alt.energy.homepower

"News" wrote in message
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> wrote in message
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>> Also, they are required to be equipped with a pilot light sensor
>> (generally using a thermocouple) which turns off BOTH and main burner
>> valve and the pilot light gas feed if the pilot light were to be
>> extinguished for any reason. The same is true for gas operated home
>> furnaces.
>
> In Europe pilotless ignition is pretty well the norm. Pilot only comes in
> when the burner is called.
>
>> Some states is the US also require a gas water heater to be equipped
>> with a "vacuum breaker" valve on the water feed line, which allow air
>> to enter the tank if a negative pressure were to develop in the water
>> supply line. This can happen if a fire developes in the neighborhood,
>> and the fire department is heavily pumping from nearby fire hydrants.
>
> An anti-vacuum valve can be anywhere on the tank. Why on the incoming cold
> mains pipe?
I would think it's to prevent siphoning of water from any part of the
househould plumbing back into the municipal supply lines.

Don Young