B767 - Fuel Jettison system

[Glonass]

We operate two B767-300, which have a low capacity jettison rate (Only one pump in each dual pump unit is activated). For those aircrafts the manual mentions that: “Flaps 25 or 30 should not be selected when using a low capacity jettison system”.
Could someone please enlighten me as to what is the reason behind this reasoning?
Thanks in advance.

[Bolty McBolt]

At the flap setting you mention the turbulent air coming from the wings/flaps causes the jettisoned fuel to spray over the empanage
Apparently this is not ideal

[Glonass]

Thanks for your reply.

Indeed, it sounds quite right, however why the precaution with the low capacity jettison rate system only; is this not so ideal situation avoided with the high capacity jettison system?

[chemical alli]

dont quote me

from memory it also has to do with the fact that fuel will hit the horizontal stab due to the turbulent air from the flaps and cause a buffetting sensation

[Bolty McBolt]

I can't confirm now but on the fleet of 767 I work with, all have the same limitation whether the jettison system be high or low capacity .

It could just be for standardisation across the fleet because the low capacity came first with the high capacity arriving on aircraft a few years later.

Need to keep it simple

[chemical alli]

you will also notice that the jettison tubes have had an extension of 10 inchs, this was a beoing ei to try and direct fuel away from stab,originally they were straight now they have a 20 degree offset

[Glonass]

Thank you much for your replies.