Why does pump evacuation cause mechanical seal damage

Pumping to vacuum can cause severe vibration in the pump, which can lead to damage to the bearings and mechanical seals.

Yes. Negative pressure can cause axial displacement of the stationary ring, leading to misalignment of its stop grooves and thus resulting in damage

When the pump is evacuated, it’s not that there is no liquid at all inside the pump’s volute; rather, a small amount of liquid remains. As a result, only part of the flow channel contains liquid while the impeller is rotating, which causes the impeller to lose dynamic balance and lead to severe vibrations and noise. This also increases the radial and axial vibrations of the shaft. Excessive vibrations can affect the stationary and rotating rings, potentially causing them to shift or move out of place; in severe cases, the stationary and rotating rings may even break apart； Therefore, when the pump is evacuated, it is not the negative pressure that causes the stationary ring to shift, but rather intense vibrations that may lead to such shifting. There is a sealing O-ring at the bottom of the stationary ring; during installation, a considerable amount of force is required to align the groove of the stationary ring with the positioning pin in order to fit it into its seat. Thus, if intense vibrations resulting from evacuation cause the stationary ring to shift, it is theoretically impossible for it to return to its original position, as the elastic compression capacity of the mechanical seal is not sufficient to generate such a force.

Mechanical seals are prone to damage because axial displacement occurs, which in turn leads to vibration

Axial displacement, severe vibration, dry grinding, temperature rise