The Design and Construction of a Visco Seal Test Facility

The visco seal is a device that provides a means of sealing a rotating shaft passing through a bulkhead wall, thereby establishing a pressure gradient across the wall. The operation of the visco seal (also called threaded seal, spiral groove seal and viscosity pump) is based on a momentum exchange principle through viscous shear.

Consider two flat plates separated by a liquid (Figure 1). As the plate moves across the liquid, it transmits momentum to the molecules of liquid adjacent to the plate. These molecules in turn collide with other molecules, which continue the process of collision in which each molecule conveys to the next molecule less momentum than was transmitted to it. As a result, the velocity of the molecules in contact with the moving plate is equal to that of the plate, and the velocity of molecules at the stationary surface is zero. For Newtonian fluids the velocity of the fluid between the two surfaces has been experimentally found to be directly proportional to the distance from the fluid element to the stationary surface when the flow is laminar and no pressure gradient is present (see Figure 1).