My apologies for the long post. Let me know when you wake up.
Maybe Dodger can fill us in on what the purpose of the "Pressure Relief" valve is...???
I have only a tiny experience to share and it is different than Alex's plumbing. The Pressure Relief Valve for the Caretaker in-floor system is installed BEFORE the 5-port Caretaker valve. So if pressure builds up trying to get through any port of the Caretaker valve, the back-pressure can be released through the Pressure Relief Valve, which is plumbed back to the pool wall returns, bypassing the 2-way valve that selected the Caretaker line. I assume there is some kind of pressure threshold (30 lbs?) the Relief valve has to reach before water actually goes through it.
Sounds like you have got everything figured out except the down position of the manual valve.
This unknown for Alex is nagging me and I still feel like this valve position is related to the Pressure Relief Valve line.
Not only that, I am actually still confused about the description of Up and Down for this manual valve. I don't know if that means the lever is up/down, or the OFF is up/down. In all the pictures, this manual valve is sideways and in between up/down, isn't it?
Also, I don't have a sense for what the "sprayers" are?
The flow is just about the same both ways for the waterfall.
Okay, never mind on this.
This is the exact order for the ultraflex zones. Starting with the waterfall first.
1. Waterfall overflow
2. Spa overflow only no popups
3. Middle top main return hole
4. Shallow end - stairs
5. Mid shallow end
6. Spa pop ups and spa overflow
7. Mid deeper end
8. Deep end
I'm trying to figure out what zone is tied to the position that tees off to the Pressure Relief Valve so we can have an idea why it's there. Not sure what #3 "middle top main return hole" is. I'm guessing the Pressure Relief is either for that or the waterfall.
The 2 spa zones should have check valves. I think I see a screw or something 180 degrees from the Jandy check valve port (at 3 o'clock vs 9 o'clock). Can you scoop away some of the lava rock to see if there is anything there?