Fig 1 shows a complete automatic spray system.
The main idea is to manually start a simple, low cost pump before a homeowner is going to evacuate. Starting the engine on a simple pump means placing the choke, by hand, in the START position, and keeping the throttle at a low setting. Once the gasoline engine starts, the choke is placed by hand in the RUN position and the throttle is moved to the MAX position. Since the fire has not arrived yet, we don't want to spray water.
The electric 2-PORT VALVE is in the closed position, and no water sprays on the house yet.
In order to keep the pump cool, a small hose feeds the pumped water back into the tank.
The homeowner evacuates.
When the fire arrives, any one of the temperature sensors can cause the
2-PORT-VALVE to OPEN, and the spray is enabled onto the house.
Fig 2 shows the case where the homeowner starts the pump, and when NO fire is nearby, the 2-Port Valve is normally in a condition where the water is NOT being sent to the Spray Hose. The water is pumped thru the Pressure Relief Valve and returns to the water tank, The PVC pipe used to return the water has a small diameter and little water flows back to the tank. This causes the pressure out of the pump to be high, and the Pressure Relief Valve allows the water to pass thru and reenter the water tank.
The gasoline tank on the recommended pump allows the pump to run for
Since the fire may not arrive for many hours, a larger gasoline supply may be added. I could not find a place to purchase such a tank for the recommended pump, but there are many YouTube videos that show how to build one.
The figure below shows that when the 2-PORT-VALVE opens because of a detection of high temperature, the water stops flowing through the
PRESSURE RELIEF VALVE. This is because the pressure will drop out of the pump when a larger volume of water is flowing out of the pump.
This lower pressure cannot get thru the PRESSURE RELIEF VALVE.