Hey Daves, thanks for the timely reply,
Yeah, I did check both of those websites, though couldn't locate that item on ShipsnThings, while Mikessubworks only offers the "tee" valve design, which apparently is only good for pump-ballast systems.
At this point it's probably one of those things that are so minor and ubiquitous that some sites may not bother to mention they have them available. Many of the SubCom folks are professional machinists, or could probably swing a cat and hit six or seven people close by who own milling machines. "Achoo! Whoops, I made a tank valve."
Well, I'll inquire directly to ShipsnThings, because I haven't done that yet.
Dave Townsend; your suggestion sounds interesting. My system is 12v. Everything (radio, 2 motors) will be drawing from a lead-acid cell in the bow. How's your design work? Solenoid? What's the amp draw, escape diameter, overall size? Got a picture?
My sub design has a ridiculously high freeboard, which makes for a large ballast tank relative to its size. So I'm expecting to have to install two conventional escape valves to get my diving time, shall we say, less-pathetic. If your design's pipe diameter is large enough, one will probably do and will simplify my time comma money comma life. Please let me know. I can send pics of what I plan to do.
Many thanks again to both for the replies. BB