I don’t plan on “pumping” the water in and out. On a real submarine, our ballast tanks have “vent” values on the top of the tanks. So if your tanks are currently full of air because you came to the surface and did either a low or high pressure blow on them, the vent valves when opened will allow air to escape while water floods in from open grates on the bottom of the tanks. Since I don’t wish to get as crazy as a real ballast system is, I plan on using a triple position electrically operated valve to either be in the vent / closed / blow position. The onboard air would be in a pressure cylinder and will be a possible one shot deal depending on the depth etc. that you operate it at.
Once you do a full or partial blow of the tank, you are loosing the air pressure etc. I wanted to go with a 250 psi system to make sure that I could overcome pressure down to maximum operating depth that the ROV would survive too. I have seen the plastic shells that are glued together on the OpenRov project and I don’t care for that at all. I will more than likely go with a full seal system on anything that comes apart and I might use epoxy casted in place windows for any optical sensors etc. One of the side benefits of my real job is having access to lots of toys. We build electronic enclosures and cable systems that we test to 2000 psi so I have had plenty of years messing with stuff that works.
We really want to have manipulator arms on our platform and the plan is also to make it so a diver can control it locally while on a wreck site to search inside where it could be to hazardous to go into. The great part for our project is I have a very large pressure tank at work that I can hydro test the platform to upwards of 1000 psi to make sure this puppy doesn’t die at the design depths we want to go to. The tank has a 48" ID and is 6 feet deep so we got plenty of play room. We also have a jib crane to load the unit into the tank with.
When we get to the point of building / testing the ballast system, I can post the info for it. Our game plan is to put a test weight system with the ballast and a timer control into one of the pressure tanks and let it sink to the bottom etc. and close the system up and run it to maximum depth pressure … and wait for the timer to trigger the blow system. I should hear it impact the tank lid when it shoots to the top of the tank while under pressure.