1. Strong corrosive medium (hydrochloric acid, sulfuric acid, acetic acid, etc.)
1. Features:
Mechanical seals need to withstand corrosion, and the corrosion rate on the mechanical seal surface is usually 10-50 times the corrosion rate of the frictionless surface.
2. Requirements for mechanical seals:
(1) The sealing ring of the mechanical seal is both corrosion-resistant and wear-resistant, and the material of the auxiliary sealing ring must be both elastic and corrosion-resistant and temperature-resistant. (Requires reliable spring use)
3. Selection of mechanical seals:
(2) The use of external mechanical seals to strengthen cooling and prevent temperature rise.
(3) If you use an internal mechanical seal, a spring plus a protective layer, a large spring jacket plastic pipe, sealed at both ends, or sprayed with a corrosion-proof layer on the surface of the spring, such as polytrifluorovinyl chloride, PTFE, etc. Large springs should be used because the wire diameter is large and the coating is not easily peeled off.
(4) Mechanical seals for bellows are adopted. The moving ring is integrated with the corrugated tube, the material is PTFE (glass fiber filling), and the static ring is ceramic; Springs are protected by plastic hoses or coatings to isolate from spilled fluids,
(5) External mechanical seals are suitable for pressure p≤0.5Mpa.
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Second, high viscosity media (grease, sulfuric acid, gear oil, cylinder oil, styrene, silicone oil, residual oil)
When the viscosity is high, the wetting performance is good, but too high will affect the floating of the moving ring, increase the transmission torque of the spring, and when the viscosity is too high, it is not easy to form a liquid film between the sealing surfaces, and the lubrication performance is poor, and the sealing ring is damaged.
Friction pair material wear resistance, spring should have enough ability to overcome the resistance generated by high viscosity media, to avoid the sealing chamber temperature is too low and cause the viscosity of the medium to increase, requiring the sealing chamber to be insulated or heated.
(1) Medium of general viscosity, when p≤ 0.8Mpa, select a single-end non-balanced mechanical seal; When p> 0.8Mpa, a balanced mechanical seal is used. When the viscosity of the medium is 700-1600Mpa.s, it is necessary to increase the design of the transmission pin and spring to resist the increased shear force due to the increase in viscosity, and when it is greater than 1600MPa.s, it is also necessary to strengthen lubrication, such as a single-end face seal through the external flushing liquid, or a double-end seal into the isolation fluid.
(2) Static double-end mechanical seal and with pressurized flushing system.
(3) The use of hard-to-hard friction pair material combinations, such as silicon carbide - silicon carbide, or tungsten carbide - silicon carbide.
(4) Consider the insulation structure to ensure that the viscosity of the medium is not increased due to the decrease in temperature.
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Third, containing solid particles of media (bottom of the tower residual oil, oil slurry, crude oil)
Causes intense wear on the end face of the sealing ring. The deposition of solid particles at the moving ring will make the moving ring lose its floatability, and the particles deposited on the spring will affect the spring elasticity.
The friction pair is wear-resistant and should be able to exclude solid particles or prevent solid particles from settling.
3. Selection of mechanical seals
(1) The pressurized double-end mechanical seal is adopted to pass the isolation fluid in the sealing cavity. The friction pair near the media side uses a material combination of silicon carbide and silicon carbide.
(2) If a single-end mechanical seal is used, a fluid slightly higher than the pressure of the sealed medium should be introduced from the outside to enter the flushing, and when the sealed medium is used for flushing, the solid particles should be separated before entering the sealing cavity, and a large spring mechanical seal should be used.
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4. Easily vaporized media (liquefied petroleum gas, light naphtha, acetaldehyde, isobutene, isobutane, isopropylene)
Poor lubricity, easy to vaporize the liquid film between the sealing ends, causing dry friction of the friction pair and reducing the service life of the seal.
Mechanical seals are required to have low friction coefficients and good thermal conductivity, especially the sealing end surface should be fully cooled to prevent the leakage of liquid caused by the sealing end surface from freezing (by the atmospheric side)
(1) Medium pressure p≤0.5 MPA adopts non-balanced mechanical seals; Medium pressure p>0.5Mpa adopts a balanced seal to reduce the end face specific pressure.
(2) Non-pressurized double-end mechanical seal is adopted to introduce the sealing fluid from the outside to the sealing cavity
(3) Friction pair materials are recommended to use tungsten carbide - graphite or silicon carbide - graphite.
(4) Install a throat bushing to ensure the necessary pressure in the sealing cavity, so that the liquid temperature between the sealing ends is about 14 ° C lower than the liquid vaporization temperature under the corresponding pressure. For example, the impeller of the pump is equipped with a throat bushing between the impeller and the seal.
(5) Strengthen cooling and flushing to ensure the temperature required by the sealing chamber.
(6) Pressurized double-end mechanical seals are adopted, but it should be noted that the isolation liquid cannot pollute the process medium, and ensure that the isolation liquid pressure is higher than the sealed medium.
The above content is excerpted from the network, compiled by Othello sealed editors, such as invasion and deletion!
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OTHELLO mechanical seals are suitable for dynamic sealing of rotating shafts, and the performance is relatively reliable, with little leakage and low power consumption under normal circumstances. Widely used in high and low temperature, high pressure, high speed of clean water, corrosive media, particle-containing media and other working conditions. Visit the official website: Mechanical seals for pumps, double-end mechanical seals - Othello Sealing Materials (China) Co., Ltd