What does a cylinder valve do?

A cylinder valve is a critical component that serves primarily to seal the contents of the gas cylinder, preventing gas from escaping when the cylinder is not in use. It ensures that the gas remains contained and maintains pressure within the tank. When the valve is closed, it creates a leak-proof seal; when opened, it allows the controlled release of gas for usage.

While other options mention important aspects related to gas cylinders, such as measuring pressure or regulating flow, they do not accurately define the function of the cylinder valve itself. The valve is specifically designed to seal and unseal the gas contents, ensuring both safety and control over gas usage.