Variable ballast tank with pumps instead of compressed air

[Travis]

I am trying to create a variable ballast tank system using 4 inch pvc sch40 pipe. However, instead of using compressed air, I want to use water pumps instead. Ideally I would like to use one pump per tank, to do the pumping out or removing of the water, and have some kind of vent mechanism to fill the tanks. What needs to happen in order for this to work? I also, thought about some type of check valve to allow water out of the tank, but prevent from refilling through the pump. I have been struggling with this idea and am not getting anywhere in my tests.

I put one hole in the 13'' pipe and fitted my small 92 GPH fish tank pump securely into the hole inside the pipe, so that it would "pump" out the water. And another hole to "vent", but instead what happens is no water is removed from the pipe, but instead flows through the pipe and out of the second hole. I feel like it shouldn't be this complicated, however, I am struggling a bit trying to figure it out. This test as well as putting the pump on the outside and pumping water in works better when its not submerged? Only when everything is full submerged do I have this issue. Instead of the air in the pipe being vented through the second hole, the water just comes racing in instead. Is the pump to small, do I need one more powerful, or is there something else important that I am missing? Should I possible implement some control valves, or something of that nature? I appreciate all the feedback hints and tips, and sorry I am clearly not all that experienced with this type of system.


Also, the tanks are 13 inch length by 4 inch diameter and capped with rubber qwik caps like these at the link below.

https://www.menards.com/main/plumbing/p ... 434796.htm


The ROV will have the ability to go to 100' however realistically I would probably only use roughly 50 as most lakes near me are about max depth of 50 or so. And I know someone is sure to recommend just adding weight to reach neutral or slightly positive buoyancy as a much simpler alternative and you would be correct, however, I really wanted to add this feature for possible helping with weight lifting and to simply solve a problem that I see no one else doing. (I am starting to see why LOL). I may have to just end up going with the added weight to achieve the neutral buoyancy, but it would be really cool if I could find a solution. Thanks.

[Ian MacKenzie]

Can you draw a picture of what you're trying to do. And maybe take a few pictures of what you've done so far. I've been thinking about a variable ballast system also.

[asesorplaza1]

Good morning.

I advise you to research on the internet about "RC dive systems", there is enough information on the net on how to get a submarine up and down in the water.

Greetings from Spain.

[asesorplaza1]

From what I'm seeing, the most commonly used system is the embolism system, a large syringe that with a mechanism absorbs or expels water. Water pumps give many problems.

Greetings from Spain.

[Travis]

Can you draw a picture of what you're trying to do. And maybe take a few pictures of what you've done so far. I've been thinking about a variable ballast system also.

This is the design im working with. The two outer tanks are the ballast tanks. Pvc which I will have to rethink if I want to use the high pressure system as it would require a pump capable of 73.5psi to force the water inside, and pvc is not recommended for applications where air pressure is applied...