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Centrifugal pump packing seal improvement process and the use of results
Nov 21, 2017

Soft stuffing seals are commonly used as seals for rotating or reciprocating motion elements in the annular space between shaft seals. Its wide range of application, medium pressure -1.3 ~ 35MPa; working temperature -50 ~ 600 ℃; sealing surface line speed of 20m / s. PetroChina Liaoyang Petrochemical Branch of the application of 20sh-9A centrifugal pump is a typical soft packing seal. Soft packing rely on packing gland axial compression, resulting in radial deformation to fill the gap surface seal. Deformation of soft packing relies on proper radial close to the shaft and the inner wall of the stuffing box to ensure reliable sealing.

First, the existing problems

20sh-9A centrifugal pump seal, is a standard soft packing seal, as shown in Figure 1, the filler for the oil asbestos.

In order to make the axial and radial force distribution, the use of intermediate seal ring seal will be divided into two sections, in order to prevent the packing is squeezed out with a certain gap filler sleeve. In order to completely solve the problem of serious leakage of sealing parts, the sealing parts and packing must be adjusted and improved.

Second, the improvement of packing seal

1. Select the packing

Comparative analysis of various fillers, the choice of expanded graphite packing - also known as flexible graphite packing. Expanded graphite is chosen because of its many advantages over asbestos packing.

2 sealed form of choice

The production of expanded graphite is carried out under the pressure of 20 ~ 50MPa with press, with the increase of the forming pressure, the density is correspondingly increased. Therefore, the application of graphite packing, under different load, the density is also different. But under the same load, its final density is the same. Therefore, a single use of expanded graphite as a packing should not be used with other packing materials with different packing density to ensure the sealing effect under various loads.

Third, the use of the rectification effect

After the improvement, after 900h operation test, the effect is very good. The temperature of the stuffing box is the same as the room temperature. When the pump is running and the pump is stopped, the drip can be leak-proof, and the motor current can drop by 1 ~ 2A during operation. Running 14000h, routine overhaul inspection, observation stuffing box in a variety of components. Inspection found that the sleeve wear is quite small; graphite ring only trace wear; asbestos packing than before, wear and tear to reduce a lot. Visible, this seal can still continue to run, and can guarantee a good sealing effect. Running 28 000h, pump disassembly inspection, observation stuffing box, graphite ring is still not a lot of wear and tear, asbestos packing has been inelastic, no impregnated grease and graphite, lost the role of seal.

From the above observations prove that the improvement is successful, both to ensure a good sealing effect, but also saving, water-saving, and can extend the pump overhaul cycle. Therefore, it can be widely used. However, due to the fact that the seal type has been tried out only in the water supply pump, the selection and collocation of the seal used in other conditions have yet to be further studied and tested.


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