I'm not quite sure what the "jet" is on the XP3 spraybar. It doesn't look like it's pushing any water, so I'm wondering what the purpose is. I constructed my spraybar to include this, but it doesn't appear to do anything. The water simply comes out of the spraybar holes.
The jet component is if you want to push a lot of water fast, such as a reef application, I believe. It is to be used without the spraybar and has a smaller output so forces the water to "jet" through it, I think. I never have used it, though I tried it out like that once out of curiosity. Also, I use the Eheim intake/outflow "installation sets" on my XP3. I like them so much better and have combined one for a very low outflow (without a spraybar).
Three Tanks...Eheim 2128 & XP3-90G, Eheim 2128-65G, Eheim 2232-25G.... Tek 4x54 watt T5-90G, Aqualight 96watt PC 65G low tech, 65 watt Aqualight-25G.... Hydors-90G & 65G ... Flourite in 90, 65, & 25 Gallons, .... Auto Water Change/Auto dosing on 90 & 65 gallon..... AGA member......