Rupture disc relief valves are used with which type of valve to stop the flow of fluid?

Rupture disc relief valves are employed in conjunction with gate and plug valves to effectively halt the flow of fluid. Gate valves serve as on/off control mechanisms, providing a straight-line flow path when fully opened, allowing fluids to pass through with minimal resistance. When paired with a rupture disc relief valve, the gate valve can quickly close off the line in case the rupture disc is activated, thereby preventing any fluid from leaking out or entering the system.

Plug valves function similarly by allowing or blocking fluid flow with a cylindrical or conical "plug" that can be rotated within the valve body. When a rupture disc activates, the plug valve can also be closed swiftly to ensure that the system remains secure.

Both types of valves are crucial for ensuring that the system can contain pressure surges effectively while also providing a reliable means of isolating sections of the system when relief mechanisms are triggered. The inclusion of both gate and plug valves as options illustrates their roles in providing immediate flow restriction upon the activation of a rupture disc relief valve, making "the 1st and 2nd answers" a correct selection.