容积损失与渣浆泵容积效率比例

泵中的容积损失主要有下列几种: 

(1)叶轮入口处密封环泄露的容积损失，如图2-34所示；

(2)轴向力平衡机构的容积损失;

(3)在多级泵中，还有级间回流损失;

(4)轴封泄漏的容积损失。
1.叶轮入口处密封环的容积损失
    在叶轮入口处，叶轮与泵体间有一个很小密封间隙。由于泵腔内的压力高于叶轮入口处的压力，所以有一小股液体通过此密封间隙从叶轮出口回流到叶轮入口，通常把这部分能量损失称为密封环泄漏损失q1。

密封环间隙宽度b一般可参考表2-1 选取，但对于耐腐泵、油泵、杂质泵、液下泵及输送黏性液体、带颗粒液体(例泵油等)的泵间隙适当放大。
    从式(2-23)可以看出，密封环的泄漏量q1,与密封环处的直径、 间隙宽度b、圆角系数、两端压差有关。为了减少容积损失，尽量减少间隙宽度b,当密封环磨损增大时，要及时修复更换。为了减少两端的压差,应增加密封环间隙的圆角系数、长度L。尤其对高扬程的泵，可将密封环做成迷宫形或锯齿形，如图2-35所示，以减小密封环的泄漏。

2.轴向力平衡机构的容积损失

轴向力平衡方法很多，机构也很多，将在第四章中介绍。常用的为平衡孔结构和多级泵中的平衡盘、平衡鼓结构。平衡孔的泄漏量仍可按式(2 -24)计算。
3.级间回流损失
    如图2-36所示级间间隙的泄漏液体，流经叶轮与导叶间的侧隙后，与叶轮流出的液体混合，经导叶和反导叶，又经级间间隙流向前级叶轮的侧隙，如此循环。由于这部分液体不

经过叶轮，不影响泵的流量，所以这部分能量损失不属于容积损失，但却损失了一部分功率。
4.轴封泄漏
    轴封泄露较小，尤其是轴封采用机械密封时。但对于小泵也应重视。尤其是当轴封失效时，泄漏量较大。
    泵的容积效率从 上面分析计算可看出与泵的结构形式及比转数n泵的流量大小有关。图2-37为一般情况下离心系的容积效率。渣浆泵

Ratio of volume loss to volume efficiency of slurry pump

The volume loss in the pump is mainly as follows:

(1) volume loss due to leakage of sealing ring at the inlet of impeller, as shown in figure 2-34;

(2) volume loss of axial force balancing mechanism;

(3) in the multi-stage pump, there is also a loss of return flow between stages;

(4) volume loss of shaft seal leakage.

1. Volume loss of sealing ring at impeller inlet

At the inlet of impeller, there is a small sealing clearance between impeller and pump body. Because the pressure in the pump cavity is higher than the pressure at the impeller inlet, a small stream of liquid flows back from the impeller outlet to the impeller inlet through the sealing clearance. This part of energy loss is usually called the leakage loss of the sealing ring Q1.

Generally, the clearance width b of sealing ring can be selected with reference to table 2-1, but the clearance of anti-corrosion pump, oil pump, impurity pump, submerged pump and pump for delivering viscous liquid and liquid with particles (such as pump oil, etc.) can be appropriately enlarged.

It can be seen from equation (2-23) that the leakage of the sealing ring Q1 is related to the diameter, clearance width b, fillet coefficient and pressure difference at both ends of the sealing ring. In order to reduce the volume loss and reduce the gap width B as much as possible, when the wear of the sealing ring increases, it is necessary to repair and replace it in time. In order to reduce the pressure difference at both ends, the fillet coefficient and length L of the seal ring gap should be increased. Especially for pumps with high lift, the sealing ring can be made into labyrinth or serrated shape, as shown in Fig. 2-35, so as to reduce the leakage of the sealing ring.

2. Volume loss of axial force balancing mechanism

There are many methods of axial force balance and many mechanisms, which will be introduced in Chapter 4. Commonly used for the balance hole structure and multi-stage pump balance plate, balance drum structure. The leakage of balance hole can still be calculated according to formula (2-24).

3. Loss of return flow between stages

As shown in Fig. 2-36, the leakage liquid of interstage clearance flows through the side clearance between impeller and guide vane, then mixes with the liquid flowing out of impeller, flows through the guide vane and anti guide vane, and then flows to the side clearance of front stage impeller through interstage clearance, so it circulates. Because this part of the liquid doesn't

After the impeller, the flow of the pump is not affected, so this part of energy loss is not volume loss, but a part of power is lost.

4. Shaft seal leakage

The leakage of shaft seal is small, especially when mechanical seal is adopted. However, attention should also be paid to small pumps. Especially when the shaft seal fails, the leakage is large.

From the above analysis and calculation, it can be seen that the volume efficiency of the pump is related to the structure of the pump and the flow of the specific speed N pump. Figure 2-37 shows the volumetric efficiency of the centrifugal system in general. Slurry pump