Which type of gas valve provides complete shut off?

The correct answer to the question regarding the type of gas valve that provides complete shut off is identified as two port. A two port valve is designed to control the flow of gas through one inlet port and one outlet port. When the valve is closed, it completely blocks the passage of gas, achieving a total shut-off. This feature is crucial in applications where safety is a priority, such as gas appliances and heating systems.

In contrast, other types of valves, such as the combination valve and three port valve, have additional functionalities that may not provide the same level of shut-off isolation. A combination valve typically incorporates multiple functions, such as safety and regulating controls, but may not serve as a definitive shut-off valve. Similarly, a three port valve, which usually allows for the diversion of gas flow in multiple directions, also does not ensure complete shut off as its main purpose often involves directing flow rather than simply stopping it completely.