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Common Leakage Phenomenon And Countermeasure Of Mechanical Seal Of Water Pump
May 08, 2018

Common leakage phenomena of pump mechanical seals and countermeasures This article summarizes the common causes of mechanical seal leakage.

The mechanical seal itself is a kind of high-precision precision component, and it has high requirements for the design, machining and assembly quality. In the use of mechanical seals, various factors should be analyzed using mechanical seals, mechanical seals apply to the technical requirements of various pumps and the use of media requirements and have sufficient lubrication conditions, so as to ensure long-term reliable operation of the seal. Keywords: Mechanical Seal Leakage Phenomenon Mechanical seal, also known as end face seal, has a pair of end faces perpendicular to the axis of rotation. This end face, under the influence of fluid pressure and compensatory mechanical external spring force, relies on the cooperation of the auxiliary seal to keep fit with the other end. , and slide relative to prevent fluid leakage. First, the common leakage phenomenon The proportion of mechanical seal leakage accounted for more than 50% of all maintenance of the pump, mechanical seal operation directly affects the normal operation of the pump, are summarized and analyzed as follows. 1. Periodic Leakage (1) The pump rotor has a large amount of axial turbulence, and there is a large amount of interference between the auxiliary seal and the shaft. The moving ring cannot move flexibly on the shaft. After the pump turns over and the static and dynamic rings are worn, no compensation displacement can be obtained. Countermeasures: When assembling the mechanical seal, the shaft axial movement should be less than 0.1mm. The amount of interference between the auxiliary seal and the shaft should be moderate. While ensuring the radial seal, the ring can be moved flexibly after being assembled. Pressing the ring against the spring will bounce back freely.) (2) Insufficient amount of lubricating oil on the sealing surface causes dry friction or napped sealing surfaces. Countermeasures: The height of the oil in the oil chamber cavity should be added to the sealing surface of the moving and static rings. (3) Rotor periodic vibration. The reason is that the stator is not aligned with the upper and lower end caps or the impeller and the main shaft are not balanced, cavitation or bearing damage (wear), this situation will shorten the sealing life and produce leakage. Countermeasures: The above problems can be corrected according to maintenance standards. 2. Shaft phenomenon caused by leakage of small submersible sewage pump seals (1) Failure of small pump seals below 715kW often generates grinding shafts. The main locations of the grinding shafts are the following: the auxiliary ring of the moving ring, the position of the stationary ring, A few springs have a grinding axis. (2) The main reason for the grinding shaft: 1BIA type double-end mechanical seal, the back pressure state is a bad working state, the particles and impurities in the medium can easily enter the sealing surface, making the seal ineffective. 2 The main part of the grinding shaft is a rubber bellows, and the upper sealing surface is in a poor lubrication state. The friction torque between the moving and the stationary ring is greater than the transmission torque between the rubber corrugated tube and the shaft, and relative rotation occurs. 3 The auxiliary seals of the moving and static rings are corroded by the weak acid and weak alkali in the sewage, and the rubber parts have no elasticity. Some have rotted, lost their proper function, and created a grinding axis. (3) In order to solve the above problems, the following measures have been taken: 1 To ensure the cleanliness of the lower end cap and the oil chamber, and to prohibit the assembly of unclean lubricants. 2 The oil line in the cavity of the machine oil seal chamber should be higher than the sealing surface of the dynamic and static rings. 3 According to different use of media choose a different structure of the machine seal. For the high lift pump, the mechanical seal structure should be redesigned. For the corrosive medium rubber, the fluoro rubber resistant to weak acid and weak alkali should be used. Machine seal static ring should be added to prevent re-sale. 2. Leakage due to pressure (1) Leakage of mechanical seal caused by high pressure and pressure waves Due to the excessive design of the specific pressure of the spring and the total specific pressure and the pressure in the sealed chamber exceeding 3 MPa, the pressure of the sealed end face is excessively large. The film is difficult to form, the sealing face wears badly, and the heat generation increases, resulting in thermal deformation of the sealing surface. Countermeasures: When assembling the machine seal, the amount of spring compression must be carried out according to regulations. No phenomenon of excessive or too small is allowed. Mechanical seals under high pressure conditions should take measures. In order to make the end face force reasonable, minimize deformation, can be used hard alloy, ceramics and other materials with high compressive strength, and strengthen the cooling lubrication measures, select the available transmission methods, such as keys, pins and so on. (2) Leakage of mechanical seal caused by vacuum operation In the process of starting and stopping the pump, due to the clogging of the pump inlet, the pumping medium contains gas, etc., it may cause negative pressure in the seal chamber, and negative pressure in the seal chamber. Causes dry friction on the sealed end face. The built-in mechanical seal will cause leakage (water) phenomenon. The difference between the vacuum seal and the positive pressure seal is the difference in the directionality of the sealed object, and the mechanical seal also has adaptability in a certain direction. Countermeasures: Double mechanical seals are used to help improve lubrication conditions and seal performance. Third, due to media-induced leakage (1) Most submersible pump mechanical seal dismantling, static seal ring and the auxiliary seal ring is inelastic, and some have decayed, resulting in a large number of mechanical seal leakage or even grinding Axis phenomenon. Due to the corrosive effect of high temperature, weak acid and weak alkali in the sewage on the static ring and the auxiliary ring rubber seal of the moving ring, the mechanical leakage is too large, and the dynamic and static ring rubber seal material is nitrile-40, which is not high temperature resistant. Not acid and alkali, when the sewage is acidic alkaline corrosion. Countermeasures: For corrosive media, rubber parts should be selected from fluoro rubbers that are resistant to high temperatures, weak acids, and weak bases. (2) Leakage of mechanical seal caused by solid particles Impurities If the solid particles enter the sealing face, it will scratch or accelerate the wear of the sealing face. The accumulation rate of scale and oil on the surface of the shaft (set) exceeds the wear rate of the friction pair, resulting in The moving ring cannot compensate for the wear displacement. The operating life of the hard-to-hard friction pair is longer than that of the hard-to-graphite friction pair because the solid particles can be embedded in the sealing surface of the graphite seal ring. Countermeasures: The mechanical seal of tungsten carbide to tungsten carbide friction pair should be selected where solid particles can easily enter. Fourth, due to other problems caused by the leakage of mechanical seals Mechanical seals also exist in design, selection, installation and other places that are not reasonable enough. (1) The spring compression must be carried out in accordance with the regulations. No excessive or small phenomenon is allowed. The error is ±2mm. Excessive compression increases the pressure ratio at the end face, resulting in excessive frictional heat, resulting in thermal deformation of the sealing surface and accelerated wear of the end face. If the compression amount is too small, the specific pressure of the end face of the movable and stationary ring is insufficient, and it cannot be sealed. (2) Install the end face of the shaft (or sleeve) of the dynamic ring seal and the seal gland (or housing) where the static ring seal is installed to be chamfered and lighted so as not to damage the static and dynamic ring seal during assembly. V. Concluding remarks The above summarizes the common causes of mechanical seal leakage. The mechanical seal itself is a kind of high-precision precision component, and it has high requirements for the design, machining and assembly quality. In the use of mechanical seals, various factors should be analyzed using mechanical seals, mechanical seals apply to the technical requirements of various pumps and the use of media requirements and have sufficient lubrication conditions, so as to ensure long-term reliable operation of the seal.