How do you control max and min water levels in ballast tank?

[Johnny Depth]

I have a Pressure Pump Ballast System with a surprisingly strong gear water pump that rapidly fills and empties my ballast tank.
It is so strong that in a test filling a soda bottle with water, it blew the lid right off.

I do not use a valve. As a safety mechanism, I allow the built-up pressure in the ballast tank to force out the water passively. So yes, my sub stays submerged for only as long as I run the pump.

When I actively operate the pump to blow the ballast tank, the pump will pump all the water out and then start pumping the air out! The problem that this creates indirectly is that once I stop operating the pump, the vacuum created sucks water back into the ballast tank and we don't want that. The only way I have to tell that I should stop operating the pump is either when the sub emerges or when I see bubbles of air indicating that a vacuum is being created.

How can I detect full and empty in order to stop the pump? I've read some things referring to probes in the ballast tank but what are they? Where can you find them? How do you make them? Is there a better way?

Even if I switch to a peristaltic pump I would still need to detect when the tank was full or empty.

I would very much appreciate any help or advice in solving this problem.

[He Who Shall Not Be Named]

Vent the tank. That keeps the tank at close to the ambient pressure, no matter what. You won't be able to hover or empty the tank with the vent under water, but you can't have everything in such a small package.

Engage pragmatism cells, my friend; don't let complexity rule over objective. Sometimes the smart thing to do is choose the well-traveled road. Don't trust pressure sensors -- you have all the makings of a busted water-balloon if it fails.

Or just slap a pressure relief valve in there and hope for the best.

[redboat219]

ballast tank rom Bob Gaito's Gato class (top) and Atlantis tour sub ( bottom)


RC Shipyard Vented Ballast tank using a solenoid valve

https://youtu.be/RqnxuMlmhkA?si=p1wM5ERPM3xRyeDQ

[redboat219]

Need to swap out the buzzer for a relay switch to stop the pump when tank is full.

[redboat219]

Check out DrSchmidt's Fantasy Neptune

https://forum.rc-sub.com/forum/builder-threads/113070-new-project-neptune-a-fantasy-boat-project

He used a tiny float switch to shut off the pump when the tank was full

[Johnny Depth]

Vent the tank. That keeps the tank at close to the ambient pressure, no matter what. You won't be able to hover or empty the tank with the vent under water, but you can't have everything in such a small package.

Engage pragmatism cells, my friend; don't let complexity rule over objective. Sometimes the smart thing to do is choose the well-traveled road. Don't trust pressure sensors -- you have all the makings of a busted water-balloon if it fails.

Or just slap a pressure relief valve in there and hope for the best.

Thanks very much.
Is there a specific pressure relief valve that people commonly use?

[Johnny Depth]

ballast tank rom Bob Gaito's Gato class (top) and Atlantis tour sub ( bottom)


RC Shipyard Vented Ballast tank using a solenoid valve
https://youtu.be/RqnxuMlmhkA?si=p1wM5ERPM3xRyeDQ

Thanks very much!

The diagram calls for a float valve, a check valve, a pressure switch, and a solenoid valve. Are there specific ones that people commonly use in their subs?

[Johnny Depth]

Need to swap out the buzzer for a relay switch to stop the pump when tank is full.

Excellent! This looks like exactly what I am looking for!
Thank you very much!