The purpose of flushing is to prevent the accumulation of impurities, prevent the formation of air pockets, and maintain and improve lubrication. When the flushing fluid temperature is low, it also has a cooling effect. The main flushing methods are as follows:
(I) Internal Flushing
1. Forward Flushing
1) Features: Utilizes the sealed fluid from the main engine, introduced into the seal chamber through a pipeline from the pump outlet.
2) Application: Used for cleaning fluids. P1 is slightly greater than P in. When temperatures are high or there are impurities, a cooler, filter, etc. can be installed in the pipeline.
2. Backflush
1) Features: Utilizes the sealed fluid from the main engine, introduced into the seal chamber from the pump outlet. After flushing, it flows back to the pump inlet through a pipeline.
2) Application: Used for cleaning fluids. P in < p1 < p out. When temperatures are high or there are impurities, a cooler, filter, etc. can be installed in the pipeline.
3. Full Flush
1) Features: The sealed medium from the main engine is introduced into the seal chamber through a pipeline from the pump outlet. After flushing, it flows back through the pipeline to the pump inlet.
(II) External Flush
Features: A clean fluid compatible with the sealed medium is introduced from an external system into the seal chamber for flushing.
Application: The pressure of the external flushing fluid should be 0.05-0.1 MPa higher than that of the sealed medium. It is suitable for applications involving high-temperature media or solid particles. The flushing fluid flow rate must ensure heat removal, meet flushing requirements, and avoid erosion of seals. To achieve this, the seal chamber pressure and flushing flow rate must be controlled. Generally, the flow rate of a clean flushing fluid should be less than 5 m/s;
Slurries containing particles should be less than 3 m/s. To achieve the aforementioned flow rates, the pressure difference between the flushing fluid and the seal chamber should be less than 0.5 MPa, typically 0.05-0.1 MPa. For double-end mechanical seals, a pressure of 0.1-0.2 MPa is acceptable. The orifices for the flushing fluid to enter and exit the seal chamber should be located near the seal end face and close to the moving ring. Tangential introduction or multi-point flushing can be used to prevent graphite ring erosion, thermal deformation due to uneven cooling, and impurity accumulation and coking. Hot water or steam can be used as the flushing fluid, if necessary.
