(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。
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.