Use of hydrated material for dynamic seal faces in shaft seal

In ocean current and tidal power generation systems, the rotating shaft, which connects the turbine in water phase and the generation system in air phase, experiences a variety of shaft speeds and high water-pressure conditions. The shaft seal is required to separate water and air with a rotating shaft, which should guarantee both a low frictional torque and a low leakage of water. Conventional shaft seals realize the low frictional torque by operating in a hydrodynamic lubrication mode at the dynamic seal face. However, the dynamic seal face suffers to form rich lubrication film against low speed shaft in water environment. Therefore, a hydrated seal ring was proposed for use in the dynamic seal faces to realize the boundary lubrication. The hydrated seal ring made of a polyvinyl formal (PVF) was adopted. Two types of shaft seals using PVF seal ring were designed, which had the similar structure to oil seals or mechanical seals. The design scheme was validated using verification tests in which the shaft rotation speed was varied from 5000 to –5000 revolutions per minute under a water pressure of 0.5 MPa. The hydrated seal ring can be further improved by avoiding deformation of the hydrated seal ring to inhibit the clearance flow in the dynamic seal face. However, it needed to consider the surface profile of the ceramics surface used as a counterface of the hydrated seal ring because the heat generation at the dynamic seal face might be occurred, which changes the material property of the hydrated seal ring.