If you are using a Modpack:

• Modpack Name: GTNH
• Version used: Current release version, 2.0.8.3

Misc Info

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•    Using GT:NH/GT:New Horizons?
•    Single Player?
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So couple of things going on with the overflow valve:

Firstly, finer control of the actual value set. Currently you can only adjust by up to 4096L at a time using the screwdriver while sneaking. This is very low considering the top tier overflow cover has a maximum overflow amount of 262,144,000 (64,000 clicks). I know you can loop around backwards, but you understand my point that it is very hard to get the value you want if it is say 100M L of fluid. Ideally players could possibly enter the value manually somehow? Not sure if this is possible with covers but would definitely be the absolute best option, either that or the ability to adjust by larger intervals using different tools or something.

Secondly, it would be nice if we could have overflow valves that go up to the max tier quantum tank value of 2.147B L. This obviously can be worked around with other means but it would be a nice addition if possible.

Thirdly, the values seem incorrect for some of the valves. For example the IV overflow valve starts at a default of 262,144, this is 1000x lower than the tooltip amount of 262,144,000L. However if you loop around to it then you can continue to increase upwards from here (Not sure how far though, would need to click 10s of thousands of times to test this). I also tested with an actual fluid and it does seem to void at 262,144L by default, so it isn't just telling me the wrong value in chat.

Also is the red and blue part meant to signify something on the cover texture? Both ends seems to do the same thing.