Open loop/Drainback system design

[jimg]

Here's my plan for throwing a bunch of odds & ends together for emergency use:

- Plumb an open loop system in the normal way (12 v pump to panel, check valve on return)

Since I need drainback, add the following:
- solenoid valve above pump
- irrigation drain above solenoid (these are cheap little brass things that are often put at the lowest point in an in-ground irrigation system to drain them when the pressure is removed)
- another irrigation drain above the check valve
- T/P valve at the top of the panel (one way air vent)

As long as the solenoid stays on, the system will remain pressurized, and not drain. As soon as the solenoid closes, the pressure will drop in the loop (it might not happen until the temp drops to relieve static pressure), and the irrigation reliefs will open, dumping the water.

This seems a lot simpler than a closed loop system especially since I have all the parts lying around the garage. Anyone see a defect in this idea?

[saniconenergy]

Quite Imaginative. I don't see the fault with the system, however, the specifications for the solenoid and irrigation drain needs to be checked as the solar water is at much higher temperature. I wonder if they are capable of handling such a temperature!

[jimg]

The solenoid says it's good for 100C, so as long as it's near the storage tank, it might be alright. The irrigation drains are mostly brass, but they do have a rubber seal, that I'll have to see if they survive. They have a plastic fitting on the drain port to discourage weeds, but I should be able to remove that. I guess we'll see...