Hey how's it going? So I'm working on a rain-barrel system that is being hooked into a sprinkler system and I have a bit of a brain teaser. There's a submersible pump in the rain-barrels that pumps water out of the barrels and into the sprinkler system with the help of a Red Lion pressure tank and pressure switch. The switch is set to 30PSI cut in and 50PSI cut out, and the tank factory pre-charged to 28 PSI. The rain-barrel portion of the system is only to water the vegetable garden zones of the irrigation system, so there is a master valve on the house water line, which is used to provide water to the rest of the irrigation system, basically because there are not enough barrels to be able to run the whole system off the rain-barrels. This master valve will open when the irrigation controller tells it to, and because the house water line will be running the pump/pressure tank side of the equation shouldn't work. When the master valve does not open but the irrigation to the vegetable gardens turns on, the system pressure goes down, pump kicks in etc.etc. There's a problem there too but that's a whole different issue.
What I do seem to face is that the system keeps increasing in pressure when I open the shut offs that isolate the pressure tank/ pump side of things and have the master valve opened- and keeps increasing! There is a 75PSI pressure relief valve at the pressure tank and it opens but pressure keeps on going up in spite of this. The house pressure measures around 60 PSI by the way. The pressure gauge measures to 100 PSI but it keeps on going right up to the pin on the high side of the gauge, probably 130 PSI or so.
Any thoughts? I'm thinking of bleeding down the pressure tank air pressure and starting from scratch; but I don't think that's going to help. I've used a couple of different pressure gauges on both the air in the tank and the system too, so it shouldn't be the gauges...

Do I understand that the house, sprinkler system and rain barrel will all be tied together when you open up the "master valve"? Back to you, Tom

Yes- The water feed off the house line for the sprinklers is the one with a "master valve" on it; it is back-flow protected in case you're wondering. The theory is that by having the controller turn on the master valve just before the zone opens, the pressure will not drop in the system and the pump will not operate. The controller will not turn the master valve on for the vegetable garden; the pressure will drop in the system, and the pump will come on. Perhaps is my theory a little wonky? I have also thought that if you had a similar valve installed on the rain-barrel line, and had it open with the zone valve, that might work better. Just shifts the problem over coming up with a way to get the controller to turn on 2 different master valves...