A few things come to mind. Do you only have one line going to each bay for WWF and air or do you have one for air and one for WWF tee’d above the bay? Your post indicates you have only one line going out to the bay. If so, this could be an issue. The automated WWF and air purge system on all my LP functions have air and WWF tee’d above the bay. I originally only had one line to each bay and it wasn’t effective at all. I had to add the additional line and tee both above the bay. If you only have one line, it may be a timing issue. WWF may not be getting to the bay.
Recently I installed a manual blowdown/WWF injection system on my HP hoses. The only difference is mine is manual and uses the weep lines connected in the Er and yours is automated and is tee’d in above the bay. Same principal. I don’t know if this is your issue, but 90% of the time when I put a bay back in service after being winterized for a day or two or more; the tip will plug with something that breaks loose in the hose/fittings. It has done it in every bay, so it’s not isolated to a single bay. I’m thinking the in-rush of water is breaking stuff lose in the cold stiff hose?
After startup, I don’t have clogging tip issues. Or any yet this witner.
I was planning on doing the same thing as you and automate the process with a plc, but this issue has me giving up on the idea. I am more than happy with the manual system. At least I am there on startup to unplug a nozzle when it happens.
Lastly, do you have SFR? CantBreak80 posted a few times about how a SFR solenoid manifold could leak by when another bay is using SFR. This is something else that can ruin your day.
Keep us posted....I really like the idea, but there seems to be obstacles to over come!