What type of fuel valve is held closed by fuel gas pressure?

A solenoid type fuel valve operates using an electromagnetic coil that, when energized, opens the valve to allow fuel gas to flow. When there is no electrical current, the valve is held closed by spring pressure. However, in the context of this question, a solenoid valve can be designed to be held closed primarily by fuel gas pressure. This means that when the pressure of the incoming fuel gas is sufficient, it keeps the valve sealed, allowing the system to maintain control over the fuel flow. This type of valve is particularly beneficial in systems where it is essential to avoid leaks when there is no demand for fuel.

In contrast, the manual type fuel valve relies on mechanical operation by a human to open or close the valve, which does not involve any gas pressure mechanisms. A check valve is designed to prevent backflow in piping systems and operates based on the flow direction rather than being held closed by gas pressure. Lastly, the float type valve operates by using a float ball to control the opening and closing based on the liquid level in a tank, which is distinct from pressure-controlled systems. Thus, the solenoid type valve is the most appropriate answer in this scenario.