Gas burners safety valve of understanding

Gas coming from the direction of the first one is the safety valve, the second is operated valve, double solenoid valve is set to double insurance, in case of a solenoid valve leak, and there is gas burner valves to ensure that does not leak. To ensure this, there are no two solenoid valves are bad, the actual operation between the two solenoid valve is also equipped with leak detector, if there is a leak valve, the burner valves can not open the solenoid valve, and thus not start burner, repair or replace the solenoid valve must ensure two solenoid valves do not leak before starting the burner. However, gas pressure switch (high and low voltage protection) is not the valve is a pressure sensing switch, if the gas pressure is low, low voltage protection switch because of low pressure, a mechanical spring or similar mechanism would disconnect switch, this switch is a string programmed in burner main power circuit, after low pressure protection switch off the burner does not start.