Secondary gas/liquid mechanical seal assembly

A mechanical seal assembly for sealing a liquid medium within a housing having a rotatable shaft passing therethrough, the mechanical seal assembly comprising:

• a primary mechanical seal assembly mounted around the shaft for sealing the liquid medium such that, in normal operation, the liquid medium exists on an upstream side of the primary mechanical seal assembly and a gaseous medium, resulting from minute leakage of the liquid medium through the primary mechanical seal face assembly, exists on a downstream side of the primary mechanical seal assembly;
• and
• a secondary mechanical seal assembly mounted around the shaft on the downstream side of the primary mechanical seal assembly such that, in normal operation, the gaseous medium exists on an upstream side of the secondary mechanical seal assembly and, upon failure of the primary mechanical seal assembly, the liquid medium exists on the upstream side of the secondary mechanical seal assembly;
• wherein the secondary mechanical seal assembly includes a first seal face element rotationally fixed relative to the housing and a second seal face element rotationally fixed relative to the shaft, the first and second seal face elements each having a front surface and a rear surface with the front surfaces in opposed relation to one another;
• wherein the back surface of the first seal face element includes a slotted configuration that, during normal operation, generates a wave on the front surface of the first seal face element sufficient to generate an opening force to drive the seal face elements apart and operate as a gaseous seal;
• and
• wherein, upon failure of the primary mechanical seal assembly, a resulting hydrodynamic loading of the liquid medium on the seal face elements transitions the secondary mechanical seal assembly to operate as a liquid seal.