Aren't decouplers supposed to block fuel flow?

[sebi.zzr]

I love the idea for jet engines to drain fuel from all parts simultaneously,because you can strap them to wings and you don't need fuel lines for them to work.But when they are used in rocket designs this becomes a problem!

This is the design of reusable bottom stage i always used for LKO(manned or for launching satellites).

When i launch the craft,engines immediately starts draining fuel from upper stage fuel tank despite there is decoupler between stages.I looked in engines *.cfg and noticed,engines use this configuration:

resourceFlowMode = STAGE_PRIORITY_FLOW

then i tried to change it to

resourceFlowMode = STACK_PRIORITY_SEARCH

,it resolved the issue with fuel drain,but made another one,now i need to use fuel lines again.I know the second command is used for engines to search for fuel in tanks they are attached to(convenient for engines using monopropellant),but i was hoping i'm wrong.

So let me ask again,why are decouplers not blocking fuel flow despite the fact,they are not fuel crossfeed capable?

Edited September 25, 2015 by sebi.zzr

[KerikBalm]

Yea... it seems weird... I don't know why they changed the way jets use fuel... I suppose it was to make fuel drain evenly so as not to upset CGs... but it has caused a lot of other annoying issues.

The only solution it to right click on the part, and disable to fuel flow (turn the green arrow into a red X)

[klgraham1013]

Still not sure how I feel about the new fuel flow for jet engines.

[Superfluous J]

Yeah I liked it as described, because as described, they didn't mention decouplers :/

[r_rolo1]

That is strange . It looks almost like they forgot the reason why they made decouplers to not allow fuel flow in the first place ... that or this is a bug.

[Sirrobert]

That's odd. I didn't play yet, waiting for mods. But that must be an oversight

[KerbMav]

Hm, I kind of remember Havester saying the atmospheric engines would pull equally from all tanks in the same stage only?

[GusTurbo]

I was having this issue with radial decouplers. I had 4 outer boosters with no crossfeed, but they were mysteriously draining fuel from the core.

[X-SR71]

Guess they just made it work like monoprop.

@sebi.zzr

What did you use for making that picture?

[Sirrobert]

Guess they just made it work like monoprop.

@sebi.zzr

What did you use for making that picture?

Monoprop is stopped by no-crossfeed parts though right?

[KerbMav]

Monoprop is stopped by no-crossfeed parts though right?

In this case it might be possible to edit the parameters in the parts and of the liquid-fuel resource.

[sebi.zzr]

Guess they just made it work like monoprop.

@sebi.zzr

What did you use for making that picture?

it is:Kronal Vessel Viewer (KVV) - Exploded ship view

[r_rolo1]

Well, I don't know yet about how monoprop really works on 1.0, but in 0.90 monoprop, electric charge and intake air worked the same: from sources to users, and not stopped by anything, including decouplers.

Like I said before, I believe this is a bug. There were reasons why the decouplers were made to not allow fuel flow in the first place ( they weren't in the beginning ), both of RL roleplay ( You don't want fuel lines inside explosive separators, , right ? ) as to avoid the kind of situation the OP is describing ( upper stage fuel draining ). Unless they forgot why they done that in the first place ... :/

[nekogod]

Monoprop is stopped by no-crossfeed parts though right?

No actually it's not.

The only solution at the moment would be to disable fuel flow on the upperstage tank by clicking the little green triangle (you'd only need to do liquid fuel) then re-enabling it just as you stage

[sebi.zzr]

No actually it's not.

The only solution at the moment would be to disable fuel flow on the upperstage tank by clicking the little green triangle (you'd only need to do liquid fuel) then re-enabling it just as you stage

Actually not quite right.Rapier engine have

resourceFlowMode = STAGE_PRIORITY_FLOW

defined for both modes.Once you change mode it will drain oxidizer as well.I think the new "aero" made flying crafts harder so trying to click on tanks to enable fuel flow and piloting the craft at the same time it's something,well more work than fun.

[TMS]

Monoprop is stopped by no-crossfeed parts though right?

A change to RCS and xenon flow was made in 0.23.5, I think. That change mean that those resources drained equally within a stage, prioritising the lowest stage. In effect, this meant that your lifter wouldn't drain your payload.

See Harv's response in this thread: http://forum.kerbalspaceprogram.com/threads/74889-Change-to-RCS-and-Xenon-flow-rules

Also details some odd behaviours.

Edited April 30, 2015 by TMS

[BoomShroom]

Monoprop is stopped by no-crossfeed parts though right?

No, however last time I checked it drained from the tanks with the most decouplers between them and root part first, so unless they changed that as well then jets drain fuel on their own logic. They should have it work like mono at least.

[Claw]

Yes, this was an intentional change. Unfortunately, it causes issues. Especially if you have a main carrier that is hauling some sort of lander that will be decoupled. Keep an eye out for it stealing from your landers or other craft that will be decoupled. Empty fuel is not an issue if you are decoupling debris, but when it's a lander it is very frustrating.

Cheers,

-Claw

[sal_vager]

If only fuel tank flow could be set to action groups.

[r_rolo1]

Yes, this was an intentional change. Unfortunately, it causes issues. Especially if you have a main carrier that is hauling some sort of lander that will be decoupled. Keep an eye out for it stealing from your landers or other craft that will be decoupled. Empty fuel is not an issue if you are decoupling debris, but when it's a lander it is very frustrating.

Cheers,

-Claw

The intended feature IIRC, was that the engines would drain equally from stuff in the same level ( unlike it happened in previous versions ). That is not what we're seeing here ...

[KerikBalm]

If only fuel tank flow could be set to action groups.

This!

I was about to make a post about this too, as I have a hard time juggling fuel flow on my SSTOs to keep them balances when lighting rockets... but now with the new jet flow, if I open one front tank on the left side of my craft, then the right one... at the end of the burn, I get a spin, because the jets take a little more out of the first tank I open (I keep the forward tanks closed, so my CG doesn't shift back when I light the rockets)

[sebi.zzr]

KSP 1.0.1 is out,but the problem is still present.

[volcanicshrimp]

I had this problem with a plane I made. It was meant to have small miniplanes that were dropped from it but this problem meant that the miniplanes' fuel was being sucked out, messing up their CoMs and stopping them from being able to fly.

[Yukon0009]

Squad, please re add decoupler no fuel flow, its rather annoying to release your booster stage then realise the core flamed out and used up upper stage fuel..

[sal_vager]

Jets are supposed to take from the lowest stage (separated by decouplers) first, this can be seen with droptanks for example.