Which device is used to cut off the water supply on a mainline?

The gate valve is specifically designed to control the flow of water in plumbing and irrigation systems. It operates by raising or lowering a gate within the valve body, which either allows or restricts water passage. This feature makes it ideal for cutting off water supply on a mainline when repairs or maintenance are needed. Gate valves provide a reliable means of isolating sections of piping without the need for complete system shutdown, ensuring that water flow can be managed efficiently.

The other tools listed serve different purposes unrelated to water supply control. A framing square is primarily used in carpentry for measuring and marking right angles. A file card is an implement used for cleaning and maintaining files, and a flaring tool is utilized for creating a flared end on tubing for connections. These tools do not have any functionality related to controlling water flow in pipelines.