Español
Pусский
In selection of mechanical seals, easily vaporized media such as liquefied petroleum gas, light naphtha, acetaldehyde, isobutylene, isobutane, and isopropylene have their own specific standards.
This fact is decided by the following features of these media: poor lubricity, easy to vaporize the liquid film between the seal end faces, causing dry friction of the friction pair and reducing the service life of the mechanical seal.
These features imply the following requirements for sealing cavity : material of the friction pair must be with low friction coefficient and good thermal conductivit,especially the sealing end face should be fully cooled to prevent itself from freezing due to leakage (at the atmosphere side).
The requirements are manifested in selection of mechanical seals as follows: 1. Working condition of medium pressure p≤0.5MPa adopts unbalanced mechanical seal; Working condition of medium pressure p>0.5MPa adopts balanced mechanical seal to reduce end face specific pressure.
2.Adopting non-pressurized double mechanical seal,and the sealing fluid is introduced from the outside to the sealing cavity.
3.As to friction pair material，tungsten carbide-graphite or silicon carbide-graphite is recommended.
4.Install a throat bushing to ensure necessary pressure in sealing cavity, so that temperature of liquid between sealing end faces is about 14°C lower than liquid vaporization temperature under corresponding pressure. For example, a throat bushing is installed between impeller of pump and mechanical seal.
5.Strengthen cooling and flushing to ensure required temperature of sealing cavity.
6.Pressurized double mechanical seal is adopted, but it should be noted that isolation fluid cannot contaminate process medium, and pressure of the isolation fluid should be higher than that of the sealed medium.
This fact is decided by the following features of these media: poor lubricity, easy to vaporize the liquid film between the seal end faces, causing dry friction of the friction pair and reducing the service life of the mechanical seal.
These features imply the following requirements for sealing cavity : material of the friction pair must be with low friction coefficient and good thermal conductivit,especially the sealing end face should be fully cooled to prevent itself from freezing due to leakage (at the atmosphere side).
The requirements are manifested in selection of mechanical seals as follows: 1. Working condition of medium pressure p≤0.5MPa adopts unbalanced mechanical seal; Working condition of medium pressure p>0.5MPa adopts balanced mechanical seal to reduce end face specific pressure.
2.Adopting non-pressurized double mechanical seal,and the sealing fluid is introduced from the outside to the sealing cavity.
3.As to friction pair material，tungsten carbide-graphite or silicon carbide-graphite is recommended.
4.Install a throat bushing to ensure necessary pressure in sealing cavity, so that temperature of liquid between sealing end faces is about 14°C lower than liquid vaporization temperature under corresponding pressure. For example, a throat bushing is installed between impeller of pump and mechanical seal.
5.Strengthen cooling and flushing to ensure required temperature of sealing cavity.
6.Pressurized double mechanical seal is adopted, but it should be noted that isolation fluid cannot contaminate process medium, and pressure of the isolation fluid should be higher than that of the sealed medium.
