Analysis of the functions and characteristics of mechanical seal flushing schemes

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This post was last edited by Zunming Machinery on 2023-7-5 10:13. In fluid machinery, the component subject to the harshest operating conditions is the mechanical seal. Achieving static sealing in environments with high temperatures, high pressures, and corrosive conditions is already quite difficult; it is even more challenging to achieve dynamic sealing on a seal surface just a few millimeters wide while the component is rotating at high speeds. To address this tricky problem, through long-term practice, two approaches have been found: one is to start with the structure and materials of mechanical seals in order to make them suitable for harsh working conditions. This **improves the performance of mechanical seals**, expanding their range of application and suitable operating conditions. Adding auxiliary systems to mechanical seals is costly, and yet it still does not solve the problem at its root. Once the seal fails, the consequences are severe. Another approach is to improve the working environment through auxiliary facilities. At present, mechanical seals that do not require any auxiliary devices in actual operation are truly rare. With the help of auxiliary facilities, certain harsh working environments can be transformed into sealed and acceptable conditions; flushing is highly beneficial for the long-term temperature operation of mechanical seals: 1. Flushing serves to dissipate heat. The heat generated by the liquid seal must be controlled. This can be achieved by flushing the sealing chamber with liquid to carry away heat and control temperature rise. 2. Lower the liquid temperature. In some cases, the liquid temperature is too high, affecting the sealing performance. In such cases, the temperature must be reduced to improve the properties of the liquid. 3. Change the pressure in the sealing chamber. In some cases, it is necessary to increase or decrease the pressure in the sealing chamber to improve performance. This can be achieved by controlling evaporation or reducing the thermal load on the seals. 4. Cleaning process liquid. If the process fluid contains inappropriate solid particles or contaminants, it is necessary to clean the fluid inside the sealed chamber. In extreme cases, it may also be necessary to supply a clean liquid from outside the sealing system. 5. Control the atmospheric side of the seal. Since the process fluids are in contact with the atmosphere, they may solidify, crystallize, or coking, affecting the sealing performance. To prevent interaction with the atmosphere, so as to avoid adverse effects on the sealing performance, etc. Referencing the latest currently applicable standard, API Std 682, the characteristics of various flushing schemes are summarized as follows: Single-face mechanical seals: PLAN 01 (self-flushing single-face seal, internal pump flushing, seal without interfaces); PLAN 02 (jacket cooling with heating, temperature reduction via heat conduction, seal without interfaces); PLAN 11 (self-flushing, seal with 1 interface); PLAN 12 (self-flushing, seal with 1 interface and filter); PLAN 13 (reverse flushing, seal with 1 interface, suitable for vertical pumps); PLAN 14 (forward + reverse flushing, seal with 2 interfaces); PLAN 21 (self-flushing with cooling, seal with 1 interface); PLAN 22 (self-flushing with cooling, seal with 1 interface and filter); PLAN 23 (internal flushing with a pumping ring, seal with 2 interfaces); PLAN 31 (self-flushing with a slurry separator, seal with 1 interface); PLAN 32 (external flushing, seal with 1 interface); PLAN 41 (self-flushing with a slurry separator and heat exchanger, seal with 1 interface). Double-face mechanical seals: PLAN 52 (series seal with a pressure-free buffer tank, seal with 2 interfaces); PLAN 53A (double-face seal with pressurized sealing fluid, seal with 2 interfaces); PLAN 53B (double-face seal with forced-circulation sealing fluid, seal with 2 interfaces); PLAN 53C (double-face seal with a pressure-boosting tank, seal with 2 interfaces); PLAN 54 (double-face seal using externally supplied sealing fluid, seal with 2 interfaces); PLAN 55 (double-face seal using externally supplied sealing fluid, seal with 2 interfaces, buffer fluid not pressurized). Cooling seals: PLAN 61 (PLAN 72 interface reserved and blocked with wire); PLAN 62 (external flushing or rapid cooling to prevent solid particle accumulation on the seal surface, seal with 2 interfaces); PLAN 65A (with a level transmitter to measure seal leakage, seal with 2 interfaces); PLAN 65B (with a drain valve to control leakage, seal with 2 interfaces). Dry gas seals: PLAN 71 (PLAN 72 interface reserved and blocked with wire); PLAN 72 (series dry gas seal using isolated nitrogen for volatile media); PLAN 74 (double-face dry gas seal); PLAN 75 (series dry gas seal for non-volatile media); PLAN 76 (series dry gas seal using externally supplied sealing gas)