双筒体多级泵结构

双简体内壳可以是节段导叶式多级系或水平中开蜗壳式多级泵，即节段导叶式多级泵或水平中开蜗壳式多级泵外体加一个圆简体。对于高参数要求(如高温、高压、高速)、高可靠性要求的泵产品，国内外一般均采用双简体结构。
(1)内壳体连接  由于是双简体，外简体承受泵的全部压力。相反的，内壳体处于泵压力之中，内壳体外压力大于内壳体内压力，故连接螺栓可以少些、小些，甚至可以不要。不过为了装配方便，一般还是有小的连接螺栓。
(2)限位吸入函体的吸入口 与外简体吸入口对中限位，有的仅在吸入函体下部开槽装键限位防转，也有的在内壳体的末级导叶与泵盖上加销(钉)限位防转。
(3)内壳体膨胀问题内壳体 相对外简体之间有一个热胀问题，一般需加一个热膨胀补偿器。有的产品采用一组(6或7个) 缠绕垫，每个中间加一个金属间隔环;有的产品采用泵盖与内壳体之间装8组小蓄能弹簧以补偿内壳体热胀伸长问题;还有一种是在内壳体与泵筒体之间装一个大的蝶簧，起到同样的作用(但由于压缩量小，这种结构一般用于常温双筒体多级泵)。
(4) 整体抽芯  这是目前世界上的新型结构，拆掉泵盖后，除芯包外，还有轴承体和轴封不用先拆卸，可随芯包由筒体内抽出。芯包包括转子部件、内壳体，而内壳体包括吸入函体、中段、导叶等件。也有将轴承体和轴封包括在芯包内的说法。
(5)内壳体高压端与低压端分开结构 由于外简体是圆形的，承压能力很强(大)，加之段与段密封较好，故一般泵可以不分高压端和低压端，但有的泵分开了，分开时必须注意下列问题:
图5-41a所示为采用某一中段端面压靠着简体内止口台阶，中间加缠绕垫或蝶形弹簧，将筒体内高低压分开的结构。当受热时，内壳体膨胀，由于补偿器的补偿，可保证其密封不会松开。这种结构，如果单从高低压分开面或单从吸入函体密封与泵补偿器来看，当膨胀时，均能达到补偿作用，越压越紧。如果我们从吸入函体密封与高低压分开面这段距离来看，当内壳膨胀时，因为吸入的体到高低压分开面这段距离有多个中段，这些中段膨胀的总值远远大于上面值，高低压分开面与补偿器的距离补偿势必使高低压分开面脱离，有松开密封的趋势，起不到高低压分开的作用。这里推辉图5-41所示结构，它是内壳体某中段外径加0形圈，渣浆泵压力高时加金属挡圈。它可以在外简体内滑动，这种0形圈胶料温度为200°C静密封压力可达100MPa，特殊订货还可以高，对锅炉给水泵来说是不成问题的。

Double cylinder multistage pump structure

The double cylinder inner shell can be a segmental guide vane type multistage system or a horizontal middle opening volute type multistage pump, that is, a segmental guide vane type multistage pump or a horizontal middle opening volute type multistage pump with a circular cylinder added to the outer body. For pump products with high parameter requirements (such as high temperature, high pressure, high speed) and high reliability requirements, double cylinder structure is generally adopted at home and abroad.

(1) Because the connection of the inner shell is a double cylinder, the outer cylinder bears all the pressure of the pump. On the contrary, the inner shell is under the pump pressure, and the external pressure of the inner shell is greater than the internal pressure of the inner shell, so the connecting bolts can be less, smaller or even unnecessary. However, for the convenience of assembly, there are generally small connecting bolts.

(2) The suction inlet of the limiting suction box is aligned with the suction inlet of the outer cylinder. Some of them are only slotted in the lower part of the suction box to limit and prevent rotation, and some of them are equipped with pins (nails) on the last stage guide vane and pump cover of the inner shell to limit and prevent rotation.

(3) There is a thermal expansion problem between the inner shell and the outer shell, so a thermal expansion compensator is usually needed. Some products use a group (6 or 7) of winding pads, each with a metal spacer ring in the middle; some products use 8 groups of small energy storage springs between the pump cover and the inner shell to compensate the thermal expansion and elongation of the inner shell; Another is to install a large butterfly spring between the inner shell and the pump barrel, which plays the same role (but due to the small amount of compression, this structure is generally used for normal temperature double barrel multistage pump).

(4) Integral core pulling is a new structure in the world at present. After removing the pump cover, in addition to the core package, there are bearing body and shaft seal, which can be pulled out from the cylinder with the core package instead of being disassembled first. The core package includes rotor parts and inner shell, and the inner shell includes suction box, middle section, guide vane, etc. It is also said that the bearing body and shaft seal are included in the core package.

(5) The high-pressure end and low-pressure end of the inner shell are separated. Because the outer shell is round, it has strong pressure bearing capacity (large), and the sections are well sealed, so the general pump can not be divided into the high-pressure end and the low-pressure end, but some pumps are separated, so the following problems must be paid attention to when they are separated:

Figure 5-41a shows a structure in which a middle end face is pressed against the inner stop step of the cylinder, and a winding pad or butterfly spring is added in the middle to separate the high and low pressure in the cylinder. When heated, the inner shell expands, and the compensation of the compensator can ensure that the seal will not loosen. This kind of structure, if only from the high and low pressure separation surface or from the suction box seal and pump compensator, can achieve the compensation effect when expanding, the more pressure, the more tight. If we look at the distance between the seal of the suction box and the high and low pressure separation surface, when the inner shell expands, because the distance between the suction box and the high and low pressure separation surface has many middle sections, and the total value of the expansion of these middle sections is far greater than the above value, the compensation of the distance between the high and low pressure separation surface and the compensator is bound to make the high and low pressure separation surface separate, and there is a tendency to loosen the seal, which can not separate the high and low pressure The role of the government. Here is the structure shown in figure 5-41, which is that the outer diameter of a middle section of the inner shell is added with a 0-ring, and the metal retaining ring is added when the slurry pump pressure is high. It can slide inside the outer cylinder. The temperature of the 0-ring compound is 200 ° C, and the static sealing pressure can reach 100MPa. It can also be high for special orders, which is not a problem for the boiler feed water pump.