Pump Mechanical Seal

Pump mechanical seal is a type of sealing, generally used for dynamic sealing of rotating parts, with the appropriate flushing scheme, can achieve a small or zero leakage of media (sealing gas/liquid into the media).

A mechanical seal is a device consisting of at least one pair of end faces perpendicular to the axis of rotation, which are protected against fluid leakage by the action of fluid pressure and compensating mechanism elasticity (or magnetic force) and by the cooperation of an auxiliary seal to keep the fit together and slide relatively.
This is a fairly ordinary single-ended mechanical seal with a large spring.

pump mechanical seal (2)

The main principle is that the spring is in a compressed state after reasonable installation, when the pump starts, the right part rotates with the shaft, the left part is still, the end of the hot sleeve static ring and hot sleeve dynamic ring under the action of the spring force to fit and do relative motion.

There are a total of 5 possible leaks in the diagram (two are missing, in fact the hot sleeve structure may also leak)
1 o-ring has compression, sealing left and right, and under the action of spring force can be laminated to the right; 3 static seal, basically do not consider the possibility of leakage, unless the o-ring is wrongly selected, or for the polytetrafluoroethylene rectangular gasket may not seal well; this structure is hot sleeve ring, not suitable for use in high temperature conditions, under normal circumstances, do not consider the leakage at the hot sleeve.

Then there are the two key points of the seal, the seal of this structure is actually in a state of micro-leakage, the approximate design value is not more than 5ml/h (depending on the shaft diameter and speed), basically the leakage is not visible to the naked eye.

pump mechanical seal (3)

The material of the contact surface of the rotating and stationary parts is SiC (commonly used material is SiC, graphite, carbide, ceramic, etc.), the coefficient of friction is small, under the action of the spring force these two surfaces tend to close, making the leakage of the two places is quite small (the best state is the formation of a liquid film between the two sides, this state of sealing the longest service life, the sealing surface is actually no relative friction), with the thickness of the end face due to friction is reduced or when the axis of the phenomenon, the left spring can compensate the end face in time, so that the two end faces are always closed.

The main difficulty of the pump mechanical seal is space constrained (such as early packing seal transformation into a mechanical seal), equipment (poor equipment accuracy, churning, etc.), media composition (strong corrosion of the o-ring, easy coking, high viscosity, etc.) working conditions (high temperature, high pressure), etc., followed by processing accuracy.

pump mechanical seal (1)