In a low-pressure gas system, what type of valve cannot be opened until the gas pilot is lit?

A manual reset valve is designed to ensure safety by preventing the flow of gas until certain conditions are met, specifically that the gas pilot is lit. This mechanism adds an essential layer of protection in a low-pressure gas system. The requirement for the pilot light to be on before the valve can be opened ensures that gas is only allowed to flow when there is a reliable ignition source ready, thereby reducing the risk of gas accumulation and potential hazards.

In contrast, automatic valves typically operate without the need for manual intervention based solely on pressure or flow conditions, making them unsuitable for scenarios where the pilot must be lit first. Safety valves are primarily intended to relieve excess pressure in a system to prevent dangerous over-pressure situations and do not require a pilot light to function. Pressure relief valves serve a similar purpose by releasing pressure but are not contingent upon the status of a pilot light. Thus, the features of a manual reset valve align specifically with the requirement of having a lit pilot before allowing gas flow.