One of the most valuable gifts I got from the Vancouver Psubs convention is a close-up picture of the main thru hull / penetration panel on the Deepworker 2000. Like Alec has promoted for several years, Phil has clustered 11 hull penetrations into a single removable SS plate. The central penetration has a Swagelok 3/8 inch, 3-way ball valve installed with the valve stem coming through the cedntral penetration into the cabin. This valve stem has a modify handle with a red ball. When the handle is in the horizontal position, all ports are closed. When the valve handle is moved down, air trapped in the MBT is released to the water and the boat decends. When the valve handle is moved up, the valve is ported such that compressed air is forced into MBT and the boat ascends. While this MBT vent valve option will not work for all psub applications (valve needs to be located above the highest point in the MBT), for small boats with a single MBT or a set of straddle MBTs , this is a very elegant solution. It is easy to maintain, keeps all the HP air out of the boat, it is very intuitive to use and minimizes the number of valves and tubing. As it uses Swagelok fittings, it has bubble tight seals. To my knowledge, the Deepworker only uses the MBT and not a VBT so that is this an extremely simple and bullet proof ballast system.
Cliff