Common requirements for mechanical seals in special working media and conditions

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1. Features of the hot water pump: A. Both the stationary and rotating rings are made of titanium, which has a low coefficient of expansion similar to that of tungsten carbide, facilitating the secure installation of these rings. B. Use a V-shaped seal ring of type F4 to ensure the followability of the auxiliary seal ring as well as the stationary and rotating rings at operating temperatures. C. The liquid after being cooled is sent into a sealed box for flushing. 2. High-temperature pump mechanical seal pump a. Hard-to-hard seal pair b. Seal box cooling protection ； 3. For sealing high-viscosity liquids, edge sealing is used: the edges are sharp, which facilitates heat dissipation; a slight amount of force is sufficient to achieve sealing, and the torque characteristics remain stable. 4. For sealing volatile liquids, a multi-point flushing system along with a combination of silicon carbide and carbon graphite is employed. 5. In cases involving solid particles, the structure (double-end face, cascade type) as well as the choice of flushing and filtering materials should be considered; additional measures such as heating can also be used. 6. For corrosive media, seal components that operate in such environments must take into account the corrosivity of each individual component, and measures must be taken to prevent galvanic corrosion when these components are combined. Sealing relies primarily on materials: the sealing surfaces are made of ceramics, F4, carbon graphite, silicon nitride, or corrosion-resistant cemented carbides ； Auxiliary sealing: For F rubber and F4 types, an external sealing arrangement is used; for those types where springs do not come into contact with the medium, an internal sealing arrangement is employed. In cases where there is a high level of risk, double-end face sealing is used along with the introduction of sealing fluid for protection. Sealing requirements under different operating conditions. The characteristics of working conditions dictate the measures required for shaft seals: at high temperatures, material strength decreases; the medium may vaporize, solidify, or crystallize; sealing rings can deform, sealing components may age, and springs can fail. Rubber aging; loose fit of the coupling rings; materials resistant to heat and high temperatures; cooling to ensure the slidability of the moving ring at high temperatures; metal bellows for sealing, metal-impregnated carbon graphite rings, and auxiliary sealing elements made of heat-resistant materials; insulation and cooling of the temperature in the sealing chamber; low temperatures leading to vaporization of the medium and dry friction ； Poor lubricity of the moving parts (excessive moisture leads to freezing); materials that can withstand low temperatures, as well as materials that provide insulation and prevent freezing. Metal bellows for sealing, along with low-temperature resistant materials; gaskets and bushings that allow dry gas to pass through, and sealants that are resistant to low temperatures. The pressure-sealing rings may deform or break under pressure ； The sealing ring is not easily squeezed out; it possesses sufficient strength and stiffness, and its structure is designed to prevent deformation through the use of high-strength graphite and anti-deformation features. Multiple sealing layers are employed, along with enhanced cooling and lubrication systems. The intrusion of air into the vacuum (negative pressure) can lead to dry friction and significant leakage. Measures are taken to prevent external air from entering, so as to maintain the necessary vacuum level and prevent the sealing surfaces from separating, thus ensuring proper operation under negative pressure conditions. Metal bellows seal, single-face seal with bushing and flushing ； Increase spring pressure to prevent seal separation; add anti-rotation pin ； Increase the sealing pressure to turn negative pressure into positive pressure. When the high-speed rotating ring moves, the spring is affected by centrifugal force; the medium generates high frictional heat, leading to rapid wear. The material used for the end faces must be able to withstand high speeds ； Rewarding the effects of centrifugal force and stirring ； Part dynamic balancing and vibration prevention ； Cooling and lubrication are optimized for high-speed operation by using material combinations with high PV values (such as WC-C, SiC-C) and static structures, as well as by improving part precision to ensure adequate cooling and lubrication ； A balanced seal is used; the rotation direction of the springs affects performance, and the components are subject to shocks. The friction conditions on the sealing surfaces are severe, which requires the components to be wear-resistant and impact-resistant. Attention should be paid to strength design as well as to strengthening the anti-rotation mechanisms. Metal bellows seals are more suitable in such situations, or a structure with multiple small springs can be employed ； Anti-rotation components for the static ring; different working fluids have varying requirements regarding sealing. Liquids that are easy to vaporize, such as liquid hydrocarbons, liquid ammonia, acetaldehyde, isobutane, and propylene, have low boiling points and high vapor pressures. Frictional heat can cause the liquid film on the sealing surfaces to vaporize, leading to dry operation. The friction coefficient of the frictioning pairs is low ； Prevent freezing of the sealing surface (on the high-pressure side): balanced type or dual-sealing design ； WC-C and SiC-C combinations for friction pairs ； Strengthen cooling and flushing measures. For paraffin, residue, asphalt, urea, liquid sulfur, phenolic resin, and plasticizers, high freezing points mean that temperature changes can cause the medium to solidify, thereby hindering the lubrication of moving parts; pay attention to maintaining proper insulation ； Flushing is required to prevent solidification; enhanced insulation measures should be adopted, as well as steam back-cooling. Thiamine, phosphamine, sodium hydroxide, calcium hydroxide, ammonium phosphate, green liquor, and butanol are prone to crystallization – changes in temperature can cause the dissolved substances to precipitate, leading to early damage of the friction pairs. Hard materials should be used, along with adequate cooling or insulation. Two sealing systems and a WC-WC hard-to-hard combination are advisable; flushing, cooling, or insulation should be intensified. A single large spring structure should be used, along with water-based back-cooling. Residual oil at the bottom of the tank or reactor, oil slurry, crude oil, and high concentrations of solid particles or impurities can cause sealing elements to become clogged or worn. The design should allow for the removal of such impurities, and hard materials should be used for the sealing surfaces. Two sealing systems and a WC-WC hard-to-hard combination are recommended. Pre-filtering, cyclone separators, and magnetic filters should be employed, with attention paid to flushing. Monomers such as polymeric furfural, formaldehyde, ethylene, vinyl chloride, acrolein, vinyl acetate, aqueous formaldehyde, and raffinate can cause polymerization due to heat generated by friction and stirring, leading to an increase in temperature. It is important to keep the temperature below the polymerization threshold and ensure adequate cooling. Hard materials should be used for the end faces. Two sealing systems should be employed, along with increased sealing fluid volume and enhanced cooling. Cemented carbide rings should be used, as well as higher spring compression forces. Metal bellows can also be utilized. Substances that are easily soluble, such as isopropanol (in water), sulfonated oils (in water), pentane (in oils), alum (in water), copper sulfate, potassium sulfate (in water), rubber (in benzene, liquid ammonia, ammonia water), and glycerol (ethanol), can cause the sealing rings to dissolve and damage the bonding material of carbon graphite. Therefore, materials resistant to water, oil, ethanol, etc., such as oil-resistant rubber, F4, or metal fillers, should be used ； Use F4 filled with glass fiber, adopt WC-WC, pay attention to corrosion resistance ； Fluororubber cannot be used with benzene, ammonia, and ammonia water. Highly corrosive and oxidizing substances such as hydrochloric acid, sulfuric acid, and chromic acid pose a severe corrosion risk; therefore, the materials in contact with these substances must be corrosion-resistant. Materials should be selected based on the corrosion resistance charts. Substances that are flammable, explosive, or toxic, such as cyclohexane, tetraethyl lead, and hydrofluoric acid, can cause accidents if they leak; it is necessary to collect the leaked liquid or dilute it ； To prevent leakage outside the machine, back-cooling methods are used for capture or dilution; two layers of sealing are employed to isolate it from the outside environment. High-viscosity sulfuric acid, grease, gear oil, residue oil, cylinder oil, silicone oil, and styrene all have high viscosity – attention must be paid to the lubricity of the moving parts. Springs are prone to being blocked, and viscosity changes with temperature; the sealing surfaces can easily get damaged. Hard materials should be used for the sealing surfaces, and the springs must be able to overcome resistance. Heating is required, and static double-sealing or edge-sealing methods are employed ； Hard materials such as WC are used, and considering the insulation structure, the tendency to solidify due to temperature constraints, increased corrosivity, polymerization, vaporization, etc., require taking corresponding measures at temperatures below or above certain thresholds