Typically, in the presence of contaminated process fluid sealing occasions, the use of common contact double-ended mechanical seal between the two seals by plugging fluid assist system injection pressure is higher than the sealing medium pressure blocking fluid to prevent the sealing medium to the outside world Give way. However, in practical engineering applications, often due to many reasons failure can not effectively prevent the leakage of sealed media, especially for the delivery of solids containing granular media, frequently open and easy to pump down process pump, the reliability of the seal far less Intentions. Sewage discharge pump of a petrochemical company single-unit process plant, due to the sealing effect is not satisfactory, its leakage has become an urgent problem to be solved. 1, submersible sewage pump mechanical seal Technical parameters The pump model WQ30-35-7.5, in normal work, the inlet pressure close to atmospheric pressure, the outlet pressure of 0.55mpa, the delivery temperature is room temperature. The mechanical seal used is a double-end multi-spring balanced structure, the inner diameter of the sealing surface is 35.2mm, the outer diameter is 44.2mm, the width of the end surface is 4.5mm and the balance diameter is 36.8mm. (2) Problems under working conditions ) Isolation fluid pressure is less than the pressure of the sealed medium In order to ensure the sealing function of the double end face, in theory, the pressure of the isolation fluid must be higher than the pressure of the sealed medium by 0.1-0.15mpa to prevent the leakage of the medium with certain toxicity. However, the actual project, the isolation fluid pressure is not greater than 0.3mpa, less than the pressure of the medium is sealed 0.55mpa, so the use of the seal is not satisfactory. (2) The transportation medium contains a large amount of solid particles. Because the sewage pump is to process equipment in the discharge to the tank in a variety of process fluids (including a large number of cooling water) regularly sent to the sewage treatment station for purification, which contains a certain percentage Of impurities in solid particles, easy to enter the seal between the severe abrasive wear, so early seal failure. If the isolation fluid assist system does not work properly and the pressure of the isolation fluid is less than the pressure of the sealed medium, the solid particles will enter between the inside seal faces and the probability of failure will be greatly increased. (3) In frequent opening and closing state The pump automatically stops operating when the liquid in the tank has been pumped out. When the liquid in the tank accumulates to the specified level, the pump automatically switches to the operating state again, precisely because the pump is in Frequent open and stop the state, so that mechanical seals appear periodically unstable state of dry friction, which is one of the main sealing frequent failures. (4) pump prone to take-off Because the pump is in frequent on-off state, when the liquid level in the tank down to a certain extent, it is easy to make the pump evacuated, resulting in severe vibration and noise, the phenomenon of this inevitable result of the seal Unstable working conditions, the possibility of seal failure greatly increased. Based on the above analysis, it can be learned that, due to the limitation of the self-sealing principle and the particularity of working conditions, the ordinary double-end-contact mechanical seal is difficult to ensure long-term sealed safe operation under the environmental conditions. Moreover, under steady-state conditions, although the use of double-face seal or tandem seal can basically eliminate the leakage of the medium is sealed, but the auxiliary seal system complexity, increased operating costs, and the reliability of the auxiliary system directly affects the use of the seal effect. 3, submersible sewage pump mechanical seal transformation Since the cone mechanical seal is particularly suitable for pumping equipment containing solid suspended matter, so the sealing surface changed to cone sealing. Static ring material is filled with tetrafluoroethylene, moving ring material is stainless steel, cone spray tungsten carbide. The main features are as follows. (1) The moving ring of the cone mechanical seal is a conical ring, with the wear of the static ring, the length of the contact busbar L increases and the outer diameter of the stationary ring also increases. (2) The busbar length of the sealing contact surface is very short Stable operation of the initial 0.3-0.5mm), so the contact end surface temperature difference between inside and outside small, low temperature, reducing the degree of adhesive wear. Static ring has a larger cross-section of compression, pressure deformation is small. (3) Both the sealing sleeve and the moving ring have a certain degree of floating, so that the sealing surface always maintains a good contact state. The suspended particles in the medium are not easy to enter the sealing surface. Medium leakage direction and its direction of centrifugal force at an angle, to reduce leakage beneficial.
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