Which statement about pressure switches is true?

• A. It is used to measure air flow
• B. It closes a circuit when pressure is reached
• C. It uses optical sensing
• D. It changes the color of the housing

Answer: (B)

A pressure switch is designed to act at a specific pressure and provide an electrical signal when that pressure is reached. It uses a sensing element, such as a diaphragm or bellows, that moves with pressure changes and toggles electrical contacts. When the sensed pressure hits the preset value, the switch changes state and closes the circuit (or opens it, depending on configuration), allowing it to start or stop equipment or trigger an alarm. This is why the true statement is that it closes a circuit when pressure is reached. It isn’t used to measure air flow—that would be a flow sensor. It doesn’t rely on optical sensing, and changing the housing color isn’t a function of a pressure switch.