What is the correct term for the valve that stops the flow of feedwater to the boiler?

The term that accurately describes the valve responsible for stopping the flow of feedwater to the boiler is "stop valve." This type of valve is designed to completely shut off or allow the flow of fluids, making it essential in systems where controlling the flow is critical. In the context of a boiler, the stop valve ensures that feedwater can be halted as necessary, whether for maintenance, safety, or operational adjustments.

Control valves and regulating valves typically serve to modulate flow rather than completely stop it, making them unsuitable for this specific function. Relief valves focus on releasing excess pressure within a system and are not intended to manage the flow of feedwater directly. Therefore, the stop valve is the correct terminology that directly addresses the need to stop the feedwater flow to the boiler effectively.