Green "Play" buttons?

[TheSandDuna]

Does anybody know (I'm assuming somebody does and I'm probably just an idiot) what the little buttons that look like a play button (such as you might find on a remote control) are for when you right click on the fuel tanks? When you click them they change to look like a red circle with a line through it, but it has no effect on my fuel, even when docked. I have successfully docked and transferred fuel by alt+right clicking, but what are those buttons for?

Edited February 7, 2014 by TheSandDuna
Answered

[breakthrough]

When in red circle mode the tank will not feed engines. You could use it to have a small tank of reserve fuel on a booster so it can use its engines to deorbit itself without micromanaging the timing of staging or spending extra part count on a transfer blocking part. Oh, and if you didn't know already you can set it to start that way in the VAB.

Edited February 6, 2014 by breakthrough
spelling

[Claw]

And you're not an idiot. It's a new feature.

Lots of items have tweakable features. Try right clicking on everything and see what you find.

[capi3101]

Actually, that feature's been around for a few versions - in flight. It's only been with the most recent version that you could lock the tanks in the VAB/SPH.

Saved my bacon on the Storax Anacostia mission, and that was around 0.21 IIRC.

[TheSandDuna]

Huh. Interesting. Thanks for the responses, I learned something new today.