Plumbing Code Information About Gate Valves
Plumbing code plays a predominant role, or should, in any type of modifications to an existing plumbing system, or the installation of a new plumbing system in new construction. A gate valve is a linear type of valve that essentially blocks or allows water to move in a line, and is a perpendicular barrier to the plumbing line. A gate valve can only be open or closed; it can not be used to moderate the flow of water at all, and is typically operated either electronically or with a knob. Gate valves are commonly used as the shut off valves when bringing water in to a structure, and may also be used as the shut off valve on the water supply line in the structure it's self.
National vs. Local Code
The only types of approved materials for gate valves is either cast iron or iron body valves. However, national plumbing code may vary from the respective state's code, and so local codes should be referred and adhered to when considering any kind of modifications. Most state's plumbing codes are available on-line. Generally a state specific plumbing code will me more limiting than the national plumbing code.