Why Does Mechanical Seal Need Flushing?

The appropriate end face flushing is one of the important auxiliary measures to improve the durability of the mechanical seal of the centrifugal pump, especially for the effect of the hot oil pump shaft seal in the refinery. In addition, for those liquid hydrocarbon shaft seals with poor lubrication and easy volatility, flushing measures have to be taken to quickly take away heat and prevent liquid film vaporization. Why should the mechanical seal be flushed regularly?

Three main functions of mechanical seals

Flushing function

Flushing is the basic function of the mechanical seal. It directly injects liquid into the high-pressure side of the single-side seal or double-side seal, two different mechanical seals types. General mechanical seals should be flushed, especially for light hydrocarbon pumps. When flushing, the purpose of isolating media, cooling, and improving lubrication should be achieved. The purpose of isolating the medium can be achieved by introducing a liquid compatible with the medium into the sealing cavity for external circulation flushing.

Decontamination and filtration function

The harm of fine solid particles, dirt and other impurities in the sealing fluid to the mechanical seal is very serious, which may cause wear of the sealing end face and block the pipeline of the cold sealing system. The sealing system software has the function of removing residue and keeping the liquid clean. When the relative density of the residue is smaller than the relative density of the liquid medium, it can be removed by a filter device, while when the relative density of the residue exceeds the relative density of the liquid medium, a centrifugal separator or a mesh filter can be used to remove the residue.

Fluid substitution function

The direct sealing of gas-phase media containing solid particles and liquid-phase media is very difficult. They are prone to evaporation and crystallization. With the help of mechanical seals, double-end mechanical seals can be used to replace the sealing medium, and the difficult-to-seal medium can be transformed into a sealing liquid medium with good lubrication and cleanliness.

Reasons for frequent flushing of mechanical seals

• Flushing for heat dissipation. The heat generated by the liquid seal must be controlled, which can be achieved by using liquid to flush the seal cavity to take away heat and control temperature rise.

• Reduce the temperature of the liquid. In some cases, the liquid temperature is too high, which affects the sealing performance. In this case, the temperature of sealing parts must be lowered to improve the performance of the liquid.

• Change the pressure of the seal cavity. In some cases, it is necessary to increase or decrease the pressure of the seal cavity to improve performance. This can be achieved by suppressing evaporation or reducing the thermal load of the mechanical seal.

• Clean process liquid. If the process liquid contains inappropriate solid particles or contaminants, the liquid in the seal cavity needs to be cleaned. In some cases, clean liquid may also need to be provided from outside the sealing system.

• Control the atmosphere side of the seal. As the process liquid comes into contact with the atmosphere, it may become dry, crystallized, or coked. It is very important to prevent interaction with the atmosphere to avoid adverse effects on sealing performance.