This valve shown above is a quality product at a low cost. The version I use is a 12 volt DC unit. It has 2 inch NPS threads which can easily attach to 2 inch PVC pipe.
The air freight from China costs more than the valve.
I will be ordering a number of valves from Covna that will be sent to me via ship. The per unit shipping cost will be approximately $15.
IF YOU EXPECT TO BUY SOME VALVES FROM ME, PLEASE TELL ME.
The spring on the pressure relief valve should be set so that the valve opens when the Ball Valve is shut. The pressure relief valve should close when the Ball Valve opens and allows the Spray to begin.
The circuit card in front of the 12 volt battery contains a heat sensor, a transistor and a resistor. The circuit card costs only a few dollars.
When a fire is detected by the heat sensor, the electric ball valve is opened and the SprayHose starts spraying.
Many heat sensors (thermistors) can be placed around the outside of a house attached to the same wire pair. Any heat sensor that detects heat will open the 2-port valve.