Which valve type is typically used for on/off control but is not considered an isolation valve?

• A. Solenoid valve
• B. Ball valve
• C. Gate valve
• D. Globe valve

Answer: (A)

On/off control devices versus isolation devices. A solenoid valve is designed to switch flow on and off quickly and remotely, using an electrical signal. It’s a compact, fast-acting control valve often used to start or stop a flow in a circuit or to divert it in simple valve configurations. However, it isn’t meant to serve as a primary isolation valve that you’d rely on to permanently block flow for maintenance; its sealing and construction aren’t focused on providing a long-term, leak-tight shutoff under system pressure.

In contrast, isolation valves like ball, gate, and globe valves are chosen specifically for their ability to provide a robust, long-term shutoff, allowing a section of a system to be safely isolated for repair or service. They’re designed to withstand full system pressure and usually offer a more reliable seal when fully closed.

So the valve type used for on/off control but not considered an isolation valve is the solenoid valve.