What does an excess flow check valve do?

An excess flow check valve is a critical safety component designed to protect fuel systems, especially those utilizing LPG or CNG. Its primary function is to automatically shut off the supply of gas if there is an unusually high flow rate, which might indicate a leak or a rupture downstream in the system.

The answer that describes the excess flow check valve accurately indicates that it will shut off the gas supply if the control valve is closed too rapidly. This is crucial because if the control valve is shut off quickly, it can create a significant pressure change or backflow, leading to potential safety hazards. The valve ensures that in such scenarios, the gas supply is effectively stopped to prevent dangerous situations such as explosions or fires from leaking gas.

The other options do not accurately represent the function of an excess flow check valve. The first choice implies that the valve allows continuous flow regardless of pressure, which is not correct as the valve is designed to restrict flow under certain conditions. The third option regarding increasing the flow rate during emergencies does not align with the valve's safety function, which aims to limit flow in hazardous situations. Lastly, while decreasing pressure may be a result of other components in the system, it is not a primary function of the excess flow check valve.