US Patent 9145983 Dummy undersea hydraulic coupling member

A dummy undersea hydraulic coupling member protects an opposing undersea hydraulic coupling member when the hydraulic lines are not operating. The dummy undersea hydraulic coupling member has a water displacement expansion chamber with a piston in the chamber that allows trapped water and/or air to move from the receiving chamber into the water displacement expansion chamber during connection of the dummy coupling member to the opposing coupling member. The piston has both a primary seal and a secondary, hydrostatic seal for preventing seawater from entering the portion of the water displacement expansion chamber that is contacted by the primary seal.