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渣漿泵的主要零部件
添加時間:2020.03.09

渣漿泵的主要零部件
一、葉輪
    葉輪是離心泵中傳遞能量的主要部件。對葉輪的主要要求是:單級葉輪能給液體較大的理論揚程,以便在達到高揚程時采用較少的級數,使機器結構緊湊,葉輪的效率較高,抗汽血性能好以及性能曲線形狀滿足工藝生産要求等。下面分析與這些要求有關的葉輪結構形式和幾何參數等。
    離心泵的葉輪大多數爲後彎葉片型葉輪,只有高速部分流泵和旋渦泵等采用徑向葉片葉輪。常用的後彎葉輪的葉片數一般在6~12 片之間。比轉速在60~250之間的泵,葉片常爲6,低比轉速泵可取9,高比轉速泵可爲4~5片。通常,增加葉片數可以改善液體流動情況,適當提高泵的揚程;但葉片數增加後又會使葉片摩擦損失變大,使流道通流面積變小,從而會降低效率,容易導致汽蝕。反之,若葉片數過少,每個葉片的負荷增加,對液體的導流作用減小,又會使泵的揚程下降。
    離心泵葉輪的葉片形狀有兩類:圓柱面狀葉片和扭曲葉片。石油儲運工程用離心泵的比轉速小于90的,般都采用圓柱面狀葉片它垂直于葉輪前後蓋板制造較容易。對比轉速大于90的泵,常采用扭曲葉片。
    後彎葉片型葉輪葉片的出口葉片角P2A和進口葉片角B人對泵的性能有重要的影響。葉片出口葉片角B:u一般是在15-~40°之間石消儲運工程用爲泵爲20-30。比轉述較低的,選擇較大的B2.可以增加揚程.減小直徑D2,,從而減少圓盤摩擦損失,提高泵的效率;但增大Bax時,在相同流量下增加葉輪出口速度C:壓液室的水力損失增加尤其是非設計流量下沖擊規時規,在以使H-Q性能曲線出現駝峰。此外必校時,葉道中液流相對速度w2更小,使流動擴散損失越嚴重,因此,爲獲得平坦下降的性能曲線,不宜過大的總間,

葉輪進口角 就是在葉口處,片工作面的切線(嚴路地說應該流面上葉片線的切線)與圓周切線間的夾角通常是接设计流量下波流进葉道时绝对速度c1的方向來定的。當流量偏離設計流量時,進口液流角p与葉片进口角队间的差记。为了提高泵的抗汽蚀性能,般采用正沖角Ap(3°~10)。因为正冲角能增大葉片进口角,减小葉片的弯曲,从而增加葉片进口过流面积,降低葉片进口处的C1w1;方面,采用正沖角時,在非設計流量下,液体在葉片非工作面形成旋涡,由于这里是低压,旋渦不易向高壓區擴散,因而旋渦是穩定的,對汽蝕影響較小。綜上所述,葉片进口角应在18°~-25°範圍內。
    就离心泵葉輪的结构形式来看,可分爲閉式.半開式和開式三種,如圖1- 58所示。
    式葉具有板和輪盤,流道是封闲的,如圖1-58(a)这种时輪水力效率較高,適用于高揚程,輸送净的液体,半开式葉輪只有輪盘。流道是半开启的:如圖,运用于输送含固体颗粒和杂质的液体它的葉片和輪盘可由整块锻件铣制成一个整体。强度较高,且制造较容易;开式葉輪既无蓋板,又无輪盤,流道完全敞开,如圖1 58(c)所示,常用来输送浆状或糊状液体。离心泵葉輪还分为单吸式和双吸式两种,单吸式构造简单,液体从葉輪一侧被吸;双吸式葉輪,如圖1- 58(d)所示,构造比较复杂,液体从葉輪两侧吸入。显然,双吸式具有较大的吸液能力,抗汽蝕性能較好,而且基本上可以消除軸向力,適用于流量較大的情況。
    另外,閉式葉輪和半开式葉輪后蓋板与泵壳之间的缝隙内,液体的压力较口侧高,这便产生了指向葉輪吸口方向的軸向推力使葉輪向吸引起葉輪与泵壳接胜处磨损。严重时造成振動。为此,可在后蓋板上钻几个小孔,称为平衡孔,让一部分高压液体到低压区,降低葉輪两侧的压力差。这种方法虽然他便,但由于體通過平短路流,增加了內泄漏量,因而降低了泵的效率。

Main parts of slurry pump

I. impeller

Impeller is the main part of centrifugal pump to transfer energy. The main requirements for impellers are: the single-stage impellers can give a larger theoretical lift of liquid, so as to adopt less stages when reaching the high lift, so as to make the machine structure compact, the efficiency of impellers is high, the resistance to steam blood is good, and the performance curve shape can meet the production requirements. The impeller structure and geometric parameters related to these requirements are analyzed below.

Most of the impellers of centrifugal pumps are backward curved impeller, only high-speed partial flow pump and vortex pump adopt radial impeller. The commonly used number of blades of backward curved impeller is generally between 6 and 12. For pumps with specific speed between 60-250, the blades are usually 6 pieces, 9 pieces for low specific speed pumps and 4-5 pieces for high specific speed pumps. Generally, increasing the number of blades can improve the flow of liquid and increase the head of pump properly; however, increasing the number of blades will increase the friction loss of blades and reduce the flow passage area, which will reduce the efficiency and easily lead to cavitation. On the contrary, if the number of blades is too small, the load of each blade will increase, the diversion effect on the liquid will decrease, and the head of the pump will decrease.

There are two types of blade shapes of centrifugal pump impeller: cylindrical surface blade and twisted blade. When the specific speed of centrifugal pump used in petroleum storage and transportation engineering is less than 90, it is easy to use cylindrical blade which is perpendicular to the front and back cover plate of impeller. Compared with the pump whose speed is more than 90, the twisted blade is often used.

The outlet blade angle P2a and the inlet blade angle B of the backward curved blade type impeller blade have an important influence on the performance of the pump. The blade angle B: u at the blade outlet is generally 20-30 for the stone elimination storage and transportation project between 15-40 °. Compared with the pump with lower rotation, the larger B2 can increase the lift and reduce the diameter D2, so as to reduce the disc friction loss and improve the efficiency of the pump; but when Bax is increased, the impeller outlet speed C is increased under the same flow rate; the hydraulic loss of the pressure chamber is increased, especially the impact gauge under the non design flow rate, so as to make the H-Q performance curve appear hump. In addition, when it has to be calibrated, the relative velocity W2 of the liquid flow in the blade channel is smaller, which makes the flow diffusion loss more serious. Therefore, in order to obtain a flat decline performance curve, it is not suitable to select a large total chamber,

The impeller inlet angle is the angle between the tangent line of the blade working surface (strictly speaking, it should be the tangent line of the blade bone line on the flow surface) and the tangent line of the circumference, which is usually determined by the direction angle of the absolute velocity C1 when the wave flows into the blade channel under the design flow. When the flow deviates from the design flow, the difference between the inlet flow angle P and the blade inlet angle is recorded. In order to improve the anti cavitation performance of the pump, the positive impact angle AP (3 ° ~ 10) is generally used. Because the positive impact angle can increase the inlet angle of the blade and reduce the bending of the blade, thus increasing the flow area at the inlet of the blade and reducing the C1 and W1 at the inlet of the blade; on the other hand, when the positive impact angle is adopted, under the non design flow rate, the liquid forms a vortex on the non working surface of the blade. Because it is low pressure, the vortex is not easy to spread to the high pressure area, so the vortex is stable and has little impact on cavitation. To sum up, the blade inlet angle should be in the range of 18 ° - 25 °.

According to the structure of centrifugal pump impeller, it can be divided into closed, semi open and open, as shown in figure 1-58.

The closed impeller has a cover plate and a disc, and the flow channel is sealed, as shown in Fig. 1-58 (a). This kind of impeller has high hydraulic efficiency, which is suitable for high lift and conveying clean liquid. The semi open impeller has only a disc. The runner is half open: as shown in the figure, it is used to transport liquid containing solid particles and impurities. Its blades and wheels can be milled into a whole by a whole forging. It has high strength and is easy to manufacture; the open impeller has neither cover plate nor disc, and the flow channel is completely open, as shown in Figure 158 (c), which is commonly used to transport slurry or paste liquid. The impeller of centrifugal pump is also divided into single suction and double suction. The single suction structure is simple, and the liquid is drawn in from one side of the impeller; the double suction impeller, as shown in figure 1-58 (d), has complex structure, and the liquid is drawn in from both sides of the impeller. Obviously, the double suction type has a larger suction capacity, better anti cavitation performance, and can basically eliminate the axial force, which is suitable for the case of large flow.

In addition, in the gap between the rear cover plate of closed impeller and semi open impeller and the pump housing, the liquid pressure is higher than that of the inlet side, which produces the axial thrust pointing to the suction port of the impeller, makes the impeller move towards the suction port, and causes the abrasion at the junction of the impeller and the pump housing. In serious cases, it will cause vibration of slurry pump. Therefore, several small holes can be drilled on the back cover plate, called balance holes, to let part of the high-pressure liquid leak into the low-pressure area, reducing the pressure difference on both sides of the impeller. Although this method is convenient, because the liquid is short circuited through the balance hole, the internal leakage is increased, so the efficiency of the pump is reduced.





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