Can someone explain fuel flow priority?

[JacobJHC]

I am confused on the new fuel priority system that 1.2 added. I like the idea but am still confused. Does adding numbers mean more fuel flows out or does a higher number mean that more fuel flows out? Thanks

[DD_bwest]

tanks with higher numbers will drain before lower ones,  so you could break down your tanks and have them drain bottom to top

eg.  53 for the lowest, 52 for the next, then 51, and finally  50. 

[JacobJHC]

Just now, DD_bwest said:

tanks with higher numbers will drain before lower ones,  so you could break down your tanks and have them drain bottom to top

eg.  53 for the lowest, 52 for the next, then 51, and finally  50. 

Thanks :D. I am currently completing the Jool 5 Challenge and my Tylo lander, which lacks fuel lines has staging issues due to even fuel draining.

[Tyko]

I kept forgetting whether it went low to high or high to low. I finally remembered by thinking "high priority" = "high numbers" and something that's high priority is something that gets done faster 

[AlamoVampire]

On October 26, 2016 at 6:10 PM, Tyko said:

I kept forgetting whether it went low to high or high to low. I finally remembered by thinking "high priority" = "high numbers" and something that's high priority is something that gets done faster 

You just saved me much in the way of headaches and time staring at pretty green lines blinking at me in the vab!

[HvP]

On 10/26/2016 at 6:10 PM, Tyko said:

I kept forgetting whether it went low to high or high to low. I finally remembered by thinking "high priority" = "high numbers" and something that's high priority is something that gets done faster 

Also, "Lower is Later".

[Loren Pechtel]

Drove me nuts until I realized it works like priorities--priority 1 is higher than priority 16.

My mining/refueling ships have a low number on their own engines and a high number on the fuel they carry to transfer and they have the pumps turned on.  Dock with the target, the fuel moves on it's own, they keep enough to get back down and make some more.

[jpinard]

The numbers go from negative to positive.  So if I have a lower tank I want to drain before an upper one, do I assign the lower tank P1?  Or P-1 (note the negative number)?  And is -1 higher or lower priority than -2?

[bewing]

1 hour ago, jpinard said:

The numbers go from negative to positive.  So if I have a lower tank I want to drain before an upper one, do I assign the lower tank P1?  Or P-1 (note the negative number)?  And is -1 higher or lower priority than -2?

The more positive the number, the sooner that tank drains. -1 is higher than -2.

[sturmhauke]

There's the base priority, and the user modifier which defaults to 0. Base priority is determined by staging order; tanks that stage away earlier will have a higher base priority and drain first. That is, unless you set a user modifier. The final priority is the sum of base + user modifier. Changing the staging order doesn't change the user modifier, only the base priority.

[Zhetaan]

Not to be pedantic about terminology, but since this topic causes a lot of confusion, I thought to add my own bit.  Since we're talking about the tank drain sequence, I prefer to avoid using the terms higher and lower to refer to that.  Those terms already have meaning for propellant tanks stacked vertically on a rocket, so a better way to describe matters of fuel flow priority is with the terms earlier and later.  To that end, I think @bewing has exactly the right idea.