My tank was not as fast as a piston tank.
But it was only a prototype. Just for testing.
The speed was only 180 rpm.
The pump on your photo looks very interesting.
there you can see a self made roller pump for use in a pump-tank system.
The pump has a rate of about 1litre per minute (approx. 1/3 gallon per minute) at full speed and operates in both directions (in and out). When stopped, the water transition through the pump is blocked so that the trimming state of the submarine will not change.
Combined with a speed controller it is also able to pump drop by drop for fine trimming at extreme low motor speed.
The pump doesn't need any sliding seals or valves and itself faces the outer pressure, not the tank. As the tank isn't exposed to the diving pressure the tank may have even forms/ cross sections that are less resistive against pressure. And the pump can act and pump against the pressure even when the battery has gone low (a piston tank needs rather high inrush currents for torques to overcome piston friction and axial force).
In general such pumps are not as fast as piston tanks but for use in a model of a modern sub this circumstance is less important.
