What is necessary for all manual gas cock valves?

For manual gas cock valves, it is essential that they be approved specifically for use with gas fuel. This approval ensures that the valves are designed to handle the specific characteristics of gas, such as pressure, flow rate, and potential corrosiveness. Using valves not approved for gas could lead to leaks, improper functioning, or safety hazards.

The other options do not relate directly to the necessary safety and functional standards required for gas cock valves. While cheaper alternatives might seem appealing, they do not guarantee safety or reliability. Self-closing mechanisms may provide additional safety but are not mandatory for all manual gas cock valves. Color-coded handles can aid in identification but are also not a requirement for the valves to operate safely and effectively in gas service. Thus, having valves approved for gas fuel only is crucial for ensuring proper performance and compliance with safety standards.