Low pressure valves for use with OpenSprinkler DC

Hi,

I recently bought an OpenSprinkler DC control unit. I bought some Rain Bird 100-DV 1″ valves to try out with it, and they seemed to work ok, so I went ahead and installed the system with more of them. Since doing so, however, I have realised that they significantly reduce the flow rate/pressure of my comparatively low-pressure gravity-fed irrigation (I have a 50000L underground tank, static head is between about 5-10m at the valves). For some zones this still works fine, but others – with smaller falls from the supply tank, or with longer pipe runs or more demanding sprinklers – the pressure loss is too much and the sprinklers no longer work reliably. When they’re on, if open the bleed valve, you can see the flow rate at the sprinkler increase quite dramatically. Reading online, I see that this is a feature of this type of valve which uses the pressure of the supply to keep the valve open.

I live off grid with solar power; I do most of my watering overnight, and between all the zones, irrigation is running for ~12h/night. Apart from the challenge of running (switched) power to a pump near the tank exit, I simply don’t have the power capacity to be running an irrigation pump for that length of time at night, so I need a solution that will work with my gravity-fed irrigation.

From what I understand, that probably means switching out some of the more problematic zones for motorised ball valves. Assuming this is correct, I have two questions:

1. Will this work for the DC opensprinkler model or do i need to be getting into additional relays for these circuits?
2. Can anyone recommend a good, reasonably-priced valve that has an auto-return spring and is available to buy in Europe?

Thanks,