Which type of valve is generally used to start or stop the flow of water in a pipeline?

The type of valve that is typically used to start or stop the flow of water in a pipeline is the gate valve. Gate valves are designed to provide minimum resistance to flow when fully opened and can effectively stop the flow when closed. They operate by lifting a gate out of the path of the fluid, making them suitable for applications where the full flow is desired when the valve is open.

While ball valves also serve to start and stop water flow and do so very efficiently, they are often preferred for applications requiring quick shut-off because of their ease of operation and tight sealing capabilities. However, gate valves are favored in larger diameter pipelines and situations where the flow doesn't need to be modulated.

Check valves are utilized to prevent backflow in the pipeline, meaning they do not actively regulate flow but instead allow it to move in one direction only. Butterfly valves, on the other hand, are more often used for throttling flow rather than simply starting or stopping it, as they can provide control over the flow rate due to their design.

Thus, the characteristics of the gate valve make it the primary choice for starting or stopping the flow, especially in applications where minimal head loss is necessary when the valve is fully open.