How Do Modifications to Seal Faces Improve Their Operation?


Excerpt from the April 2022 Pumps & Systems Article by the Hydraulic Institute

Face treatments increase the opening force by hydrostatic or hydrodynamic methods.

Pumps are at the heart of most industrial processes and the second most common machine in the world (after the electric motor). Because they are so common, pumps are often overlooked as a potential source of improved productivity or a cause of excess costs if not operated properly.

The most common seal face pattern is a plain flat surface designed to operate with minimal friction. However, various treatments can be done to seal faces to meet specific application needs. In general, seal face treatments are a means of modifying the pressure distribution between the seal faces. Images 1 and 2 show two more common face treatments that include spiral grooves and hydropads.

The most common objective of face treatments is to increase the opening force and thereby reduce the force of the mechanical contact. It can be useful when friction must be reduced to prevent vaporization of the fluid film or in applications involving a combination of high pressure and low viscosity of fluid.

Face treatments increase the opening force by hydrostatic or hydrodynamic methods. Hydrostatic forces do not depend on the rotational speed, whereas hydrodynamic forces vary with the rotational speed and viscosity of the fluid.

The simplest face treatment is a plain face that is angled. This design produces forces that are primarily hydrostatic. An example is a face subject to pressure at the outer diameter that is lapped so it touches the mating ring at the inside diameter. This means that the leakage path is converging. Care must be taken in determining the optimum angle, as too little taper will reduce the lubrication to the faces causing them to run hot. Too much taper will cause face separation with high leakage.

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