Which of the following is not a plumbing system control device?

• A. Fixture
• B. Thermowell
• C. Sensor
• D. Valve

Answer: (A)

In a plumbing system, control devices are those that sense conditions or modulate the flow to achieve a setpoint or desired state. A fixture, such as a faucet or toilet, is simply an end-use outlet that delivers water to occupants; it does not participate in sensing or regulating the system. The other options play a role in control: a sensor detects a condition and provides a signal to the control system; a valve can open or close to adjust flow based on control signals; a thermowell houses a temperature sensor so measurements can be taken safely and fed into the control logic. Because fixtures don’t participate in sensing or regulation, they’re not a plumbing system control device.