Brian,A K sub doesn't not use any pumps. The standard system is, air from SCUBA tanks displacing ballast water. Captain George Kittredge is working on a system where he can pump water, or air when surfaced, to change ballast. The standard K sub does not have this. My sub ballast is the standard air displacing system. I don't know what pumps George is using.The captain is quite the guy. In his eighties and still actively inventing,Dan H.