrease suction lift requirement 5. Install larger pump running slower which will decrease the Net Positive Suction Head Required by the pump(NPSHR). 6. Increase discharge pressure. 7. Fully open Suction line valve. 20 (3. For discharge cavitation: 1. Remove debris from discharge line. 2. Decrease discharge line length 3. Increase discharge line diameter. 4. Decrease discharge static head requirement. 5. Install larger pump, which will maintain the required flow without discharge cavitating. 6. Fully open discharge line valve. (4. For Recirculation cavitation: the pump for lower suctionspecific speeds and limiting the range of operation to flow capacities above the point of recirculation. 2. Raising the suction head.