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In selection of mechanical seals,high viscosity media such as grease, sulfuric acid, gear oil, cylinder oil, styrene, silicone oil, residual oil have their own specific standards.
This fact is decided by the following features of these media: when viscosity is moderately high,lubricating performance is good, but if viscosity is too high, floating of rotary face will be affected and transmission torque of spring will be increased.That’s because it is difficult to form a liquid film between sealing surfaces and sealing performance will be harmed When viscosity is too high.
These features imply the following requirements for mechanical seals: Friction pair material is wear-resistant, and spring must have enough ability to overcome resistance caused by the high-viscosity medium , and sealing chamber is required to be kept warm or heated to avoid increase of viscosity of the medium caused by low temperature of the sealing chamber.
The requirements are manifested in selection of mechanical seals as follows:
1. For medium with general viscosity, when p≤0.8Mpa, use a singl unbalanced mechanical seal;When p>0.8Mpa, a balanced mechanical seal is used. When viscosity of the medium is 700-1600Mpa.s, it is necessary to enlarge drive pin and spring to resist increased shear force due to increase in viscosity.When viscosity of the medium is greater than 1600Mpa.s, it is also necessary to strengthen lubrication, such as single seals leading to external flushing fluid, or double seals leading
to isolation fluid.
2.Adopting static double mechanical seal and a pressurized flushing system.
3.Adopting a combination of hard-to-hard friction pair materials, such as silicon carbide-silicon carbide, or tungsten carbide-silicon carbide.
4.About thermal insulation structure,take measures to ensure that the viscosity of the medium does not increase due to the decrease in temperature.
This fact is decided by the following features of these media: when viscosity is moderately high,lubricating performance is good, but if viscosity is too high, floating of rotary face will be affected and transmission torque of spring will be increased.That’s because it is difficult to form a liquid film between sealing surfaces and sealing performance will be harmed When viscosity is too high.
These features imply the following requirements for mechanical seals: Friction pair material is wear-resistant, and spring must have enough ability to overcome resistance caused by the high-viscosity medium , and sealing chamber is required to be kept warm or heated to avoid increase of viscosity of the medium caused by low temperature of the sealing chamber.
The requirements are manifested in selection of mechanical seals as follows:
1. For medium with general viscosity, when p≤0.8Mpa, use a singl unbalanced mechanical seal;When p>0.8Mpa, a balanced mechanical seal is used. When viscosity of the medium is 700-1600Mpa.s, it is necessary to enlarge drive pin and spring to resist increased shear force due to increase in viscosity.When viscosity of the medium is greater than 1600Mpa.s, it is also necessary to strengthen lubrication, such as single seals leading to external flushing fluid, or double seals leading
to isolation fluid.
2.Adopting static double mechanical seal and a pressurized flushing system.
3.Adopting a combination of hard-to-hard friction pair materials, such as silicon carbide-silicon carbide, or tungsten carbide-silicon carbide.
4.About thermal insulation structure,take measures to ensure that the viscosity of the medium does not increase due to the decrease in temperature.
